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Bringing your gear back to life!
Old 21st April 2019
  #1
Gear Maniac
Bringing your gear back to life!

In some weird way I have recently come up with an obsession for fixing recording equipment. I have built 2 capi bt50 EQs, 2 capi vp28 preamps, a hairball audio Lola preamp, and one micparts U47 microphone and psu.

I am very good at following direction builds. However, I have no idea how circuitry works nor do I know how to read PCB boards.

I guess my question for you all is...

How do I start learning about how electronica flow works, and most importantly to me how to fix it?

I have a trident 65 board I am looking to make mods to as well as repair. Also, I was given an Amex classic that I am determined to put together and get working.

Any little information you could provide me would be so helpful and appreciated. I am a visual learner, so YouTube videos would be the best approach.

As always, Thank YOU so much for taking the time to read this. This community has helped me so much, and I hope to be at the other side of it providing wisdom from those in need...but one step at a time!
Old 21st April 2019
  #2
Lives for gear
 
EvilRoy's Avatar
Same boat. I know how to wire a guitar but little else. My projects I want to work on include a couple of tape decks and a mixer. Started reading Electronics for Dummies. Pretty sure that and some soldering skill will get me started.
Old 22nd April 2019
  #3
Gear Maniac
 
drsaamah's Avatar
posting to follow.
Old 22nd April 2019
  #4
Lives for gear
 
Brian M. Boykin's Avatar
I joined Gearslutz in 2005. I’ve spent most of my time on Geekslutz learning circuit design and how to, as I say, update gear. I choose gear with known mods and follow directions. I’ve gotten myself into trouble from time to time but I always learn. The goal is to make mistakes once. Here are some lessons learned:
1) you can’t always drop in op amps. Sometimes feedback loop compensations caps are not in the original design so they must be added.
2) local psu bypass caps are a good thing. I’ve never regretted adding them even when it’s to an op amp I didn’t swap.
3) when recapping, stick to original values unless you know what your doing
4) lower noise, lower distortion, and increasing bandwidth are my goals for mods. This always produces a piece of gear that’s more versatile and easier to assimilate into daily workflow.
A) I lean towards transparency. I want to clean up any color the gear has. I get my color at the source and use the gear to mix it into music.
5) power supplies get stressed with upgrades because of current draw, you need to check specs or you’ll smoke your gear.
A) I held off going balls to the wall on my console until I had a new power supply in place that could handle the mods. I’m reworking Ashly SC55’s as we speak because the power supplies didn’t like all the opa2134’s and opa134’s I dropped in.
6) kits are an excellent way to learn. I build mic’s from Microphone Parts kits and they turn out great for way less money then new.
7) ground and lots of it is your friend

Learn to read schematics. Learn the different op amp circuits and why and how they work and their practical applications. Read datasheets and technical articles. Analog Devices and Texas Instruments our out great reads. There’s a book called “Optimizing Op Amp Performance” by Jerald Graeme. I have it. I’ve never made it all the way through but I continually try and every time I learn more.

There are tons of mod threads out there. I’ll google the gear with mods after the name and see what comes up. The threads are not always laid out step by step but are dudes sharing what they did. You have to sort through them. You will screw the pouch because of this. Chalk it up to education. It’s just gear. It can usually be fixed. If it’s a beloved piece of gear, send it out to be modded by a professional. You can then see what they did and learn.

If I think of more I’ll add.

Brian
Old 22nd April 2019
  #5
Good advice from Brian above. I would add...

Start simple. You don't want reconditioning a big mixer to be your first project.
You will find that there were things you could have done while you had it dismantled, and you wish you had known better.

I was taught by my dad when young how to read a schematic (it's easier than you think, with lots of instructional material online). Understanding what you are seeing is a whole different matter.

What was helpful for me were some YT vids about modding guitar pedals that I watched. They usually discuss signal path first, which gets you used to tracing the signal from input to output, somewhat like those mazes you find on restaurant place mats. That gets you used to the fun part of circuits, where some minor changes can have a big effect, and the differences between the components involved.

A little more tricky are power supplies (PSUs). Guitar pedals are easy because the PSUs are batteries or external, and not part of learning process as much.
On a mixer, the PSU is incredibly important, and if not working correctly will give you no end of problems, which is true of all gear that uses AC for power.
Basically it takes the AC wall current, converts it to DC (for most gear) and breaks it down into a voltage level that is more useful for whatever device you have. Not sexy, but vitally important.
The device might require 15v, 18v, 24v, 48v, etc. DC, and in the case of gear with tubes, much higher and more dangerous voltages and sometimes AC. So at the beginning, stay away from tube gear.

Don't expect to pick it up fast unless you have lots of time and motivation. Be patient.

Start looking at GroupDIY, but avoid posting. Just lurk and learn for a while, and see what mistakes other folks have made. Once you can ask intelligent questions (and provide schematics!), those folks are true saints who can be very helpful. Most likely, a search will reveal someone has asked this question already, and the answer is already there.

Online searches about specific gear are helpful, and will lead you mainly back here to GS or GroupDIY. Read completely until you understand.

Soon, you will be able to look at a piece of malfunctioning gear and have an educated guess about why it isn't working correctly. Then you'll know you are getting somewhere.

As far as mods go, I generally have come to a point where most of what I do involves capacitors, and trying to clean up the signal path. I find most chip swaps are not worth it, with a few exceptions. Sometimes the initial design with older chips is what gives a piece it's character, and you can lose that in the process. There is LOTS of misleading info online about mods, because people aren't really testing their results.
The Alesis 3630 comes to mind here. This comp CAN be made better, but there sure is a lot of BS about it on the web.

As far as repairing mixers goes (I have rebuilt and recapped about 6 of them so far), the first thing I suggest is recapping them (replacing the electrolytic caps) to get them into their original state, especially if they are over 15 years old with no previous recaps.
Just get it back in it's proper working order first. This alone will likely make it sound much better.
Start with the PSU and the output channels (definitely suggest bypass caps in the signal path here, whether you do it on all channels is another matter), and if you don't have a good temp-controlled iron and lots of experience using it, get that first before you start replacing the hundreds of caps you will find inside.
This leads to even understanding how to order so many caps, where to get them, and what kind to buy, which is another entire field of knowledge.
If the mixer isn't modular (each channel can be removed separately), then you have a quite a big project ahead of you, with no working mixer in the meantime.

So good luck, have fun, and be patient.
Old 22nd April 2019
  #6
Gear Maniac
Quote:
Originally Posted by drsaamah View Post
posting to follow.
Great! We are looking forward to hearing what you have to say
Old 22nd April 2019
  #7
Gear Maniac
Lots of great informal here, Bryan. I appreciate the time and thought you put into it.

I just downloaded a video on learning schematics. I will watch it tonight.

Could you explain what a PSU bypass is? I imagine it means adding a switch to a channel of your mixer that turns of power going to it? Maybe I am wrong?

Thanks again!

Quote:
Originally Posted by Brian M. Boykin View Post
I joined Gearslutz in 2005. I’ve spent most of my time on Geekslutz learning circuit design and how to, as I say, update gear. I choose gear with known mods and follow directions. I’ve gotten myself into trouble from time to time but I always learn. The goal is to make mistakes once. Here are some lessons learned:
1) you can’t always drop in op amps. Sometimes feedback loop compensations caps are not in the original design so they must be added.
2) local psu bypass caps are a good thing. I’ve never regretted adding them even when it’s to an op amp I didn’t swap.
3) when recapping, stick to original values unless you know what your doing
4) lower noise, lower distortion, and increasing bandwidth are my goals for mods. This always produces a piece of gear that’s more versatile and easier to assimilate into daily workflow.
A) I lean towards transparency. I want to clean up any color the gear has. I get my color at the source and use the gear to mix it into music.
5) power supplies get stressed with upgrades because of current draw, you need to check specs or you’ll smoke your gear.
A) I held off going balls to the wall on my console until I had a new power supply in place that could handle the mods. I’m reworking Ashly SC55’s as we speak because the power supplies didn’t like all the opa2134’s and opa134’s I dropped in.
6) kits are an excellent way to learn. I build mic’s from Microphone Parts kits and they turn out great for way less money then new.
7) ground and lots of it is your friend

Learn to read schematics. Learn the different op amp circuits and why and how they work and their practical applications. Read datasheets and technical articles. Analog Devices and Texas Instruments our out great reads. There’s a book called “Optimizing Op Amp Performance” by Jerald Graeme. I have it. I’ve never made it all the way through but I continually try and every time I learn more.

There are tons of mod threads out there. I’ll google the gear with mods after the name and see what comes up. The threads are not always laid out step by step but are dudes sharing what they did. You have to sort through them. You will screw the pouch because of this. Chalk it up to education. It’s just gear. It can usually be fixed. If it’s a beloved piece of gear, send it out to be modded by a professional. You can then see what they did and learn.

If I think of more I’ll add.

Brian
Old 22nd April 2019
  #8
Gear Maniac
Hi tchgtr, thank you for this useful information! I am going to sign up for groupdiy right now.

I do have a good soldering iron that is temperature controlled. Do I need an oscilloscope, or can I get an app for the computer to do that?

I am going to download videos on how to read schematics. Do you have a good search phrase to follow up a new category to check out after I watch that video?

I have a trident 65. Each channel is modular!

Also, very good point on ordering caps. I am ALWAYS confused when I get to that point with all of the options

Quote:
Originally Posted by tchgtr View Post
Good advice from Brian above. I would add...

Start simple. You don't want reconditioning a big mixer to be your first project.
You will find that there were things you could have done while you had it dismantled, and you wish you had known better.

I was taught by my dad when young how to read a schematic (it's easier than you think, with lots of instructional material online). Understanding what you are seeing is a whole different matter.

What was helpful for me were some YT vids about modding guitar pedals that I watched. They usually discuss signal path first, which gets you used to tracing the signal from input to output, somewhat like those mazes you find on restaurant place mats. That gets you used to the fun part of circuits, where some minor changes can have a big effect, and the differences between the components involved.

A little more tricky are power supplies (PSUs). Guitar pedals are easy because the PSUs are batteries or external, and not part of learning process as much.
On a mixer, the PSU is incredibly important, and if not working correctly will give you no end of problems, which is true of all gear that uses AC for power.
Basically it takes the AC wall current, converts it to DC (for most gear) and breaks it down into a voltage level that is more useful for whatever device you have. Not sexy, but vitally important.
The device might require 15v, 18v, 24v, 48v, etc. DC, and in the case of gear with tubes, much higher and more dangerous voltages and sometimes AC. So at the beginning, stay away from tube gear.

Don't expect to pick it up fast unless you have lots of time and motivation. Be patient.

Start looking at GroupDIY, but avoid posting. Just lurk and learn for a while, and see what mistakes other folks have made. Once you can ask intelligent questions (and provide schematics!), those folks are true saints who can be very helpful. Most likely, a search will reveal someone has asked this question already, and the answer is already there.

Online searches about specific gear are helpful, and will lead you mainly back here to GS or GroupDIY. Read completely until you understand.

Soon, you will be able to look at a piece of malfunctioning gear and have an educated guess about why it isn't working correctly. Then you'll know you are getting somewhere.

As far as mods go, I generally have come to a point where most of what I do involves capacitors, and trying to clean up the signal path. I find most chip swaps are not worth it, with a few exceptions. Sometimes the initial design with older chips is what gives a piece it's character, and you can lose that in the process. There is LOTS of misleading info online about mods, because people aren't really testing their results.
The Alesis 3630 comes to mind here. This comp CAN be made better, but there sure is a lot of BS about it on the web.

As far as repairing mixers goes (I have rebuilt and recapped about 6 of them so far), the first thing I suggest is recapping them (replacing the electrolytic caps) to get them into their original state, especially if they are over 15 years old with no previous recaps.
Just get it back in it's proper working order first. This alone will likely make it sound much better.
Start with the PSU and the output channels (definitely suggest bypass caps in the signal path here, whether you do it on all channels is another matter), and if you don't have a good temp-controlled iron and lots of experience using it, get that first before you start replacing the hundreds of caps you will find inside.
This leads to even understanding how to order so many caps, where to get them, and what kind to buy, which is another entire field of knowledge.
If the mixer isn't modular (each channel can be removed separately), then you have a quite a big project ahead of you, with no working mixer in the meantime.

So good luck, have fun, and be patient.
Old 22nd April 2019
  #9
Quote:
Originally Posted by shortyboyboy View Post
Hi tchgtr, thank you for this useful information! I am going to sign up for groupdiy right now.

I do have a good soldering iron that is temperature controlled. Do I need an oscilloscope, or can I get an app for the computer to do that?

I am going to download videos on how to read schematics. Do you have a good search phrase to follow up a new category to check out after I watch that video?

I have a trident 65. Each channel is modular!

Also, very good point on ordering caps. I am ALWAYS confused when I get to that point with all of the options
Oscilloscope is handy, especially in combination with a signal/waveform generator, but you can get by without one at the beginning. I don't have a good recommendation as I use an old CRT version, and haven't used software versions. I imagine they are very good.

The video I liked of is one where a guy goes thru the BOSS SD-1 circuit, but I'm sure there are many other pedals that get the same treatment.

I used to work on a Trident 24, and one of their mini-Trident 16 boards. The 24 needed attention, but was still a nice board. The mini was really nice, and newer.
Just getting that 65 back to original condition will give you a great mixer.
Do you have the schematics? Find them. Cherish them.

In regards to your question to Brian about "bypassing" there is lots of confusion, but usually people are referring to putting a 2nd, smaller, capacitor across the same junction point of a circuit in parallel with an electrolytic cap. In the signal path, this helps more hi frequencies pass thru unhindered, and in power supplies, this stabilizes the power being delivered to the circuit.
AC wall power needs to be sanitized as it's converted by the PSU to keep noise out of audio devices.
For example, if you have an old rack device that works but has noise, you might look at the PSU caps to see if they are worn out, and can no longer filter the noise.
In the signal path, bypass caps allow more hi-end stuff thru, which electrolytics tend to filter out. Usually, a polypropylene cap is used for best sound.

I find The Lab at GroupDIY has the most interesting stuff, but be sure to search the archives (top of lab page, I think) for projects that interest you, and start reading. You will learn a lot.

The Panasonic FC and FM caps tend to be the universal electro replacements. They are inexpensive, and well regarded. Try to get the 105 degree Celsius versions.

If you read enough on GDIY, all of this is there.
Old 23rd April 2019
  #10
Lives for gear
 
Brian M. Boykin's Avatar
Here are some pics of .1 mono ceramic caps from the v+ and v- pins of op amps to ground. That’s 2 per op amp. It lowers power supply noise and gives the op amp more available power since upgrading op amps usually means they require more power. Not always though. I use Panasonic FM and FC electro’s because they’re readily available and sound good to my ears. I bypass the electro’s in the audio path with .01/250 WIMA’s for the reasons described above. I’m in the process of swapping all the carbon film resistors in my console with dale metal films. Jim Williams says he hasn’t measured any difference in distortion but I agree with him that they sound better. Transistors can be swapped also. All to more modern lower noise and lower distortion parts. It does make a difference but can also change the sound of the gear so it’s a trade off. I prefer clean transparent audio so it doesn’t concern me much. I have yet to mod a piece of gear and be unhappy with it. Here the pics.
Attached Thumbnails
Bringing your gear back to life!-87bbcf83-5137-408f-9126-2a12248e862a.jpg   Bringing your gear back to life!-b2daab68-6ac3-4141-9da5-f98b7a4923a2.jpg  
Old 23rd April 2019
  #11
Gear Maniac
 
drsaamah's Avatar
Quote:
Originally Posted by shortyboyboy View Post
Great! We are looking forward to hearing what you have to say
I said to follow, not to contribute

But yeah I've also been interested in learning to mod, but don't know where to begin with the theory. Do I study a ton of electrical engineering and then learn how that applies to audio processing? I did just get done with DIYre's mod kit for the Alesis 3630, which was great in that it forced me to finally get good at soldering and desoldering (let me tell you, soldering a lead onto a lead is just as terrible as it sounds) but I'm sort of annoyed because I feel like I didn't learn anything about *why* these modification are supposed to make the unit better. Are the brands of these capacitors and ICs just known to be better? And also... what is better? I guess, I just want to understand how these things actually affect audio signals so I can make decisions for myself. Like an actual understanding of what is going on.
Old 23rd April 2019
  #12
Gear Addict
 
audiospecific's Avatar
 

Quote:
Originally Posted by shortyboyboy View Post
I guess my question for you all is...

How do I start learning about how electronica flow works, and most importantly to me how to fix it?
Well, you can take vocational courses at a college like I did. Work in a repair shop or work with someone who repairs things.

I started in the world as a Tv/VCR repair guy. I went to a special school that exclusively taught me how to fix Tv, Vcr, video disk, cd players, tape players, amplifiers, and radios. Unfortunately, very few appreciate my 3 year course I went through, because it was just a certificate course instead of a degree.
When the consumers went to a throw away society, I was out of a job. I regathered myself, and went into the Air Force. There I learned about power generation and some other stuff, but advanced very quick because of my advanced knowledge I already had. I was fixing stuff and other stuff I would modify, enhance and upgrade fighter jets with a special group of people tasked to do this. When I got out I worked at different factories doing RMA repair. The city I ended up in the company moved off and I got stuck here because I married someone that has an established career in this area. I had to use or lose my education benefits (GI BILL), so I ended up using it up to get an associates degree in electronics technology that I guess people think they can do what I can do.

Combined in this 15 years of learning and working with stuff. This is how I learned. I worked for a guy while fixing tvs that got me into tube technology. Interesting that those old guys had different terminology for things. And you will run across things that have different ways to look at the same circuit.

After about 4-5 years, I learned how to fix everything without a schematic because the majority of things do not have a schematic available to be used. Audio is easy to begin with, but the pro audio sector is the easiest to get around quickly because there is service data for most things.

Some guys here give me a bad time. But when I look back at, it its because their knowledge base is not the same as me, and I see it can intimidate others.

I'm in the pro audio field because I love music. Some don't understand why I volunteer doing stuff in the music community nor why I would work as a stagehand or a theater carpenter, or go do other non-technical stagehand things.

There are two levels you want to learn. How it works and how do I troubleshoot this thing. I know you want to "experiment a little" which is fine, but you do that on a simple circuit or unit to do that with.

Then setting up a work area for doing the repairs: Tools, and lighting, and all that stuff..

Its been hard to find anyone near the same level to talk about stuff in person. I found a couple on here I can have a few theoretical discussions with without it being trolled too badly.
Old 23rd April 2019
  #13
Lives for gear
 
EvilRoy's Avatar
Dear lord, is it mandatory to mod a 3630 first to learn on? I actually still have mine and thought about it but don't want to waste my time. The reviews of a post-mod 3630 are meh.

Thought I would just jump in and start with the MCI JH-5 preamps with their big fat juicy circuit boards. Most of what I need to do is recap older gear and would like to know enough to put in better ones. My D&R mixer uses TL072 op amps throughout and they're all socketed. I know that chips have improved since '98 but I also know that I probably need a circuit mod to take advantage of them. The dude who builds The Silver Bullet also has a D&R that he's modded the heck out of and I'd like to do the same. No transformers in the D&R which is why I want to recap my tape decks' pres first. I actually do know how to read a schemo, just don't know why it all works. Getting some good tips from this thread. Much appreciated. Currently pricing oscilloscopes, will need one anyway to calibrate the decks.

Like Shorty...it's hard for me to plow through a book containing circuits and math equations (electronics is a LOT of math), as exciting as that sounds. I think what all us newbs want is to fast track an education that took decades for the old pros to learn, with a couple of videos. Please and thank you.



Edit: Newbs may first want to learn how to wire a guitar, a passive circuit, that's how I started. It taught me what a variable resistor is and how a capacitor affects tone, and more importantly...why they work. After a small amount of reading, I now know what a diode does, op amps etc. and am starting to understand active circuits a little better.
Old 23rd April 2019
  #14
Lives for gear
 
Brian M. Boykin's Avatar
Quote:
Originally Posted by EvilRoy View Post
Dear lord, is it mandatory to mod a 3630 first to learn on? I actually still have mine and thought about it but don't want to waste my time. The reviews of a post-mod 3630 are meh.

Thought I would just jump in and start with the MCI JH-5 preamps with their big fat juicy circuit boards. Most of what I need to do is recap older gear and would like to know enough to put in better ones. My D&R mixer uses TL072 op amps throughout and they're all socketed. I know that chips have improved since '98 but I also know that I probably need a circuit mod to take advantage of them. The dude who builds The Silver Bullet also has a D&R that he's modded the heck out of and I'd like to do the same. No transformers in the D&R which is why I want to recap my tape decks' pres first. I actually do know how to read a schemo, just don't know why it all works. Getting some good tips from this thread. Much appreciated. Currently pricing oscilloscopes, will need one anyway to calibrate the decks.

Like Shorty...it's hard for me to plow through a book containing circuits and math equations (electronics is a LOT of math), as exciting as that sounds. I think what all us newbs want is to fast track an education that took decades for the old pros to learn, with a couple of videos. Please and thank you.

My console is a Soundcraft 400b. No transformers and was loaded with tl072’s and tl071’s. I put opa2134’s in the input stage, opa2134’s in both the EQ stages, and lme49710 for the fader buffer. I recapped with Panasonic FM and bypassed all the electrolytic caps in the audio path with .01/250 WIMA’s. It made a considerable difference. I had several channels in different stages and can say the recap made the biggest difference, however, swapping the op amps made a huge difference as I began mixing and summing channels. All the EQ caps were swapped from the box films to WIMA’s. I did value for value. Again, made a difference. I just finished switching all the carbon films to Dale metal films in 8 channels. Again, made a sonic difference. What I’ve found is it’s easier to get everything to sit in the mix and requires less EQ. I mostly use subtractive in the mids and boost the highs and lows just a hair. Sometimes no EQ is required at all. One of the biggest improvements was building a new power supply from Power One modules. I can push the levels much farther into the red and it doesn’t fall on its face. I learned all this from this sub forum. Mostly Jim Williams, John Roberts, Nosebleed, Audiospecific, Recordruff, Brian Roth, Radardog, Richard Crowley, Matt Syson, Gyraf and many others I’m probably forgetting. These guys know their **** and have test equipment to prove they know their ****. They can be a little rough from time to time but most of the time that’s what you need. A smack upside the head. I say, pick a piece of gear you can stand to mess up and search mods for it. Organize the mods on paper. Maybe do it in stages. You do it all at once and it goes bad you’ll have a harder time finding where you messed up. I’d start with recapping. Makes a big difference and it’s pretty easy if you stay with value for value. This requires piping the top and writing down values. Mouser is where I do most of my purchasing. They’re in Tx and I’ve ordered before like 3:00 on a Monday and had it on my doorstep the following morning. Digikey, Parts Express, Allparts, and EBay if you can find a trusted seller. EBay is last resort for me.
Old 23rd April 2019
  #15
Lives for gear
 
EvilRoy's Avatar
Quote:
Originally Posted by Brian M. Boykin View Post
My console is a Soundcraft 400b. No transformers and was loaded with tl072’s and tl071’s. I put opa2134’s in the input stage, opa2134’s in both the EQ stages, and lme49710 for the fader buffer.
Sigh, I'll never get rid of that 3630.

Thanks for the response, quick follow up question. I know there are pin for pin replacements on the TL072 (theoretically). Did yours require a circuit mod?
Old 23rd April 2019
  #16
Lives for gear
 
Brian M. Boykin's Avatar
Quote:
Originally Posted by EvilRoy View Post
Sigh, I'll never get rid of that 3630.

Thanks for the response, quick follow up question. I know there are pin for pin replacements on the TL072 (theoretically). Did yours require a circuit mod?
I added the .1 mono ceramic from the power pins to ground and some I added 23pf mono ceramics in the feedback loop where they were missing. Only if a resistor was present in the feedback loop and there was not a cap. The original design had 100pf caps already in place for some of the feedback loops. Some use surface mount caps soldered between the appropriate pins, I used actual caps across the appropriate pins. Someone like Jim will measure distortion with his Audio Precision and optimize the circuit for the lowest distortion. I’ve read many threads on D&R mods. Search it out. They are solid platforms for modding from what I’ve gathered. People who have them love them. Soundcrafts do not get much love and people tend to roll their eyes but mine has been very easy to mod and very stable. I actually combined 2 into a 32/8/2.
Old 23rd April 2019
  #17
One of the reasons the TL072 is used so much in gear is not just the low cost to manufacturers, but also the low amount of current it needs to operate.
If you replace all of them in a mixer, you may run into troubles because the chips you use to replace them are drawing more current.
TI makes an upgraded version of the chip: the TLE 2072, which draws about the same amount as the original, and does sound slightly better.
If you fill a mixer with OPA 2134 (which DO sound nice!) you may unintentionally overtax the power supply. If you use Burr Brown, each chip needs 4 times the power of a TL072!
Once again, I recommend that newbies start simply. Making a complete overhaul of your mixer in one fell swoop is asking for trouble, especially if you are new to the whole shebang.
For example, many great recordings have made using a Trident 65, so just getting one back to original shape should set you up just fine.
I saw a very good comment once that THD specs for even the cheapest modern gear are so much better than what was used by top-line artists and producers in the 60s and 70s that people should just forget about it all and get to work making music.
There's some truth to that IMHO, but I understand the fun of taking inexpensive gear, and hopefully making it better.
Just remember to use a fan when soldering to blow the solder fumes away.

P.S.
I have had good results with replacing SSM 2017 in some mic pres with SSM 2019, and using OPA 2134 as output chips or some of the fancier LME stuff that Brian references above. This way the current draw on the PSU might be more, but you don't have so many chips dragging it down. Add bypass caps on the signal path, and you'd be surprised how good an inexpensive pre can sound. I refitted an old Behringer Pre Q according to some Jim Williams recommendations on this forum, and it sounds very nice. Not a lot of gain on that pre, but very clean and balanced, with good transients.
Also...
Somewhere on here are Jim's recommendations for upgrading the dbx 163x. I now own two that I modded, and they are fantastic.

P.S.S.
Condenser mics are also simple circuits, and a good place to start. Get some cheap, used MXLs, and play with them. All the schemos are easy to find online. My advice is to avoid the small condensers like the 990 and it's variants.
If you can find a cheap 2003, you can make it much better by just replacing a few caps, and you will have a nice mic in the end. It has a better capsule than the 2001. Look for any Chinese LCD mic with a white plastic ring around the capsule, and not the brass ring.
The M-Audio Nova has a nice capsule, but a crappy circuit. I bought a few for next to nothing used and put their capsules into an MXL 9000 tube mic, replacing the brass-ring K67 copies. Suddenly I have a pair of wonderful tube condensers, and a few donor bodies for mic projects.
One of the bodies became a Big Ugly tube mic (see GroupDIY...similar to Royer Mod) with a Chinese C12 capsule, and it's one of my favorite condensers for my own voice.
It's a big world out there. You have lots of reading and research to do. Don't worry too much about the math at first, but definitely familiarize yourself with Ohms Law.
Old 23rd April 2019
  #18
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Brian M. Boykin's Avatar
PSU considerations cannot be stressed enough. I swapped out a few channels to see what the fuss was about. Once I heard I did not do anymore until I had a new power supply. I built it myself and came in at about a 3rd to 1/2 the cost of having one built. Also as mentioned above. I’ve built many of the MicParts LDC mic circuits and SDC circuits and it’s very simple and the results are great when paired with an aftermarket capsule. I used MXL bodies from mics I used till I was able to upgrade. I began all this because money doesn’t grow on trees around my house so this was a great way to A) come away with great sounding gear and B) learn what’s in the gear to make better purchases later. I very rarely buy anything new. Except maybe cables, mic stands and patch bays. All the rest is older gear I’ve recapped and updated for better performances.
Old 25th April 2019
  #19
Deleted 3cb98a6
Guest
My advice would be to start with simple scratch-builds from schematic. Learn to troubleshoot these builds and then move on to repairing.

It.s a road that requires patience...
Old 25th April 2019
  #20
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nosebleedaudio's Avatar
 

Quote:
Originally Posted by Brian M. Boykin View Post
My console is a Soundcraft 400b. No transformers and was loaded with tl072’s and tl071’s. I put opa2134’s in the input stage, opa2134’s in both the EQ stages, and lme49710 for the fader buffer. I recapped with Panasonic FM and bypassed all the electrolytic caps in the audio path with .01/250 WIMA’s. It made a considerable difference. I had several channels in different stages and can say the recap made the biggest difference, however, swapping the op amps made a huge difference as I began mixing and summing channels. All the EQ caps were swapped from the box films to WIMA’s. I did value for value. Again, made a difference. I just finished switching all the carbon films to Dale metal films in 8 channels. Again, made a sonic difference. What I’ve found is it’s easier to get everything to sit in the mix and requires less EQ. I mostly use subtractive in the mids and boost the highs and lows just a hair. Sometimes no EQ is required at all. One of the biggest improvements was building a new power supply from Power One modules. I can push the levels much farther into the red and it doesn’t fall on its face. I learned all this from this sub forum. Mostly Jim Williams, John Roberts, Nosebleed, Audiospecific, Recordruff, Brian Roth, Radardog, Richard Crowley, Matt Syson, Gyraf and many others I’m probably forgetting. These guys know their **** and have test equipment to prove they know their ****. They can be a little rough from time to time but most of the time that’s what you need. A smack upside the head. I say, pick a piece of gear you can stand to mess up and search mods for it. Organize the mods on paper. Maybe do it in stages. You do it all at once and it goes bad you’ll have a harder time finding where you messed up. I’d start with recapping. Makes a big difference and it’s pretty easy if you stay with value for value. This requires piping the top and writing down values. Mouser is where I do most of my purchasing. They’re in Tx and I’ve ordered before like 3:00 on a Monday and had it on my doorstep the following morning. Digikey, Parts Express, Allparts, and EBay if you can find a trusted seller. EBay is last resort for me.
Thanks for remembering me...
One thing for sure Every tech I ever worked around/with ect new different things and had different ideas about things and no doubt was exposed to different types of gear and their common problems...ALL VERY valuable..
But was IS very confusing esp. when your starting out in certain areas of electronics is how some can have a very negative attitude about things such as "Caps are not important" ect..That one came from a well known tech in Atlanta in the 80's...
No doubt Egos can & do influence what some claim ect...

Knowing what to do and what NOT to do is very important, obviously that takes TIME...
I could not do much without a scope. Having a nice bench with ALL the truly needed tools & gear is a must to do most tech stuff..It's kinda like the Recording business, you really need many little items as well as the larger more $$ things..
I have at least 100+ cables of all types to do testing/demos ect...
Plus the many $$$ testing/adjusting type of gear, some I may only use a few times a YEAR...but would not sell them..
Some love to debate caps/chips/discrete/Transformers for ever, at some point you have to use something and record something...Ha ha...

Yesterday I was testing the change of Phase with the AC power, a Non grounded tape machine and before the polarized Two pin power cable, one way I measured (between Chassis & a Known ground) 14V AC, other way 93V AC...I checked the Phase on the power transformer and it was as expected LOW (14V) when IN Phase...This can & IS a problem with AC outlets needed to be on the SAME AC phase from the panel, something MANY don't know about or even don't think it makes a difference...It does..Hope the above does NOT confuse you just an example of knowing what truly CAN make a difference IF its not correct...

Sorry for the LOONG post, that's kinda rare for me..Hate to type..
Old 25th April 2019
  #21
Gear Addict
 
audiospecific's Avatar
 

Quote:
Originally Posted by drsaamah View Post
I said to follow, not to contribute

But yeah I've also been interested in learning to mod, but don't know where to begin with the theory. Do I study a ton of electrical engineering and then learn how that applies to audio processing? I did just get done with DIYre's mod kit for the Alesis 3630, which was great in that it forced me to finally get good at soldering and desoldering (let me tell you, soldering a lead onto a lead is just as terrible as it sounds) but I'm sort of annoyed because I feel like I didn't learn anything about *why* these modification are supposed to make the unit better. Are the brands of these capacitors and ICs just known to be better? And also... what is better? I guess, I just want to understand how these things actually affect audio signals so I can make decisions for myself. Like an actual understanding of what is going on.
You asking is contributing too.

Ok, well you want to know about modifying stuff. Well when I approach something i haven't modded, I ask myself "what do I want it to do differently?"
Then I analyze each stage and find what needs to be done to get the desired effect I want.
To me, parts are parts. Some parts work better than others in certain circuits so there is no really bad or good parts, its what works the best for that circuit operating within the set conditions.
Old 25th April 2019
  #22
Gear Addict
 
Pindrive's Avatar
I've just finished video 3 from this guy. I'm working down the same path as many of us...trying to learn more. This is the only learning source i've been able to stick with. He breaks it down pretty slowly & thoroughly.
https://youtu.be/OGa_b26eK2c
Old 25th April 2019
  #23
Lives for gear
 
EvilRoy's Avatar
Quote:
Originally Posted by Pindrive View Post
I've just finished video 3 from this guy. I'm working down the same path as many of us...trying to learn more. This is the only learning source i've been able to stick with. He breaks it down pretty slowly & thoroughly.
https://youtu.be/OGa_b26eK2c
Excellent.

He kinda rambles a bit, 45 minutes to cover a 10 minute chapter in "Electronics for Dummies", but he's very thorough and understanding this stuff/Ohm's Law is critical. The whole concept of 'electricity doesn't actually move' is a little weird for me.

Many thanks to the previous responders for the info on my specific needs. The D&R I bought was never commissioned or used, essentially spending the first 20 years of it's life in climate controlled storage. It was turned for 1 hour in 2000 for a Mix mag. photo shoot and again for 6 months a few years later. That's it, not a scratchy pot or fader on the thing (although 5 of my Panasonic motors died). I was lucky enough to buy Black Oak Arkansas' old 48 channel, sans master section for $500. I now have a buncha dynamics cards to install and spare monos up the wazoo. Need to figure out if the dynamics cards need they're own PSU or not (now have a non-working 12v and 18v also). I have a recommendation for a PSU genius from drBill so I'll probably go that route but the plan is to recap/mod a couple of spare monos then slowly go through the mixer, swapping out 2 monos at a time. Hoping that by the time it needs a recap, it will already be complete. Definitely wanna try some of those master mods Ive read about, one day. Brad, who modded his Vision, claims it sonically smokes an SSL now.
Old 25th April 2019
  #24
Gear Maniac
 
drsaamah's Avatar
Quote:
Originally Posted by audiospecific View Post
You asking is contributing too.

Ok, well you want to know about modifying stuff. Well when I approach something i haven't modded, I ask myself "what do I want it to do differently?"
Then I analyze each stage and find what needs to be done to get the desired effect I want.
So how do you go about analyzing a stage? I doubt simple voltage and resistance readings will give me much insight on what's going on between the I/O. I'm guessing I probably need to invest in an oscilloscope.
Old 25th April 2019
  #25
Gear Addict
 

Way back... in the early 1980s... I began with an old edition of the Forrest M. Mims III book, "Getting Started in Electronics". It's rather basic, but it does contain some good learning projects. Build projects. Some won't work right away, but you'll learn more from those than from the ones that work immediately. You'll gain practice in troubleshooting by working on these well-documented projects.

And, don't fear surface-mount technology. It takes some modification of soldering techniques to work on SMT gear, but in some ways it's easier than through-hole.
Old 26th April 2019
  #26
Lives for gear
 
Brian M. Boykin's Avatar
Quote:
Originally Posted by EvilRoy View Post
Excellent.

He kinda rambles a bit, 45 minutes to cover a 10 minute chapter in "Electronics for Dummies", but he's very thorough and understanding this stuff/Ohm's Law is critical. The whole concept of 'electricity doesn't actually move' is a little weird for me.

Many thanks to the previous responders for the info on my specific needs. The D&R I bought was never commissioned or used, essentially spending the first 20 years of it's life in climate controlled storage. It was turned for 1 hour in 2000 for a Mix mag. photo shoot and again for 6 months a few years later. That's it, not a scratchy pot or fader on the thing (although 5 of my Panasonic motors died). I was lucky enough to buy Black Oak Arkansas' old 48 channel, sans master section for $500. I now have a buncha dynamics cards to install and spare monos up the wazoo. Need to figure out if the dynamics cards need they're own PSU or not (now have a non-working 12v and 18v also). I have a recommendation for a PSU genius from drBill so I'll probably go that route but the plan is to recap/mod a couple of spare monos then slowly go through the mixer, swapping out 2 monos at a time. Hoping that by the time it needs a recap, it will already be complete. Definitely wanna try some of those master mods Ive read about, one day. Brad, who modded his Vision, claims it sonically smokes an SSL now.
I don’t know what you paid for your D&R but I paid $200 for the 24/4/2 and $400 for the 16/4/2 that I combined into a 32/8/2. I have a spare master module and 8 spare input modules. I paid roughly $500 in parts to build the power supply. $250 to have Jim mod the Master module. And off the top of my head maybe a couple grand in op amps, caps, transistors, and metal film resistors. It sounds good. I don’t have a max budget. I’ll keep going till it’s complete. Even if I hit $5k total I still feel like I have a better product than anything in that price range new or old unmodded. The goal was transparency and that it is. If I had to do over I’d start with a 600 32/8/2 from the get go. I just didn’t have that kind of money in 2005. So I’ve chipped away at what I’ve got.

Learn how to mod. You won’t regret it. Listen to those who have gone before you. They’ve seen the inside of gear over the last 30 to 40 years. They know. You’ll be happier with your purchases and your recordings.
Old 26th April 2019
  #27
Gear Addict
 
Pindrive's Avatar
Quote:
Originally Posted by Blackandwhite View Post
Read my post, I've explained how to trouble shoot electronics with a scope.

@ Pindrive ; you'll learn electronics by building electronic gadgets, especially the mistakes you're going to (which you're going to make for sure when you start your own projects). If you make these projects you'll start to learn more about how your new gadget works and why it works. You should check out the books I recommend in my previous post.
Thanks. Yes, I've built a pedal kit & repaired a few synths. I'm going back to basics, myself, to try to understand more. To understand, as you say, How It works.
Old 26th April 2019
  #28
Lives for gear
 
EvilRoy's Avatar
Quote:
Originally Posted by Brian M. Boykin View Post
I don’t know what you paid for your D&R but I paid $200 for the 24/4/2 and $400 for the 16/4/2 that I combined into a 32/8/2. I have a spare master module and 8 spare input modules. I paid roughly $500 in parts to build the power supply. $250 to have Jim mod the Master module. And off the top of my head maybe a couple grand in op amps, caps, transistors, and metal film resistors. It sounds good. I don’t have a max budget. I’ll keep going till it’s complete. Even if I hit $5k total I still feel like I have a better product than anything in that price range new or old unmodded. The goal was transparency and that it is. If I had to do over I’d start with a 600 32/8/2 from the get go. I just didn’t have that kind of money in 2005. So I’ve chipped away at what I’ve got.

Learn how to mod. You won’t regret it. Listen to those who have gone before you. They’ve seen the inside of gear over the last 30 to 40 years. They know. You’ll be happier with your purchases and your recordings.
I thought I would just pretend to buy a Silver Bullet, then suck out Brad's brains with a straw while he wasn't looking, haha!

Yeah, getting to know this mixer has been a bit of a process. Got to understand it a lot better when I had my eproms cloned. The tech I hired to pull the master and reinstall it couldn't figure out the second part and bailed. Had to put this thing back together myself. Oh, turns out you don't need to pull the master to pull the eproms, live and learn. Nothing in this mixer is wired normally, all the db25s are backwards and non standard. Those Dutch like to march to the beat of a different drummer, I guess. So far the mods have only involved routing stuff. It has 256 tie lines in the bay, half of which are now half normalled. I have to dive into the wonderful world of ribbon cable building to install those dynamics cards. The dynamics metering consists of a throbbing yellow LED. Luckily the cards have meter outputs on 2 pin Molex connectors, gonna build a cable to spare db25 slots on the back. I kept the bridge from my Mackie 32/8 which just happens to have 64 inputs switchable between channel and mix, perfect. Wanna rehouse that above the D&R bridge for dynamics meters. Probably have to do some electronic trickery to match voltages and have the faceplate rescreened. It also has a now redundant Stems section, which is essentially a (2x24)x6 summing amp which feeds the surround master. The groups are floating so the 1st 24 modules handle mix or tape on the lower faders. 25-32 get their mix feed from whatever is in the channel, kinda useless. Was wondering about feeding 6 of those mix inputs from the Stems modules instead. The Stems inputs only have solo and mute switches but I kept my 2 Mackie Ultra 34s also for automated level (I'm thinking future keyboard inputs since they don't match D&R sonics). Either that or I'll wire them externally to monitor the groups with a button push without losing a tape input. Also have the code to the automation bridge and am currently porting it to AU (getting close!). Just a straight port at first but then I wanna modify so I can flip control of the faders and control the channel inputs and their small 60 mils with the motors on the bottom, link faders in pairs (sick of trying to match level with 2 monos on a stereo signal) add mute groups and midi scenes. No reason this can't be a really big midi controller also.

All that before I start thinking about modding the electronics. Have a couple of tape decks with 12 transformer balanced pres and a Dolby system that are crying for attention much louder than the D&R. Seriously thinking a Master Section/Jim expense would be money well spent...if I ever have any. Paid waaaay more than you did, about the price of a used Honda Civic. Had to. When I was looking for a vintage mixer, this one just jumped up and cried "Take me home!"

It was love at first sight.
Old 27th April 2019
  #29
Gear Addict
 
Pindrive's Avatar
Quote:
Originally Posted by Blackandwhite View Post
@ shortyboyboy : fixing electronics isn't hard, it's a great and fun hobby. I can suggest you to read some books about electronics, especially if you're a beginner. I can recommend you the following books:


For beginners/novice:
- Make Electronics by Charles Platt
- Electronic Gadgets For The Evil Genius (2nd Edition) by Dave Cutcher
- Practical Electronics for Inventors (4th Edition) by Paul Scherz

Fixing electronics:
- How to Diagnose and Fix Everything Electronic by Michael Jay Geier
- Electronic and Electrical Servicing by Ian Sinclair

MUST HAVE:
- Electronic Projects for Musicians by Craig Anderton (you def must own this book if you're into fixing audio equipment)
- Encyclopedia of Electronic Components Volume 1, 2, 3 by Charles Platt

Tools you should have:
Solderstation: Get a Weller WS 81, it's one of the best solderstations out there. A friend of mine bought this one back in the 80ties and has been using it every single day and it never broke. He is still using it now. A de-solderpump is a must have.

Solder wire: Soldering is very easy, you can get these experimental PCB boards they have these holes in them. You can use them for small projects which will also increase your soldering skills. Avoid lead free tin, it's horrible AVOID IT LIKE A DISEASE. Go for the Sn60Pb40 type, preferably 0.5mm so it's easier to control the amount of the solder you're applying. Multicore solder is very good, it flows good. I can recommend you that. Stannol is also a good brand.

Multimeter: Go for a Fluke if you're serious about this hobby. They produce some of the finest multimeters.

Oscilloscope: IMHO a must have if you're going to fix audio equipment. I can recommend the Rigol DS1054Z, get the 400USD model. Some of the features will be unlocked and you have to pay for them buy entering a license key, but there is a hack for this which unlocks all the features on this scope. Once you unlock it it will be the same scope as the expensive model. (spend the rest on a synth lol).

Components: it's always to have components laying around, they're dirt cheap. You should get the E24 resistor series kit, capacitor kit, tactile switches, IEC connectors, insulated wire, 1N4XXX diode kit, a bunch of IC sockets, a bunch of voltage regulators (+5v, -5v, +12v, -12v, +15v, -15v), heatshrink tubes.

There is an Asian equivalent of Mouser, they supply components from top Asian brands which are very cheap. Dave Jones from the EEVBlog has reviewed this website and they seem to be legit: Electronic Components Distributor | EasyEDA Parts Online Store - LCSC

Here is a fun fact: I've seen people selling these tactile switched for the Juno 106 for a ridiculous price on eBay. On the site I provided they sell exact the same component for just 1 cent. Go figure.

Component tester: also a must have, with this device you can test out components like transistors, diodes, capacitors, voltage regulators. Sometimes a capacitor looks normal, but it's broken internally. With an ESR meter you can be sure of this. Most component testers have an ESR meter. They're pretty cheap.

Learn to use a 3D CAD program
Learn how to make custom components in a 3D cad program. For an example you're working on some kind of equipment and the buttons are all messed up. What do you do? You'll either over pay some greedy guy on eBay or you recreate the component in a 3D CAD program and send off the model to some 3D CNC milling company in China after which you'll receive a brand new component for less the price. This is good for buttons, slides caps, knobs and heatsinks. You're going to need a good digital caliper to measure everything. You don't need to be an expert in a CAD program, there are so many tutorials on YouTube. Also you can find these CNC milling companies on Alibaba.

Fixing audio equipment
The very first thing you need to do is to open up the gear and check the PCB's and components, in many cases if a component has burned out you'll see it (it's literally burned) often it will damage the surrounding components or the traces on the PCB. In a case like this you'll need to fix the traces, you do this by soldering thin solid wires to the traces, so the signal can continue. You'll also need to replace the component. Or one of the caps is leaking, in this case you need to remove the cap, clean the board, replace the cap with a better one just like the Panasonic caps mentioned by the other poster.

Usually when fixing a synth for an example if one of the keys doesn't work, in most cases it's a case of a bad contact. You can open it up and clean the contacts. If doesn't turn on, usually there is a problem with the power supply in most cases it's a bad capacitor or the fuse has broke, I would also check and test the power switch with a multi meter, if it gets the power but doesn't deliver the output on it's rails then it's probably a voltage regulator. You can use a multimeter to test these regulators.

If it doesn't produce any sound the problem might be a dead voice. For this you need to get the schematic and use the scope to follow the trace right from the sound generator. Like IC1 produces the sound, the IC has a voltage input and audio output. You'll need to check out the datasheet of the IC, the next step would be probing, so you'll see if it gets an input and output. If it doesn't get a voltage input, you'll go one step back, whats the source of the voltage output for this IC. If it the source is putting out the voltage, in this case the IC is dead. If for an example the IC doesn't have an audio output then it's broke. If it's fine you'll check the next component which receives the audio signal of the IC. Rinse and repeat. You can literally see the audio waves on your scope thats why a previous poster also recommend to have a scope.

If a button doesn't work in most cases the button needs to be replaced but it also can be cleaned as you can open up some buttons (for an example like the ones in vintage drum machines like the Drumulator). If it's one of those small tactile switches you can easily replace them since they're very cheap. If it's a custom switch you can either look for the original part or you can make an adapter with a tactile switch and a custom button (thats why I recommend you to learn some CAD program). But for this you need how to make PCB's which is also damn easy.

With 7 segment displays, if it doesn't work it's either the led driver, the resistors on the led drivers output or the display itself that has died. But also in a case like this you can use the previous troubleshooting method I mentioned. There are two kind of 7 segment displays, common anode and common cathode. If your vintage synth uses a common cathode display, a common anode display won't work.

In some cases a LCD display doesn't get the proper voltage for operation, in this case you'll need to check out the voltage regulator thats responsible for providing the voltage to the LCD display. You can find this in the schematic. If it's dim , the chance is big that the voltage regulator doesn't provide enough juice. In a case like this you must replace the regulator.

Sometimes you can save something on a device like a synthesizer, in most cases the battery needs to be replaced because it has no juice or it's leaking. There is a nice trick, get one of those AA battery holders and remove the old battery holder. Solder the new battery holder and glue it somewhere with hotglue. Now you can use those special batteries they use in smoke detectors etc. They will last you way longer.

An another reason why a scope is so important is when you've been swapping out components on a voice card of a synth you'll need to re calibrate it. You can always find these steps in the service manuals. Usually you'll have a point you need to probe, while playing on a certain key the signal should be a fixed variable, you can see this on the scope. If it doesn't match there is some kind of trimmer you can turn, you'll turn this till you get the required signal. It's the same with some power supplies, in that case you'll need to use the voltmeter, for an example you replaced the voltage regulator and now you need to calibrate the powersupply. You just put the probe on the output of the power supply rail and see which trimmer you must use to increase or decrease the output voltage. You'll turn it till you get the required output. If you changed lets say a 5v regulator, the output should be 5v.

Troubleshooting goes like this, whats the problem, find the area where the problem is, start probing till you find the dead signal. It's like fixing a puzzle. If you're interested in those books just send me a PM. And good luck on your journey.
Thanks for this!
Old 1st May 2019
  #30
Gear Maniac
Thanks for this useful information. I am having a bit of him from a few pieces of outboard gear when insert them into channels of the console. I read that you should ground external gear to the console. Does that mean run a line from the casing of the gear to the casing of the console? Also, have you had experience grounding a
Console into the earth with a stake ? I hope I’m saying this correctly. Ha!

Quote:
Originally Posted by tchgtr View Post
Oscilloscope is handy, especially in combination with a signal/waveform generator, but you can get by without one at the beginning. I don't have a good recommendation as I use an old CRT version, and haven't used software versions. I imagine they are very good.

The video I liked of is one where a guy goes thru the BOSS SD-1 circuit, but I'm sure there are many other pedals that get the same treatment.

I used to work on a Trident 24, and one of their mini-Trident 16 boards. The 24 needed attention, but was still a nice board. The mini was really nice, and newer.
Just getting that 65 back to original condition will give you a great mixer.
Do you have the schematics? Find them. Cherish them.

In regards to your question to Brian about "bypassing" there is lots of confusion, but usually people are referring to putting a 2nd, smaller, capacitor across the same junction point of a circuit in parallel with an electrolytic cap. In the signal path, this helps more hi frequencies pass thru unhindered, and in power supplies, this stabilizes the power being delivered to the circuit.
AC wall power needs to be sanitized as it's converted by the PSU to keep noise out of audio devices.
For example, if you have an old rack device that works but has noise, you might look at the PSU caps to see if they are worn out, and can no longer filter the noise.
In the signal path, bypass caps allow more hi-end stuff thru, which electrolytics tend to filter out. Usually, a polypropylene cap is used for best sound.

I find The Lab at GroupDIY has the most interesting stuff, but be sure to search the archives (top of lab page, I think) for projects that interest you, and start reading. You will learn a lot.

The Panasonic FC and FM caps tend to be the universal electro replacements. They are inexpensive, and well regarded. Try to get the 105 degree Celsius versions.

If you read enough on GDIY, all of this is there.
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