Learning how to work on a Soundcraft 200B
Old 31st October 2007
  #1
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Thread Starter
Learning how to work on a Soundcraft 200B

I am trying to learn more about electronics on a Soundcraft 200B. The 200B seems to be pretty simple and easy to work on. I've build some SCA pres and am handy with a solding iron and want to learn more. I was hoping to get some advice from the knowledgeable folks here who are so generous with their time (thanks!) and make sure I am not off track. I don't want to blindly start switching out parts based on what I've read in a bunch of different posts, but also understand why I'm doing it.

I have read the famous Eddie Ciletti grounding modification and will be starting with that, it seems to be a consensus amongst folks that this is very beneficial and the first thing to do with these consoles.

Next, I want to go through each channel strip and clean everything and do some key replacements. First I would clean the edge connectors with alcohol. Spray out the faders and switches with compressed air. Spray the pots with tuner cleaner. Use deoxit to clean the jacks. Then look for any bad solder joints and fix those.

Looking at the schematic (SC 1447 Issue 4), the first thing that microphone level audio passes through is C1 and C2, 47u 63v capacitors, used for blocking phantom power. I've read that if you replace these 2 caps with larger value (1000u, 63v) electrolytics, the preamp will perform better at high gain. Specifically, the low end will be extended.

Next, there are the coupling capacitors. These are electrolytics which block DC voltages as the audio signal passes to the next stage. For example, C24, 47u 25v connects the preamp section to the EQ section? I have read that Jim Williams suggested replacing these with a larger value 220u 35v in order to extend the low end.

Another suggestion was replacing the feedback capacitors. As I understand it, this is a capacitor which connects an op amps output to the input. For example, at the first Integrated Circuit stage, a TL072 op amp, a ceramic capacitor C9, 100p, connects pin 1 of the TL072 to pin 2. I've read it is a good idea to replace these with Polystyrene or Wima FKP of the same value. Changing the value will perhaps cause oscillations and other bad things.

The power decoupling capacitors connect the rail voltage (in this case +17v, -17v) to ground. These capacitors C21 & C22, 47u, don't necessarily need to be replaced unless they are leaky or open? Would changing the value of these caps provide any benefit? Or would it put more stress on the power supply?

There are a two different kinds of EQ sections for the 200B, standard (4 fixed frequencies) and deluxe (sweapable mids), I will have a mix of both deluxe and standard modules. The one thing which seems to be a consensus is that the High Frequency shelving EQ can get a little harsh and it is possible to change a capacitor to improve this. Is this the capacitor that connects two of the legs of the pot, in this case a 100n ceramic? I could replace this with a Polystyrene or Wima FKP of the same value?

I have yet to get to the Master section schematic as it's a little more complicated, but I'm hoping what I learn from this will help me conquer that part next.

For the power supply, I plan to replace the main decoupling electrolytic capacitors, C1 & C2, 4700u, 50v. There are so few parts here, I thought I could just replace all the other capacitors. Of course, perhaps the best thing to do is buy a new Power One Supply and be done with it, but learning the different parts of the power supply is educational... One other question, I have a 8 channel 200B and a 24 channel 200B. The 24 channel one is missing the power supply. Did Soundcraft use the same power supply for all 200Bs?

Thank you for any advice you can offer!
Jeff

Last edited by jeff deff; 31st October 2007 at 08:12 PM.. Reason: uh, this is complicated stuff, and I'm a drummer
Old 2nd November 2007
  #2
kid
Gear Head
 

I am planning on re-capping a Soundcraft Delta200. The first thing I am going to do is send the Master section off too Jim for his upgrades. I asked him about re-capping the channels and he recommended oI send him one channel and see what he does and then I can match the values of the caps he changes. Sound like a good idea. I just need to free up some time for the board to be down in order to send it.
Old 2nd November 2007
  #3
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Brian M. Boykin's Avatar
 

Quote:
The first thing I am going to do is send the Master section off too Jim for his upgrades. I asked him about re-capping the channels and he recommended oI send him one channel and see what he does and then I can match the values of the caps he changes. Sound like a good idea. I just need to free up some time for the board to be down in order to send it.
Do it, just got my 400b master back and it was well worth it. Made my ashly sc55 that's inserted on the main mix noticeably in need of work. The master is where you want to start, then you can hear the difference in other mods. I'm slowly making my way through "Optimizing Op Amp Performance" by Jerald Graeme. If you can grasp the math in it then you won't just be dropping op amps, caps and resistors in here and there but actually using math to optimize the circuit. Jeff, ditch the factory power supply and build one with power one modules. I started a thread titled "Power one module question", lots of good info from the brains of geekslutz. As for schematics, I got mine from music parts.com. Can't remember if they had 200b's, but take a look.

Good luck,

Brian
Old 3rd November 2007
  #4
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Thread Starter
Brian,
Thanks for the advice. I just ordered a new power supply. I got the Power One PFC375-1015F. I hope it works out, it is adjustable between 12-17 VDC and has both positive and negative rails, so I should be able to set it to + and - 17VDC. Also, it has a built in fan and is 25 amps so it should have plenty of power if I want to upgrade op amps. I hope buying it off eBay wasn't a mistake...

Now I'll have to look into upgrading the master module with Jim Williams.
Old 16th November 2007
  #5
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Question Mods for 200b

Im planning on taking on a 200b mod as well,

I would like to take out a few modules and rack mount them as outboard MIC pre's/ channel strips... Feasilbe?

I would also want to replace any caps and other components as J. Williams has suggested.

Any sugestions?

BTW: check Astrodyne for power supplys, I spoke with a rep there, and they offer AC/DC units up to 150w not requiring a fan! example:
[FONT='Arial','sans-serif']http://datasheet.astrodyne.com/RS150.pdf[/FONT]
Old 16th November 2007
  #6
Quote:
Originally Posted by jeff deff View Post
Looking at the schematic (SC 1447 Issue 4), the first thing that microphone level audio passes through is C1 and C2, 47u 63v capacitors, used for blocking phantom power. I've read that if you replace these 2 caps with larger value (1000u, 63v) electrolytics, the preamp will perform better at high gain. Specifically, the low end will be extended.

Not so. These are big enough, use 100 uf max. The cap under the gain pot should be changed to 100 uf that will extend low end at high gains.

Next, there are the coupling capacitors. These are electrolytics which block DC voltages as the audio signal passes to the next stage. For example, C24, 47u 25v connects the preamp section to the EQ section? I have read that Jim Williams suggested replacing these with a larger value 220u 35v in order to extend the low end.

Good call.

Another suggestion was replacing the feedback capacitors. As I understand it, this is a capacitor which connects an op amps output to the input. For example, at the first Integrated Circuit stage, a TL072 op amp, a ceramic capacitor C9, 100p, connects pin 1 of the TL072 to pin 2. I've read it is a good idea to replace these with Polystyrene or Wima FKP of the same value. Changing the value will perhaps cause oscillations and other bad things.

Or not. I use 10 pf across the 22k feedback resistor and another 10 pf from pin 3 to ground. Cutting the 22k feedback resistor from the inverting input and then tying it to the emitter of the transistor that feeds the invering input creates a Trans-Amp. That lowers THD a lot and allows +60 db gains without the dirt.

The power decoupling capacitors connect the rail voltage (in this case +17v, -17v) to ground. These capacitors C21 & C22, 47u, don't necessarily need to be replaced unless they are leaky or open? Would changing the value of these caps provide any benefit? Or would it put more stress on the power supply?

I use 1000 uf, 25 volt Panasonic FM's there. Replace the 75 ohm fusing resistors to 1/2 watt 10 ohms.

There are a two different kinds of EQ sections for the 200B, standard (4 fixed frequencies) and deluxe (sweapable mids), I will have a mix of both deluxe and standard modules. The one thing which seems to be a consensus is that the High Frequency shelving EQ can get a little harsh and it is possible to change a capacitor to improve this. Is this the capacitor that connects two of the legs of the pot, in this case a 100n ceramic? I could replace this with a Polystyrene or Wima FKP of the same value?

That cap is there to prevent out of band HF noise from being boosted, leave it. The film cap that does the HF EQ should be the Wima FKP-2, a value lower to get the EQ out of the mids.

I have yet to get to the Master section schematic as it's a little more complicated, but I'm hoping what I learn from this will help me conquer that part next.

For the power supply, I plan to replace the main decoupling electrolytic capacitors, C1 & C2, 4700u, 50v. There are so few parts here, I thought I could just replace all the other capacitors. Of course, perhaps the best thing to do is buy a new Power One Supply and be done with it, but learning the different parts of the power supply is educational... One other question, I have a 8 channel 200B and a 24 channel 200B. The 24 channel one is missing the power supply. Did Soundcraft use the same power supply for all 200Bs?

Too often. Get a Power One HDD-15-5A and call it a day. Add the small 1/2 amp 48 volter for phantom. Get a Hakko 808 desoldering tool or you will mess it up real good.

Thank you for any advice you can offer!
Jeff
Jim Williams
Audio Upgrades
Old 16th November 2007
  #7
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Question 200b Newbie Question

Newbie QUestion: What is the difference in a "British EQ" and would the eq's on the 200b be considered british eq's?

Newbie with O.C.D. and soldering iron question:
What cap componenets relate to the british eq, and the relation to the mods mentions by J. Will.

I am in left field...
Old 16th November 2007
  #8
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jeff deff's Avatar
 

Thread Starter
Well, I received my 24 channel 200B. I took out each module and blew out the switches and faders. Some of the nuts holding on the pots had come loose so I tightened those up. One channel was having trouble with the line/mic switch and wouldn't pass a mic signal. I sprayed out the switch with Deoxit and pushed the button in and out 40 times and it was fixed. Also, the monitor volume pot was acting funny. It wouldn't pass audio through the left channel and made a clicking sound if you tapped it. I sprayed it out with tuner cleaner and turned it back and forth 40 times. Then I used deoxit on the headphone jack. Plugging in headphones interrupts the signal flow to the control room speakers so I wanted to be sure this was clean. Problem solved and everything is now working fine! (*knock on wood*)

Having pulled out each module to clean it, I noticed that this board was stock, with the exception that someone had soldered the fader connection wires. I have an 8 channel 200B that has crimp connectors attaching the faders. I did my first session with it and it sounded great. I was real happy with the sound of the EQ and preamps. The knobs and faders all feel great. No scratchiness or intermittent connections or hum. My only complaint is the Aux sends were a little noisy for the headphone feed, but this wasn't noticed until vocal overdubs, it wasn't a problem while tracking basics. My hope is that the grounding mod will help this.

I received my first bit of the (potential) new power supply. I got the Power One PFC375-1015F supply and realized (should have read the other posts closer) that I will need another one to get both +/- voltages. For kicks, I decided to attempt some measurements using an oscilloscope. I hook up to the Power One DC output (positive lead on the + terminal, negative lead on the -) to see if I can see any ripple. It looks pretty good until I zoom way in and then you can definitely see a little bit. OK, so now let's compare it to the stock Soundcraft power supply that I've been using. Not sure if this is a fair test because I'm testing the Soundcraft under load and the power one was not hooked up to anything but the oscilloscope. Wow, the soundcraft power supply has less ripple as far as I can tell with the scope set the same. I think the PFC375-1015F maybe isn't the best choice for what I'm trying to do here.

Next I ran a 500 HZ square wave through a channel to see what I could find. It actually looked pretty good. There was a tiny little peak at the front of the wave and it sloped ever so slightly downward, but better than I expected. All the EQ controls caused the expected results with the waveform. Now I lowered the square wave down to 100Hz and the square wave starts to slope downwards. I guess this is where I start losing low end. At 20Hz the square wave is not looking very square and more like a sawtooth. So now I guess the test would be to replace the coupling capacitors with the higher values (220uF) and compare to see if it helps out the low end?

Overall, I'd say I'm real happy with the sound of the board stock. Way better than the standard contemporary mixers I've used of the mackie and A&H varieties.

So hopefully Monday, I'll do the ground mod and see if that helps. That is of course unless I'm not cooking pumpkin pie in preparation for thanksgiving. Hey anyone know any turkey mods???
Old 16th November 2007
  #9
Quote:
Originally Posted by Alex Specht View Post
Newbie QUestion: What is the difference in a "British EQ" and would the eq's on the 200b be considered british eq's?

Newbie with O.C.D. and soldering iron question:
What cap componenets relate to the british eq, and the relation to the mods mentions by J. Will.

I am in left field...
To me, "British EQ" is cheap mylar box EQ caps run by TI TLO72 opamps, just how it comes. One might add a ceramic cap to the top EQ band for a bit more spit. It was always an EQ that said, "don't turn me up too far, I'll bite back".

Not my cup of English Tea.

Jim Williams
Audio Upgrades
Old 16th November 2007
  #10
Quote:
Originally Posted by jeff deff View Post
I received my first bit of the (potential) new power supply. I got the Power One PFC375-1015F supply and realized (should have read the other posts closer) that I will need another one to get both +/- voltages. For kicks, I decided to attempt some measurements using an oscilloscope. I hook up to the Power One DC output (positive lead on the + terminal, negative lead on the -) to see if I can see any ripple. It looks pretty good until I zoom way in and then you can definitely see a little bit. OK, so now let's compare it to the stock Soundcraft power supply that I've been using. Not sure if this is a fair test because I'm testing the Soundcraft under load and the power one was not hooked up to anything but the oscilloscope. Wow, the soundcraft power supply has less ripple as far as I can tell with the scope set the same. I think the PFC375-1015F maybe isn't the best choice for what I'm trying to do here.
Sounds like you bought a switcher, bad choice. Get the H or F series linears.

Jim Williams
Audio Upgrades
Old 17th November 2007
  #11
Gear Head
 

Quote:
Originally Posted by Jim Williams View Post
To me, "British EQ" is cheap mylar box EQ caps run by TI TLO72 opamps, just how it comes. One might add a ceramic cap to the top EQ band for a bit more spit. It was always an EQ that said, "don't turn me up too far, I'll bite back".

Not my cup of English Tea.

Jim Williams
Audio Upgrades
and we don't like your president!!
Old 17th November 2007
  #12
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razorz's Avatar
 

Quote:
Originally Posted by StephenGiles View Post
and we don't like your president!!
Oi!
Old 17th November 2007
  #13
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Wes Kuhnley's Avatar
 

One of the guys at work is building a 40 channel 200b. You can find him at logan(at)lowgain-audio(dot)com
Old 18th November 2007
  #14
kid
Gear Head
 

I'm a little confused about the Power One HDD-15-5A recommendation. I have a Delta 200 so perhaps it uses a different supply but my CPS450 power supply is 17V. The Power One is 15V correct? Am I correct in assuming this would not work well for a Delta 200? Is the Power One really a high priority recommended improvement?

I had a question regarding switches in these channels. On mine there seems to be some pops here and there when engaging the EQ, or On switches. Should these be replaced? If so what parts are correct replacements? I had a tech go over them once before along with the pots I'm not sure what he used but he did it was special stuff. It improved but from time to time they need exercising to get rid of the pops and even then they are a little dirty. and I think he used Stabilant in them but I'm not sure.
Old 18th November 2007
  #15
Quote:
Originally Posted by StephenGiles View Post
and we don't like your president!!
I see the point, the "British EQ" can be fixed, our Presidente Jorge Bush cannot.

Just keep in mind 59 million voted for him in a country of 330 million people.
Hardly a national endorsment.

If you don't like him, wait for the next selection! They just seem to get worse every time.

No one should ever "like" a politician, that's when you get into trouble. Be wary of all of them, they cannot ever be trusted on any level and should be watched like a hawk. They should also never be career pols, it should be a temporary position, throw them all out regularly and they will realize who they are working for.

Jim Williams
Audio Upgrades
Old 18th November 2007
  #16
Quote:
Originally Posted by Wes Kuhnley View Post
One of the guys at work is building a 40 channel 200b. You can find him at logan(at)lowgain-audio(dot)com
That may be a problem. A 5532/4 opamp will run low on loop gain if required to sum more than 25~30 channels. The mix gets increasingly dirty. This is the limitations of the inverting/summing opamp design. A trans-amp design summing amp using a very low noise high gain discrete transistor will overcome these limitations so 80 to 100 channels can be summed without the grunge and dirt from the opamp summing design. Take 30 db of dirt off the stereo mix and it's a good thing.

Jim Williams
Audio Upgrades
Old 18th November 2007
  #17
Quote:
Originally Posted by kid View Post
I'm a little confused about the Power One HDD-15-5A recommendation. I have a Delta 200 so perhaps it uses a different supply but my CPS450 power supply is 17V. The Power One is 15V correct? Am I correct in assuming this would not work well for a Delta 200? Is the Power One really a high priority recommended improvement?

I had a question regarding switches in these channels. On mine there seems to be some pops here and there when engaging the EQ, or On switches. Should these be replaced? If so what parts are correct replacements? I had a tech go over them once before along with the pots I'm not sure what he used but he did it was special stuff. It improved but from time to time they need exercising to get rid of the pops and even then they are a little dirty. and I think he used Stabilant in them but I'm not sure.
The 15 volt Power One's can be trimmed to 16.25 volts max. If you want more, use the 24 volt supplies and contact the apps guy at Power One and they will tell you how to reset the dividers that set the voltage. The 5 amp dual is just enough for this console at 24 inputs. Use the 9 amp or 12 amp singles for more ummmph.
If your tech used Stabilant 22A in the carbon pots, they are being disolved from the alcohol carrier. The apps note warn against this and you may end up replacing all of them. It can only be used in it's pure form on conductive plastic faders, the apps notes do explain that. Stabilant will not recover the wear on switches. Buy them from Mouser, use a Hakko 808 to remove them, treat the new switches with Stabilant, less is more.

Jim Williams
Audio Upgrades
Old 18th November 2007
  #18
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JohnRoberts's Avatar
 

Quote:
Originally Posted by Jim Williams View Post
That may be a problem. A 5532/4 opamp will run low on loop gain if required to sum more than 25~30 channels. The mix gets increasingly dirty. This is the limitations of the inverting/summing opamp design. A trans-amp design summing amp using a very low noise high gain discrete transistor will overcome these limitations so 80 to 100 channels can be summed without the grunge and dirt from the opamp summing design. Take 30 db of dirt off the stereo mix and it's a good thing.

Jim Williams
Audio Upgrades

Just to clarify, the loop gain margin limitation is not related to topology (inverting vs. non-inverting), but simply the number of signals being combined and the requirement for make up gain, using off the shelf parts typically designed for unity or near unity gain stability.

While the "transamp" is an elegant solution for the loop gain deficit that also tracks with the number of channels assigned, for a known fixed number of channels a discrete solution can be rolled with adequate loop gain to deliver respectable performance. Note: inadequate loop gain margin also causes phase shift at HF.

There are also other ways to skin that cat but too complicated for simple modifications.

JR
Old 18th November 2007
  #19
Gear Head
 

Quote:
Originally Posted by Jim Williams View Post
I see the point, the "British EQ" can be fixed, our Presidente Jorge Bush cannot.

Just keep in mind 59 million voted for him in a country of 330 million people.
Hardly a national endorsment.

If you don't like him, wait for the next selection! They just seem to get worse every time.

No one should ever "like" a politician, that's when you get into trouble. Be wary of all of them, they cannot ever be trusted on any level and should be watched like a hawk. They should also never be career pols, it should be a temporary position, throw them all out regularly and they will realize who they are working for.

Jim Williams
Audio Upgrades
I like it! We are getting pictures of the main contenders in our newspapers and they look like a couple of kids waiting to see the headmaster at school for being bad!
Old 19th November 2007
  #20
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ulysses's Avatar
 

Quote:
Originally Posted by StephenGiles View Post
and we don't like your president!!
That's okay, neither do we.
Old 19th November 2007
  #21
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Alex Specht's Avatar
 

Unhappy British Eq vs 200b

Quote:
Originally Posted by Alex Specht View Post
Newbie QUestion: What is the difference in a "British EQ" and would the eq's on the 200b be considered british eq's?
Foolishly, I had tried to procrastinate by letting my mind drift into the realm of capacitors and potentiometers, rather than working on my internet research paper for political science class.

Apparently, this was not the case.

BTW: no one answered my question
Old 19th November 2007
  #22
Quote:
Originally Posted by Alex Specht View Post
Foolishly, I had tried to procrastinate by letting my mind drift into the realm of capacitors and potentiometers, rather than working on my internet research paper for political science class.

Apparently, this was not the case.

BTW: no one answered my question
No difference. The parts come from all over, the designs are from all over, they are traded about by engineers like baseball cards. English EQ is an EQ designed by someone who speaks english.

Countries don't have exclusives to designs in audio.

Jim Williams
Audio Upgrades
Old 19th November 2007
  #23
Gear nut
 
jeff deff's Avatar
 

Thread Starter
As I understand it, "British EQ" is a term that marketing folks came up with. There were some British made consoles in the 60's and 70's, like Neve, Trident et al. that became famous for their "musical" sounding EQ circuits. I think to generalize, "musical" EQ means it has a wide Q, excelling at making broad strokes. The opposite would be "surgical" EQ which would have a narrow Q and would be good for cutting or boasting very narrow bands.

The Soundcraft 200B would fall into the "British EQ" category. Just remember there are two different input modules, the standard which has 4 fixed EQ bands, and the deluxe which has four bands: a high shelf, two bands of sweepable mids and a low shelf, plus a high pass filter to boot. The deluxe module is much more flexible, so given a choice, you'd want that one.
Old 19th November 2007
  #24
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JohnRoberts's Avatar
 

Quote:
Originally Posted by Alex Specht View Post
Newbie QUestion: What is the difference in a "British EQ" and would the eq's on the 200b be considered british eq's?

Newbie with O.C.D. and soldering iron question:
What cap componenets relate to the british eq, and the relation to the mods mentions by J. Will.

I am in left field...
At one time consoles were considered to sound quite different from each other and to have characteristic sounds. This is generally attributed to differences in the EQ section. Choice of EQ section center frequencies, bandwidth, and control law impacts the sound shaping you can create. Otherwise similar nominal EQ specifications can also have subtle differences due to topology, for example EQ sections in series vs, in parallel.

Graphic EQs are the classic example of this "same but different", where all 1/3rd octave EQs while nominally the same fall into a handful of different characteristic response curves due to internal filter topology used.

Getting back to the "British sound" this is not uniquely described anywhere (AFAIK) and no, there is no single console EQ sound that "all" British consoles share, they vary between manufacturers as little or much as consoles from other countries.

FWIW the AES standards committee is currently looking at ways to more completely describe EQ sections so someday we should be better able to describe these differences. This has become an issue when trying to replicate EQ curves between different DSP platforms that use different software EQ algorithms.

JR
Old 24th November 2007
  #25
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Alex Specht's Avatar
 

Wink SOundcraft Delta DLX

Ended up with the SOundcraft Delt DLX instead...

Looking for new thread to start on that one
Old 25th November 2007
  #26
Gear nut
 
Brian M. Boykin's Avatar
 

DLX

Way to go!!!

Brian
Old 25th November 2007
  #27
I have 3!

Jim Williams
Audio Upgrades
Old 26th November 2007
  #28
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Alex Specht's Avatar
 

Old 27th November 2007
  #29
Gear Head
 

Quote:
Originally Posted by jeff deff View Post
Well, I received my 24 channel 200B. I took out each module and blew out the switches and faders. Some of the nuts holding on the pots had come loose so I tightened those up. One channel was having trouble with the line/mic switch and wouldn't pass a mic signal. I sprayed out the switch with Deoxit and pushed the button in and out 40 times and it was fixed. Also, the monitor volume pot was acting funny. It wouldn't pass audio through the left channel and made a clicking sound if you tapped it. I sprayed it out with tuner cleaner and turned it back and forth 40 times. Then I used deoxit on the headphone jack. Plugging in headphones interrupts the signal flow to the control room speakers so I wanted to be sure this was clean. Problem solved and everything is now working fine! (*knock on wood*)

Having pulled out each module to clean it, I noticed that this board was stock, with the exception that someone had soldered the fader connection wires. I have an 8 channel 200B that has crimp connectors attaching the faders. I did my first session with it and it sounded great. I was real happy with the sound of the EQ and preamps. The knobs and faders all feel great. No scratchiness or intermittent connections or hum. My only complaint is the Aux sends were a little noisy for the headphone feed, but this wasn't noticed until vocal overdubs, it wasn't a problem while tracking basics. My hope is that the grounding mod will help this.

I received my first bit of the (potential) new power supply. I got the Power One PFC375-1015F supply and realized (should have read the other posts closer) that I will need another one to get both +/- voltages. For kicks, I decided to attempt some measurements using an oscilloscope. I hook up to the Power One DC output (positive lead on the + terminal, negative lead on the -) to see if I can see any ripple. It looks pretty good until I zoom way in and then you can definitely see a little bit. OK, so now let's compare it to the stock Soundcraft power supply that I've been using. Not sure if this is a fair test because I'm testing the Soundcraft under load and the power one was not hooked up to anything but the oscilloscope. Wow, the soundcraft power supply has less ripple as far as I can tell with the scope set the same. I think the PFC375-1015F maybe isn't the best choice for what I'm trying to do here.

Next I ran a 500 HZ square wave through a channel to see what I could find. It actually looked pretty good. There was a tiny little peak at the front of the wave and it sloped ever so slightly downward, but better than I expected. All the EQ controls caused the expected results with the waveform. Now I lowered the square wave down to 100Hz and the square wave starts to slope downwards. I guess this is where I start losing low end. At 20Hz the square wave is not looking very square and more like a sawtooth. So now I guess the test would be to replace the coupling capacitors with the higher values (220uF) and compare to see if it helps out the low end?

Overall, I'd say I'm real happy with the sound of the board stock. Way better than the standard contemporary mixers I've used of the mackie and A&H varieties.

So hopefully Monday, I'll do the ground mod and see if that helps. That is of course unless I'm not cooking pumpkin pie in preparation for thanksgiving. Hey anyone know any turkey mods???

I did this mod on my 24 CH 200B a couple years ago. I really noticed how much quieter it was as I engaged more channels. It didnt have near the cumulative noise it had before the mod. Some have claimed more extended top end etc. but I didnt hear that improvemrnt. Perhaps a recap is order. Anyone know a supplier of quality caps for this board. Everytime I check Mouser or Digikey it seems not all the values are available and I just decide to put it off. But Im thinking the board could REALLY use it.

Last edited by B.Rupe; 27th November 2007 at 08:50 PM.. Reason: spell
Old 28th November 2007
  #30
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DamnYankee's Avatar
 

Quote:
Originally Posted by Jim Williams
I see the point, the "British EQ" can be fixed, our Presidente Jorge Bush cannot.

Just keep in mind 59 million voted for him in a country of 330 million people.
Hardly a national endorsment.

If you don't like him, wait for the next selection! They just seem to get worse every time.

No one should ever "like" a politician, that's when you get into trouble. Be wary of all of them, they cannot ever be trusted on any level and should be watched like a hawk. They should also never be career pols, it should be a temporary position, throw them all out regularly and they will realize who they are working for.

Jim Williams
Audio Upgrades
You just got my vote for "Post of the Year"!
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