The No.1 Website for Pro Audio
Apex 460 to C12 Step By Step
Old 12th September 2011
  #91
Here for the gear
 
🎧 5 years
apex 460 PSU mod zener removal

hay all this looked as good as any of a place to ask if any one
has done the PSU mod for the apex 460 Paul talks about ?
if so do any of you no the implications of removing the 2 zeners at the front
and replacing with the 3.3uf 400v solen cap does it raise the voltage on the capsule or the other way around iv heard when done write it makes a huge difference
Old 6th October 2011 | Show parent
  #92
Gear Maniac
 
theBF's Avatar
 
🎧 10 years
I replace the Zener Diodes in the stock 460 supply with 1N4759A diodes. They are 60V diodes + or - 5%. since they are in series they give you a simple regulator at around 120V.

Yes this does make a difference. It gets the voltages on the capsule down in the range where the classic mics were (55 to 65 V) with the stock circuit in the mics. The capsule voltage affects the tension of the diagphragm a little because of the static attraction to the back plate. I have done some studies showing that this influences the high end response a little and the sound seems to change with higher voltage. The lower voltage makes me think of a softer/slower sound and the higher voltage has more "crack" to the sound.

You could leave the power supply alone and just adjust the voltage divider resistors to create the 60V capsule voltage, but you have to do the same to the voltage on the polar pattern control too. Doubles the effort and complexity of the mod.

I don't see a 3.3uF cap in my 460 supply. There is a 1uF cap that filters the output from the polar pattern voltage switch.

Oh and the implications of the removing the Zener Diodes is that with no mic plugged in to it the power supply voltage will rise to well over 200 Volts. With the mic plugged it will drop quickly to some nominal value that I have never tested. If you don't like the Zeners then the old fashioned approach was to put "bleeder" resistor in circuit where the zeners go and hold the voltage down to some value by brute force (absorb some current). Something like 200K at 1W would work in these supplies. (do some tests, I am guessing here)

This also provided a way for the big filter caps to discharge after you turn it off, which helped kept more repair technicians alive by preventing lethal electric shock. :-)

BF

Last edited by theBF; 6th October 2011 at 01:21 AM.. Reason: incomplete response
Old 6th October 2011 | Show parent
  #93
Gear Maniac
 
jordan s's Avatar
 
🎧 10 years
This is a really well laid out guide. I recently did a very similar mod to a pair of 460's based off of the C24 schematic and I am very happy with the results. I would recommend changing the diodes in the power supply too. I noticed a difference. Also, this will keep the mic from popping and making noises when changing the pattern. Mine was making noise at first and I believe this was because the capsule was getting sucked in due to too much voltage.
Old 9th April 2012 | Show parent
  #94
Here for the gear
 
🎧 5 years
This is fantastic! Thanks so much to NothingTheory for the great instructions!

I'm having an issue with my mod, and if anyone has any advice to troubleshoot that would be nice. I installed every component and moved every wire exactly as the instructions said to do. I replaced the capsule with the Advanced Audio AK12 as well. When i fired it up, it was clean and noise free. As soon as I send a loud source through the mic, it starts to get really quiet and then make a hissing sound. Anyone had this issue before?

I even modded a second 460 right after, following the same instructions, and I'm getting the same symptoms!!! Thanks in advance.
Old 11th April 2012 | Show parent
  #95
Gear Maniac
 
NothingTheory's Avatar
 
🎧 10 years
new info

Thanks for the compliment. Im creating a new website that I will be moving the MOD page to soon, but will link it over for a while and in here as well to ensure continuity.. Some new stuff coming ( eventually ) as well. I have a working prototype of something I've done from the ground up, but its not ready for prime time yet.

As I said in PM the most likely cause when you can hear sound and then it dies out pretty soon .. is a bad tube. I had several brand new Tung Sols ( new stock ) that did that. The new stock tung sols I have found out don't like cathode follower circuits much, so I now don't recommend them for those applications. If you can hear sound at first then you prob have things wired up correctly but it doesn't hurt to print out the schematics and go connection by connection and use a highlighter to check each path as correct. When I built mine I ended up having a connection in the wrong place and found it that way. But the symptom for me in that case - was no sound.

Also a cold solder joint can do MANY weird things. When soldering ensure that you are heating the metal and not the solder. Let the solder flow into the metal from the heat of the metal not the off the iron. ( so your not "dipping" solder onto anything from the iron ) Ensure the iron has a little solder on it at first as well to be conducive to heat exchange ( a dry iron will easily overheat components while you wait for proper temp).

Iron quality - I know its not feasible for just one small project but I'll tell you I had troubles now and then until I just broke down and bought a Weller pro station and now I have zero problems and can't believe I didn't just buy one to start with. Some of the cheaper Wellers are probably better than say the Zallman ( which is one brand I used and had issues with ) .

Since the MOD only uses one side of the triode - if you have two then Definitely wire the other mic to use the other side of the triode.. this way as the tubes age you can swap the tubes between the units and get full use of the tube. You can also check for a bide side of the triode that way too. NOS 6072's are not cheap and that trick will go a long way to saving $.

To do that its a simple pin swap

1 = 6
2 = 7
3 = 8

So on the second mic you'd move the 1, 2, 3 wires to 6, 7, 8 and then ground the 1, 2, 3 to pin 9 ( or wherever your ground wire was coming in ) . Be sure your counting the pins from the right side.

Since I fist did this I have read like 50 books on tubes. ( thanks in large to Pete Millet Technical books online as well as Morgan Jones - side note .. what is UP with the 4th edition in print sheesh !! and others too )

So with my transistor background "backdated" to tube tech - I went back and did the math on this setup to double check the circuit. The specs passed on to me by JJ are right on the money and the circuit is as I would have done it ( or close enough to ) and is right on with specs for a 6072 as well. I plan on posting more info and load line chart when I move to the new web site.

Some one was asking about the power supply earlier and Im not hearing any ripple noise, and the voltage is right on for spec, so changing that would mean altering the circuit .. so I'm not convinced anything is needed there, but plan on looking at it some day too.


Hope this helps !
Old 4th May 2012 | Show parent
  #96
Gear Maniac
 
jlipoth's Avatar
 
🎧 10 years
still looking for a matching C4 cap

Does anyone know where I could find a ROHM 1000pf polystyrene?.....I've tried a couple different polystyrene's but I think I like this one the best.
Old 11th May 2012 | Show parent
  #97
Gear Maniac
 
jlipoth's Avatar
 
🎧 10 years
Update

I did some more testing again....I'd had lost interest in the mod last year because my mics started sounding grainy, but I picked it up again because I needed something to record some piano with....I'm not sure why, but it seems that the Nichon Muse I was putting at C6 (I got it from mouser.com), was giving a strange grainy sound after I left the mic on for 48 hours to burn in (this happened to both of my mics). I ordered some Elna R20 caps and after 48hrs they sound great; even since I've let them burn in. I am almost done both my 460 mods which means I'll be taking them to a studio in town to compare to a real vintage c12 soon! It's been crazy to see how much a different cap/transformer or combination of parts can really change the sound!
Old 11th May 2012 | Show parent
  #98
Lives for gear
 
3 Reviews written
🎧 10 years
Quote:
Originally Posted by jlipoth View Post
I did some more testing again....I'd had lost interest in the mod last year because my mics started sounding grainy, but I picked it up again because I needed something to record some piano with....I'm not sure why, but it seems that the Nichon Muse I was putting at C6 (I got it from mouser.com), was giving a strange grainy sound after I left the mic on for 48 hours to burn in (this happened to both of my mics). I ordered some Elna R20 caps and after 48hrs they sound great; even since I've let them burn in. I am almost done both my 460 mods which means I'll be taking them to a studio in town to compare to a real vintage c12 soon! It's been crazy to see how much a different cap/transformer or combination of parts can really change the sound!
cool!

who's capsule do you have in them now? I lost track in this thread...
Old 12th May 2012
  #99
Gear Maniac
 
jlipoth's Avatar
 
🎧 10 years
I'm using the AA capsule. I was going to do the Peluso, but Dave accidentally sent me one of his so I kept it and he sent me a second one (his are half the price of the Peluso). I suppose Tim Campbell's would be a better choice to get as close as possible, but they're 4x the price. I am curious to see how close I can get for a mic mod that only costs around $500 (mic included).... ...they are definitely different sounding mics since I modded them. Did you end up modding one Dkelley?
Old 12th May 2012
  #100
Gear Maniac
 
NothingTheory's Avatar
 
🎧 10 years
Quote:
Originally Posted by jlipoth View Post
I did some more testing again....I'd had lost interest in the mod last year because my mics started sounding grainy, but I picked it up again because I needed something to record some piano with....I'm not sure why, but it seems that the Nichon Muse I was putting at C6 (I got it from mouser.com), was giving a strange grainy sound after I left the mic on for 48 hours to burn in (this happened to both of my mics). I ordered some Elna R20 caps and after 48hrs they sound great; even since I've let them burn in.
Interesting note on the cap, I wonder what else might be an interesting option there??

I would also like to point out to folks that when you "burn in" always have music flowing through the device you are burning in. For a mic stick it next to a radio speaker or something. It affects how the burn in takes hold, especially on caps with large burn in times like the sozo mustard caps at 100+ hrs. Also certain tubes can be destroyed or otherwise negatively affected ( ex the 5814 i think ) if they are left at voltage for long times without a signal. This always conerns me when running only 1 channel on a stereo pre for long periods as well.. plug a mic into the second channel even if your not recording that side.

Mark
Old 12th May 2012 | Show parent
  #101
Lives for gear
 
3 Reviews written
🎧 10 years
Quote:
Originally Posted by jlipoth View Post
I'm using the AA capsule. I was going to do the Peluso, but Dave accidentally sent me one of his so I kept it and he sent me a second one (his are half the price of the Peluso). I suppose Tim Campbell's would be a better choice to get as close as possible, but they're 4x the price. I am curious to see how close I can get for a mic mod that only costs around $500 (mic included).... ...they are definitely different sounding mics since I modded them. Did you end up modding one Dkelley?
yea, well keep in mind that I actually started modding these mics the year they came out (which is several years ago now). But I stopped bothering for a long time and now am getting back into it with all of the new information in threads like this one - takes the R&D and much of the extreme guesswork out of it for me which is a huge help.

So I have one sitting here modded which is already pretty good but still with the stock capsule. Trying to decide what capsule to get. I'm pretty much set on a c12 type of mic eq more or less (as opposed to k47 cap with the mid forward thing). I might start with the cheap one (from microphoneparts) and if I dislike it in any way will move up from there if I like it find the eq difference in that cap compared to a real 12 cap to be too different from what I'm looking for. I'm aware of the differences in sound of the microphone parts 12 cap compared to the real thing. but it's so cheap LoL, and undoubtedly more of what I'm looking for compared to the k67 in there now, even if the k67 in there now seems to be a pretty good one compared to many I've heard in stock apex 460s.
Old 12th May 2012
  #102
Gear Maniac
 
jlipoth's Avatar
 
🎧 10 years
Nothing theory - Good call with the burn it tip. I forgot to do that on one of my mic burn ins, but I set it up in the living room where there is some periodic noise. The other one was 15" from a speaker playing low-med level music. I got the same result with both, using the Muse caps at c6.

Dkelley - I'm sure you'll find a rather big difference in the overall tone of the mic with a different capsule. There is something about how an edge terminated capsule picks up the transient and tail that is different from a center terminated one.
Old 17th May 2012
  #103
Gear Maniac
 
jlipoth's Avatar
 
🎧 10 years
I just burned in the Relcaps at C4 - nothing like the Rhom polystyrene sound but very nice! It gives a little more prominence to the transient that the silver mica, with gave a detailed but slightly softer transient. Does anyone know how much C3 and C5 affect the sound?
Old 17th May 2012 | Show parent
  #104
Gear Maniac
 
NothingTheory's Avatar
 
🎧 10 years
Quote:
Originally Posted by jlipoth View Post
I just burned in the Relcaps at C4 - nothing like the Rhom polystyrene sound but very nice! It gives a little more prominence to the transient that the silver mica, with gave a detailed but slightly softer transient. Does anyone know how much C3 and C5 affect the sound?
Jlipoth, Where did you source the Rhom caps ?

I havent tried anything other than the silver mica at C3 and C5 ... however I have figured out the ( original ) purpose for the C7 cap - which is a recommended removal. If you have a crappy cheapo cap at C6 - a small value cap in parallel at C7 will help the cheap cap sound more musical - to a degree. Since we are replacing caps with high quality and fast acting caps the need for the C7 cap diminishes. Im using this technique in a power supply for a new project to help the large slow caps in the PS deal with radio frequency noise better. Works perfectly in that application, and you can see a similar setup in the PS of the Apex mic. The Apex schematic shows a 1000p caps .. Im using 100n in a similar setup.. both that the start of the filtering chain and at the end, as well as directly across the AC portion of the HT bridge rectifier.
Old 17th May 2012 | Show parent
  #105
Lives for gear
 
Haz-Mat-Strat's Avatar
 
🎧 10 years
Quote:
Originally Posted by NothingTheory View Post
Jlipoth, Where did you source the Rhom caps ?

I havent tried anything other than the silver mica at C3 and C5 ... however I have figured out the ( original ) purpose for the C7 cap - which is a recommended removal. If you have a crappy cheapo cap at C6 - a small value cap in parallel at C7 will help the cheap cap sound more musical - to a degree. Since we are replacing caps with high quality and fast acting caps the need for the C7 cap diminishes. Im using this technique in a power supply for a new project to help the large slow caps in the PS deal with radio frequency noise better. Works perfectly in that application, and you can see a similar setup in the PS of the Apex mic. The Apex schematic shows a 1000p caps .. Im using 100n in a similar setup.. both that the start of the filtering chain and at the end, as well as directly across the AC portion of the HT bridge rectifier.


For C3 & C5 I use 4700pf Philips MKT mustard caps or Russian Paper in Oil.

As for C6 & C7, the common value used in the classic mics for the cathode bypass capacitor is 22uf to 47uf. The larger the cap the more bass can be had out of the circuit. Also the larger the capacitor the slower it reacts to HF and transients. The 100uf capacitor in the 460 adds bass to the bright capsule/circuit and rolls off the top slightly. The small 0.1uf capacitor bypassing the 100uf, restores the speed and frequency response.

That being said the C800g uses a 330uf cathode bypass capacitor


Old 18th May 2012 | Show parent
  #106
Gear Maniac
 
jlipoth's Avatar
 
🎧 10 years
I never did track down any more Rohm polystyrene caps. I do have one left from another build, but I'd like 2 (one for each of my 460 mics). I ended up ordering the relcaps instead. Right now the mic that still has the cathode follower setup lacks bit of transient detail compared to the one that I removed. The only other difference in the cathode follower mic is that the C3 and C5 caps are silver mica (I put polypro in the other). I think I may order some more polypro to see if that evens things out.
Old 10th July 2012 | Show parent
  #107
Gear Maniac
 
jlipoth's Avatar
 
🎧 10 years
I've pretty much matched components in my 460 mods based from this thread and all I can say is WOW! I just mic'd up a grand piano and I couldn't believed the results. Here is my parts list:
C3, C5 silver mica 4700pf
C4 Relcap polystyrene 1000pf
C6 Elna R20 47uf
C8 panasonic polypropylene 1.5uf
EH 6072 Tube
Cinemag transformer C2480
Advanced Audio ACK12
Remove inner layers of mesh
Remove CCDA (once you do this, finding the right components is crucial)

Finishing touches I am considering:
If I wanted to get really picky, an authentic C12 sound should have a bit more of a "scoop" to the sound than my mics, and a bit more low end "authority". While I think a more authentic transformer and capsule jto the design in the C12 would be obvious upgrades (and the most expensive), I am thinking of soldering 2 C8 caps parallel to get as close as i can to 3.3uf without completely tight packing the components. Anyone have advice recommendations on this? In the meantime, I plan on getting some mileage out of my current transformers, and capsules.

Note: I should mention that there are still 2 differences between my 2 mics. One of them does not have the resistor at R7 swapped and the other one has the military grade silver wiring in it. I should test the mics out to see how much of a difference this makes, because replacing ALL the wiring is a lot of work!

Anyways, thanks to everybody and especially to nothingtheory for starting this thread. I never thought I'd have a stereo set of mics that sound like this!
Old 13th July 2012 | Show parent
  #108
Gear Maniac
 
NothingTheory's Avatar
 
🎧 10 years
Newbie DIY info

Jlipoth, thanks for the kind words, it has been my pleasure. The site still gets over 1000 hits a month from all over the world. Im in the process of moving it to a more permanent home with some new stuff, but I was using iWeb and that software is depreciating so im now using sandvox and the conversion is not cut and paste. The old site will redirect when the new permanent home is up, hopefully sometime this summer.

I recently fixed a couple of these mods. I didn't charge anytning ( um, no thats unfortunately not an open invitation, sorry I just don't have the time for unlimited free bench work but I'll certainly give e-mail help where I can if you really truly get stuck ) becasue i wanted to see the problems from an unknown point of view. I know how I create and fix my own problems, and being handed an unknown was a challenge... here is what I learned from the experience. Hopefully this can help first time DIYers.

Dont touch the capsule face ! I found fingerprints on capsules. In my instructions I didnt go over capsule replacement becasue there are other great sites that do that, but now I think that was a mistake. I have a K67 capsule on order im going to put into an MXL2000 and I'll document that and add it to the eventual new site to go along with this one. Lucklily the capsules were not destroyed, but I have to wonder what even the slightest touch does to the capsule tension, not to mention the added mass from oils and grime. Add to this .. don't mess with the screws on the capsule except the ones needed to mount it. Don't over tighten mounting screws, they are tiny and fragile. Snug is good.

Be sure that leads from componants do not inadvertantly touch other leads.. and this can be difficult when trying to situation the larger caps so the cover actually goes back on. Stuff may get slitghtly squished in a bad way when re-mounting the casing. Mount then remove and check, and remount again after your sure nothing has moved in a bad way. Use heat shrink on long leads ( particularly C8 ) if available.

Some PCB boards have copper tracks that are SUPER THIN !! Poor Quality Control I imagine .. so thin in fact that when you push the new componants through they instantly pop pads off the PCB board. Paticularly watch the silver mica caps that seem to have a slightly thicker lead. When I repaired the lifted pads with some tin bus wire it noticably improved the sound of the mic as well ! A new drop in PCB with nice thick copper would sure be a bonus I think. I've added that to my "maybe someday" list.

Similarly , Changing the wire in the mic from the provided to new military grade silver based wire improves sonic quality. There is a wire that connects the 2 PCB boards together and I decided that I wanted a longer wire there to work on the unit without contantly connecting and disconnecting and just that one wire made a slight difference - which is how I discovered this and was surprised that just one wire could be heard. I imagine if you re-wired the entire unit the difference would be much more noticable, and i have not done that yet to my unit, but have been considering. It just goes to show that with such a sensitive device, every little piece contributes, and all the little things can add up in a big way.

I had one unit that was passing signal but changing the dial on the power supply to different patterns had no effect. This turned out to be a bad polystyrene cap at C4, or possibly not sized right as I couldnt read it. I replaced with the same that I linked in the article, and wala..fixed. So if you get that symptom, C4 might be a good place to start.

I got to compare a mic that was identical to mine down to the tube - only it had a Mundorf M-Cap at C8. I found the M-Cap to be more "airy" and reminded me a little of a Blueberry ( I have one so its something Im used to hearing ) while the Erse cap was more rounded with slightly more low end. Personally I like the old school 50's sound and dont mind loosing a little of the highs or air to get that, I still prefer the Erse, but this is simply a matter of taste.

One mic sounded good, but after leaving to burn in for a couple of hours sounded MUCH better. My mic now has about 100 hours on it approx. and it sounds way better than the day I built it. Give ample time for burn in before making a final judgement. Tubes take 20-40 hours to burn in ( If you get tubes from Bowie he will pre burn them for you if you ask ) and some caps can take even longer. Burn in with music playing through the mic, not just sitting in a quiet room. Remember to mount tube mics upsidedown so the heat from the tube goes up away from the electronics and capsule if leaving on for extended periods of time.

.. and thats what I know... hope this helps folks out there.
Old 13th July 2012 | Show parent
  #109
Gear Maniac
 
jlipoth's Avatar
 
🎧 10 years
Quote:
Originally Posted by NothingTheory View Post
Jlipoth, thanks for the kind words, it has
Some PCB boards have copper tracks that are SUPER THIN !! Poor Quality Control I imagine .. so thin in fact that when you push the new componants through they instantly pop pads off the PCB board. Paticularly watch the silver mica caps that seem to have a slightly thicker lead. When I repaired the lifted pads with some tin bus wire it noticably improved the sound of the mic as well ! A new drop in PCB with nice thick copper would sure be a bonus I think. I've added that to my "maybe someday" list.

Similarly , Changing the wire in the mic from the provided to new military grade silver based wire improves sonic quality. There is a wire that connects the 2 PCB boards together and I decided that I wanted a longer wire there to work on the unit without contantly connecting and disconnecting and just that one wire made a slight difference - which is how I discovered this and was surprised that just one wire could be heard. I imagine if you re-wired the entire unit the difference would be much more noticable, and i have not done that yet to my unit, but have been considering. It just goes to show that with such a sensitive device, every little piece contributes, and all the little things can add up in a big way.
I had the same issue on one of my mics. I couldn't figure out why only one side of the capsule worked and distorted at higher SPL Levels. It turned out that C3 C4 and C% had pulled off the poor quality PCB board. I ended up running wire to fix it too. My other mic was made with much better component (almost looked like it was from a different factory or used different parts...) and was much easier to mod. It's crazy how changing one component can change the sound on these mics. It takes patience to find the right combination of parts to get the sound you want. For example, I think the JJ audio Dutch sounds great from the samples I've heard, and it uses the Nichon Muse at C6 from my understanding. When I tried the same cap at C6, the mid range was out of control! I would imagine if I used different components elsewhere the Nichon would be great...
Old 13th September 2012 | Show parent
  #110
Gear Maniac
 
NothingTheory's Avatar
 
🎧 10 years
Update

The instructions referenced in this thread has moved to -

APEX 460 Mod | Mark-O-Matic

The old one will be taken down soon and a redirect placed up.

I also added an update. When comparing to another mic I discovered that I had forgotten that a single stage plate follower tube output is INVERTING, duh.. so the output will be inverted.

Usually not a big deal on a single source, but you will need to swap the wires on the primary or secondary on the transformer for it to be the same output phase as other mics, or you'll need to remember to flip the invert switch on your pre when using this mic when needed.
Old 13th September 2012
  #111
Gear Nut
 
BootsyGraham's Avatar
 
🎧 5 years
Hey NothingTheory, when comparing your modified Apex schematic to an actual C12 schematic, how close are they?
Old 14th September 2012 | Show parent
  #112
Gear Maniac
 
NothingTheory's Avatar
 
🎧 10 years
compare

Both the original schematics for a C12 and for the mod are available as links on the Mark-O-Matic site. I think I need to make the links bright RED or something people are sometimes missing them.

I had a lot of help from other folks on this design and it was an attempt to take the Apex to a C12 in a manner that was simple to DIY and sounded good, emphasis on the sounds good. The tube section is certainly wired the same way, but its not meant to be an exact clone.

Part of the problem of doing an exact clone has to do with limitations in the Apex power supply, but I've recently have been talking with Scott over at Hamptone (Hamptone Home Page) and its pretty likely there will be another iteration of this mod to include the -3V bias from the supply like the original C12. I like the mic so much i'm itching to build another anyways. I don't have a timeline yet though.
Old 14th October 2012 | Show parent
  #113
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by jlipoth View Post
I've pretty much matched components in my 460 mods based from this thread and all I can say is WOW! I just mic'd up a grand piano and I couldn't believed the results. Here is my parts list:
C3, C5 silver mica 4700pf
C4 Relcap polystyrene 1000pf
C6 Elna R20 47uf
C8 panasonic polypropylene 1.5uf
EH 6072 Tube
Cinemag transformer C2480
Advanced Audio ACK12
Remove inner layers of mesh
Remove CCDA (once you do this, finding the right components is crucial)

Finishing touches I am considering:
If I wanted to get really picky, an authentic C12 sound should have a bit more of a "scoop" to the sound than my mics, and a bit more low end "authority". While I think a more authentic transformer and capsule jto the design in the C12 would be obvious upgrades (and the most expensive), I am thinking of soldering 2 C8 caps parallel to get as close as i can to 3.3uf without completely tight packing the components. Anyone have advice recommendations on this? In the meantime, I plan on getting some mileage out of my current transformers, and capsules.

Note: I should mention that there are still 2 differences between my 2 mics. One of them does not have the resistor at R7 swapped and the other one has the military grade silver wiring in it. I should test the mics out to see how much of a difference this makes, because replacing ALL the wiring is a lot of work!

Anyways, thanks to everybody and especially to nothingtheory for starting this thread. I never thought I'd have a stereo set of mics that sound like this!

Hey jlipoth,

It's way cool that your mics are giving you a boner like that, if you drop some tim campbell ck12s in those, they will sound twice as good!!! Like viagra for your mics!sorry
Old 14th October 2012 | Show parent
  #114
Lives for gear
 
Haz-Mat-Strat's Avatar
 
🎧 10 years
Quote:
Originally Posted by NothingTheory View Post
Both the original schematics for a C12 and for the mod are available as links on the Mark-O-Matic site. I think I need to make the links bright RED or something people are sometimes missing them.

I had a lot of help from other folks on this design and it was an attempt to take the Apex to a C12 in a manner that was simple to DIY and sounded good, emphasis on the sounds good. The tube section is certainly wired the same way, but its not meant to be an exact clone.

Part of the problem of doing an exact clone has to do with limitations in the Apex power supply, but I've recently have been talking with Scott over at Hamptone (Hamptone Home Page) and its pretty likely there will be another iteration of this mod to include the -3V bias from the supply like the original C12. I like the mic so much i'm itching to build another anyways. I don't have a timeline yet though.

With some modification the Apex power supply can be changed to supply the negative voltage for the grid. You can disconnect the ground on pin 4 or 7 on the connector and use it to supply the voltage to the mic. With a trim pot on the negative voltage, you can easily tune the bias of the mic to get the best sound from the tube.

Warning!!..... .....This mod involves cutting traces and changing the grounding structure on the power supply. This is not as simple as changing out components.........





Jim Jacobsen
JJ Audio






.
Old 14th October 2012 | Show parent
  #115
Lives for gear
 
Haz-Mat-Strat's Avatar
 
🎧 10 years
Quote:
Originally Posted by Tonycamp View Post
Hey jlipoth,

It's way cool that your mics are giving you a boner like that, if you drop some tim campbell ck12s in those, they will sound twice as good!!! Like viagra for your mics!sorry
.......Tim Campbell's capsule is the single best component mod for these microphones.........







Jim Jacobsen
JJ Audio







.
Old 6th December 2012 | Show parent
  #116
Here for the gear
 
🎧 5 years
Quote:
Originally Posted by NothingTheory View Post
I also added an update. When comparing to another mic I discovered that I had forgotten that a single stage plate follower tube output is INVERTING, duh.. so the output will be inverted.

Usually not a big deal on a single source, but you will need to swap the wires on the primary or secondary on the transformer for it to be the same output phase as other mics, or you'll need to remember to flip the invert switch on your pre when using this mic when needed.
One little correction:

The final circuit of your mod won't have a different polarity than the original.

Yes, a single common cathode (plate loaded) stage will invert, however the second stage in the 460 is a cathode follower and does not invert the signal applied to it.

So the net result is the signal applied to to the transformer is inverted compared to that supplied to the first tube stage, whether you use the original 460 circuit or your modded circuit which removes the cathode follower.

I don't know anything particular about the phasing of the original chinese transformer, but fortunately the fix if you notice the polarity of your mic is wrong is simple: flip one set of wires as you'd noted already.
Old 6th December 2012 | Show parent
  #117
Here for the gear
 
🎧 5 years
Other circuit theory tweaks:

The plate-loaded stage which the mod leaves you with is not a "plate follower".

A plate follower is a normal plate loaded stage, but also includes feedback from the output to the input which results in a net gain of 1 or less. So it's similar to a cathode follower, but has the output at the plate instead of the cathode.

The typical name for the type of tube gain stage the mod uses is called a "plate-loaded" circuit or a "common cathode" circuit (because the cathode is common to both input and output circuits).

Also, the "constant current draw amplifier" is a name applied by John Broskie to a common cathode stage followed by a cathode follower.

The key is the plate load resistor of the first stage must be equal to the cathode load resistor of the cathode follower. In the stock Apex 460 circuit, this is not the case (R2 and R8 are different values).

In actual fact, the common cathode stage followed by a cathode follower is a pretty common circuit, and has been used in tons of guitar amps on both sides of the pond. It's primary advantage (other than lowered output impedance due to the cathode follower) is that the extremely high input impedance of the cathode follower helps maximize the gain of the stage ahead of it, to the extent allowed by the parts used in the first stage.

I know none of this helps you make your mic sound better, but hopefully if you have a strong desire to be knowledgeable of the electronics involved, this will help you lay the right foundation.
Old 6th December 2012
  #118
Gear Maniac
 
NothingTheory's Avatar
 
🎧 10 years
Brian,

Thanks for your input. I don't know how much of that is attributable to me, but I will say that though I have somewhat of an electronics background when I originally wrote the post I was winging it and hadn't even read a single book on tube design at that time. I've probably read 30 or more now, but am not going to go back through and correct every post.

I do think your description of a plate follower sounds more like a charge amplifier..with a gain of 1 or less and Broskies own CAD tool will create endless textbook plate followers with gain, unless that too is "his creation" and not based upon a wider accepted design ?

For people looking for the right foundation.. what sources do you suggest ? Anything other than the obvious Morgan Jones...???

Old 6th December 2012 | Show parent
  #119
Here for the gear
 
🎧 5 years
Understood about changing old posts. I worried that I was resurrecting something from years ago, but I happened on the post while looking at ways to upgrade some cheapo mics I've gotten recently.

Quote:
Originally Posted by NothingTheory View Post
I do think your description of a plate follower sounds more like a charge amplifier..
Maybe ("charge amplifier" is a new term to me also, though I get where it's coming from). But it seems the key to a charge amp is that you have a capacitor or piezo element as the signal source. That jives with condensor mics.

The defining element of a plate follower (or anode follower) seems to be feedback from the plate output back to the grid.

Quote:
Originally Posted by NothingTheory View Post
... Broskies own CAD tool will create endless textbook plate followers with gain, unless that too is "his creation" and not based upon a wider accepted design ?
No, not Broskie's creation.

I never paid attention to the circuit before, but I've found some references from '53-'57 which describe the anode follower circuit and talk about enabling a gain greater than unity by adusting the component(s) used for the feedback. Norman Crowhurst describes the circuit in High Fidelity Circuit Design ('57) and A.W. Keen wrote an article for Wireless Engineer on anode follower derivatives in '53.

Quote:
Originally Posted by NothingTheory View Post
For people looking for the right foundation.. what sources do you suggest ? Anything other than the obvious Morgan Jones...???
It depends on whether you want to approach it as an electrical engineer or from some other standpoint. Me personally, I'm coming from the standpoint of a guitarist that wanted to repair/tweak his own stuff; later I had such an interest I started down the path towards an EE degree. Now I can design and build pretty much whatever I'd like rather than buy it.

So "best" resource for me was someone who already knows this stuff and can break down complex ideas into a digestible form. Dunno if PRR ever frequents this forum, but he helped me a lot on some others.

The other invaluable resource was the old books. A good source for these is Pete Millett's website, although I'll warn you some of the books are more readable than others, even when covering the same topic.

BTW, thanks for not taking my comments as sharpshooting... I didn't intend to come off like a troll. Just hoping to pass along some good info.
Old 6th December 2012
  #120
Gear Maniac
 
NothingTheory's Avatar
 
🎧 10 years
Well Met Brian,

Tone is so hard to read in e-mail and posts. I may not always succeed but I do try not to read too much into things when Im not face to face.

Pete Millet's books are a treasure trove and thats actually where I started off at to bridge the gap between my silicon based background and the tube stuff I wanted to do. I havent read every one but probably most of them. It made me realize a few things. Like , wow, we had a bunch of really smart people back in the 50's and 60's and much of that knowledge is becoming lost, or will be within the next generation. Well .. I mean we did go to the moon in the 60's, but I just didn't generally think of that era as being "high tech" .. and there indeed was a lot of high tech back then.

Appreciate the discussion and I will at least go back through and peruse my web site for technical or lingo errors.
πŸ“ Reply

Similar Threads

Thread / Thread Starter Replies / Views Last Post
replies: 126 views: 77528
Avatar for justinheronmusic
justinheronmusic 11th August 2015
replies: 460 views: 82883
Avatar for John Willett
John Willett 29th June 2010
replies: 73 views: 21778
Avatar for monkeyxx
monkeyxx 24th May 2013
replies: 5904 views: 749332
Avatar for Jonathanvl
Jonathanvl 1 week ago
Post Reply

Welcome to the Gearslutz Pro Audio Community!

Registration benefits include:
  • The ability to reply to and create new discussions
  • Access to members-only giveaways & competitions
  • Interact with VIP industry experts in our guest Q&As
  • Access to members-only sub forum discussions
  • Access to members-only Chat Room
  • Get INSTANT ACCESS to the world's best private pro audio Classifieds for only USD $20/year
  • Promote your eBay auctions and Reverb.com listings for free
  • Remove this message!
You need an account to post a reply. Create a username and password below and an account will be created and your post entered.


 
 
Slide to join now Processing…
πŸ–¨οΈ Show Printable Version
βœ‰οΈ Email this Page
πŸ” Search thread
πŸŽ™οΈ View mentioned gear
Forum Jump
Forum Jump