Samson C02 - SDC mods

[gs3333]

Hi guys. Long time lurker, first time poster here!

I've read lots of the info on here in the past regarding DIY SDC mics. I've just been given a pair of Samson C02s. They're cheap, noisy little things but I suspect they may be worth modifying since they're based on the Trans-Sound TSB160A capsule.

I've uploaded the schematic here: http://img171.imageshack.us/img171/5371/co2schem.jpg

I've read the general advice regarding Schoeps circuits but does anyone have any specific recommendations for mods to this mic? C5 and C6 are SMT caps but the rest of the components are through-hole so it should be easy to work with. There also appears to be a 22pF capacitor in parallel across the capsule which isn't on the schematic.

Cheers

Greg

 

[zapnspark]

Remove R7 and R8 (27k)
Change C5 and C6 from 1 ufd to .1 ufd 50 V plastic film types
Replace Q1 and Q2 with 2SA1084 (or 2SA1085) matched for hfe
(Could also use BC559C or BC560C transistors)
Put 6.8 volt zeners across emitter/collectors of Q1 and Q2
(Zener cathode to emitter, anode to collector)

Cheers.

ZAP 

 

[gs3333]

Thanks ZAP, I'll give that a try.

 

[gs3333]

Well, we have a mixed result. I've carried out your recommendations - removed R7 and R8, fitted .1uf caps in place of C5 and C6 and replaced Q1 and Q2 with BC559C and 6.8V zeners - but both mics now have very low output. Obviously I took as much care as I could to avoid static and defluxed the board after soldering.

The signal I'm getting through sounds good but I'm having to turn my preamps to the max and even then the levels are incredibly low.

Any suggestions as to what I might have done wrong?

Thanks!

 

[zapnspark]

I modified two Takstar PCM-6100's (they appear identical to the Samson's)
The level came up on these after modifications -- as expected.
Here are some likely things to check:

The BC559C(or BC560C) have european pinouts for E, B and C leads.
Check the data sheet. They might be installed backwards

The zener cathodes (the banded end) go to the emitters of the respective
PNP transistors. The anodes go to the respective collectors.

Make sure the zeners are 6.2 or 6.8 volt types.

Cheers.

ZAP

 

[gs3333]

Transistors the wrong way round! What a stupid mistake to make. Oh well, problem solved.

Thanks ZAP, they sound pretty good from the first quick tests. I'm looking forward to trying them out as drum overheads now.

 

[nhaudio]

what transistor is q3? 5401?

nhaudio

 

[solderspongebob]

I fancy buying a pair of these and modding them. I've pasted zapnspark's mods onto gs3333's schematic (hope you don't mind gs3333) but could one of you cast your eyes over it and check I've got it right please? Ta.

 

[zapnspark]

solderspongebob,

Nicely done. The modded diagram is correct.
Note the R3 is labeled 1.5 v in the original.
That should be 1.5 k

Cheers.

ZAP

 

[3nity]

this thing looks alot like the scott dorsey mod!!!
what you think?

 

[zapnspark]

3nity

The Dorsey mod and many inexpensive china manufactured condensor microphones are based
on the original Schoeps CMC-5 microphone design.

Cheers.

ZAP

 

[snaimpally]

Bought a pair of C02s from B&H last week for $78.  I can't get the bottom screw undone to get a peek into the insides.  Any suggestions?

 

[steenamaroo]

try turning it the right way??  ;D ;D ;D

you don't screw the screw out,,,,,you screw it in.

 

[snaimpally]

try turning it the right way??  ;D ;D ;D

you don't screw the screw out,,,,,you screw it in.

Ahh ha!!!  That worked.

Can I get all the components at Frys or RS?  Any suggestions for where to mail order the components?

 

[lambchop]

Hi Everyone!

I'm a newbie here with this first post.  A buddy of mine who is an avid mod'er turned me on to this post knowing that I have two CO2's and now I definitely want to try this mod.  It'll be my first but I'm fairly certain that my friend will hold my hand through the process (I hope!). 

He was nice to scope out the parts available at mouser for this.

BC560C Transistors, Mouser Part # 512-BC-560C

Zenor Diode 1N4728A - 1N4758A, Mouser part # 512-1N4736A

Nichicon Plastic Film Capacitors .1uf 50v 5%, Mouser part # 647 QYS1H104JTP

So; these parts will work for this mod, right?

This feels like getting your feet wet at your first swimming lesson.

 

[abechap024]

Gs3333 looks like your good to go! Good luck with your first project.
AC.

 

[lambchop]

Hi Gs3333,

I'm attempting to perform the same mod (a first for me, by the way).  One question: when you mentioned that you "fitted .1uf caps in place of C5 and C6" did you use the sockets where the old caps were desoldered or did you use the designated sockets on the board that have nothing in them?  I've placed a picture of the board just in case I'm not making myself clear here.  It appears that there are two caps soldered on the board in between the C5 & C6 sockets.  Any help will be greatly appreciated.  Thanks!

 

 

[lambchop]

Er, would anyone here know the answer to my question above?  I'd really appreciate any help you might be able to offer.

 

[lambchop]

bump!

 

[skipwave]

Hard to see in the photo. A shot of the other side, showing where those traces go to would help.

Are those little surface mount capacitors that are between the two thru-hole capacitor footprints? They look like it. Are the pads connected to the through hole footprints by traces, putting them effectively in parallel with the unused pads? If so, they laid the board out to allow either SMT or through hole caps to be used, possibly because they wished to be able to sub in whatever was on-hand at the factory.