Samson C02 - SDC mods

[lambchop]

Hi Skipwave!  Okay here's a pic of the underside of the board.  It appears to my uneducated eye that the surface mounted caps follow a different path than the C5 & C6 sockets.  What do you make of it?  Is it okay for me to just pull the surface mounted ones and put the new ones in the C5 & C6 sockets?

 

[lambchop]

Would anyone be able to answer my question above?  I've now placed pics of both the front and back of the circuit board.  Any help is really appreciated for an uninitiated one like myself.  Thanks!

 

[0dbfs]

lc,

It's sort of hard for me to tell by looking at the pics but it does look like the small surface mount parts are connected to different traces than C5 and C6.

It might be very helpful (for you) to draw out the PCB traces and components and turn it into an actual schematic that is in the same layout as the schematic referenced earlier (pencil & paper). Going through that process will force yourself to both identify and connect the dots/nodes so to speak and compare the differences between the schematic and the current implementation. At least to get a better understanding of how they are related to eachother (or not!).

Hope that helps!

Best,
jonathan

 

[lambchop]

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 

Hey, a buddy of mine looked at the circuit board and the recommendations and immediately said, "You don't want to replace Q1.  You want to replace Q2 & 3.  If you replace Q1 the board won't work."

Now, if you look at the board Q2 & 3 appear to be matched components.  Q1 looks entirely different.  Also; the schematics refer to Q2 & 3 being matched hfe.  So; you should replace Q2 & 3.  Right?

Can somebody please confirm for me?  Thanks!

 

[zapnspark]

My Takstar microphones had different parts designations from the Samson mics.
Thus the confusion.
The schematic in this thread refers to the matched PNP transistors as Q2 & Q3.
Those are the ones to replace.
(They are side by side on the board)

Cheers.

ZAP

 

[lambchop]

Thanks for the clarification, ZAP!

I hope you don't mind a newbie making sure of what he's attempting to do.  The help here is really appreciated.  I'm actually finally just breaking the tip of an iceberg of knowledge that I have wanted to learn for a very long time.

Thank again!

 

[mitsos]

A few questions for someone who understands this circuit?  I don't have these mics, but I'm curious.

Skipwave's comment made me wonder about the through-hole (C5 and C6,unstuffed.. not sure they are really through-hole?) vs smd caps, stuffed. Seems if you stuff one or the other, you change which BJT transistor the source and drain of the FET go to. For example, if you follow 1 of the 2 traces coming off the FET (bottom of PCB, the left-most solder-pad), it connects to both the vertical (in the topside pic) SMD cap and C5.  So if you stuff one, the signal continues to Q2, if you stuff the other, it goes to Q3... why?

Also, the schoeps circuit has the 150K resistors bypassed with a 470p cap. Any reason to do this here?

What about the other part of the circuit left out? Is it to bias the capsule? Doubt one could fit it in there unless you totally redid the PCB, but I still wonder why it's not there. Not like it's got expensive parts or anything, just one more transistor.

FWIW, here is the schemo (I think this is zebra50's site):
http://www.xaudia.com/xaudia/Schematics/Pages/Schoeps_Sony_files/Media/Schoeps/Schoeps.jpg?disposition=download

 

[zapnspark]

Mitsos,

I can't comment on the board thru-hole layout since my Takstar microphones are a bit different.

The 470 pF caps roll off the high end frequency response. A good idea for stability and RF immunity.

The Samson/Takstar microphones use an electret microphone capsule which does not need a polarizing supply voltage. The Schoeps CMC-5/3 capsules are not electret and require that 1 transistor Hartley oscillator circuit to generate ~60 volts DC for the capsule. (seen at the bottom of the Schoeps CMC-5/3 schematic)

Cheers.

ZAP

 

[Gus]

I worked on a pair of the Samson C02s when they first came out.  After I changed parts they sounded about the same to me as they did stock.  I think the capsule has more to do with that microphones sound than the circuit and stock parts

What are you people hearing that is good about that microphone and what do you use it for?

 

[lambchop]

Zap, sorry to bother you again, but you said,

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

I just finished my 1st mic and I get a signal, but just like the other guy I have a very low output.  I installed the transistors in the same directions as the originals.  Did you mean by your comment that the orientation of the E,B & C is the opposite of the transistors that were originally on the piece and that I should reinstall them in the opposite direction of the originals?

I would really appreciate some guidance.  Thanks!

 

[zapnspark]

Lambchop.

If you are using the BC559C or BC560C transistors then, yes, you need to install them in the opposite orientation to the original transistors.

Cheers.

ZAP

 

[lambchop]

Once again, thanks ZAP!

I actually just found this nice diagram of the 3 common pinouts and was going to try to compare it against the original schematic.  I'll still do it for practicing/educational purposes, but am heartily grateful that you confirmed this for me.

http://www.armory.com/~rstevew/Public/Tutor/TransistorPinouts/transpinouts.htm

 

[lambchop]

Okay, I switched the transistors around and the gain increased.  However, now I have an annoying hum.  What can it be?

 

[thomasdf]

I was recently given a pair of these mics with hypercardio capsules on them.
I havent had the opportunity to test them yet but I'm used to use much more expensive mic and pro mics... So I told myself why not mod them?
Does the mod described here brings other things than just boosting the level and lowering radio sensibility? I may be tempted to add that "schoeps" style condenser on the 150K resistor, but which one are we talking about?

 

[thomasdf]

Any help is welcome!
As some pointed out earlier on this thread, my mic doesn't have caps on the C5 and C6 pads... (same as the one in the pics)

 

[xaidi]

Hi Dear gs3333..!
I need that schematic of samson c03 but the link you uploaded isn't working now. Can you please send me clear pic at my email here  :  [email protected]

I shall be great thankful to you..!!

 

[RuudNL]

What is the idea behind the 220 pF capacitor in parallel with the electret capsule?
One would think this acts like a pad.
I thought it was there to make a higher SPL possible, but I lifted one leg and it seemed (to my surprise!) that the output stayed the same.
Measured capacity of the capsule is around 30 pF.
(The idea behind removing the capacitor was trying to get a higher output and/or a better signal to noise ratio.)

 

[geertvdijk90]

Disclaimer: I think I'm doing the right thing resurrecting this one, as the original schematic photo doesn't work anymore and this could possibly help others as well, but sorry in case I'm wrong on this.

I recently got (amongst others) a pair of C2's dirt cheap, and I want to doublecheck before trying anything:
based on the attached schematic (mainly worried about labeling differences), is this right?

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)

Where Q1 and Q2 would probably be Q2 and Q3 in both cases, I presume?

 

[RuudNL]

I had them... Returned them the same day to the seller, way too noisy!

 

[geertvdijk90]

I had them... Returned them the same day to the seller, way too noisy!

Got them with a couple of other microphones for no real money, returning isn't an option and perhaps something can be made of it, I just wanted to doublecheck before going to town.
But I don't expect them to be replacing my SE3's any time soon, so don't worry (though I might try the SE3s as room OH and these as drum OH in a live recording, see what it does).