Open source project: "Generic" Shoeps-style microphone PCBs on Osh Park

[user 74717]

You can always consult the original Schoeps schematic if you aren't sure about something on this schematic http://recordinghacks.com/microphones/Schoeps/CMC-5

Very cool, thanks!

Those diodes aren't always used in this type of mic and there's more than one part that could go there if they do get used.

Okay so I should use a 6.2V zener like TZX6V2D-TAP then. But different components would work as well...is there a different component that would be better? I certainly have no need to recreate the original for any reason.

there's 10 resistors of that value in the cart. That should be enough to find a pair close to 0.1%.

Sounds like something I need to learn how to do! 

Reread the PMs I sent you last week. I explained what parts are associated with the pad and HPF.

In your PM you said I could leave out C1 and leave out "one resistor" but you don't say which R. You also mention removing the 1G resistor. Should I remove/jump R1 and R11? And can I forego the pad and hpf trimmers?

Attached is an image of the PCB design for what I'm planning based on my current understanding of what you've said. Please let me know where I've gone wrong, and thanks again! <3
[Edit: The image below shows R1 jumped but that's a mistake, I have R1 installed].

 

[user 74717]

Oh and I was also planning on jumping R4 and R5 but don't have that shown in the image I attached.

 

[user 74717]

For anyone still interested, my PCBs arrived this weekend and I've just finished a successful build using midwayfair's linked PCBs and most of the BOM (I replaced some resistors and caps with Dale and Wima ones that I had left over from a previous project). I also left out R11 and C1, and jumped R4 and R5. I also did not included pad or hpf switches. I currently have it in a BM800 body but it's VERY tight. This first build uses the LEDs for D4-6, but for build #2 I am planning on trying the 12v D3 with D4/5 jumped and the 470 C9, just out of curiosity.
[edit: I originally left out R1 but now do have the 1G at R1. The mic was fairly noisy at first but is very quite now with R1 installed.]

So far I haven't done much but talk into the mic to verify that it's working, but it sure sounds crisp! Looking forward to putting it to use.

 

[midwayfair]

For anyone still interested, my PCBs arrived this weekend and I've just finished a successful build using midwayfair's linked PCBs and most of the BOM (I replaced some resistors and caps with Dale and Wima ones that I had left over from a previous project). I also left out R1, R11 and C1, and jumped R4 and R5. I also did not included pad or hpf switches. I currently have it in a BM800 body but it's VERY tight. This first build uses the LEDs for D4-6, but for build #2 I am planning on trying the 12v D3 with D4/5 jumped and the 470 C9, just out of curiosity.

So far I haven't done much but talk into the mic to verify that it's working, but it sure sounds crisp! Looking forward to putting it to use.

Thanks for the extra verification

 

[user 74717]

Image attached of two of three of the finished builds.

They're in BM700 bodies, which can be found for $15 including a surprisingly nice shockmount on amazon and aliexpress. The bodies are metal and feel nice. I also like the heavy brass Aurycle bodies, but these are close to half the size and much lighter AND way cheaper. If you want it to fit in a BM700, you'll have to sand down the edges of both boards a bit, or make the board more narrow in Eagle if you know how.
The BM700 rail screws/holes are 31mm apart and use M2.2 screws. I had my as-is boards tied down to the rails with trimmed leads, but it proved unreliable and now they're just super-glued to the rails  :-[
If I make more I will definitely have to figure out how to modify the board a bit in eagle.

I'm using various Rayking capsules from alibaba and couldn't quite say which one I prefer. I haven't used them too much to be honest but would say I generally prefer their more open sounding edge-terminated style. This weekend  I've been using one side-by-side with my beloved MP S-12 which has a similar circuit and expensive MP capsule. They sound incredibly similar.

 

[Lowfreq]

How important is it to match the inductors? Resistors are easy, and getting hfe matched on the 2n4403 is easy, but I haven't seen many other projects getting the inductors down to 0.1% matching.

 

[midwayfair]

How important is it to match the inductors? Resistors are easy, and getting hfe matched on the 2n4403 is easy, but I haven't seen many other projects getting the inductors down to 0.1% matching.

This might have been a copy and paste mistake. I don't think I've ever matched the inductors. Someone else who knows more might be able to say whether it's worth doing.

 

[Lowfreq]

I finally got round to doing this project. I had to trim a little bit of the pcb to fit it in a bm800, but not much.

I've got and RK47 capsule (from the group buy) in there, and I've wired it up in fig8 for now, until I decide on how I want to add switches to the body. I have plenty of other mics that do cardio and omni, so I might just keep it fig8. I plan on doing a pair for some Blumlein stereo stuff.

I needed up using a 4.7v zener diode and some white leds. I couldn't quite get the full 12 volts with any of the 3.3 - 3.9 range of zeners, so I'm guessing my leds aren't quite hitting the 3.2v forward voltage that the specs say.

I'm using a 2n3819 from mouser. I also have some J305s to try to compare noise levels. Either way, it sounds quiet enough at the moment that I wouldn't have too many issues even on quiet sources.

I'm also messing around with your Transformer-couple FET+BJT circuit, but still having some issues (which I'm sure I'll post about in the other thread, if I can't figure it out myself with some tinkering).

Definitely happy with this little mic, and I'm definitely gonna to try it in some sessions soon.

​

 

[kingkorg]

Great work! You might want to pay attention to midrange with f8 and k47. The k47 has already a bump in the midrange. F8 by it's nature in multi pattern mics pushes this exact point k47 has accentuated. So it might be a bit too much mid forward.

 

[ToneShack]

I know this is an old thread. But I am looking to give this circuit a shot.

Anyone have any info to share on the HPF resistors R4,5?

 

[midwayfair]

I know this is an old thread. But I am looking to give this circuit a shot.

Anyone have any info to share on the HPF resistors R4,5?

The form a LOW pass filter (not HPF -- if you want that, it's R11) with C4 and C5.

If you already know what you want frequency-wise (like, say, you've looked at the frequency plot for the capsule you're using and you know you want to cut at 10KHz or something) or just aren't sure what their effect is you can use this calculator:
http://sim.okawa-denshi.jp/en/CRlowkeisan.htm

 

[ToneShack]

The form a LOW pass filter (not HPF -- if you want that, it's R11) with C4 and C5.

If you already know what you want frequency-wise (like, say, you've looked at the frequency plot for the capsule you're using and you know you want to cut at 10KHz or something) or just aren't sure what their effect is you can use this calculator:
http://sim.okawa-denshi.jp/en/CRlowkeisan.htm

So if I want to build it without the LPF, I jumper R4,5 and omit R11?

 

[midwayfair]

So if I want to build it without the LPF, I jumper R4,5 and omit R11?

Yes

 

[komikuapples]

I'm a little confused by how the low-pass works on the circuit, how do I increase and decrease the value. Is that by changing out the pair of resistors and caps?

 

[midwayfair]

I'm a little confused by how the low-pass works on the circuit, how do I increase and decrease the value. Is that by changing out the pair of resistors and caps?

Use the calculator linked above for an RC filter. Your "R" is R4 and your "C" is C4. Then match R5 and C5.

Play around with the filter and you'll see how the values change. Look up the spec sheet for your capsule and try to find values that hit a frequency you think is going to help.

 

[jsender]

you can even just omit the oscillator completely and this works as an Alice

I recently got a couple electret capsules and am planning on trying out my first "Alice" build. I found an Alice PCB to order, but realized that the circuit was very similar to the board for this mic which I have a couple of and love.

Then when looking back through this thread I saw where midwayfair mentioned that this board could be used in an Alice build without the partner oscillator circuit, which would save me a PCB and BOM order since I have an extra of these lying around still.

Are there any component changes or unnecessary components when putting this board together to use as an Alice mic? And I suppose I'll ground the capsule to the gnd pad that would be connecting to the oscillator board?

 

[midwayfair]

I recently got a couple electret capsules and am planning on trying out my first "Alice" build. I found an Alice PCB to order, but realized that the circuit was very similar to the board for this mic which I have a couple of and love.

Then when looking back through this thread I saw where midwayfair mentioned that this board could be used in an Alice build without the partner oscillator circuit, which would save me a PCB and BOM order since I have an extra of these lying around still.

Are there any component changes or unnecessary components when putting this board together to use as an Alice mic? And I suppose I'll ground the capsule to the gnd pad that would be connecting to the oscillator board?

I think maybe you don't want to use the bias trimpot or maybe just twist it straight to ground, but maybe that doesn't matter. I also don't actually know if C1 will work for a pad or what the value would need to be for it, I've never put a pad in an Alice circuit.

 

[jsender]

Wanted to update: I used this board for an electret "Alice" build and it sounds great! I don't have any other 'Alice' mic to compare it to, but it is very quiet and very high output. Compared to the 34mm with oscillator version of this mic, the electret is much more contained sounding with a significant low-mid dip, but still sounds quite nice. Would surely sound even better with a better electret capsule. Very cool!

I also was wondering about the impact of the hFE value for Q2/Q3 out of curiosity -- I had enough of these transistors to get fairly close hFE matches, but in my batch of about 20 of the 4403 transistors, their hFE values have a very wide range (like 150hFE to 400hFE) -- what impact will this hFE value have? Would a build with two matched 175hFE transistors function the same as a build with two 375hFE transistors?

 

[thor.zmt]

I also was wondering about the impact of the hFE value for Q2/Q3 out of curiosity -- I had enough of these transistors to get fairly close hFE matches, but in my batch of about 20 of the 4403 transistors, their hFE values have a very wide range (like 150hFE to 400hFE) -- what impact will this hFE value have? Would a build with two matched 175hFE transistors function the same as a build with two 375hFE transistors?

How about switching to P-Channel MOSFET's? Instantly near infinite HFE.

Thor

 

[midwayfair]

They're just buffers, I can't think of any reason to fuss about the hfe beyond matching them. But maybe someone more knowledgeable can chime in.