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

[midwayfair]

I'll see if I can fix the link next time I'm on a desktop, but my username there is the same as here.

 

[Lowfreq]

I had a look through your projects linked to your name on there. The other transformer based mics and the oscillators seem to all be there (along with some other cool looking projects), but the shoeps styled pcb doesn't seem to be in the lineup.

 

[midwayfair]

Should be fixed now.

 

[Lowfreq]

Awesome!! Thanks.  I just ordered some Schoeps boards and also some oscillator boards. I'll update progress on this project once I get stuck into it.

 

[rbarreiros]

Hi,

I've been trying to find D1/D2 values and caouldn't figure them out. I realize R4,R5 values vary according to the the freq one whishes the HPF to be, but I'm failing to understand with which cap is the HPF being formed to make the math ?

Also, has anyone tested the PCB yet ?

 

[midwayfair]

Hi,

I've been trying to find D1/D2 values and caouldn't figure them out. I realize R4,R5 values vary according to the the freq one whishes the HPF to be, but I'm failing to understand with which cap is the HPF being formed to make the math ?

Also, has anyone tested the PCB yet ?

D1/2 are the equivalent of D3/4 here:
http://www.sdiy.org/oid/mics/Schoeps.gif

They're 6.2V zener diodes in the original. Maybe someone else can confirm if you can substitute them with other values. I don't think they're really necessary.

I don't know if anyone's independently verified this, and although I did stuff a PCB and verify voltages, I don't have the parts to put it in a microphone (and it's not looking likely that I'll be able to do so while I'm in school).

EDIT: forgot to answer your second question. The filter is formed with C4 and C5. Normally they see only the source impedance from the input transistor, so adding more resistance there lowers the cutoff frequency. Exactly what value they should be, if you make them anything but a wire, requires knowing where a specific capsule is likely to have problems (if any).

 

[ln76d]

These are pretty usefull, esepcially when you making a lot of different tests
First thing which will die during any short are exactly these diodes. 6.2V is pretty good  value for purpose. Going to 6.8V doesn't harm - some chinese schoepslookalike have factory installed 6.8V

 

[rbarreiros]

Thanks.

I made a few pcb's to test them out, I have a cheap MXL 2006 at home, will use it as a test bed.
I was wondering what are the typical mv that the diaphragms of these mics would run at, thinking of building a Smaart test rig, injecting pink noise into the capsule input and read the preamp result.

P.S.
Got some doubts about the connections that I can't find any indications anywhere.

In the schematic there's a pad switch, one side connects to the front of the capsule/diaphragm, the other side connects where ?
The pad near the bias trim connects where ?

The XLR1/2/3 are pretty much self explanatory, the OSC pad connects to the OSC pad on the oscillator PCB, and on the oscillator PCB, Back goes to the back of the capsule/diaphragm, correct ?

Thanks

 

[ln76d]

Thanks.

I made a few pcb's to test them out, I have a cheap MXL 2006 at home, will use it as a test bed.
I was wondering what are the typical mv that the diaphragms of these mics would run at, thinking of building a Smaart test rig, injecting pink noise into the capsule input and read the preamp result.

P.S.
Got some doubts about the connections that I can't find any indications anywhere.

In the schematic there's a pad switch, one side connects to the front of the capsule/diaphragm, the other side connects where ?
The pad near the bias trim connects where ?

The XLR1/2/3 are pretty much self explanatory, the OSC pad connects to the OSC pad on the oscillator PCB, and on the oscillator PCB, Back goes to the back of the capsule/diaphragm, correct ?

Thanks

Just out of curiosity - why you are using these PCB's when you have schoeps "type" topology already in mxl 2006?

 

[midwayfair]

Got some doubts about the connections that I can't find any indications anywhere.

In the schematic there's a pad switch, one side connects to the front of the capsule/diaphragm, the other side connects where ?
The pad near the bias trim connects where ?

The XLR1/2/3 are pretty much self explanatory, the OSC pad connects to the OSC pad on the oscillator PCB, and on the oscillator PCB, Back goes to the back of the capsule/diaphragm, correct ?

I'm sorry that some of the connections were unclear.

G2 near the bias is an extra ground in case it's needed. Most builds probably won't need it, but I had room on the board so I put it there just in case.

If you AREN'T using the pad: The capsule back is connected directly to the "Back" pad on the oscillator PCB.

If you're using the pad: Connect the back of the capsule to a lug of the pad switch and then run a wire from the same switch lug to the "Back" pad on the oscillator PCB. In other words, the back of the capsule will be wired through the switch so it's connected all the time, but there's only one wire going down into the body of the mic.

The pad switch is single pole, single throw, so the lug that gets connected when the switch is thrown will have the wire that goes to the main PCB's "Pad" pads. When you're looking at the front of the board, the pad to the righthand side is the one that is connected to C1.

Hopefully that explains it. I never really got a chance to do a real build doc for these.

---

Looking at it now, I should not have used a "switch" part in Eagle for the schematic, because it makes it look like the left hand pad labeled "Pad" should be connected to the switch, even though it doesn't connect to anything. I wasn't really expecting the pad switch to get much use to be honest!

 

[django32]

Just a word of warning, these don't fit the bm800 bodies I recently got, I think they may have shrank since the pcbs were made

 

[midwayfair]

Just a word of warning, these don't fit the bm800 bodies I recently got, I think they may have shrank since the pcbs were made

Uh oh

How far off are they? Any chance you can measure with calipers?

 

[django32]

from the centre of the mounting hole to the other one its 30mm, which is a fair bit off

 

[midwayfair]

from the centre of the mounting hole to the other one its 30mm, which is a fair bit off

I can't remember off the top of my head but I seem to recall the holes being 35mm. I'm worried that even if I modify the board to have 30mm holes the rails would be touching some pads, so I think I will just remove the BM800 from the list of compatible bodies. I do know the Auryle fits as of last year and that it was still the same as a couple MXL bodies.

I'm really sorry for the mess up.

 

[django32]

I can't remember off the top of my head but I seem to recall the holes being 35mm. I'm worried that even if I modify the board to have 30mm holes the rails would be touching some pads, so I think I will just remove the BM800 from the list of compatible bodies. I do know the Auryle fits as of last year and that it was still the same as a couple MXL bodies.

I'm really sorry for the mess up.

to be fair, they could of just changed the design since you did the pcb. I'm wondering if the bm-700 or bm-8000 are any different internally? Or maybe It is worth just investing a little more money.

 

[analogguru]

to be fair, they could of just changed the design since you did the pcb. I'm wondering if the bm-700 or bm-8000 are any different internally? Or maybe It is worth just investing a little more money.

At least the following el-cheapo-china-microphones have all 30mm distance:

noname    BM-300
AGPtek      BM-700
Neewer      BM-700
ShengYue  BM-700
Tonor        BM-700
Floureon    BM-800
noname    BM-800 (blue)
noname    BM-800 (black)
Yinger        BM-800
ATL            PK-999
Neewer      NW-1500

BTW, the dimension from outer-frame-to-outer-frame is approx 35,5mm.

 

[midwayfair]

Thanks for the list, analogguru.

BTW, the dimension from outer-frame-to-outer-frame is approx 35,5mm.

Yeah, that's narrower than the entire board (at the top).

I had an old test mic body that I had picked up used (it was free but trashed and I couldn't have actually got a mic in it if I wanted to), it's possible that it just wasn't ever a BM. They were cheap enough and I should have just bought one to be sure I had the real thing before listing it as one of the bodies that fit.

If someone wants to do the measurements, I could redo an Eagle file that IS compatible with the El-Cheapo bodies, order one, and ensure it fits in the body. I can't get to it until late May, though, I just have too many this semester to dedicate any appreciable time (or money, honestly, but I already have the parts) to hobbies.

I'll also go update the other thread.

 

[user 74717]

Just wanted to say THANK YOU midwayfair! I am so glad that I found this thread!

I know it's an old topic but the space between screw holes on the current cheapo BM800s on aliexpress (also very cheap on amazon now too) is 31mm. But I've had luck using aurycle and MP boards with these bodies by only screwing one side and securing/grounding the other side with trimmed leads.

Thank you for the eagle files! They're almost exactly what I was hoping to do myself.

 

[user 74717]

I'm looking to try this build and have a couple questions, hopefully someone can help me out!

1) What component should I use for D1 and D2...I can't find that info anywhere.

2) Are R6 and R7 supposed to be 1% like in the BOM or 0.1% like the schematic?

3) Are C2-7 supposed to be 100V like in the BOM or 50V like in the schematic?

4) I'm hoping to build a stripped down version that is cardioid only with no pad, no HPF or LPF, and no patter switch. Would anyone be able to tell me which components could be left out with such a build?

I've been getting more into DIY audio the past couple of years but don't know much about circuits  :-\ any help would be appreciated!

 

[midwayfair]

I'm looking to try this build and have a couple questions, hopefully someone can help me out!

1) What component should I use for D1 and D2...I can't find that info anywhere.

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

Comparing the two schematics will be good practice for reading schematics. For the most part this is just copied from that.

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. If you want to build it like the original mic, though, use what's specified in the original Schoeps schematic.

2) Are R6 and R7 supposed to be 1% like in the BOM or 0.1% like the schematic?

0.1% might not have been available or overly expensive when I made the cart. You can always change out parts in the mouser cart.

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

3) Are C2-7 supposed to be 100V like in the BOM or 50V like in the schematic?

4) I'm hoping to build a stripped down version that is cardioid only with no pad, no HPF or LPF, and no patter switch. Would anyone be able to tell me which components could be left out with such a build?

Reread the PMs I sent you last week. I explained what parts are associated with the pad and HPF. I also explained that there are no parts on this PCB that have anything to do with the polar patterns.