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

[ricardo]

Audio improv didn't measure an increase in noise with the added resistors.

Actually if you look at his measurements carefully, you'll see that he DOES measure a SMALL increase in noise.  (You'll have to  search through his excellent website to find this)

It means the dominant noise source in his example is somewhere else.  If you were anal, you could easily dream up examples where the INCREASE in noise is greater or smaller but there will ALWAYS be an increase.

But in the scheme of things, I don't like using something which needs more bits and doesn't provide better performance or increased capability.

WHAT SORT OF INCREASED CAPABILITY?

In my MicBuilders Files, I show how to  increase the LF extension  of the discontinued WM55 to better than  Schoeps MK4 & DPA4011.

But the increased capability I'd really like is to have 12dB/8ve LF cut like U67.  You MUST have some LF cut in a cardioid or Fig-8.

I've not been able to do this sensibly (with low noise, THD, simplicity bla bla) until Homero's Charis.

 

[midwayfair]

Ricardo, thanks for popping in, and you're right, what he said was that the noise from the air hitting the capsule predominates.

I've considered just removing the resistors because I feel like they're distracting from the purpose of the project (which was to provide a cost-effective *generic* Schoeps replacement PCB for mics that used to be common mod platforms before they went to SMD) ... the zener/LED ladder is more of a case of "too awkward to solder PTP on the back of the PCB," and the HPF and pad were basically free once I saw there was a bit of extra space when the layout came together, but I think there are far too many modifications out there to the original circuit and too many methods of achieving any particular end for me to include space for them all.

EDIT: I also removed the earlier reference to adding Ricardo's mods. There are multiple reasons, but the main was was doing so would be getting further and further away from the purposes of the project.

 

[dchang0]

hm. okay. I'll change the size of the holes and re-upload in a moment.

Mouser doesn't seem to carry them (or if they do, the measurements for their screws and fasteners section is too arcane for me). Anyway, to the hardware store go I.

When you buy M1.6 screws for the capsules, use 5mm length for the screws that go through the saddle and 3mm length for the screws that attach the solder tab to the backplate. 5mm screws are too long for the latter task.

 

[midwayfair]

There's a mistake in the oscillator -- I'll fix it in a few minutes. Actually nevermind, I think it's okay as drawn.

I also think we can do without the filtering caps on the oscillator PCB, which would make the board smaller. They weren't there in the original Schoeps circuit anyway. Does anyone have any strong opinions either way?

 

[vizcities]

What's the word on these boards? Have they been tested/independently corroborated yet?

 

[midwayfair]

What's the word on these boards? Have they been tested/independently corroborated yet?

I verified one, but only electronically. I don't have a microphone body to put it in, so I can't test how it actually sounds. I'm back in school now and on lock down for play money. I honestly don't know when I'll be able to get another microphone body to put it in.

If anyone wants a PCB set and is willing to independently verify them, you can PM me. I have two left.

 

[Wordsushi]

Has anyone built one of these mics from these boards yet?

 

[Khron]

I've put together four, with my own version, and they work just fine

Can't really comment on the "sound" yet, but i plan on measuring them compared to my calibrated measurement mic, in the near future...

 

[midwayfair]

! Thanks, Khron.

I started school in the Spring and can't really justify the cost of mic bodies for a while to be able to do even cursory tests in a DAW or really the time to build much of anything (computer science and math classes are both really time consuming, at least for me). I did use two of the transformer-based ones, and I could probably gut a mic body at least temporarily to give one of these a home, if I ever find myself flush with free time again.

 

[Wordsushi]

I've put together four, with my own version, and they work just fine

Can't really comment on the "sound" yet, but i plan on measuring them compared to my calibrated measurement mic, in the near future...

Thanks Khron,
What is the difference in your own version? Can't wait to hear samples of them if you ever have time.

 

[Khron]

I've detailed some of my choices and motivations for them, in my BM800 mod thread:

https://groupdiy.com/index.php?topic=61845.msg783516#msg783516

The designs "nowadays" are pretty much the same, i just tweaked the board layout a little bit, but no major changes

Basically, i went for a / the more feature-rich approach (switchable high-pass, 10dB-ish pad, 3-pattern) , so as not to inherently limit the flexibility of the design from the get-go.

Should one wish, i think the "audio" boards could be used on their own, without the switch-pcb or the DC-DC converter board. You might just need to bridge some pads / traces (to "replace" the pad / HP switches). I've also included components to derive and filter the capsule bias voltage straight from the phantom input, for cardioid-only designs.

I've used that electret-Schoeps version in my four BM800's (three with group-buy CK12's and one with a franken-K67, but i wanna swap that for a group-buy K47), and the JFET-PNP one in... was it three(?) of my sE2200A's (two with K47's and one CK12, if memory serves).

Thanks Khron,
What is the difference in your own version? Can't wait to hear samples of them if you ever have time.

 

[Wordsushi]

Very interesting. Thanks for that Khron. Looks like you really went above and beyond.

I'm still interested in boards I can order that will fit into a MXL V63 or similar, that pretty much mimic what those boards do so I can tinker further on some mod ideas I have done. Midwayfair's boards look interesting, but I'm waiting for someone else to build, test and post files first before I try them.

So, if anyone else out there feels inclined to create a dead on copy of that boring old vanilla MXL/CAD/Alctron/Everyone Else... Schoeps circuit boards, kinda like what RuudNL used to have, and make them available on OshPark or somewhere else, I'd be interested.

I've detailed some of my choices and motivations for them, in my BM800 mod thread:

https://groupdiy.com/index.php?topic=61845.msg783516#msg783516

The designs "nowadays" are pretty much the same, i just tweaked the board layout a little bit, but no major changes

Basically, i went for a / the more feature-rich approach (switchable high-pass, 10dB-ish pad, 3-pattern) , so as not to inherently limit the flexibility of the design from the get-go.

Should one wish, i think the "audio" boards could be used on their own, without the switch-pcb or the DC-DC converter board. You might just need to bridge some pads / traces (to "replace" the pad / HP switches). I've also included components to derive and filter the capsule bias voltage straight from the phantom input, for cardioid-only designs.

I've used that electret-Schoeps version in my four BM800's (three with group-buy CK12's and one with a franken-K67, but i wanna swap that for a group-buy K47), and the JFET-PNP one in... was it three(?) of my sE2200A's (two with K47's and one CK12, if memory serves).

 

[Khron]

Well, if you take a good look at my board and schematic, it can be easily "trimmed down" to a basic / normal Schoeps with only a couple wire jumpers There's plenty of component-leg-holes to use for those.

Very interesting. Thanks for that Khron. Looks like you really went above and beyond.

I'm still interested in boards I can order that will fit into a MXL V63 or similar, that pretty much mimic what those boards do so I can tinker further on some mod ideas I have done. Midwayfair's boards look interesting, but I'm waiting for someone else to build, test and post files first before I try them.

So, if anyone else out there feels inclined to create a dead on copy of that boring old vanilla MXL/CAD/Alctron/Everyone Else... Schoeps circuit boards, kinda like what RuudNL used to have, and make them available on OshPark or somewhere else, I'd be interested.

 

[Wordsushi]

Do you have your board available for order? I'd need it totally dumbed down like that. That's why I like working with the boards in MXL's and such, but they're getting harder to source these days.

Well, if you take a good look at my board and schematic, it can be easily "trimmed down" to a basic / normal Schoeps with only a couple wire jumpers There's plenty of component-leg-holes to use for those.

 

[Khron]

The circuit variant i used is the one shown and described in the link below (albeit with a few component value changes and a couple twists):

http://audioimprov.com/AudioImprov/Mics/Entries/2014/12/18_Another_Chinese_mic_Circuit.html

If you compare that to the plain / classic Schoeps:

http://audioimprov.com/AudioImprov/Mics/Entries/2015/4/23_Basic_FET_Microphone_Circuits.html

You'll notice that in the BM800 / my circuit, that PNP transistor in the middle is where the JFET is in the Schoeps circuit. You with me so far?

So all that would be necessary to use my board as a standard Schoeps is to install 2.2k resistors in the drain and source of the JFET, skip installing all the (other) components between the JFET and the two coupling caps in the bases of the two output PNP's, and run two wire-jumpers from the drain/source to the above-mentioned caps

If needed, i could do a screenshot of a schematic, and annotate it.

Oh, and no, i don't have boards available for order, and i've never used OshPark, but if there's some demand, i'll see what i can do about uploading my gerbers there (not 100% how they work, though - i've only dealt with "normal" manufacture )

 

[Wordsushi]

That's super interesting, Khron. If you have the time to annotate a schematic, I'd love to see it.

Yeah, I'm looking for boards I can order. It may not be worth the time to set it up, but if you ever did, that would be kinda cool!

The circuit variant i used is the one shown and described in the link below (albeit with a few component value changes and a couple twists):

http://audioimprov.com/AudioImprov/Mics/Entries/2014/12/18_Another_Chinese_mic_Circuit.html

If you compare that to the plain / classic Schoeps:

http://audioimprov.com/AudioImprov/Mics/Entries/2015/4/23_Basic_FET_Microphone_Circuits.html

You'll notice that in the BM800 / my circuit, that PNP transistor in the middle is where the JFET is in the Schoeps circuit. You with me so far?

So all that would be necessary to use my board as a standard Schoeps is to install 2.2k resistors in the drain and source of the JFET, skip installing all the (other) components between the JFET and the two coupling caps in the bases of the two output PNP's, and run two wire-jumpers from the drain/source to the above-mentioned caps

If needed, i could do a screenshot of a schematic, and annotate it.

Oh, and no, i don't have boards available for order, and i've never used OshPark, but if there's some demand, i'll see what i can do about uploading my gerbers there (not 100% how they work, though - i've only dealt with "normal" manufacture )

 

[Khron]

I think the simplest(?) way, considering how tightly packed my board design is, is to draw where the wire jumpers would go, and to list the components to omit.

Wire jumpers = yellow lines
JFET drain = the "southern" pin of that 2-pin "header" symbol that's on the board (and the "northern" in the schematic)
JFET source = the opposite of the above
JFET gate = onto the teflon stand-off that goes into that grey "bullseye" on the middle-left of the board

Right, components then:

Omit (don't install) = R3, R4, R5, R6, R7, R17, C1, C3, C5, U$1
Optional to jumper over = R8, R9

You could install R2 "standing up", with one leg where R4 "used to be", and the other leg to ground, and then run the upper wire jumper on the top of the board. With C5 skipped, you'll have that terminal-hole free.

Does that make any sense? If there's anything still unclear, don't be afraid to say so / ask

 

[Wordsushi]

Thanks again. It looks very interesting. I do need to find some unpopulated generic Schoeps boards though that I can order and use. I wish Poctop would offer them with his other boards.

I think the simplest(?) way, considering how tightly packed my board design is, is to draw where the wire jumpers would go, and to list the components to omit.

Wire jumpers = yellow lines
JFET drain = the "southern" pin of that 2-pin "header" symbol that's on the board (and the "northern" in the schematic)
JFET source = the opposite of the above
JFET gate = onto the teflon stand-off that goes into that grey "bullseye" on the middle-left of the board

Right, components then:

Omit (don't install) = R3, R4, R5, R6, R7, R17, C1, C3, C5, U$1
Optional to jumper over = R8, R9

You could install R2 "standing up", with one leg where R4 "used to be", and the other leg to ground, and then run the upper wire jumper on the top of the board. With C5 skipped, you'll have that terminal-hole free.

Does that make any sense? If there's anything still unclear, don't be afraid to say so / ask

 

[Khron]

Even a "generic" circuit would need to be on a "custom" board to fit the mic body you wish to install it into Just sayin'...

 

[Lowfreq]

What happened to the Osh Park link for this circuit? Seems to have gone, which is a shame coz I was keen to order some. All the other mic circuits and oscillators are still there.  Is there a reason this one is down?