Dual Output Microphone: 2x Schoeps Circuit + K87 capsule BM-800 Donor Body)

[RBeTT]

hey,

5% is fine, but you got enough of the 340s i guess. should make life and decision easy in that case.

for the jfet - i usually got a hundred and measured. most of the times the numbers matched then within the precision of my meter. that would be something like 3% then for the jfet values. however, i read others accept up to 10% in numbers for the jfet.

hope that helps,
best regards,
michael

Hi,

It's 6 mics, 12 PCBs, unfortunately, I didn't have enough 340's and yet had a bit changed since I'm remeasuring all of them before soldering.

For JFET I'm waiting for the breadboard to arrive. I will consider your recommendation regarding to buy a bigger quantity.

 

[RBeTT]

Hello @mihi_fuchs

Finally, I could pull together the final assembly and my very first build, another 9 to go.

Yet, there are some details which I must clarify and some little bit of noise [I have a slight doubt if it’s ground missing on the capsule grill].



| CAPSULE + Connection |


1. Just need to clarify if each side of the capsule should have a yellow wire [diaphragm wire] and black wire [backplate] connected to each side respectively. Is that correct?

If so, does each respective side of the capsule go to each PCB accordingly [front and back]?




2. Is there a problem with some sort of overlap of a bit of the washer to the immediate next opposite backplate?




| MIC BODY |


I’m using the Aurycle mic body to do this build. It comes with low cut and -10db pad switches on which I had to desolder the wires since I will use these options in the software.


Yet I encountered this white cable which I doubt is GROUND for the capsule. If so, should I solder to GND on the top of the PCB and jumper between both PCB’S?




| LOW PASS FILTER |


Just to clarify in another word…In case you use a removable C17 via socket, you don’t need to do anything about J3, is that correct? Essentially J3 is an “on and off switcher” if you have a permanent C17 cap, correct?


| PCB’s Screw’s |

This build doesn’t right fit to this mic body frame within the mounting holes. I have put zippers for the testing, but I need a permanent solution such as M screws with washers and nuts. Yet looks like I need M1.2 screws with about 15-20mm long but I can’t find anywhere.

Should I drill a bigger hole to fit another kind of screw so I could use screws such as M1.6x20mm?


| JFET |

To JFET match the only thing that mostly matters is Idss ?

I’m having some inconsistent readings. Should I look always for the first number that comes up on the multimeter as the final reading?



| PROBLEMS and CLARIFICATIONS |

I have finished 2 mics before making sure about my question. Both have the same problem.


1. For final calibration on RV1 onboard potentiometer, the PCB for the back of the capsule whatever I do doesn’t change the SCT_T – GND value, looks like it gets maxed out and starts clicking when turning the screw. What is wrong?



2. I have a Slight High pitch sound, but that vanishes when my hand goes on the capsule grill. Is anything to do with the screws on the frame? the white wire as referred above?


3. What is this 51g hole for? Alternative connection for the capsule diaphragm wire?




Thanks in advance,

Best
RB

 

[mihi_fuchs]

Hello @mihi_fuchs

Finally, I could pull together the final assembly and my very first build, another 9 to go.

Perfect - Congrats! Looks good ...

Yet, there are some details which I must clarify and some little bit of noise [I have a slight doubt if it’s ground missing on the capsule grill].

View attachment 136810View attachment 136818

| CAPSULE + Connection |


1. Just need to clarify if each side of the capsule should have a yellow wire [diaphragm wire] and black wire [backplate] connected to each side respectively. Is that correct?

Jop, that's correct. Additionally the backplates need to be electrically insulated towards each other by capsule design.

If so, does each respective side of the capsule go to each PCB accordingly [front and back]?

View attachment 136811View attachment 136812


2. Is there a problem with some sort of overlap of a bit of the washer to the immediate next opposite backplate?

Make sure there is no electrical connection. Measure if you are not sure. otherwise use another washer, omit the washer or make an insulation between the washer and the opposite backplate. However, as the backplates only have the voltage supply attached, and the signal is taken from the diaphragms, it may be that it works also with the backplates connected. I guess your noise issues are coming from somewhere else.

View attachment 136813


| MIC BODY |


I’m using the Aurycle mic body to do this build. It comes with low cut and -10db pad switches on which I had to desolder the wires since I will use these options in the software.

Sure, thing, however, you can by J3 make the low pass filter switchable if you want.

Yet I encountered this white cable which I doubt is GROUND for the capsule. If so, should I solder to GND on the top of the PCB and jumper between both PCB’S?

View attachment 136814

Yes, solder it to 1 of the two PCBs. You can use the TOP connector, GND hole for that purpose. Connection to one PCB should be sufficient, GND comes from the same source all the way.

| LOW PASS FILTER |


Just to clarify in another word…In case you use a removable C17 via socket, you don’t need to do anything about J3, is that correct? Essentially J3 is an “on and off switcher” if you have a permanent C17 cap, correct?

No, you need to jumper it by wire. Or you use one of your switches and make it switchable from the outside. If not, and you want to use the LPF you have to jumper J3 by a small piece of wire.

| PCB’s Screw’s |

This build doesn’t right fit to this mic body frame within the mounting holes. I have put zippers for the testing, but I need a permanent solution such as M screws with washers and nuts. Yet looks like I need M1.2 screws with about 15-20mm long but I can’t find anywhere.

Should I drill a bigger hole to fit another kind of screw so I could use screws such as M1.6x20mm?

The holes of the PCB actually connect your mic body to GND. Your rails connect to the pads around the hole. As a consequence your mic body is grounded and acts as a shield for noise.

| JFET |

To JFET match the only thing that mostly matters is Idss ?

I’m having some inconsistent readings. Should I look always for the first number that comes up on the multimeter as the final reading?

No, actually both values you check should match.

Actually I got a bit more into the topic, as I'm currently matching JFETs for compressors. Here you can find actually the way I'm trying now. It check the JFET under more conditions and the matching should be better:
https://axtsystems.com/axtsystems/proj_1176_fetmatching.php

Maybe give it a try, if you have time and a quick way to fix up the circuit.

| PROBLEMS and CLARIFICATIONS |

I have finished 2 mics before making sure about my question. Both have the same problem.


1. For final calibration on RV1 onboard potentiometer, the PCB for the back of the capsule whatever I do doesn’t change the SCT_T – GND value, looks like it gets maxed out and starts clicking when turning the screw. What is wrong?

View attachment 136816

I'm not so sure I get your issue right. The RV1 should make the ca. 1/4 of the VCC on the SCT pad. So you get ca. 4V just on the backplate PCB board?

2. I have a Slight High pitch sound, but that vanishes when my hand goes on the capsule grill. Is anything to do with the screws on the frame? the white wire as referred above?

It sounds very likely to be a grounding problem. Attach the white wire and see what happens. Make sure you have grounded the basket (measure the resistance towards GND).

3. What is this 51g hole for? Alternative connection for the capsule diaphragm wire?

View attachment 136817
#

51g translates actually to Sig ... hahaha ... it means it's the connection for the signal wire. If you do not work with the turret, you can use this connection to attach the capsule. So in your case it's redundant. However, you can use the GND pad to connect the basket wire and ground the basket.

Thanks in advance,

Best
RB

No problem - you're very welcome. Hope some of the stuff helps. Let me know how it worked out ...

Best regards,
Michael

 

[RBeTT]

| PCB’s Screw’s |

This build doesn’t right fit to this mic body frame within the mounting holes. I have put zippers for the testing, but I need a permanent solution such as M screws with washers and nuts. Yet looks like I need M1.2 screws with about 15-20mm long but I can’t find anywhere.

Should I drill a bigger hole to fit another kind of screw so I could use screws such as M1.6x20mm?

Is there any solution that you recommend since the holes don't line up? ideas?

Jop, that's correct. Additionally the backplates need to be electrically insulated towards each other by capsule design.

I confirmed with 3u Audio Guosheng, that they are.

Make sure there is no electrical connection. Measure if you are not sure. otherwise use another washer, omit the washer or make an insulation between the washer and the opposite backplate. However, as the backplates only have the voltage supply attached, and the signal is taken from the diaphragms, it may be that it works also with the backplates connected. I guess your noise issues are coming from somewhere else.

I will see what fits better. In the worst case, I will drill a new hole in the saddle to accommodate the screw likewise for the front part of the capsule.

Sure, thing, however, you can by J3 make the low pass filter switchable if you want.

I will use the -10db pad as the switch from outside. To do that, I guess I should split the wire in parallel across both PCBs, is that correct?

No, actually both values you check should match.

Actually I got a bit more into the topic, as I'm currently matching JFETs for compressors. Here you can find actually the way I'm trying now. It check the JFET under more conditions and the matching should be better:
https://axtsystems.com/axtsystems/proj_1176_fetmatching.php

Maybe give it a try, if you have time and a quick way to fix up the circuit.

I will have a look and do that.

I'm not so sure I get your issue right. The RV1 should make the ca. 1/4 of the VCC on the SCT pad. So you get ca. 4V just on the backplate PCB board?

Exactly that. I will fix the remaining problems, and check the values again.

51g translates actually to Sig ... hahaha ... it means it's the connection for the signal wire. If you do not work with the turret, you can use this connection to attach the capsule. So in your case it's redundant. However, you can use the GND pad to connect the basket wire and ground the basket.

I guess I will use SIG all the way then...Haha...It's more secure and more likely to have less wire and turret size to interfere between PCBs.


---

I will do it later today to fix the remaining issues hopefully. As soon as I do that, I will get back to you.



Thank you very much for your time Sir!
Best,
RB

 

[mihi_fuchs]

Is there any solution that you recommend since the holes don't line up? ideas?

It depends - are the existing holes on the rails too narrow or to wide apart. If too wide apart, use a Dremel tool and open the holes towards each side off the PCB. Should be still enough pad to make the Ground Connection, I guess. Maybe worth to consider.

I confirmed with 3u Audio Guosheng, that they are.

Perfect, I remember now that you told me already. Sorry, I forgot - my apologies for the redundancy.

I will see what fits better. In the worst case, I will drill a new hole in the saddle to accommodate the screw likewise for the front part of the capsule.

Yes, it's no rocket since, and if you have connection now, it may work well even with connected backplates. I actually never tried.

I will use the -10db pad as the switch from outside. To do that, I guess I should split the wire in parallel across both PCBs, is that correct?

I actually do not get exactly what you mean. Could you provide a pic with drawn wires or a schematic of that.

I will have a look and do that.

Sure, hope the links and infos help. I'm about to do the same for the 1176. So we're kinda in the same boat ...

Exactly that. I will fix the remaining problems, and check the values again.

That's odd. Both PCBs are the same and should get the same voltage. If the issue remains, please send me a pic from front and back of the Backplate PCBs.
Make also sure that those PCBs do not short somewhere along the rails.

I guess I will use SIG all the way then...Haha...It's more secure and more likely to have less wire and turret size to interfere between PCBs.

Just be aware, that you should not use the turret system then. It should be fine, as modern PCBs are well in keeping current where it belongs. however, I never tried it without the turret.

---

I will do it later today to fix the remaining issues hopefully. As soon as I do that, I will get back to you.

Perfect - looking forward to hear from you.

Thank you very much for your time Sir!
Best,
RB

Very welcome - have a nice evening.
BR
Michael