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

 

[RBeTT]

Hi @mihi_fuchs

After some days with Life getting in the way, I’m back with my mic working without noise issues. I feel a little bit more confident about my work and more understanding of the first build.

Yet some things to fix before finally closing it up...

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.

It doesn't match. I don't see another alternative so I'm just considering using M1.6 and opening the holes with Dremel but the screw must be long enough so I pass from one front PCB to the back PCB with nut and washer. I must use ground from the Ground on top of the PCB and it will spread along all of it, 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.

This is what I did. I split the wire from the low-cut switch and distributed it to both PCBs accordingly.




Yet I need to clarify since I don't hear much difference with C17 engagement ON.

1. How can I see on DAW when C17 works?

2. With the above question in mind, on J3, J = ON, which mean's J3 hole is the wire to engage or the opposite? I'm not sure I understood properly the schematic.

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

Just finished the mic in order to be sure so I can proceed before buying more JFET. Since now got it working, I will buy more HFE and JFET in order have options to proper match. As soon i do it, I will follow up here.

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.

Looks like was ground. I soldered the white wire from the capsule ground to the front PCB and just to be extra sure, did a second wire from the same soldering point to the back PCB. At least for now, it's working without any noise.

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.

For now, I left it like it is. Yet explain me something...So if I use without Turret I would connect JFET to R12 and just do the diaphram capsule wire to 51G?

Perfect - looking forward to hear from you.

I will order a bigger quantity of JFET and HFE and redo the PCB's wiring to 26AWG PVC wire since I'm not happy with 24awg silicone ones...to bulky.

First impressions, sounds very clean and creamy. I really Like it.


In the mid-time, I will do the remaining work on the other 5 mics and about to start your U87s for another 4 mics I feel more comfortable now to do this new project.

Thank you!

 

[mihi_fuchs]

Hi @mihi_fuchs

After some days with Life getting in the way, I’m back with my mic working without noise issues. I feel a little bit more confident about my work and more understanding of the first build.

Yet some things to fix before finally closing it up...

Great news, happy to hear you're getting close

It doesn't match. I don't see another alternative so I'm just considering using M1.6 and opening the holes with Dremel but the screw must be long enough so I pass from one front PCB to the back PCB with nut and washer. I must use ground from the Ground on top of the PCB and it will spread along all of it, is that correct?

You gonna Dremel the rails or the PCB? The holes were actually padded to the ground. So it represents your GND connection of the Body. Using the GND from top is one option. But you can connect anywhere to the GND net, where it is feasible. Maybe it is better to use your the XLR pin and have to cables run from it. Maybe it is even possible to connect to the XLR chassis connection, but make sure this one is connected to the mic - in a lot o mic bodies it actually is ...

This is what I did. I split the wire from the low-cut switch and distributed it to both PCBs accordingly.

View attachment 137103

The problem with this setup is, that you run both signals (back and front) over the same poles of the switch. In my opinion, you will need an DPDT switch. As it seems the current one is a SPST. Maybe you find another switch which is DPDT or two separate SPST switches for each side. The current version is mixing signals on a stage, where you do not want it to happen.

Yet I need to clarify since I don't hear much difference with C17 engagement ON.

1. How can I see on DAW when C17 works?

mostly C17 attenuates the high frequencies. You should see a dip in the frequencies > 3 kHz. You can check with an analyzer and white noise coming from your monitors. just make sure to mute the mic so you do not run into a feedback loop ...

2. With the above question in mind, on J3, J = ON, which mean's J3 hole is the wire to engage or the opposite? I'm not sure I understood properly the schematic.

View attachment 137104

If J3 is on, the LPF is engaged. With it being not connected no attentuation is happening. A switch would be wired to this connector.

Just finished the mic in order to be sure so I can proceed before buying more JFET. Since now got it working, I will buy more HFE and JFET in order have options to proper match. As soon i do it, I will follow up here.

Perfect, just do not overdo it. At some points the costs do not reflect in improvement anymore ;-) ... At least not in objective one ...

Looks like was ground. I soldered the white wire from the capsule ground to the front PCB and just to be extra sure, did a second wire from the same soldering point to the back PCB. At least for now, it's working without any noise.

Great, that was an easy fix then ... The head basket resembles a faraday cage or the capsule. If it is not grounded, it does not work as supposed to.

For now, I left it like it is. Yet explain me something...So if I use without Turret I would connect JFET to R12 and just do the diaphram capsule wire to 51G?

If you use the turret, JFET pin3 and R12 connect on the turret. The turret is isolated from the board, so all your signal which runs on HiZ is not run near the board. This keeps it safe from parasitic small currents running in the board. Nowadays, board resistances are usually good enough, so you do not need it. However some people swear it makes the sound better - both options and opinions can be satisfied by the board.

I will order a bigger quantity of JFET and HFE and redo the PCB's wiring to 26AWG PVC wire since I'm not happy with 24awg silicone ones...to bulky.

As said, do not overdo things. internal wiring is shielded by the body, it does not need to be gold standard. But I'm concerned about your money - it is your built and your decisions. I'm sure you will do good ones

First impressions, sounds very clean and creamy. I really Like it.

Cool. happy you like it. hope it serves you well and brings out a lot of great music ...

In the mid-time, I will do the remaining work on the other 5 mics and about to start your U87s for another 4 mics I feel more comfortable now to do this new project.

Your mic locker will be extended significantly I guess ... hope you have a lot of good experience recording with the mics.

Thank you!

Always welcome. Have a nice start into the week.

 

[RBeTT]

Great news, happy to hear you're getting close

After 2.5 years thinking about this with a lot of faith and over 100 hours of work in just the last 3 weeks, well deserved I guess!

You gonna Dremel the rails or the PCB? The holes were actually padded to the ground. So it represents your GND connection of the Body. Using the GND from top is one option. But you can connect anywhere to the GND net, where it is feasible. Maybe it is better to use your the XLR pin and have to cables run from it. Maybe it is even possible to connect to the XLR chassis connection, but make sure this one is connected to the mic - in a lot o mic bodies it actually is ...

I intend to drill the PCB. The rails holes doesnt give space for PCB to align. I have tried to redo the rails the other way around but broke one trying to do that. I think it's safer to stick with this option. For my needs, it must look clean and secure just to make sure nothing happens using them. As a last resort, I will think to do as your recommendation.

The problem with this setup is, that you run both signals (back and front) over the same poles of the switch. In my opinion, you will need an DPDT switch. As it seems the current one is a SPST. Maybe you find another switch which is DPDT or two separate SPST switches for each side. The current version is mixing signals on a stage, where you do not want it to happen.

Since I have the -10 pad switch, I will split and isolate each part of the capsule in each switch independently. Glad I questioned, because I never heard about it. I will do my research on the difference between DPDT vs SPST.

mostly C17 attenuates the high frequencies. You should see a dip in the frequencies > 3 kHz. You can check with an analyzer and white noise coming from your monitors. just make sure to mute the mic so you do not run into a feedback loop ...

I will do this test as soon I finish with JFET and HFE [waiting on parts, should arrive next week]

If J3 is on, the LPF is engaged. With it being not connected no attentuation is happening. A switch would be wired to this connector.

Sorry about that. I still learning how to read a schematic. I have found a thread here on the website that I'm studying to understand it better.

Perfect, just do not overdo it. At some points the costs do not reflect in improvement anymore ;-) ... At least not in objective one ...

Well...I want these mics to be the best I can. I will call it out at some point haha

Great, that was an easy fix then ... The head basket resembles a faraday cage or the capsule. If it is not grounded, it does not work as supposed to.

Always learning! thank you for being very generous with your insight and time!

If you use the turret, JFET pin3 and R12 connect on the turret. The turret is isolated from the board, so all your signal which runs on HiZ is not run near the board. This keeps it safe from parasitic small currents running in the board. Nowadays, board resistances are usually good enough, so you do not need it. However some people swear it makes the sound better - both options and opinions can be satisfied by the board.

Got it.

As said, do not overdo things. internal wiring is shielded by the body, it does not need to be gold standard. But I'm concerned about your money - it is your built and your decisions. I'm sure you will do good ones

I have a problem. I'm a perfectionist by nature I just want to make sure it's properly done.

These costs are properly aligned with the purpose, so I'm at peace with it.

Cool. happy you like it. hope it serves you well and brings out a lot of great music ...

I'm excited. This will bring very good things in my personal and professional life.

Your mic locker will be extended significantly I guess ... hope you have a lot of good experience recording with the mics.

Yup. On the road to the Grammy!

Always welcome. Have a nice start into the week.

I appreciate your time and very valuable insight to get this done.

I will keep you posted.

Have a great Week!

RB

 

[mihi_fuchs]

After 2.5 years thinking about this with a lot of faith and over 100 hours of work in just the last 3 weeks, well deserved I guess!



I intend to drill the PCB. The rails holes doesnt give space for PCB to align. I have tried to redo the rails the other way around but broke one trying to do that. I think it's safer to stick with this option. For my needs, it must look clean and secure just to make sure nothing happens using them. As a last resort, I will think to do as your recommendation.



Since I have the -10 pad switch, I will split and isolate each part of the capsule in each switch independently. Glad I questioned, because I never heard about it. I will do my research on the difference between DPDT vs SPST.



I will do this test as soon I finish with JFET and HFE [waiting on parts, should arrive next week]


Sorry about that. I still learning how to read a schematic. I have found a thread here on the website that I'm studying to understand it better.



Well...I want these mics to be the best I can. I will call it out at some point haha



Always learning! thank you for being very generous with your insight and time!



Got it.



I have a problem. I'm a perfectionist by nature I just want to make sure it's properly done.

These costs are properly aligned with the purpose, so I'm at peace with it.



I'm excited. This will bring very good things in my personal and professional life.



Yup. On the road to the Grammy!



I appreciate your time and very valuable insight to get this done.

I will keep you posted.

Have a great Week!

RB

here‘s some info: https://www.littelfuse.de/technical...ehicle-technical-center/poles-and-throws.aspx

 

[RBeTT]

here‘s some info: https://www.littelfuse.de/technical...ehicle-technical-center/poles-and-throws.aspx

Thank you! Bookmarked! I will include this in the electronics study tonight.

 

[RBeTT]

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.

Hi @mihi_fuchs

I tried to follow your recommendation yet something is off:

1. First, I don't understand why it's necessary to use 2x 9V batteries,
2. Second, Did I understood right from this FET Matching Circuit schematic that i need to use some resistors [10k, 5M] for better results in matching?
3. Third, Do I need 2 DVM's working simultaneously so i can see the input [Vgs value] and Output [Vds value] at the same time?
4. I downloaded the FET Matching spreadsheet to input the values but need to understand first how to measure them

This is my last step to complete the circuit in 6 mics, excited!

 

[RBeTT]

View attachment 137689


Hi @mihi_fuchs

I tried to follow your recommendation yet something is off:

1. First, I don't understand why it's necessary to use 2x 9V batteries,
2. Second, Did I understood right from this FET Matching Circuit schematic that i need to use some resistors [10k, 5M] for better results in matching?
3. Third, Do I need 2 DVM's working simultaneously so i can see the input [Vgs value] and Output [Vds value] at the same time?
4. I downloaded the FET Matching spreadsheet to input the values but need to understand first how to measure them

This is my last step to complete the circuit in 6 mics, excited!

Hi @mihi_fuchs

I ended up following the first recommendation. The last time I confused the order of the Drain, Source, and GATE accordingly in the breadboard. Actually, it was the pdf of the JFET 2n5458 [Datasheet] in the website of your last recommendation that I understood what I was doing wrong. So thank you!

Now, this are the measurements in order:

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.

1. When you said about 3% it means for Vp and Idss?

2. As an example, 3% of a -2,26v Vp JEFT = -0,0678v = -0,06v . So in practice, it's acceptable to put in the same group from -2,20v up to -2,26v up or -2,26v up to -2,32v?



Thank you!

Best,

RB

 

[mihi_fuchs]

Hi @mihi_fuchs

I ended up following the first recommendation. The last time I confused the order of the Drain, Source, and GATE accordingly in the breadboard. Actually, it was the pdf of the JFET 2n5458 [Datasheet] in the website of your last recommendation that I understood what I was doing wrong. So thank you!

Now, this are the measurements in order:

View attachment 137697



1. When you said about 3% it means for Vp and Idss?

2. As an example, 3% of a -2,26v Vp JEFT = -0,0678v = -0,06v . So in practice, it's acceptable to put in the same group from -2,20v up to -2,26v up or -2,26v up to -2,32v?



Thank you!

Best,

RB

Hi Ruben,

keep in mind your tolerances and accuracy of your voltmeter.

Yes, batch them in reasonable groups. Then determine Idss. Both values should match within the range required.

I matched according to this: https://axtsystems.com/axtsystems/proj_1176_fetmatching.php

In my hand that worked perfectly.

However, I have to admit, the highest impact on the matching was given on the turning point of the curve. If you know roughly the turning point, you can only measure on that point.

Regarding the questions from before:
1. First, I don't understand why it's necessary to use 2x 9V batteries,

The two 9V batteries are required as you need + and - 9V. So Ground is tapped from inbetween the batteries.

2. Second, Did I understood right from this FET Matching Circuit schematic that i need to use some resistors [10k, 5M] for better results in matching?

yes.

3. Third, Do I need 2 DVM's working simultaneously so i can see the input [Vgs value] and Output [Vds value] at the same time?

no. first you adjust the Vgs, then measure Vds on the "other side" of the schematic.

4. I downloaded the FET Matching spreadsheet to input the values but need to understand first how to measure them

From Vgs you have your x-values for the x-axis. From Vds you calculate the Idss via Ohm's law. The Idss values are your y-values. Now you plot Vgs vs. Idss. Take the curves that match best. You can also calculate the deviation of the points. The highest deviation is your worst-case range.

Best regards,
Michael

 

[RBeTT]

Hi @mihi_fuchs

I matched according to this: https://axtsystems.com/axtsystems/proj_1176_fetmatching.php

In my hand that worked perfectly.

Ok, You convinced me to give it another try!

3. Third, Do I need 2 DVM's working simultaneously so i can see the input [Vgs value] and Output [Vds value] at the same time?

no. first you adjust the Vgs, then measure Vds on the "other side" of the schematic.

4. I downloaded the FET Matching spreadsheet to input the values but need to understand first how to measure them

From Vgs you have your x-values for the x-axis. From Vds you calculate the Idss via Ohm's law. The Idss values are your y-values. Now you plot Vgs vs. Idss. Take the curves that match best. You can also calculate the deviation of the points. The highest deviation is your worst-case range.

Got it!

2. Second, Did I understood right from this FET Matching Circuit schematic that i need to use some resistors [10k, 5M] for better results in matching?

yes.

Any 10k and 5M resistor will do? I have looked in the BOM of your builds [Dual Output and U87, that's the only materials I have available for my builds] and haven't seen any that would exactly fit this purpose.

To have more to choose from, I will do another extra JFET order from the Mouser website.
It would be best to add the 10k and 5M resistors to this order too.

Is there any chance, you can recommend direct links from the Mouser website?


Once again, I appreciate your time and patience. I am sorry for the inconvenience.

Best,
RB

 

[mihi_fuchs]

Hi @mihi_fuchs

Ok, You convinced me to give it another try!




Got it!



Any 10k and 5M resistor will do? I have looked in the BOM of your builds [Dual Output and U87, that's the only materials I have available for my builds] and haven't seen any that would exactly fit this purpose.

To have more to choose from, I will do another extra JFET order from the Mouser website.
It would be best to add the 10k and 5M resistors to this order too.

Is there any chance, you can recommend direct links from the Mouser website?


Once again, I appreciate your time and patience. I am sorry for the inconvenience.

Best,
RB

no inconvenience here so far, all good. happy if i can help.

take a multiturn potentiometer. https://www.mouser.at/ProductDetail/652-3296W-1-103LF

any 10k and 5M will do.
https://www.mouser.at/ProductDetail/603-MFR25SFTE26-10K
https://www.mouser.at/ProductDetail/Vishay-Dale/CMF605M0000FKBF?qs=aJ2yuOZXyBESWcdbRIi7Dg==

use fresh 9v blocks.

i think your matching will be fine too. so as i said before - use your resources wisely …

hope your mics turn out well … all the best for the last steps…

best regards,
michael

 

[RBeTT]

Hello @mihi_fuchs

no inconvenience here so far, all good. happy if i can help.

I really appreciate it!

take a multiturn potentiometer. https://www.mouser.at/ProductDetail/652-3296W-1-103LF

any 10k and 5M will do.
https://www.mouser.at/ProductDetail/603-MFR25SFTE26-10K
https://www.mouser.at/ProductDetail/Vishay-Dale/CMF605M0000FKBF?qs=aJ2yuOZXyBESWcdbRIi7Dg==

I just added to a new Mouser order. Now just have to wait.

so as i said before - use your resources wisely …

I want to everything turn out well. I spent a little more but this way I'm more confident I have done correctly.

hope your mics turn out well … all the best for the last steps…

Thank you! I keep you posted.



Best,

RB

 

[RBeTT]

no inconvenience here so far, all good. happy if i can help.

take a multiturn potentiometer. https://www.mouser.at/ProductDetail/652-3296W-1-103LF

any 10k and 5M will do.
https://www.mouser.at/ProductDetail/603-MFR25SFTE26-10K
https://www.mouser.at/ProductDetail/Vishay-Dale/CMF605M0000FKBF?qs=aJ2yuOZXyBESWcdbRIi7Dg==

use fresh 9v blocks.

i think your matching will be fine too. so as i said before - use your resources wisely …

hope your mics turn out well … all the best for the last steps…

best regards,
michael

Hello @mihi_fuchs

Finally back with great result





I figured through the build pictures that the problem I was having with the values on the trimmer adjustment was due to not have drilled space for the turret to be inserted into the PCB. I had to take all apart, drill and redo it again. Since I couldn't figure out very well how to put together on the breadboard the schematic of you last recommendation for match JFET, I end up using the first match method and turned out ok with less parameters [Vp, Idss]. Sounds great!

Now I'm facing with other minor problems to resolve in some mics [just to say I have been very diligent with the cleaning of the builds [fingers cots all the time, alcohol cleaning with toothbrush and ear tips in all joints] and rechecked for solid soldering in all points on the front and back PCB's].


| QUESTIONS |

1. What is the normal procedure to test the frequency response of a mic? is there any software to do it? something like REW?

2. I have done the trimming without the C17 engaged [low pass filter]. This is how it should be done or doesn't make any difference?

3. I'm having some unexpected spikes on some frequencies and when I turn the volume up on the 2nd channel usually make noise when adjusting the preamp volume knob:

1. I have taped the rails for not having any interference with the board itself. Is this anything to do with ground? Should I connect it to the rails? I have left one extra ground wire to be connected if needed via pin1.
2. Does this have anything to do with the fact I have all the cables connected into the inside part of the PCB?
3. I Still have to paint the bodies. Will the paint protection and help to balance the frequencies?
4. Should I put a pad into the inside of the mic body?

---

Thank you always for your time and patience.

Best Regards,
RB