npc00

Input on this ?
« on: May 31, 2019, 11:16:27 PM »
So I’m pretty new to the group I just started building the u87 clone and everything was a smooth sail with soldering.

The problem is I’m getting no output from the microphone. The mic is calibrated at 11.5 volts

Anything helps! Thanks.



npc00

Re: Input on this ?
« Reply #1 on: May 31, 2019, 11:19:44 PM »
P2

Ricardus

Re: Input on this ?
« Reply #2 on: May 31, 2019, 11:45:29 PM »
None of your switches look wired.
Audio mastering for hire..

npc00

Re: Input on this ?
« Reply #3 on: June 01, 2019, 12:08:30 AM »
None of your switches look wired.

I’ve been told switches don’t have to be apart of the pcb but the question is what do I have to do differently

Khron

Re: Input on this ?
« Reply #4 on: June 01, 2019, 05:35:01 AM »
Not sure starting a second thread about this was warranted, but anyway...

Can you post a photo where the capsule and its wires are visible, as well?
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npc00

Re: Input on this ?
« Reply #5 on: June 02, 2019, 01:38:58 PM »
Not sure starting a second thread about this was warranted, but anyway...

Can you post a photo where the capsule and its wires are visible, as well?


npc00

Re: Input on this ? picture
« Reply #6 on: June 02, 2019, 01:41:38 PM »
p2

npc00

Re: Input on this ? What I did
« Reply #7 on: June 02, 2019, 01:45:25 PM »
So I soldered the white wires attached to the diaphragm to “FD” à “Front Diaphragm”, “RD” à “Rear Diaphragm and the side screw with the wire attached to the “FBK” à “Front Backplate”, “RBK” à “Rear Backplate”.

Khron

Re: Input on this ?
« Reply #8 on: June 02, 2019, 02:03:33 PM »
Well, at least in theory, it should work "by default" in cardioid mode, even without any of the switches wired up.

What voltage are you getting on the positive ends of C11 / C13?
« Last Edit: June 02, 2019, 02:14:13 PM by Khron »
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npc00

Re: Input on this ?
« Reply #9 on: June 02, 2019, 10:03:46 PM »
Well, at least in theory, it should work "by default" in cardioid mode, even without any of the switches wired up.

What voltage are you getting on the positive ends of C11 / C13?

C11 - 0.49
C13 - 0.96


Khron

Re: Input on this ?
« Reply #10 on: June 03, 2019, 06:11:18 AM »
Well, there's your problem - no bias voltage is getting to the capsule, hence no sound.

Time to start actually troubleshooting - check the soldering (cold joints, shorts between pads, etc), check that you've populated the correct parts in the right places, connecting wires between the two boards...

I've attached the U87 schematic in the other thread. I hope these boards have the same component designations as that.

If you're getting voltage at the drain of the JFET (connected to C7, C9 and R12), then the feed from the common point of R18/19 should be fine.

Thus, you'll want to focus on the R16 - R15 - R13 area (top of the schematic). You might try removing R13, and see what you measure across C11/C13 then.
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npc00

Re: Input on this ?
« Reply #11 on: June 14, 2019, 07:44:15 PM »
Well, there's your problem - no bias voltage is getting to the capsule, hence no sound.

Time to start actually troubleshooting - check the soldering (cold joints, shorts between pads, etc), check that you've populated the correct parts in the right places, connecting wires between the two boards...

I've attached the U87 schematic in the other thread. I hope these boards have the same component designations as that.

If you're getting voltage at the drain of the JFET (connected to C7, C9 and R12), then the feed from the common point of R18/19 should be fine.

Thus, you'll want to focus on the R16 - R15 - R13 area (top of the schematic). You might try removing R13, and see what you measure across C11/C13 then.

C11=-0.982
C13=-0.505

npc00

Re: Input on this ?
« Reply #12 on: June 14, 2019, 07:45:34 PM »
After removing R13

Khron

Re: Input on this ?
« Reply #13 on: June 14, 2019, 07:59:47 PM »
R13 is 330k, right?

What can you measure across C14? And across C12 (ie. between its positive end, and ground)?

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npc00

Re: Input on this ?
« Reply #14 on: June 14, 2019, 08:09:34 PM »
R13 is 330k, right?

What can you measure across C14? And across C12 (ie. between its positive end, and ground)?

C12=-2.36
C14=15.24

Yes r13 is 330k

Khron

Re: Input on this ?
« Reply #15 on: June 14, 2019, 08:16:55 PM »
Well, something's definitely drawing loads more current than it should.

At least in theory, you should be measuring around 24V across C12, and considerably more than that across C14.

What voltage are you getting between XLR pins 2 (or 3) and ground, then?

And if you're measuring a measly 2V on C12 (are you sure you got the probes the right way around?), how did you manage to get 11.5V on the JFET's drain??? :o
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npc00

Re: Input on this ?
« Reply #16 on: June 14, 2019, 08:22:42 PM »
Well, something's definitely drawing loads more current than it should.

At least in theory, you should be measuring around 24V across C12, and considerably more than that across C14.

What voltage are you getting between XLR pins 2 (or 3) and ground, then?

And if you're measuring a measly 2V on C12 (are you sure you got the probes the right way around?), how did you manage to get 11.5V on the JFET's drain??? :o

2=16.88

Khron

Re: Input on this ?
« Reply #17 on: June 14, 2019, 08:27:19 PM »
What if you remove / disconnect R17 (56K)?
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npc00

Re: Input on this ?
« Reply #18 on: June 14, 2019, 08:37:39 PM »
What if you remove / disconnect R17 (56K)?

2=17.3
C13=-1.034
C11=-0.534

After disconnecting r17

Khron

Re: Input on this ?
« Reply #19 on: June 15, 2019, 05:00:50 AM »
Hum-de-humm... Do you happen to have another preamp / interface you could use for testing?

It's starting to sound like the phantom power voltage itself might be way lower than normal.

Although that still doesn't explain the apparent success(?) of the "mic is calibrated at 11.5 volts". :o
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