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npc00

Member
Joined
Nov 19, 2018
Messages
17
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.

 

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Ricardus said:
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
 
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?
 
Khron said:
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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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”.
 
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?
 
Khron said:
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
 
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.
 
Khron said:
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
 
R13 is 330k, right?

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

 
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??? :eek:
 
Khron said:
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??? :eek:

2=16.88
 
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". :eek:
 
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