Troubleshooting U87 build?

[Greenie]

I wonder if anyone have a understandable way to troubleshoot a new U87 build. I have only noise in it, but I can hear that there is a contact with the capsule in the sense that I can hear spoken voice in it when the recording is turned up loud. I suspect that it might be a case of solder spillover, but it's difficult to see.

I can regulate the voltage on the jfet, it's now 11.5.

 

[Khron]

Photos of both sides of the pcb? Are you using a pre-made kit?

 

[Greenie]

The pcbs are from Vintage michropone.

 

[Ricardus]

I have the 1.3 boards, and the back board (the high impedance board) looks different. Like you had to raise one of the leads of the FET and solder it to that post, on my build there were a few leads you had to do that with also on that board.

 

[Greenie]

Interesting, do you have pic of yours?

 

[RuudNL]

Do you get a loud hum when you touch the gate of the FET?
If so, there might be something wrong with the connection of the capsule, or the polarisation voltage is missing (or low).

 

[Ricardus]

Interesting, do you have pic of yours?

Yes. This is all I could find for now. The board, and the finished board in the mic body.

 

[Greenie]

Do you get a loud hum when you touch the gate of the FET?
If so, there might be something wrong with the connection of the capsule, or the polarisation voltage is missing (or low).

No, theres no sound there.

 

[RuudNL]

Did you measure the transformer windings? (Ohms setting with a multimeter.)

 

[Greenie]

Yes I did, they they are 452 and 28.

 

[RuudNL]

Very strange... So you can bias the FET, the transformer measures normal, but you don't get any signal or hum when you touch the gate of the FET!
I can only think of two things: there is no coupling between the drain of the FET and the transformer, or the gate of the FET is for some reason connected to ground.

 

[RuudNL]

Is the problem solved now, or doesn't it have a very high priority?

 

[Greenie]

I have bought another PCB from Vintagemicpcb's, the blue version. And I will try to build again. Might be that I was sending something to ground that shouldn't go there.