Neuman U87i Kit getting no sign wave

[Rob_K]

Hi there,

I have built a U87 clone from the mic and mod kit, but after following all the instructions, can't get to calibrate it as I can't get a sign wave from it.

Have it all set up as shown in the build tutorial with function generator on R6 and to ground and with the Ocilloscope probe to the drain leg of the Fet and to ground. Turn on phantom power, and the signal goes up to approx 11 volts but no sign wave. If I switch the function generator on or off, no difference. Where do I start with this troubleshoot?

Any help would be very much appreciated.

 

[Arkenberg]

Hi there,

I have built a U87 clone from the mic and mod kit, but after following all the instructions, can't get to calibrate it as I can't get a sign wave from it.

Have it all set up as shown in the build tutorial with function generator on R6 and to ground and with the Ocilloscope probe to the drain leg of the Fet and to ground. Turn on phantom power, and the signal goes up to approx 11 volts but no sign wave. If I switch the function generator on or off, no difference. Where do I start with this troubleshoot?

Any help would be very much appreciated.

Which circuit board do you have? (Green/blue) if you have the blue one and you flipped r6 compared to the screen print on the board then that is your problem. If you have the green board and didn't switch r6 compared to the screen print then that would be the problem. When Danny made the blue boards he fixed them so you could inject the sign wave. I screwed up and switched r6 on the blue board and it didn't work also.
Hope this helps

 

[Rob_K]

Thanks that makes a lot of sense, the signal I assume is mimicing a signal from the cap, so needs to be on the cap side of the resistor, heading the the gate on the J fet, not ground side, as that would result in what I have of the signal being swallowed by Ground.

 

[Arkenberg]

Thanks that makes a lot of sense, the signal I assume is mimicing a signal from the cap, so needs to be on the cap side of the resistor, heading the the gate on the J fet, not ground side, as that would result in what I have of the signal being swallowed by Ground.

I think you've got it.
Hope it helps!

Jon

 

[Rob_K]

Thanks for you help, the mic actually works, so job done.