The JFET I use is 2sk170, but it needs to be powered up for 5 minutes before it can start working. I can't find the reason, I have tried many times. If an oscilloscope and a signal generator are used to measure the intact waveform, the bias voltage is 9V, and after a period of use, it will no longer work.
The following is the chart I used the software to measure in the relatively quiet room. Please help me, thank you


gyraf

..could be contamination on the PCB, maybe? Have you tried cleaning well, specially in the high-impedance area around the input?

..Hum in a microphone, if that is the problem, can ONLY come from two sources, both are really external: Poor shielding or Poor phantom power.

Jakob E.
..note to self: don't let Harman run your company..

..could be contamination on the PCB, maybe? Have you tried cleaning well, specially in the high-impedance area around the input?

..Hum in a microphone, if that is the problem, can ONLY come from two sources, both are really external: Poor shielding or Poor phantom power.

Jakob E.
Thank you for your answer.

I will try to clean it again, but the microphone will not work within five-fifths of every time I use it. I measure the bias voltage of JFET only about 2V. After five minutes, it will rise to the working voltage, about 11V, and the microphone will work.

mhelin

Faulty cap, or incorrect component values like too large resistor => too long RC time constant.
Mikko

How about you post circuit of Dan D87 or a link ?

What do you mean 'start working'?  Do you mean no noise until after 5min?

That circuit uses a 2n3819 for the JFET. You might need to make changes to use the FET you’re using? I’m not sure, but if the rest of the circuit is the same, that would be the first thing I’d look at.

abbey road d enfer

Thank you for your answer.

I will try to clean it again, but the microphone will not work within five-fifths of every time I use it. I measure the bias voltage of JFET only about 2V. After five minutes, it will rise to the working voltage, about 11V, and the microphone will work.
Where do you measure this voltage? 11V cannot be a correct bias voltage.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


 

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