Hi maxpou
As Dr EM said you may have a shielding problem. Can you borrow another power amp to check whether your preamp is picking up the noise, or another preamp to see if that is noisy with your power amp.
When I built a valve amp some time ago, I was surprised how effectively these pick up hum. Andrew T pointed out that you have a 1Meg pot which for transistors is almost open circuit.
In my valve amp, I had to mould some brass shim around the noisy part of the track and solder it to the nearest ground to stop hum pickup. After all, the input impedance of a triode is Gohms or so - they're almost an electrostatic monitor.
Ever since then I've been careful to make sure no wire is exposed outside of a shield even in transistor amps.
cheers
John
As Dr EM said you may have a shielding problem. Can you borrow another power amp to check whether your preamp is picking up the noise, or another preamp to see if that is noisy with your power amp.
When I built a valve amp some time ago, I was surprised how effectively these pick up hum. Andrew T pointed out that you have a 1Meg pot which for transistors is almost open circuit.
In my valve amp, I had to mould some brass shim around the noisy part of the track and solder it to the nearest ground to stop hum pickup. After all, the input impedance of a triode is Gohms or so - they're almost an electrostatic monitor.
Ever since then I've been careful to make sure no wire is exposed outside of a shield even in transistor amps.
cheers
John
Hi Guys,
thank's for reply but when Mr. Pass, audioreseach or Classé design a preamp with input jfet they don't mould some brass shim around the noisy part. Why us it sould be done?
i tried my preamp with a another poweramp and i have same noise.
I have a 20K pot and 1Meg of input impedance but i have tried a 47K//47p cap.
Maxpou
thank's for reply but when Mr. Pass, audioreseach or Classé design a preamp with input jfet they don't mould some brass shim around the noisy part. Why us it sould be done?
i tried my preamp with a another poweramp and i have same noise.
I have a 20K pot and 1Meg of input impedance but i have tried a 47K//47p cap.
Maxpou
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