duncanamps.com

[Gubbe]

Hi!
I have built a small (15W) SE amp, it doesn’t have an EQ or any fancy stuff.
It's a simple 3 gain stages one power stage, gain and master volume amp.
The amp works fine, but it is terribly noisy.
I have put the amp in a small chassie, and built the whole thing on one single PCB.
When I first started the amp there was a loud HUM, I managed to get rid of most of the hum, by cutting all the ground connections to the heaters, and then soldering wires from the LT rectifier cap.
But I still have some strange noise issues.

* When I first start the amp (gain = 0, master = 0) there is a hum, not enormous but annoying.

* When I turn the master slowly up (gain = 0), the hum gets lower until it's almost silent, if I continue to turn up the volume there is a lot of white noise increasing fast.

* If I turn up the gain (master 10), then hum and buzz is increasing, until I get to a certain point, then the amp is dead quiet. If I then continue to turn up the gain, oscillation and strange noises appear at a certain point of the pot, then the noise comes back stronger than ever!


I am most happy for any suggestions....