B22 causing oscillation?

[ivant]

AC ground is not used. Input and preout jacks not isolated though i could install the isolating washers if needed. Headphone jack is isolated.

 

[amb]

Since the jacks are not isolated their grounds should already be connected to each other and there is no need for that common "ground star" at the right. I suggest simply running the ground wires from the jacks to the volume pot, and then from there to each β22 board.

The above may or may not make a difference. You should also check that C1-C5 on each beta22 board are well soldered and are the correct values for the gain setting you chose. The ground channel is different in this regard than the left and right. See the "parts list" section of the β22 website for details.

Does the problem occur on both channels?

P.S. Not wiring the AC ground to the case is a potential safety hazard, but if you do, then you'll need to isolate the input jacks and use a ground loop breaker.

 

[ivant]

Quote:

Originally Posted by amb /img/forum/go_quote.gif Since the jacks are not isolated their grounds should already be connected to each other and there is no need for that common "ground star" at the right. I suggest simply running the ground wires from the jacks to the volume pot, and then from there to each β22 board. The above may or may not make a difference. You should also check that C1-C5 on each beta22 board are well soldered and are the correct values for the gain setting you chose. The ground channel is different in this regard than the left and right. See the "parts list" section of the β22 website for details. Does the problem occur on both channels? P.S. Not wiring the AC ground to the case is a potential safety hazard, but if you do, then you'll need to isolate the input jacks and use a ground loop breaker.

The "ground star" was done actually more for the sake of convenience as its easier than soldering 2 wires to a tab.

The capacitor values are correct.
Yes, its present on both channel.

I tried moved the pre-out wiring further away from the input wiring and the pop at the anticlockwise position of volume knob dissappeared, leaving a slight hiss. The pop at full clockwise position is still present. Maybe I should try using shielded cables for the wirings?

 

[amb]

Quote:

Originally Posted by ivant /img/forum/go_quote.gif I tried moved the pre-out wiring further away from the input wiring and the pop at the anticlockwise position of volume knob dissappeared, leaving a slight hiss. The pop at full clockwise position is still present. Maybe I should try using shielded cables for the wirings?

Yes, that's a good idea. Maybe there is capacitive coupling between wires causing positive feedback at ultrasonic frequencies.