Klemt echollette m40 hum and feedback

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I've been trying to get my m40 to stop humming for days now, but to no avail.

After shielding some wires and moving some grounds around it seemed to be pretty quiet, but the sound output was way to low and without bass. So I started checking things and found out that I forgot r23, a 200k grounding the grid of Rö.4.

After adding this the amp makes way more hum/noise and starts squeeling (feedback I guess) at around 3 on the master volume. I have no idea way except maybe grounding isues?

This is the orignal shematic:
http://music-electronics-forum.com/attachments/33826d1430776785-echolette_m40-din-input.jpg

This is the way the shematic looks now after disconnecting some unneeded (for now) parts:
http://i.imgur.com/cysd9ro.jpg

I believe that my simplifications didn't add any more problems, but I'm not sure.

Right now I have two main grounding points, about 2 cm apart (at the fasteners for the rectifiers).
G1 has the power transformer ground, the power tubes buss bar ground, the heater balance pot, and the output transformer secondary ground.
G2 has the buss bar for the phase inverter, the buss bar for Rö.4, and the buss bar for both Rö.3 and Rö.1.

Does this grounding sheme make sense? And what could cause the feedback?

Thanks and happy christmass!
 
I hope you don't have two separate audio grounds, connected to different points on the chassis. That puts audio currents through the chassis, rarely a good idea.

Squeeling when the gain is turned up means unwanted feedback, which can take several routes:
1. via the supply rails, if decoupling is inadequate;
2. via stray capacitance, if coupling caps etc. are too large or too close to other parts of the circuit or signal cables are long and/or unscreened;
3. via magnetic induction, if circuit loops are too large;
4. via poor grounding

If this is an instrument amp then this thread ought to be in the Instruments & Amps forum section.
 
Thanks for the advice, I have modified it so that it has 2 main star ground points, S1 and S2, which are connected together and only S1 is connected to the chassis.

S1 is also connected directly to the mains transformer center tap, the output transformer secondary, preamps filament pot and power stage grounds.

S2 is conncected to the phase inverter and preamp grounds and power stage filament center tap.

Sadly the problem still remains, I grounded like is shown in this picture:
VONmi1n.jpg


Regarding your points:
1. I believe decoupling is fine
2. I can't find any faults in the layout and I shileded as much wires as possible.
3. Not sure how to improve this.
4. I hope this is ok now but I'm not sure.

The problem also remained when I grounded the grids of Rö.3, in which case no signal should be passed to Rö.4. But when I also grounded the grid of of Rö.4 thats connected to Rö.3 the feedback went away, so some signal must have still made it to Rö.4.
 
Its more of a white noise kind of hum above 50 hertz, it doens't really have a frequency it on my scope.

But the noise isn't even such a problem, the high squeel of the feedback is. Is there any way to simplify this problem, for example by disconnecting parts?
 
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