audio-talk

Cant offer any help but you have my sympathy. Finding parts is still not recovered from 2020.

Earthing is often a case of try everything and keep what works.

Probably wont make much of a difference but I would not pass the gnd through the boards like that, I would take them all to the same point where the F&S0 connection comes in from the regulator. And I would move the ground point in the power supply at least to the other side of the smoothing caps...

I think those purple wires are the voltage reference for the heater regs. They're taken off the raw DC ground reference lift. I thought this would be adequate for the heater references? Maybe, but every little helps, if the reference is moving WRT the amp 0v there will/may be some coupling via the ...

And going back to the circuit of the regulator. I don't like the way that's drawn. In theory its fine, but in practice, the F0 and S0 need to be bonded together at the common 0v point and the ground connected there not somewhere back on the nominal 0v line. Any The regulator will regulate WRT 0v at ...

Looking at the picture of the breadboard. You seem to have lots of purple wires coming together on the dual cap, I would not treat the -ve teminal of the cap as the earth point, as that will move WRT the output of the regulators if the current in the 0ve line of the regulators in move. I would treat...

I would either make up some phono plugs with 100R resistors in them to make up some shorting plugs to put into the input of the amp, or solder some 100R resistors across the input phono to make sure you are chasing hum in the phono stage not from the inputs floating (which they can, certainly with 4...

Which suggests things are fine up to the Aikido?

Maybe, is the circuit of the amp in this thread somewhere (will go and look)? It certainly makes me think that its not a issue with HF thats causing the wide trace. I think its just induced hum.

Nice work Dave.

Andrew: you could make a voltage reduction autoformer out of a toroid to reduce the mains voltage into the amp and hide it away in the body of the thing to avoid replacing the mains transformer.

All the other traces are with the input shorted.

No, sorry, I meant the input to the scope being shorted, that way you could see what the trace was like in the known absence of a signal.

I would compare the trace to that with the input shorted to see if its a badly focused trace or something more before trying to fix it. Check the signal going into the riaa, if there is HF the riaa will attenuate it so checking before would show more if its there.

Its also hard to read any values from the scope. I would try turning the brightness down and try and play with the focus.

Hang on, a x10 probe is a 1:10 attenuator, not a probe with gain. If the scope is set at 1v per div, and its not a scope that talks to the probe, then that is indeed 3.4v displayed on the scope, the applying the x10 probe, that means that the actual supply has 34v P/P ripple.

Good list.

In the interest of ideas from the past, you could try taking the cathode of the OA2 to the cathode of the d3a. This will allow you to both reduce the cathode resistor valve because of the extra current and also the g2 voltage will be fixed with respect to the cathode as it should be and not wanderin...