Amplifier: grounding, how to

KungFu electronic proverb goes: "Drink upstream to avoid the beaver piss." D from BC

See Eeyores post.

A good technique, once you have the basic amp up and running is to put a audio millivoltmeter across the output, I still use a Lindos LA1 from the 70's, (and it has an internal speaker, so you can hear the hum).

Use a thick piece of flexible wire, like a silicon covered multistranded test lead and short between all the ground points wrt the star point and see which grounding techniques reduce the hum the most

There is nothing like doing measurements, to see what works best

martin

Oh dear,

I found out that the headphone output jack's metal screw is connected to its ground pin. This means that there is a connection with the chassis, which is connected to ground already. It means there is a kind of loop, also.

Is there a solution for this or should I try to get an isolated jack plug?

Just add a copper jumper wire between those two jacks, to make sure you are not relying on the clamping to carry signal current, and tie that jumper back to the ground point that ties the two 1000 uF caps together. You can use the jumper between the two jacks as the star ground, if you want to keep the small drop in the wire back to the caps from injecting its small voltage back into the input. Regardless, keep that wire as short as possible and wrap the two output wires from amps to jacks, around it.

That wire will have some signal current induced voltage drop, that bounces the supply common a bit, but it can be made small by keeping the wiring short and heavy.

Of you come up with insulated holes for these jacks.

Each stage in the amplifier consists of an opamp. For signal ground, there is a 'local' ground point at each stage.

The supply voltage for each stage's opamp has a 100n cap to ground. Is it advisable to have a separate ground for this? (i.e. not use the signal ground)