Grounding questions

[rutledj]

I have a xfmr that has a 24vac winding that I will use for the relay supply. My question is would it be ok to connect the ground of the relay supply to the other grounds in the system?

Thanks,
Rut

[Bob-I]

I have a xfmr that has a 24vac winding that I will use for the relay supply. My question is would it be ok to connect the ground of the relay supply to the other grounds in the system?

Thanks,
Rut

Should be. I've done that many times and it's fine. (I'm fighting a hum issue with another build so my confidence is lower than it usually is. )

[Funkalicousgroove]

Your relay supply ground should be separate from any signal path grounds, but it's pro'lly OK with the ground from say your first filtering stage(which should be separate itself, and grounded with the PT)

[rutledj]

I gave this a try last night. Basically I have a separate winding on the PT (18v) that feeds a small board with a bridge rectifier (one of those self-contained units), then to a 7812 regulator and a 100uf cap across output.

If I connect the gnd to any other ground in the system the bridge rectifier gets super hot. If I keep it separate and just run it to the relays then I have no problem.

Only thing about this is that I can't use the chassis ground for switching via a footswitch. I have to use one wire just for the ground. Just curious why mixing the ground caused a problem with the bridge.

rut

[mlp-mx6]

Is the relay supply ground from the xfmr, or from the bridge rectifier? When using a bridge, the ground should be from the bridge. IF there is a ground wire for the xfmr, DO NOT USE IT! Just tie it off somewhere unconnected.

[rutledj]

No. The xfmr doesn't have a gnd (centertap) for that winding. The ground is off the bridge.

[BobW]

This sounds like the 18 vac is actually two voltage taps from a common ground or source. The voltage difference of your two relay leads may be 18vac, but is there also a voltage difference from any other PT leads? If so, these leads are taps, and not isolated.

You may want to re-check there is no continuity from either 18v leads to something else.

[rutledj]

Well, I can't measure them to any other winding and the print from the amp I salvaged it from shows it as an independent winding.

I guess I'll just live with it:)

[heisthl]

Do you get around 25 volts out of the bridge? (18 x 1.414)

[rutledj]

Not sure since I've already mounted everything and wired it up.