Star ground for Gainclone

[meat]

I am building a Gainclone with Brian's boards and was wondering if I can just connect a wire from the chassis gnd on each channel to the ground lug on the AC connnector?

I am confused with the chassis ground. Do the 3 wires that make up a star ground have to connect to the chassis?

[Peter Daniel]

The grounds can be connected in few different ways. I wouldn't connect AC ground terminal directly to the PCB.

One way is to connect chassis directly to AC ground lug and then each board's ground (marked as CHG: chassis ground) through some 10ohms resistor to the same point on a chassis.

Another way, which I sometimes use, is not connecting AC ground at all, not using CHG ground point from a board, but connecting negative output (grounded) of binding posts (from each channel) directly to the chassis (by not using isolating washers here).

One other way is to connect the chassis to AC ground only, without neccessarily connecting PCB grounds to the chassis.

All those methods will work, some better than other, depending on a rest of a system.

[meat]

Thanks Peter. So whichever method I use, I do not want to use isolating washers?

[Peter Daniel]

You don't use isolating washers only when using the ground output binding post for chassis ground connection. Otherwise the posts should be grounded (with other 2 methods I mentioned).

Don't forget that positive binding posts (amps output) has to be always isolated

Not isolating bindig posts method will work best, when both channels outputs are relatively close to each other.

[jan.didden]

... but unless you use two completely separated channels, including supply, grounding both neg speaker terminals to the chassis will certainly set up a ground loop. Wheter that leads to problems or not depends on a few other things, but you are taking your chances. I would only ground ONE of the two, and isolate the other. Better yet, use the other method recommended by Peter with the 2 resistors.

Jan Didden

[Peter Daniel]

Originally posted by janneman
I would only ground ONE of the two

That's what I was doing originally (at least with inverting amp) and it didn't work well.

The AMP-1 chassis is using separate PS and using only 8 wires in umbilical cord, I had no way of connecting permanently another ground wire from AC ground lug in PS to the amps chassis.

So I decided to connect the chassis to output signal ground, using only binding post in one channel. This worked OK in the amp. However, when one guy in Sweden decided to use amps in bi-amp configuration (one amp per channel, feeding tweeter and bass separately), he experienced some distortion problems. I adviced him to connect both ground binding posts with a jumper, and it fixed the problem.

From now on I connect both chanels posts to the chassis. Actually, this is not exactly what I'm doing in AMP-1. I'm taking the wires from binding posts (binding post is connected centrally between main PS caps) and run them to the central point on rear panel. But in the integrated chassis I did that by not isolating both posts and it worked fine.