two-point star ground q

[neilium]

Hi all,

I want to double-check that my understanding of two point star grounding is correct, as per Randall Aiken's article on the subject.

1. First cap after the rectifier, B+ center tap and output stage cathode resistors are grounded on one star ground, preferably close to the first cap's negative.

2. All other stages are grounded to a second point close to the screen supply cap's negative. Individual stages can gang their grounds at a point local to the stage and then run one wire to the second star point. Stages out of phase with one another can also gang their grounds.

3. The ground lead from the AC cord is connected to the chassis with as short a wire as possible.

OK, now my questions: Should the two star grounds be connected directly or each grounded to the chassis? Should the chassis be connected to the star grounds at all?

I feel like a fool asking: I've built hifi stuff for years using buss and star grounds and haven't had any problems with hum. It's just that none of that stuff (not even my RIAA pre) has as much gain as a guitar amp, so I'd like to know what's worked for others.

Thanks,
-neil

[1965mt]

i haven't built a wreck but i did have to use that exact scheme on a 5e3 that i built. it had a bad hum until i separated the grounds. i only have two ground points that are not connected except through the chassis. the first is the power cable ground with the ps caps and the 6v6 cathodes and the second takes the little tubes.
other amps that i have built do fine with a single buss ground.
i don't think there is a right answer for some reason, it seams like there are as many different ways that have all worked.
i know an rf guy that insists on soldering to the chassis where amp guys usually just use a bolt for connection....

[Elcabong]

The two star grounds must be connected to the chassis. In the case where they would also be connected together, it becomes a one star ground.

Have you looked at this site?
http://www.geofex.com/Article_Folders/s ... targnd.htm
There is a good star ground example at the end.

[rhinson]

hello there, ground the filter caps for the screen supply with the caps for the plate supply, cathodes, h.v. ct (if your power trannie has one) , etc. all on the the power trannie side of the amp----like to a solder lug attached by one of the bolts holding the power trannie to the chassis. (also 6.3v ct on that side as well) ground all the rest of the caps, preamp cathode grounds, etc at a solder lug on the opposite end of the chassis----ie. where the input jacks are. that's all there is to it---power amp stuff on one side and preamp stuff on the other . good luck. rh