Outboard power supply grounding ?

[woody]

I have a grounding question. I am thinking about building 2 monoblock amps and want to use a common outboard power
supply consisting of a fullwave bridge,center taped transformer
and 2 10,000uf caps then 2 10,000uf caps in each amp. Where should I connect the signal ground. Should I just treat the junction of the 2 caps in the amp as the star ground or return
the signal ground back to the outboard power supply.

[goldkenn]

For me, I will ground the signal to the chassis of the amplifier section via a small cap like 0.01uF, then ground the chassis to the PSU 0V ground, then of course to the power cord earth.

[gain]

good question. the important thing is for the signal ground to have a separate path that is independent of the return to ground for the rest of the amp, particularly the OPS, and to not create a ground loop. a couple thoughts ...

run a separate sig ground wire from each of the monoblocks to the neg terminal(s) of the PS caps. however, this may create an antenna. coax would help this, with the outer braid and center conductor connected to the star point on the PS end, and the braid connected to the chassis and the center as the signal ground on the amplifier end.

another possibility is to use a ground lift circuit ... usually a low ohms resistor (10 ohm is about right) in parallel with a small cap connected between signal ground and chassis ground in the amp itself.

[hollowman]

Originally posted by gain
The important thing is for the signal ground to have a separate path that is independent of the return to ground for the rest of the amp, particularly the OPS, and to not create a ground loop. a couple thoughts ...

run a separate sig ground wire from each of the monoblocks to the neg terminal(s) of the PS caps. however, this may create an antenna. coax would help this, with the outer braid and center conductor connected to the star point on the PS end, and the braid connected to the chassis and the center as the signal ground on the amplifier end.

I agree with most of this.

For CD players, I've currently been experimenting with a couple of outboard PS configurations. Here's what I suggest...

- if possible and as 'gain' seems to imply above: use separate (neg., or pos. for neg. pwr pins) grounds for each important ckt-regulator combo. E.g., my digital filter IC (SAA7220) has a dedicated transformer, PS, and regulator board; the + and - are "terminated" (as close as possible) to the IC's Vdd and gnd pins, respectively.
- use shielded, twisted pair cable(s) (ground shield to metal chassis) to bring in regulated DC into CDP.
- if you have to run pwr-wire lengths inside (any) chassis, use same shielded, twisted pair cable if possible.

A topic tangentially similar to this thread's subject was recently discussed on diyhifi.org

Here's a pic of a work-in-progress outboard PS box, which incorporates some of the stuff I noted above:

[woody]

Thanks for the input (pun implied). I was asking this about a power amp. For some reason I want to do the rectification
and raw dc filtering in the outboard power supply. But it just
occured to me my transformer has 2 30v windings it's not
a 60v center tap. Well I can just build 2 floating power supplys
in the outboard box and only join them at the internal star ground.

[gareth]

Hi woody et al,
The centre tap of your supply transformer should be your 'star' point. You could connect an earth-block (for domestic electrical earth installation) to your 'star' point and then from here out to..
Using the centre point of the reservoir caps will place your signal earth right in where the largest charge currents are being produced and should probably be avoided so as not to interfere.
Thanks
Gareth

PS You could join the neg of one 30v to the pos of the other 30v et voila...60v centre tapped