A common ground between preamp and amp

[marthaman]

I'm about to build a pre-amp to connect to my amp (Velleman 4004B) and need to know if there are any problems in grounds between different sources (the amps and the audio input and output).

For example, my battery operated pre-amp (I could make one powered by a plug-in transformer) will have a common ground with my audio input and audio output. The output of the pre-amp will then become the audio input of the next stage, the power amp. This amp also has a common ground between audio input, the amp itself and then audio output.

Should I have any concern that two different amps (pre-amp and amp), powered from two different power supplies [one possibly a battery where (-) is ground] is also tied to audio in and audio out with a common ground? Will that create any problems? If so, what are the solutions?

[Gordy]

It's difficult to comment without seeing the circuit, however in general there should be no problems with a 'ground' formed from a battery being tied to mains ground. In effect the mains ground becomes the reference point and the battery ' + ' supplies a voltage relative to the mains ground.

Grounding is not an easy subject, so best advice is to indulge in a little background reading...

http://www.gbaudio.co.uk/data/ground.htm
(Ground loops...)

http://rane.com/note151.html
(Grounding and shielding notes from Rane)

http://www.tcaas.btinternet.co.uk/jlhearthing.htm
and
http://sound.westhost.com/earthing.htm
(Grounding basics)

[marthaman]

Thanks. Yikes....it's complicated.

Indeed, I had two concerns in an audio circuit: ground loops and audio hum. The references authoritatively talk about those subjects.

[AndrewT]

Hi,
I suggested in another thread that the pre-amp grounds for each channel be kept separate for best immunity to loops and hum.
The consensus was this should not be necessary.

[Gordy]

Originally posted by AndrewT
Hi,
I suggested in another thread that the pre-amp grounds for each channel be kept separate for best immunity to loops and hum.
The consensus was this should not be necessary.

If taking things to extremes I would look at separating them as you suggest. However in practice it's more a case of separating the signal (i.e. current) return loop flow paths. If done with consideration this can be done well while still using a single overall ground plane (...assuming that a pcb is used).