Grounding issues

[miguel2]

Hi,

After some major rebuilding I have now to connect a preamp and a GC in the same case to make an integrated amp. So I have:

1 - input socket, isolated from chassis
2 - volume pot
3 - preamp with its own psu
4 - GC with its psu

When I connect all grounds together I have no music at the output.
Connecting the grounds of 1, 2 and 4 I have music and hum. In this part the ground of the pre is not connected to the others. After measuring I found a difference of 7VDC between the ground of the pre and of the GC.
Connecting the grounds of 1, 2 and 3 directly and 3 and 4 with a parallel arrangement of 100R/0.1u the grounds of the pre and of the GC become at the same voltage but I have no music again.

So how are these things connected? I have no connection to the chassis yet but I think that this is not the problem.

A second issue is how to use the same tx from the GC to make a sub amp. Can I connect another bridge to the GC tx and make the sub amp? This is because I want to add more capacitance in the sub amp.

Miguel

 

[jan.didden]

Can you sketch the power supply arrangement? Are there separate xformers and bridges?

Jan Didden

 

[miguel2]

Hi Jan,

They are separate txs and bridges.

Preamp
15-0-15 VAC, one bridge for + and -, central tap of the tx for ground.

GC
2 separate bridges, 1 for + and 1 for -, ground connection to the point between bridges.

Miguel

 

[jan.didden]

Hi Jan,

They are separate txs and bridges.

Preamp
15-0-15 VAC, one bridge for + and -, central tap of the tx for ground.

GC
2 separate bridges, 1 for + and 1 for -, ground connection to the point between bridges.

Miguel

I have a hunch that there is something fishy in that GC supply. Can't you hand-sketch the circuit and scan it and post it?

Jan Didden

 

[miguel2]

Can't you hand-sketch the circuit and scan it and post it?

It is the usual one. The GC works very well without the pre!

Miguel

 

[2Bak]

Do you have hum if no interconnects are plugged in, i.e. no source?