ground bus for inputs on preamp - what's best?

[cbutterworth]

I am in the process of installing multiple (6) inputs for my Aikido. In my old passive preamp, I simply had an Elma 2-pole, 6-position switch (pn 04-1261). I ran signal +ve to this switch, the single signal +ve from the switch ran to the volume pot.

For the signal gnds, I simply bussed the grnd lugs with a single twisted pair of cat5E along all the input gnd lugs and the output gnd lug. Left and Right gnd busses connected at a single chassis grounded bolt. Two twisted pairs then ran to the gnd lug of the volume pot.

This worked very well.

Of course, I want to remove this from my system and use my Aikido with Goldpoint volume installed.

So, how best to wire this?

I have Canare twisted pair, shielded cable that I have used for interconnects. I was thinking of using this inside my Aikido, with the shield connected to input gnd. If I do this, I end-up a bunch of cbale in the preamp, and the trouble of having to join a bunch of ground wires and shields to something.

Will Cat5e work as well as the Canare? I know that it would then be unshielded, but maybe that doesn't really matter. Should I endeavour to keep Left and Right signal and output gnds separated?

I'd really appreciate some feedback on this.

Right now, the signal gnds are isolated from the chassis, except via the Aikido PCB star-earth, which is connected to the chassis at a single point. I suppose that this would mean that the L and R signal gnds do come together at a single point without messing-up channel separation.

I want to avoid a separate GND bolt for the signal gnds. So far, the 60Hz hum on the Aikido is almost inaudible. I reinstalled small value heater shunt caps on my AC heater (suggested as possible by Broskie). The hum level did increase, so I removed them. I may also increase my GND lift resistor from 20 ohms to 30 ohms. Although given the increase in hum when I added the shunt caps, I suspect that DC heaters may be the final solution. Ah...well.

Thanks,
Charlie

[jduffy]

Great question. I'm in the process of working out my layout for a preamp and have the same question. I'd like to have a minimum of wire running around for a clean look and ease of moving around inside the preamp to modify things later.

Looking forward to the answers your post gets.

[whitelabrat]

I'm having a similar problem myself. I made a post shortly after yourself. I'd be interested in the outcome of this thread.

[mach1]

I may also increase my GND lift resistor from 20 ohms to 30 ohms.

It might be worth trying a yin-yang diode ground lift instead.

pm

[cbutterworth]

Mach1,

I think that this is essentially what I am doing. The circuit (and jpeg) is taken from Rod Elliot's website (sound.westhost.com). In place of his recommended 10 ohms, I am using 20 ohms.

Regards,
Charlie

[mach1]

I think that this is essentially what I am doing.

You sure are...

pm

[kevinkr]

I use a heavy ground buss and buss together all of my input grounds which I then connect to signal ground at the audio star grounding point. I also use yin-yang diodes and a 10 ohm resistor between chassis and audio star ground to break ground loops. This seems to work very well in my system where everything including the tuner has a three wire power cord. I no longer design or build anything with two wire power cords in fact.

My current line stage is transformer coupled and I bring back each output ground through a 10 ohm resistor to either chassis or the audio ground.. In a more conventional set up you might want to just connect the output jack grounds directly to the audio/signal ground.

Note that for this to work properly most of the other components in the system need to be treated the same way. You can at most get away with one component (in my system the PA) that has power and audio/signal ground directly tied together. (In this case the 10 ohm resistors and transformer coupling mentioned above break the loop. Someday I will update my amplifier too, it's only 2 yrs old, but it hasn't broken recently. )

Note: I use 14 ga copper conductors from romex for most of my ground busses these days, to keep it from oxidizing over time I tin it with silver solder. (Recent house rewiring so I have lots of scraps around.)

[pforeman]

I just built a simple se amp:no hum (with cd player connected directly)
I have a cj preamp: no hum
put them together: lots of hum
I can't change it's level in any way.
I don't quite understand what you are doing here.
Can I just connect a ~ 10 ohm resister in series between my input ground, and another one between my two speaker grounds? Or do I only do this with the diode set up?
Thanks,
Paul

[bigwill]

Are the diodes there to conduct fault current in the event of one?

[David Davenport]

Originally Posted by cbutterworth

ground bus for inputs on preamp - what's best?

Hi Charlie,

Here is a link to a summary of an article that has information that may help you design your grounding system.

http://www.raleighaudio.com/Audio%20...%20Summary.pdf

Dave