Timber amp with solid copper plate as earth and ground plane - diyAudio
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Old 8th February 2013, 11:29 PM   #1
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Join Date: Oct 2011
Location: Brisbane Australia
Default Timber amp with solid copper plate as earth and ground plane

Hi All

My name is Dave and I live in Brisbane Australia.
I have been looking at the various threads about earthing and cannot find an answer to my question.
I am building a PP kt88 stereo amp based on Ian Miller's design with only 2 output tubes rather than 4.
I am building the chassis entirly out of timber 35mm on the sides and 5mm on the top, The top will have a 2mm solid copper sheet under the timber with additional support for the transformers.

I would like to use the copper plate as the functional earth for the amplifier as well as the ground for the circuit with each ground connection connected directly to the copper plate right next to the componant (leads as short as possible)
The amplifier will be wired point to point except for the Cascode input circuit boards from Curcio Audio.
This amplifier will beBuilt on a single chassis, single power transformer (Hammond 387CX) and two Hashimoto outputs.
From what I understand the resistance of a 450mm x 450mm x 2mm copper plate will be far less than any wires I could use for grounding.
I do not fully understand the theory behind eliminating humm and ground loops although my background is in industrial control and electrical.

This is my third amp build and the others used star grounding and point to point and were very quite but looked like a birds nest inside.

I would be greatfull for any ideas and input about this kind of earth/ground system.

I have seen that Pete Miller has used pcb's as the ground plane with great success but have not found anyone using a solid copper chassis and direct earthing/grounding to it.

Looking forward to your replys and ideas and any help you can give.

Cheers
Dave
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Old 9th February 2013, 03:36 AM   #2
DUG is offline DUG  Canada
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Join Date: Jan 2003
Location: mississauga ontario canada
In old tube TV chassis the ground was the aluminum that all of the tubes and electrolytic caps were mounted on.

Are you planning to screw down to it or solder direct?
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Old 9th February 2013, 06:46 AM   #3
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Join Date: Oct 2011
Location: Brisbane Australia
Hi Doug
Thanks for your reply
I am planing to screw all the trannys and tube holders to the copper and to silver solder tabs directly to the plate to connect the grounds to as too much heat would be required to solder directly onto the plate as I am assembling the amp.
The main earth for the mains cable will be bonded to the plate under the power transformer.
the B+ capacitors will be mounted to the plate sticking up through the timber, the bias caps will be mounted to the side timber frame.
Bias pots and test points mounted on the plate and through the timber top.
The tube holders are all mounted in gold plated computer fan guards and screwed to the copper plate with a slightly smaller hole(55mm in the copper and 50mm in the timber) in the timber so the copper is not visable.
All mounting bolts will be countersunk 316 ss 4mm , 5mm for the outputs and 6mm for the power transformer ( all countersunk screws will be soldered to the copper plate to mimamize electrolysis and enable replacement of parts from inside).
Hope this gives you the info you wanted.

Cheers
Dave
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Old 9th February 2013, 10:15 AM   #4
DF96 is offline DF96  England
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Join Date: May 2007
Direct grounding to a chassis/ground plane works fine for RF because it gives a low inductance ground for everything, and inter-stage coupling often uses transformers so ground noise is less of a problem. Audio needs a low resistance ground at lower frequencies. The chassis also provides that, but you can lose control of where the ground currents go. That is why modern audio practice is not to use the chassis as a ground connection for the circuit stages but as just a shield/screen and safety ground.

It might work; it might not. Careful positioning is everything. You still need to think about return currents even though you have less control over them.
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Old 9th February 2013, 02:01 PM   #5
DUG is offline DUG  Canada
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Join Date: Jan 2003
Location: mississauga ontario canada
Quote:
Originally Posted by Dave from down under View Post
Hi Doug

All mounting bolts will be countersunk 316 ss 4mm , 5mm for the outputs and 6mm for the power transformer ( all countersunk screws will be soldered to the copper plate to minimize electrolysis and enable replacement of parts from inside).
Solder to 316SS?

Is this possible?

What about brass?
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