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 Post subject: Earthing a Step Up Amp.
PostPosted: 15 Jun 2017, 09:47 
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Joined: 25 May 2016, 16:30
Posts: 45
I've built a small battery powered step up amp in an aluminium case. What are your suggestions for best earthing practice?

1. Connect the case to signal negative

2. Connect the case to an earth post and connect back to the chassis earth on my tube preamp

Thanks!


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PostPosted: 15 Jun 2017, 09:56 
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Joined: 05 Aug 2016, 14:35
Posts: 216
Juancho wrote:
I've built a small battery powered step up amp in an aluminium case. What are your suggestions for best earthing practice?

1. Connect the case to signal negative

2. Connect the case to an earth post and connect back to the chassis earth on my tube preamp

Thanks!


Generally, best-practice is to eschew multiple grounds to avoid ground-loops. As you have not told us what you are stepping up I suggest the following:

If this is a MC-phono-cartridge step-up amp, then grounding through signal-negative is best.
If this is a line-level step-up amp, start with signal-negative, and if that creates issues, *ADD* a chassis-ground to the pre-amp.
And then, experiment between no signal-negative and with signal negative in this configuration.

Now: BEFORE you connect anything to anything, obtain a sensitive VOM and measure any potential, AC or DC, between the battery device and whatever you are connecting to it/it to. If it is anything more than a few millivolts, find out why before going further.


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PostPosted: 21 Oct 2017, 18:22 
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Joined: 23 Feb 2017, 02:02
Posts: 130
I recomend connecting from 220v supply directly to the star loop where all audio ground returns to, keep this audio ground away from transfomers and 220v ac line.


When you connect case directly as ground, this means theres some sort of resistance from main retun parth of star loop where all grounds return to.
This actually means your audio ground has some sort of very low voltage causing noise.


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PostPosted: 22 Oct 2017, 18:17 
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Joined: 23 Feb 2017, 02:02
Posts: 130
I actually made this mistake myself when designing and building my own tube pre amp. I directly grounded my case to mains, while leaving other grounds ungrounded to case.

I fixed this today and greatly reduced hum, to very accetable values. I did this by directly hooking up parallel ground wires directly to main return parth star loop, ground at rca termal both input and outpus.
The case was also left directly grounded.


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