Any schematic(s) for simple Ground loop buster(s)?

[tubeswell]

Hi y'all

I am looking for a schematic for a simple ground loop buster to go between the output of a stand alone reverb unit and the input of the (whichever) amp so I can DIY one.

If anyone has any schematic(s) - or link to any schematics - that would do the job, please feel free to let me know.

Cheers

[andrew_k]

Forgive me if you've already tried this; I've been trying to follow your related threads as I'm building a 6G15 as well and would like to have an inbuilt solution to the hum...

http://www.generalguitargadgets.com/...d=16&Itemid=26

^ R.G's hum-free A/B/Y. Although the specs for the xformer state it's only good down to 300khz, a post by R.G. on diystompboxes describes how he got it much lower using the opamp to drive it. I'm considering build the above unit as an isolation device directly into my 6G15.

Edit: This transformer has more suitable freq. specs and is available closer to home... not sure about the impedance suitability though - http://australia.rs-online.com/web/s...duct&R=2106380

[tubeswell]

Edit: This transformer has more suitable freq. specs and is available closer to home... not sure about the impedance suitability though - http://australia.rs-online.com/web/s...duct&R=2106380

Hi Andrew

I think the transformer in your 2nd link might not be up to the task for an isolating transformer - from what I gather it needs to be high impedance in and out - anything less than 10k/10k is not worth looking at I believe. I tried 3k2/3k2 as a passive transformer and it is no good because of the high output impedance of the reverb recovery stage. (It doesn't sound so bad when the mixer is on the CF side, but its is absolute crap on the reverb recovery side, and that is far from perfect - besides not fulfiling my expectations)

When I build my next reverb unit, I'm going to put a parallel CF stage after the mixer and before the output to get really low the output impedance and high current, so it will drive a good passive isolating transformer really well. Meantime I'm looking for loop buster - maybe R.G.'s splitter will fit the bill?

Another idea I am toying with is a passive shielded box with a 100R pot (suggested by dai h.) for elevating the signal ground coming out of the reverb unit. The alternative would be to build a soft earth inside the reverb unit with a small resistor to lift the signal/pre-amp star grounding point and another identical value resistor to lift the output stage star grounding point (since I like the split ground system) from the chassis ground with everything otherwise isolated from the chassis.

But since I've already built a reverb unit that seems to almost perfectly match the chassis 'ground' potential in my 5G9 (it is virtually silent), I don't want to change the reverb unit any more and its fine to use forevermore with that amp. (But if I had a little loop buster I could use it with other amps too).

(Maybe I'm just going to have to get really disciplined at building amps that have the same 'ground' potential as each other on the chassis?)

[Enzo]

Keep in mind it is not a DC potential difference here.

[tubeswell]

Keep in mind it is not a DC potential difference here.

Hi Enzo

I think what you are saying is that the difference is between the 'neutral' points of the respective AC voltages in each chassis - (please correct me if I'm wrong) - and since we are talking about the return path, the AC voltages are the 'aggregate sum' of all the AC that is dumped in the return path (making the difference being between the respective aggregate sums of AC voltages of both amps?)?.
Nevertheless would not a large enough resistor (without being too large as to actually inhibit the audio return path) in the audio return path between the two amps put a sufficient buffer between the two 'ground' voltages so that loops are no longer an issue? (I was thinking of using a 100ohm linear pot to dial-in the right amount of buffer in each case) Or have I got the wrong end of the stick or is that too simplistic (leaving high-quality 1:1 audio transformers aside for the moment)?

I'm just trying to come to terms with what is happening

[Enzo]

Leave the amps plugged in side by side, but remove that cord between their inputs from my last experient. Set your meter to AC volts and measure the AC voltage between the two chassis. That voltage is going to add itself to an input signal.

If you wired a large chunk of copper between the chassis then you might squash this. But if there is a quarter volt of AC, I don;t see how adding a resistor will diminish it.