Adding Transformer Isolation to an existing buffer design

[sjaltenb]

I noticed that I am getting some ground loops in my Send/Return design.

On my board, I split a signal 4 ways : 1) Dry to mixer, 2) To an onboard delay 3+4) To two external send/return jacks that go to a rack delay. They all get mixed back together and send to the output.

I noticed that the two external send/returns are causing some ground loop noise. I would like to add isolation transformers to the existing buffer to the two Send jacks. How would this be done?

I am guessing that much of the GEOFEX circuit is simply the buffer/splitter. Because I already have this 4 way JFET splitter, it should be very simple given the right transformer? Correct? Any wiring diagram and additional components needed would be great!!

[brett]

Hi
not an answer to your question: a simple way to eradicate some problems is to "lift" the ground on the output.  Replace the signal DC ground connection with a 0.1uF capacitor.  This breaks the low frequency low voltage high current loops that sometimes show up.

Concerning your question:  With a high impedance load like a JFET, you can use almost any simple small transformer and get good results (because the transformer will appear as a high impedance to your pickups/stompboxes).  Try a 1k:1K, 3k:3k or other 1:1 transformer from Xicon etc.  Your Mouser catalog or local electronics supplier will have lots of options for little cash.
cheers

[sjaltenb]

Great, that is what I have gathered so far, that you must use a 1:1 transformer, and I will continue to read up on what other people have posted about good quality transformers. RG if you are reading I am learning! The reason for the active buffer circuit is because the passive transformers are very expensive. Thus you need a buffer to drive an active circuit into a less expensive transformer. And the MAX1044 was used to improve headroom on your original design.

So, I can just copy the left side of the GeoFEX amp splitter, as far as the transformer wiring and the 10k resistor/.001 capacitor on the output, using my buffers outputs and my board's star ground as the 'input and input ground' and the new, isolated ground on the send jack.

Sounds pretty straight forward!

[wavley]

Great, that is what I have gathered so far, that you must use a 1:1 transformer, and I will continue to read up on what other people have posted about good quality transformers. RG if you are reading I am learning! The reason for the active buffer circuit is because the passive transformers are very expensive. Thus you need a buffer to drive an active circuit into a less expensive transformer. And the MAX1044 was used to improve headroom on your original design.

So, I can just copy the left side of the GeoFEX amp splitter, as far as the transformer wiring and the 10k resistor/.001 capacitor on the output, using my buffers outputs and my board's star ground as the 'input and input ground' and the new, isolated ground on the send jack.

Sounds pretty straight forward!

I have an AMZ Jfet buffer with one of those $4 triad transformers tacked on the end, I omitted the output cap because the tranny isn't going to pass DC anyway.  It works great.

[sjaltenb]

Sounds like I should be good to go. Thanks!