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PostPosted: Fri Sep 14, 2012 9:58 am 
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Joined: Fri Sep 14, 2012 9:51 am
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I'm in the midst of building a pedalboard for a friend, and he wants stereo outputs from the board for the purposes of running two amps and stereo pedals. Is there a way to modify the router so that it doesn't have any switches is always in "Y" mode running both inputs to both outputs. I'm really just looking for the transformer isolation and ground lift circuitry, the switching/routing aspect is really unimportant for this application. Can the circuit be run without power (no LED's of course)? I'm just having trouble finding a good schematic for transformer isolation in a guitar application. Is it wise to buy this pedal and try to simplify it? Or can I adapt the circuit into a much simpler form without the larger PCB and extra parts? Whatever is the simplest way to have isolated outputs.
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PostPosted: Fri Sep 14, 2012 10:16 am 
If you literally leave out the foot switches altogether and don't plug anything into the B input then the BYOC Amp Selector and Stereo FX Router will be permanently in Y mode. Y mode is not running both inputs to both outputs. In A to Out A and In B to Out B is split or straight stereo mode.

In that case you can leave out the LEDs but it will need power to supply the op-amps. If all you want is the ground isolation then I suppose you could put 2 isolating transformers in a box but you have to make sure that whatever you drive them with won't be loaded by the transformer input impedance. With the op-amps the BYOC ASSFR has a 1 Meg input impedance. I guess you could dump IC3 (and all the resistors LEDs and switches between the transformers and the outputs of IC1b, IC2a) and just drive the transformers from the outputs of IC1b and IC2a.


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PostPosted: Wed Sep 19, 2012 10:54 am 
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Thanks for the help! I meant stereo mode, not Y mode, my bad. So from what you're saying, it is possible to remove the unnecessary LEDs and switches, and use part of the circuit as a ground lift/isolator? Will it be difficult to use the pre-existing PCB for that? Would I be better to build that portion of the circuit separately? I'm a big fan of the BYOC kits, and I'm not the most skilled or knowledgeable with the circuitry, so the easiest and most cost-effective way is what I'm looking for.

So simply putting a transformer in the signal path might cause problems because the guitar impedence level might be a mismatch for the transformer? So what you're recommending is building the circuit up to the outputs of IC1b and IC2a, and then connecting those outputs to the input of the two transformers? Would I need the portion of the circuit connecting the two sides (with IC1a and R7 and R8)? It seems like a pretty simple circuit if that's all I need.

If I can do it more simply without the kit, maybe I'll just pick up the parts and put the extra money towards the Soaring Skillet kit that I'm dying to try out.

Thanks for all the help Tark, really appreciate it.


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PostPosted: Wed Sep 19, 2012 11:34 am 
>>So simply putting a transformer in the signal path might cause problems because the guitar impedance level might be a mismatch for the transformer?

Yes, you can't really build a transformer with a 1Meg impedance. Guitars need to see a high impedance otherwise you lose treble and the controls don't work smoothly. The general consensus is that 1 Megohm is a suitable impedance, although some of the early guitar amps had much higher input impedances of up 4 or 5 Meg and many guitar effects pedals go as low as 500K to 200K. Some pedals actually rely on loading the guitar as part of the sound and don't work properly if inserted later in the effect chain. If you knew that you would always have an effect in the chain that was not true bypass and had a 1M input impedance then you might get away with driving the transformers without any buffering.

You could modify the BYOC kit, or buy just the parts you need and build from that. The sightly unusual parts are the isolating transformers and I don't know if BYOC sell those as a separate item. Otherwise you need to source some suitable audio isolation transformers from somewhere. Since you are only dealing with guitar signals the transformers don't really have to be that great in terms of fidelity.

Based on the BYOC design you could route the outputs of IC1b and IC2a directly to the primaries of the two transformers.

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