Isolation transformers following 1@3 switcher - Impedance and buffers

[Willow]

Hi,
I'm trying to determine a simple and effective method to isolate my split guitar signals from my lehle 1@3 switcher so as to feed multiple amps.
Effectively I want to build a box with up to 4 separately isolated inputs/outputs (a la Joe Bonamassa's pedal board - coincidentally have the same 1@3 so I stole the iso idea... http://www.premierguitar.com/articles/Rig_Rundown_Joe_Bonamassa_2013_)
so: Guitar into effects pedals - from effects pedals into 1@3 Lehle - From Lehle output 1 - input 1 iso box - output 1 from iso box to amp.
and same for I/O 2, 3, 4 - Config most likely will vary.

It has probably been discussed a million times so I'm sorry if this is old hat, but I couldn't find a definitive solution. So, here we are...

I am thinking: input using TRS input socket into standard op amp buffer circuit as per http://www.beavisaudio.com/techpages/Buffers/ (I've got a bunch of TL071 OpAmps lying around), driving a 42TL018-RC Transformer with output stage as per http://www.geofex.com/FX_images/spltr2.gif using plastic TS socket with Sleeve not connected to ground.
Op Amps powered by 9V DC supply from regulated power supply which feeds all my pedals.

Also considering phase invert toggles on the output stage before TS socket.

Can anyone see any problems with this. Potential tone loss, complete circuit failure, etc.

As I don't know exactly how I want to configure my pedals to which amp yet, I want to make it hassle free by being able to just move connections around as I see fit.

I'm no expert, obviously, so any constructive advice would be much appreciated.

-Willow

[merlinb]

Yes that's fine. So basically you're going to build RG's transformer isolator, but using a single 9V supply instead of bipolar (so you'll need input/output caps and Vref etc), yes?

Do you actually need amplification? The alternative is to use a 10k:600R transformer rather than 10k:10k. Amplify the signal by 4x with the opamp, then it will be divided by 4 by the transformer, thereby giving overall unity gain and providing a lower impedance output.

[Willow]

Thanks a lot! Cheers!

[Willow]

I was basically looking for a 1:1 output. figured I would have some signal loss just using the transformer so hoped the buffer circuit could negate that a little.

I'm assuming you mean virtual ground setup with resistors and caps between Vcc+ and Vcc- teeing to Virtual ground?

[Willow]

I was thinking along the lines of http://www.beavisaudio.com/techpages/HIW/buffer_opamp.gif if that helps, which has voltage divider and will obtain unity gain.
Like I said, I'm no expert, so there's a good chance I'm missing something. 

[merlinb]

I was thinking along the lines of http://www.beavisaudio.com/techpages/HIW/buffer_opamp.gif if that helps, which has voltage divider and will obtain unity gain.
Like I said, I'm no expert, so there's a good chance I'm missing something.  

Yes that would work in place of the opamp in RG's circuit, since it runs off a single 9V supply. RG's circuit has its input buffer configured for a gain of about 2 (actually 2.1, I have no idea why) which will overcome any loss in the transformer, and then some. You can of course, arrange your input buffer to provide any level of gain you like.

[Willow]

Thanks. I'll have a play around with it once I get a transformer.
Appreciate the advice!