Gibson Varitone stereo guitar to mono pedal

[Buffalo Tom]

I have been asked if I can build a converter pedal to make it possible to use an old Gibson Varitone stereo guitar connected to a standard mono guitar amp input. Originally, Gibson intended these guitars to be used with their two channel amps. You needed a Y-cable going into both amp channels. The neck pickup would be on one channel, the bridge on the other. Those amps had reverb on one channel only. The extra tube gain stage on the reverb side reverses the signal 180 degrees, so the two channels are out of phase with one another. To compensate for that, Gibson flipped the magnet on one humbucker, so that the two pickups are now magnetically out of phase. Played through out of phase channels, this brings it back to 360 degrees, or in phase.

My idea is to simulate the phase thing on their two channel amps in a pedal with two op-amps and then a third op-amp to sum the signals together to mono. Will this schematic work and solve the phase issue?

[antonis]

In case of TIP/RING signals are 180^o out of phase, it will work fine..
(although, it also could work fine without op-amps 1 & 2)

For present schematic, lower R3, R7 & R8 values by a factor of 10..

[Buffalo Tom]

In case of TIP/RING signals are 180^o out of phase, it will work fine..
(although, it also could work fine without op-amps 1 & 2)

For present schematic, lower R3, R7 & R8 values by a factor of 10..

Thanks antonis! Yes tip/ring signal from the guitar is out of phase with each other.  Those 100K values was taken from the Keeley mixer.. But I will lower them to 10K as you suggested. But keep R5 and R6 1M to obtain the high impedance.

[PRR]

R5 1Meg is a lot of added hiss.

Buffer both with non-inverting, then feed to a differential amplifier using ~~10k impedances.

[Buffalo Tom]

R5 1Meg is a lot of added hiss.

Buffer both with non-inverting, then feed to a differential amplifier using ~~10k impedances.

That sounds like a brilliant idea. Thank you!
So the 10uF caps I had after the input buffers in the previous schematic is not needed?

NEW VERSION:

[willienillie]

Does the user plan to ever run through two out-of-phase amps in stereo?  Personally I would just flip one magnet, and rewire the guitar to mono.

[Buffalo Tom]

Does the user plan to ever run through two out-of-phase amps in stereo?  Personally I would just flip one magnet, and rewire the guitar to mono.

No not two amps. But maybe a super reverb using both channels.  He don't want to modify the guitar. Its mint from the 60's. I was asked if I can build a box that solves phase issue and sums both pickups to mono, so he also has the option to plug into a one channel amp without issues.

[willienillie]

I understand, collector value and all.  I would say that a whole lot of those old stereo Gibsons have been "fixed" over the years, and it might not hurt the value as much as other mods.  A future potential buyer might be relieved that they don't have to wrestle with the decision themselves.  But it would bug the piss out of me to have a cool old Gibson that I can't just plug straight into my amp and play normally.  Strokes for folks, all that.