How difficult to mod a Behringer UV300 for stereo vibrato?

[dimebucker]

Hello all,

Just checking if this worth pursuing or would it be more hassle than its worth?

..maybe two UV300 pedals with rates somehow synchronized (180° offset)?


 

[iainpunk]

yeah, you need two of them and replace one of the LFO's with a signal inverter that doesn't change the bias level.

you take off the slave unit's DEPTH control, ignoring the outer pins and leaving a mark (piece of tape) on the wire that connected to the middle pin. and keep the unused LFO from working by taking out the RATE control

the master unit's DEPTH pot, you splice a wire to the middle pin to feed it to a daughter board containing basically this
it inverts the LFO without changing the bias. it works as long as the LFO isn't slower than 0.03Hz or 33.33 seconds

the output form this daughter board goes to the marked wire that was on the middle lug first.

cheers, Iain

[dimebucker]

Cheers Iain, this is exactly the information I wanted.. I think I will attempt this!

Just out of interest, have you done this mod in the past or is this a general way to synch 2 vibrato boxes?

Thanks again

[dimebucker]

Looking for anyone to reply on this:


The circuit above shows a 10uf non-polarized capacitor, correct?

Would it be ok to use either a film or ceramic type?

[antonis]

It would be OK even with polarized electro.. 

[iainpunk]

yes, it could be a polarized one as well, and bigger is better.

cheers, Iain

[dimebucker]

Ah, so the capacitor acts to remove high-frequency noise from the circuit 

Where do these high frequencies originate from? the opamp?

[iainpunk]

no, the capacitor is to eliminate the AC part of the LFO from that pin on the opamp, and to leave only the DC part in. if the AC isn't fully taken out at that point of the opamp, it won't nicely invert the signal, but just phase shift it slightly and you change the stereo effect.

you'll see that the filter breaks over at 0.03Hz, that translates to a wave of 33.333 seconds, this 33.333 sec wave is phase shifted 90 degrees. that means a pure sine of 3.333 seconds is fully flipped 180.

if you want to change the phase difference, you might want to change the 500k reisistor to a 500k potentiometer, so you can determine the phase offset between the two channels.

cheers, Iain

[dimebucker]

Excellent


Thanks, I fully understand now

[iainpunk]

ow, forgot to mention, its called an ''All Pass Filter'' by the way

[Ben N]

Just out of curiosity, have you tried it just wet/dry?