Help Boss Pedal Mod: Momentary Switching

[NFXP]

My friend use to own a Boss VB-2 and that pedal had swtichable modes to choose how it was activated which let him to have the effect for as long as he had his foot on the switch. Now he has a TR-2 and there is no such feature, needless to say he wants it back. theres a big price difference between the 2 pedals so buying another VB-2 is unfeesable for such a simple feature.

My thoughts were to convert the TR-2 to true bypass and then use a momentary switch instead of a latching switch to direct the signal path so the effect is only on while his foot is on the switch.
Can some one have a quick look at the schematic cause maybe im missing an easier way i,e wiring the stock switch differently.

[Enzo]

How about just rewire the switching circuit?

Right now you have the standard bi-stable flip flop that changes state with each closure of the switch. That results in the two JFETS alternating on and off, one or the other at a time. If I read the drawing, they are Q1,Q3. Rework Q6,7 (if I read them) so the FS turns one on, but it doesn;t latch, then the other transistor is used as an inverte3r so the other JFET is opposite the first in function. In other words break the flip flop and make it a simple drive with inverter.

[NFXP]

how should i so go about doing that. I would try a few things but its not my pedal. what woud you do.

[Mark Hammer]

Making the one like the other will involve much more than switching the switch. The VB-2 has additional circuitry that fades in the LFO. The TR-2 does not have such circuitry.

At the same time, the TR-2 uses a VCA chip (M5207), and reducing the current to the chip, or rather the modulation current, might provide an "on-demand" tremolo function, just not one that with variable fade-in.

R19 and R27 set the degree of amplification of the LFO output. Because R19 is 10k and R27 is 1k5, it is actually reducing that LFO output a bit, from what I gather. If R19 is increased, the LFO will be attenuated more. So, let's say that R19 was replaced with a 100k fixed resistor. You ought not to hear much modulation at all, in theory. If one had a momentary switch that connected a second fixed resistor (say 11-12k) in parallel with the 100k, you would restore the full depth of the LFO to whatever the Depth control was set to.

[NFXP]

He didnt mention anything about variable fade in. I think hes just after converting it to on demand switching.

[Enzo]

My suggestions were made without regard to the actual functioning of the effect, I only addressed the action of the foot switch. I don;t think he intends to convert the one to the other, I think he just wants to control it differently.

I have done this to Boss pedals in th past, but don;t recall the particulars.

I am not going to design it for you, but basically, the FS has a pullup resistor, so that means there is a voltage that gets grounded off when the switch is closed. Pick one side of the flip flop and control it with this voltage - there are caps blocking the direct connection in the stock pedal. Then wire the other half of the flip flop to be controlled by the first, so when one is on the other is off. Classic one transistor inverter. The flip flop acts as it dooes because each transistor is coupled to the other. You would rmove that cross coupling.

The newer effect might fade in, but the OP was suggesting wiring a true bypass around the pedal and leaving it on anyway, so that feature wouldn't happen.

[NFXP]

yeah i was never concerned with changing the effect just changing the way it switches on. Thanks for the info since i dont think they make a momentary dpdt switch ill have to modify that circuit.

EDIT: My bad, They do make such a switch but my local store doesnt carry it.

[NFXP]

After looking over this i think its alittle out of my league, and not being my pedal i dont want to fry anything. I think ill do the true bypass mod idea. A la:



and then contol it with one of these.

2, Momentary N/O + N/C DPDT Push Switch,3P3 - eBay (item 290540190706 end time Mar-07-11 23:09:29 PST)

Hopefully ill beable to make that fit in the stock location. that would be cool.
Ill just leave the LED on all the time since its not a 3pdt switch