Add clean boost to a true bypass circuit?

[Buendia]

I use a true bypass strip and one of my vintage goodies has a considerable volume drop. I hate to have to put a boost pedal in series with it and was thinking about modding my strip and adding in a boost that I can control with a pot so I can just adjust the pot my pedal volume is unity.

The more basic the better as it's going inside a bypass strip hehe. I'm familiar with using a volume pot, but a volume pot fully opened up just gives you 100% right? I need to be able to get to at least 130%.

Anybody have any ideas, suggestions?

Thanks again!

[liakos]

i think you need a buffer

[Buendia]

I have a buffer. That doesn't raise the volume of a pedal with a volume drop.

[remmelt]

Build an NPN boost? The boost is pretty clean as long as you use a 2N2222. I like the cleaner sounds that the metal cased ones give me better than the plastic ones (TO92). The hotter the transistor, the dirtier the output, so use something that's just clean.

[Mark Hammer]

Don't confuse the fact of a boost with how much boost.  For instance, a number of commercial pedals (many of our favourites) incorporate a a single-transistor gain-recovery stage that simply raises the level back up a bit to compensate for passive volume loss through tone controls.  Just about ANY clean preamp stage with a wee bit of gain will solve your problem.  Remember to place it after the effect output and keep the gain well below x3.  It should not create any signal dirt or risk of unintenional overdriving of subsequent stages.

[Buendia]

Yes, I only want enough to bring a volume dropped Electric Mistress back up to unity (and I'd like in general to learn how to do it) does anybody have a schematic, diagram or layout they can point me to? Or maybe just tell me a little more about the circuit?

Thanks a million,

Nic.

[Dragonfly]

Tillman preamp.

http://www.till.com/articles/GuitarPreamp/

[Mark Hammer]

That's an excellent example, although given the nature of the request, I think a few more details are needed to get you up and running.  Note that, in the schematic shown, there is a 10uf cap to ground from +9v (C2).  Since you've already got the supply decoupled (jeez, I certainly hope the circuit you want to add this to has a big-ish cap from V+ to ground), there is no real need to add/use the 10uf cap shown in the schem.  As well, since you will be feeding it with the output of a circuit, rather than a passive pickup, the 3M resistor (R1) on the input becomes essentially superfluous, so you can omit that as well.  Everything else stays.

The advantage of this circuit is that it has a high input impedance.  Since you'll be feeding it with a low-ish output impedance from the effect circuit, the use of a FET provides no real advantage.  On the other hand, it doesn't hurt and is quiet, and doesn't cost any more than a bipolar alternative.  It's also smaller than an op-amp alternative.  That all makes it an excellent suggestion/choice. 

If The preset gain proves to be more than you needed, you can always replace R4 with a 50k log pot and maybe a series resistor to ground (the pot is more likely to be in the 47k range, so consider a 3k9 fixed resistor between the pot and ground).