My Crybaby Wah transistors Hfe

[shredgd]

I've been experimenting with different trannies in my GCB-95 wah lately and I want to share the results.

I tried BC109s and 2n3904s (the latters are in Steve Vai's "Bad Horsie" wah, or at least this is what the schematic says), but I've ended up putting the MPSA18s back: they give a more pronounced wah effect, although the BC109s sound cleaner. I've not experimented much with the 2n3904s because the two I had around were equal in gain (see below), however they were clean sounding as well, but again less expressive than the MPSA18s.

What surprised me about the stock trannies is the Hfe I measured for Q1 and Q2 is 545 and 930 respectively, that is Q2 has an higher gain than Q1, in contrast with the common suggestion to make Q1 "gainier" than Q2. I did try and inverted the two, but they definetely sound better in their original position.
Did anyone notice that before?

Moreover, although both MPSA18, the two trannies are different in appearance, the one in Q1 having a "silver" front face, so the big difference in gain is not casuality!

Hope someone finds this helpful!

Giulio

[Paul Marossy]

Huh, very interesting.

[jonathan perez]

i will try that later...with a germ tranny as q2 

[Paul Marossy]

I've been wondering how Ge transistors would sound in a wah pedal, but I've not done it because they are so touchy to changes in ambient temperature...

[jonathan perez]

well, its roughly the same temp. EVERYWHERE i go...oddly...

im going to find out, tonight. i jusy built a clyde mccoy, so id like to hear it...ill post sound clips!

[rockgardenlove]

I've put germs in the Q1 position.  Sounds nice, mellow and full sounding.  Warmer.

[jonathan perez]

which germaniums?

ive got a bunch of arons...

[petemoore]

  Must Be NPN Ge, [MPSA18 is NPN] Aron sells them. 
  Inductor, pot, transistors, sweep range cap, other things...all interactive to one degree or another, I found it hard to say...much about wahs...tune 'em with the parts, get better parts and re-tune em again, mod...I figured the trick is to find a sweep you like, try to improve it for a while, and use it.
  I think I tried a Ge, ended up with a BCxxx in Q1 and something else in Q2...lol...tried many actives...I found having a parallel sweep range [or is it voice cap...little one .oo22 or something like that, tacked on so I could double it's value while trying transistors out [iirc Q1 varied the eq a good bit]...anyway deciding on a sweep...then using it !!!

[rockgardenlove]

Yep, I used Aron's.

Lower the 470(Dunlop)/510(Vox) ohm resistor, it sounds better with the germaniums IMO.

[Paul Marossy]

Hmm... I have some Ge transistors lying around, I should give this a try.