Whats a good transister to use for wahs

[paulyy]

I've been having some fun with my tweaking my wahs and been swaping out transister to what they sound like. It had the stock mpsa13 but I thought they sounded to harsh. I've tried the bc109's and 108's. really nice but some what noisy to me. I've tried 2n2222 thru 2n5089 and not bad. Right now i'am using cen2n5172's and sound really good. Is there any other type of transister's out there that can be used in wah's? Thanks.

[petemoore]

  Bipolars 'work' much the same as other bipolars. BCxxx's do distort mildly, 2n3904's may make more noise than a 2n5088 [when in doubt grab the 2n5088 [low noise/high gain transistor, very nice], otherwise it's mostly the gain of the transistor and how it relates to the circuit/sound.
   Q1 is a boost stage ? lower gain or higher gain transistors seem to have sufficient boost capability [ime's].
  Having put in sockets and tried BC's, 2nxxxx's and various other transistors, with no super particular druthers about which transistor except 2n5088 or MPSA18 [the 5088's and MPSA 18's were very very similar] or BC108's for the '108 grind'..for slightly different sound. 2n2222's sounded different and good also.
  2n4401's...NPN Ge's, various other transistors popped in for a try.

[digi2t]

I have an old Schaller Bow-wow yoy-yoy wah. It's got a trio of BC109C's in it, and sounds pretty good. Then again, I'm a bit impartial, since I'm a big BC108-9 lover 

[Paul Marossy]

You could try 2N5088s. They are quieter than BC109s...

[ryanuk]

+BC109s

My wah ended up with 2 BC109B - I think the last letter denotes a different gain category selected at the factory.

I wouldn't spend too much time on swapping transistors. Yes, they do alter the gain characteristics, but the tone of the wah will remain the same. Higher gain will "sound" more noisy but can make the wah muddy. Lower gain give a clearer wah but too low and it'll sound weak. You want to check the datasheets and look for gains of around 400-500 from memory.

I toy'd with my wah for ages. Swapping out caps, pots and inductors. It can get quite costly given the hype some of these parts attract. In the end, I finished up with largely a standard circuit with some different value resistors. One or two resistors in the curcuit can make a huge difference, I cant recall which ones although is all over the net. All other mods were sublte. I think I did upgrade the caps but only to reduce noise - they were standard panasonic jobs - not mojo replacements. Also added a switch for different sweeps. Changed the wah completely but the inductor and pot were the standard dunlop parts.

RyUK

[Paul Marossy]

The standard Dunlop inductor isn't bad IMO. There's far more to be had by tweaking everything else.

[R.G.]

I'd like to reinforce Paul's very insightful advice.

The circuit for the signal transistor in the stock wah circuit is a collector-base feedback setup. The DC conditions are dependent on the collector resistor, the emitter resistor (if any), the resistance between the base and collector, and -> the gain of the transistor <-  so if you leave the resistors the same and swap in another transistor, the bias shifts. This produces not only a different AC gain, it shifts the operating point of the circuit so that the new transistor may be closer/further from distorting, and makes a big difference in whether there is clean sound, soft distortion or possibly bits of hard distortion. Then the change in AC gain also changes the "peakiness" or Q of the resonance, changing the tone.

It is very human to say "I changed the transistor from Brand X to Brand Y, and it sounded better; therefore Brand Y is better than Brand X" but that is very much like saying "the last brunette I say smiled at me, but the last blonde frowned, therefore brunettes are better than blondes."

Paul is correct in saying that the other stuff around the transistor has a huge effect. Tweaking those parts can make big differences in the sound, probably bigger than changing transistors.  Transistors give you a bag of possibilities. The rest of the circuit gives you the realization of those possibilities.

[ryanuk]

I guess thats what I was also trying to say - but in a different way.

[Paul Marossy]

I'd like to reinforce Paul's very insightful advice.

The circuit for the signal transistor in the stock wah circuit is a collector-base feedback setup. The DC conditions are dependent on the collector resistor, the emitter resistor (if any), the resistance between the base and collector, and -> the gain of the transistor <-  so if you leave the resistors the same and swap in another transistor, the bias shifts. This produces not only a different AC gain, it shifts the operating point of the circuit so that the new transistor may be closer/further from distorting, and makes a big difference in whether there is clean sound, soft distortion or possibly bits of hard distortion. Then the change in AC gain also changes the "peakiness" or Q of the resonance, changing the tone.

It is very human to say "I changed the transistor from Brand X to Brand Y, and it sounded better; therefore Brand Y is better than Brand X" but that is very much like saying "the last brunette I say smiled at me, but the last blonde frowned, therefore brunettes are better than blondes."

Paul is correct in saying that the other stuff around the transistor has a huge effect. Tweaking those parts can make big differences in the sound, probably bigger than changing transistors.  Transistors give you a bag of possibilities. The rest of the circuit gives you the realization of those possibilities.

That's just my findings after tweaking and building wah pedals for a few years. 

[R.G.]

I guess thats what I was also trying to say - but in a different way.

You're right - it is!

Yeah - what Ryan said, too!

[zombiwoof]

I like BC109B, in hfe (gain) range of 350-400.  This is suggested by Fuzz Central to help get the original vintage Vox sound.  However, just about any silicon NPN transistor will generally work fine if it's in that gain range (this is supposing you are using the stock vintage Vox/Crybaby circuit).  The transistors Dunlop uses are MPSA18, which very high gain, which is probably one of the reasons for their version of the Crybaby not sounding like the vintage ones (along with other subtle circuit changes, and the inductor).  I modded my older V847 Vox wah to original Clyde McCoy specs using the info at Fuzz Central, with BC109B's and transistor changes to the original values and it sounds great.

Good Luck,
Al

[joegagan]

boomerangs usually measure about in the 220 -270 hfe range in the late 60s to early 70s. of course, that is sort of a whole other circuit, but worth noting.

for giggles i have been putting an NPN ge in Q1 paired with a 140 -ish hfe si for Q2. pretty neat, mellow boomer.

[paulyy]

I see we have some big fans of th bc109's. Again I thought they sounded pretty good but not enough to want to keep them in my wah's. Maybe I have a crappy set. Who knows. I been digging the 2n3904's. I think there just as good as the 2n5172's.

[Paul Marossy]

I see we have some big fans of th bc109's. Again I thought they sounded pretty good but not enough to want to keep them in my wah's. Maybe I have a crappy set. Who knows. I been digging the 2n3904's. I think there just as good as the 2n5172's.

Yeah, I have heard some people say good things about the 2N3904s. They would be roughly equivalent Hfe-wise to what was used in the Maestro Boomerang, and probably the original CryBaby as well.

[Ronan]

I am curious about the 2N5172's, I never heard of them until recently when I found some in a Chinese Fulltone Ultimate Octave copy. Have they been used in other pedals?

[paulyy]

I am curious about the 2N5172's, I never heard of them until recently when I found some in a Chinese Fulltone Ultimate Octave copy. Have they been used in other pedals?

I ran across some article online some where about someone trying to match the sound of a really old vox wahs. He had a set of fairchilds and a set of central semiconductor 2n5172's. He went with the central transistor because they sounded fatter to him. The pinouts on these transistors are different from the standard npn transistors in case you want to try for your self. I forgot what it is. I'd have to look.

[Gus]

Standard two transistor wha like in the wha patent

Measure the collector and emitter voltage of the first transistor in the wha setup you like.  Record the bias resistor value for the first transistor.  Now different transistors will bias a little different with the "patent" wha circuit and this can be one of your issues with tone

The output emitter follower(EF) is biased with a resistor from Q1 collector to Q2 base.
The hfe of Q2 will effect the voltage drop across the resistor.
 
So what to do?

First select a gain you want for Q1 gains stage.  Next adjust the bias for the collector voltage you want with the transistor you want to use.  Easy place to do this without effecting much is the resistor in parallel with the electrolytic "under" the inductor.  The resistor is bypassed with a cap so you can shift the DC voltage of the collector and not do much with the AC part(there is a SMALL effect depending on cap value)

IMO Q2 does not make much of a difference if the hfe is high enough and the Q1 and Q2 bias are adjusted.

look for patent number 3530224

[zombiwoof]

I see we have some big fans of th bc109's. Again I thought they sounded pretty good but not enough to want to keep them in my wah's. Maybe I have a crappy set. Who knows. I been digging the 2n3904's. I think there just as good as the 2n5172's.

Are you talking about a standard Dunlop Crybaby with a buffer circuit here?.  I noticed you said the stock trannies were MPSA13, but actually the MPSA13 in those Dunlops is part of the input buffer circuit.  The two transistors that really matter are the MPSA18's.  If you changed out the MPSA13 as well, that might be part of your problem (noise) as you in that case are changing the buffer circuit.  Maybe you really meant MPSA18, but it just occurred to me that you might have changed out that buffer transistor too.

There are a couple of other changed components in the Dunlop wahs from the original vintage circuit, that were probably made to make up for the higher gain of the MPSA18's.  To get the vintage sound (if that's what you're after), you need to change those components (I think it's just a couple of resistors) to the original values and keep the gain of the two main transistors in the 350-400 hfe range.  Of course, if you have trimpots installed to adjust certain values, you can get away with different gains of the transistors with adjustments.  If you've already done other mods to the circuit, that can also be part of the problem.  What I did was compare the circuit of my V847 to the original Clyde McCoy schematic, changed out the components that differed in the V847 to the vintage values, and put in two BC109B's in the recommended gain range.   I also did the true bypass mod.  I am probably going to also change out the inductor when I get around to it, but those changes really got mine sounding more like a vintage Vox.  Again, I used the information on Fuzz Central about the Clyde McCoy wah, it was very helpful in dialing in the sound.

http://fuzzcentral.ssguitar.com/mccoy.php

Al

[Johan]

as much as I hate when people say this or that part is better than anything else ( a well designed circuit should accept substitutions without hickups), I've personaly had good results with BC550C in othervise stock GCB95 circuits..the tone seemed "stronger"

skip to 2:58 for some wha action..(rehearsal recording from when that song was writen..appologies about the soundquality and light)
J

[paulyy]

I see we have some big fans of th bc109's. Again I thought they sounded pretty good but not enough to want to keep them in my wah's. Maybe I have a crappy set. Who knows. I been digging the 2n3904's. I think there just as good as the 2n5172's.

Are you talking about a standard Dunlop Crybaby with a buffer circuit here?.  I noticed you said the stock trannies were MPSA13, but actually the MPSA13 in those Dunlops is part of the input buffer circuit.  The two transistors that really matter are the MPSA18's.  If you changed out the MPSA13 as well, that might be part of your problem (noise) as you in that case are changing the buffer circuit.  Maybe you really meant MPSA18, but it just occurred to me that you might have changed out that buffer transistor too.

There are a couple of other changed components in the Dunlop wahs from the original vintage circuit, that were probably made to make up for the higher gain of the MPSA18's.  To get the vintage sound (if that's what you're after), you need to change those components (I think it's just a couple of resistors) to the original values and keep the gain of the two main transistors in the 350-400 hfe range.  Of course, if you have trimpots installed to adjust certain values, you can get away with different gains of the transistors with adjustments.  If you've already done other mods to the circuit, that can also be part of the problem.  What I did was compare the circuit of my V847 to the original Clyde McCoy schematic, changed out the components that differed in the V847 to the vintage values, and put in two BC109B's in the recommended gain range.   I also did the true bypass mod.  I am probably going to also change out the inductor when I get around to it, but those changes really got mine sounding more like a vintage Vox.  Again, I used the information on Fuzz Central about the Clyde McCoy wah, it was very helpful in dialing in the sound.

http://fuzzcentral.ssguitar.com/mccoy.php

Al

Sorry. I meant the mpsa18's. I yanked the buffer out when I did true bypass. Whoops