Do the transistors for my wah project need to be matched/tested/etc.?

[skiraly017]

Do I need to test and match them or can I just put them on the board and go? Thanks.

[lacto]

Well, they don't HAVE to be tested, but transistors in the 300hfe to low 400hfe sound best in a wah. Some people like both tranny's pretty closely matched and some like the Q1 to be higher than Q2. If you have a good ear you will hear differences in higher and lower hfe's in a wah circuit and a mismatch versus closely matched transistors.

[Paul Marossy]

I've used sockets for transistors on a couple of my wah projects before. Sometimes I just can't seem to decide on what I like best, so that saves the PCB from a certain death from repeated soldering/desoldering...

[R.G.]

Well, they don't HAVE to be tested, but transistors in the 300hfe to low 400hfe sound best in a wah.

How does it sound with transistors under 300?

How does it sound with transistors over 400?

Can you describe "best"?  Is that loudest? Vocal-est? Most resonant? Widest sweep? Most - or least?  - distorted? "Sweetest"? "Punkiest"? What?

If you have a good ear you will hear differences in higher and lower hfe's in a wah circuit and a mismatch versus closely matched transistors.

That's probably true. In the stock wah circuit, everything effects sound somewhat, so changing anything will cause a difference.

But since the first transistor is running with a voltage gain and the second one is running as an emitter follower, I'm not sure what to match. In the case of the first transistor, the gain is pretty much determined by the ratio of it's collector resistor to its emitter resistor. In the case of the second transistor there is NO collector resistor, and the gain is very close to one. Transistor gain has little to do with what the first transistor does as long as it's big enough. Likewise, for the second one, as transistor gain approaches infinity, the voltage gain approaches one. And they run at different collector currents. Bipolar gain is a variable depending on collector current.

I'm not sure what matched gains will do for this circuit. Can you tell me?

What do we match? Hfe? Vbe? At what current? Both currents?

[lacto]

I was just contemplating a response to the thread this evening when we had a three and a half hour power outage on a 103 degree day. Nice huh?

I knew I would be in a bit of trouble with the way I worded some things, but I was trying to give a minimalist response while still answering the question.    R.G. I would never pretend to be able to teach you anything about electronics, you are the resident expert around here, and everywhere really. I was going to put a caveat IMO to the transistor statement about hfe, but it is not  just my opinion about the optimal range for wah tone, I should clarify VINTAGE wah tone. Now, that word is open to all sorts of interpretation, but I'm not going to debate that here.  Several of the well known boutique wah pedal makers, that we are not supposed to mention here, agree that for vintage wah tone a hfe between 300-400 is optimal. The lower end of the range tends to be a little fuller and bassier and the higher end of that range sounds thinner and brighter and more trebly. Below 300 starts to get a little muddy and much above 400 starts to get into the higher gain modern tone, which is not bad if that is what you want. It is just not at all vintage sounding.

These are generalities, because there are differences between different types of transistors too. I am just refering to low gain versus high gain in a wah circuit.  Obviously, everything I have said is a subjective statement without an electronic explanation, but try it and see if you don't agree with regard to the general tonal difference between high and low gain transistors in a wah circuit. Preferences are another thing.

"Best" in terms of a vintage tone is more vocal, not overly bright , quacky with the full spectrum of bass-mid-treble across the sweep, all of which are also affected by all the other components in the circuit too. Remember the original Clydes were supposed to be imitating the sound of a trumpet muted off and on.

As far as matching transistors, I was only referring to hfe. It seems to many, myself included that the Q1 transistor affects the tone of the wah, while the Q2 affects the sweep more. I can't give you a technical explanation for this, maybe you can. It seems like pretty closely matched transistors render a milder, mellower more sedated tone, not unlike in a Fuzz, which is a totally different circuit. And transistors pairs that are mismatched by at least 30 hfe render a wilder, quackier, ever so slightly more distorted tone.

These "opinions", though subjective were arrived at through the reverse engineering of prize vintage wah pedals. Knowing the ultimate tonal outcome, and discovering the component values and materials that render that tone. If "that" tone is not what one covets, then the whole exercise is of no consequence.

I would always defer to you R.G. for a technical explanation of such "opinions". It may be interesting to note that many of my opinions were formed before I "discovered" the conclusions that were reached by those famous wah builders of note.  I trust my ears and the many other famous ears, but this is certainly not the gospel of wah...   

[Pedal love]

I really have to agree with R.G. here. People ask me for matching transistors all the time. Are they between 300-400 hfe? How the hell do I know? I don't check for 300-400 hfe and then match them accordingly.   Tons of them infact on the open market, are well above 500 hfe, I'm told. I never said my transistors had any particular gain at all. I never said they were matched, pulverized, or otherwise and don't see much difference in them, in a relative sense. The men down at Vox in the mid/late sixties, probably didn't see much difference as they tossed transistors in and packaged wah pedals up.(believe me thats how they did it)

On one hand, I hear how great all the early ones are compared to the current issue. Then, of course, some were better than others, right?Unfortunately, I think some of you are looking for wah pedals that only exist in your heads and would get a lot further in your pursuit of tone nirvana, if you looked for what is and isn't possible electronically and then moved on accordingly.

[R.G.]

I should explain.

I apologize if I sounded snotty. There is some possibilty that the gains do have an effect, as *everything* has an effect in that circuit. I just couldn't see how.

And I really was wondering what effects you heard. You do a good job of expressing that.

I can see that a higher gain first transistor would give a higher input impedance and more bass response because the input was less loaded. I will have to think a bit about the sweep effect on the second one.

How were your measuring hfe? Just sticking transistors into a meter?

[waldo041]

i completely removed all the components off of a GCB-95 board and populated to vox clyde mccoy, eliminated the buffer and used a custom wound halo inductor and fulltone pot. i tried the stock transitors mps18  and some 2n5088 and some bc109's from small bear.
I found that the higher gained transistor's that i tested with a meter for Hfe were more susceptible to picking up radio frequency and airy(?) in the circuit.. i settled for a 2n3904 in q1 with a metered Hfe of 220  and a bc109 from small bear that happened to be around 320Hfe.  this range was perfect for my circuit. i did notice while swapping transistor's that they somehow set the overall frequency range. i could make adjustment's with the pot for the most part but alway's seem to catch radio interference in the toe down position with the higher gain transistors. adjusting the pot took too much away from the toe up position. so lowering the the gain of the tranny's allowed for a useable wah with a clyde circuit values.

hope this help's

peace,
waldo

[lacto]

No apology necessary, you didn't sound at all snotty R.G. With your expertise coupled with an analytical mind, it is a forgone conclusion that you would require explanations for an effect to based in sound electronic principles.

Regarding the vintage wahs from the late 60's, there is this theory that it was pretty much haphazard and they used whatever components that were on the bench at the time (conforming to the established values) and slapped them on the boards. That sure seems to be the case, but it is also interesting to note that if you look at a lot of the old boards, some have after market symbols, dots etc. on the transistors. Is it possible, they measured the transistors and marked which were destined for Q1 and which for Q2?

All I can say is if someone is interested, use sockets and try some transistors in different hfe ranges, matched and not, and see what you think. If you take unmatched transistors and switch the Q1 and Q2, there is a difference. As far as measuring, I have a pretty decent DMM and for non-germanium transistors, I do measure hfe with it.  As an aside, I much prefer unmatched transistors.

I have no doubt that many of the new wah pedals have transistors that are very high gain and inductors that are much higher than 500mH and they sound terrible from one seeking a vintage tone.

There is one truth that must be stated here, which permeates this whole forum. Some people have better hearing than others. Some may have incurred hearing damage, particularly with the higher frequency spectrum, that they are unaware of. Just because one person can't hear differences between varying cap /resistor/transistor values doesn't mean they do not exist. It is just that they are of no consequence to them.

All that matters is we are able to create/modify effects pedals that satisfy us with the help and support from this forum and the exchange of ideas/experiences.  I, for one, am very grateful for all the help I have received from this forum the past several months.

[Dooter]

Well, I know this is an old post but I was considering changing the trannys in my wah and got here via google. I just took out my stock tranny's mpsa18's and was horrifieds to read both their Hfe's at 800 on my dmm! I socketed the board to receive the new tranny's. I had spent a few minutes yesterday harvesting some old BC548B's from an 80's B&O TV. I tested them and selected a pair with Hfe's 320 and 350.

WOW!

I have tried all the usual mods (Vocal, sweep cap, 33k resistor, new fasel inductor, moving rest position on pot etc.) and this by far had the best effect on the tone. Less trebly but less muddy in the Bass too. Much more like affecting the tone of the guitar in it's natural note range. Smoothed out the transition too. I've had my GCB95 for ten years and never been happy with the pedal till now.

Whatever the science behind it - the transistors MASSIVELY affect the peformance characteristics of the pedal. No question.

[lethargytartare]

What you could do to really add to the body of knowledge here is try several, measure hfe values, and log your opinion of the effect.  The gist I got from the earlier discussion was that everything affects the tone, but there's less certainty about consistent predictable results like "hfe in this range, and matched according to these parameters, yields this impact to wah's tone"  If users started posting specs on their trannies and the effect they perceive, patterns might become apparent.

[Mark Hammer]

I forget what I put in my wah, but what ultimately mattered was setting the gain of Q1 properly by sticking in a trimmer for the  emitter resistor to ground and fiddling with it.  That may be just as important as what transistor is used.