When is it critical/advantageous/trivial to match transistors/components?

[notnews]

Hey all,

I'm building a phaser. I ordered a set of 4 matched 2N5457s, installed them and they sound great. Just for the sake of learning and experimentation I removed one of those transistors and replaced it with a random 2N5457 from my drawer... I noticed a change in sound, the phaser wasn't as washy and clean (for lack of better adjectives), it just didn't seem like the phasing effect was being achieved as fully and nicely.

So this raises a question that I can't seem to find an answer to on the internet... at least in the form I'm phrasing it..

When is it important to match transistors in an audio circuit?

I've read that phasers benefit from matched transistors, but it's almost more of a mandatory criteria than a beneficial one, like I described above. I've also read that heavy gain circuits like a Fuzz Face benefit from matched transistors... like I said, benefit, like the circuit is more controllable and the distortion is more pleasing if the transistors are matched. Does anyone have experience with this?

So on to the general question.. in what circuit applications do matched transistors play a role in the sound of the circuit? Do all circuits prefer to see matched transistors? In what circuits is it totally trivial to match transistors?

Any reading on the applications of matched transistors vs. unmatched transistors, and how to know when a circuit can benefit from matching transistors, would be great if you could post a link.

Thanks all

[rocket88]

hey man. i may be able to shed some light on some of your questions. first, keep in mind that it's hard to make widespread generalizations, since different circuits behave differently due to overall design.

with phasers, like the mxr phase 90, you're using FETs as opposed to BJTs like you'd find in a fuzzface for example. this doesn't have the whole answer, but i think it can help with your understanding, and i'm nowhere near as knowledgeable as RG so i won't try to paraphrase him. the one thing is that in phasers the FETs are being used as a variable resistor if i'm not mistaken. frank is the FET master in the community as far as i'm concerned and has a lot more experience with them then i, so hopefully he'll chime in about them.

as far as matching BJTs it definitely depends on the effect. when you say and i say matched transistors i'm referring to them having similar gains. in some effects like the superfuzz 2 of the transistors need to be matched in order to get the octave up effect, i forget which ones ATM. in pedals like the fuzzface i don't think it makes it better, just gives a different flavor of fuzz so to speak. here's a demo with different transistors in a fuzzface and different gains, but as he mentions since they're different transistors it's hard to really nail a generalization, but may give a bit of an idea.



in some fuzzes like the big muff i find that matching my transistors help give a bit of a smoothness to the fuzz that you don't get when you through in random ones. that being said, a big muff sounds great with unmatched transistors. the big muff is also highly effected by transistor hfe, lower gain = bassier tone, higher gain = more treble in tone.

as always, and i'm sure i'm not the only one that would say it, but i think it's best to do what you did with the phaser build and try swapping transistors for matched and unmatched and give it a listen. if it sounds good and you dig it, go for it, if not then do the other.

i don't know of any good reading, but i will definitely keep my eye out and post anything good i find for ya.

[notnews]

right on, thanks for the post man. Much appreciated.

I'm somewhat new to DIY.. I don't have a massive parts inventory just yet.. so when it comes to transistors, it's not necessarily easy to find a matched pair with what I have. For the phaser I specifically bought a matched quad online.. I have a small handful of random 2N5457s, but no pair of those are close enough to be considered "matched", at least when you hold the values of the matched quad I bought as a standard for what is matched and what isn't.

I should probably measure all the transistors I have and log their values, so in the future I know whether or not I have any pairs or quads or if I need to go out of my way to purchase a matched set.

Are there any other effects anyone has noticed that matching transistors plays a substantial role in the sound?

[Travis]

One thing I want to point out is that people often use the term "matched" transistors when referring to the transistor sets for fuzz faces or tone benders, etc.

Usually when they say this, they don't mean that the transistors are actually matched for hfe/leakage, but rather that the transistors have been measured and selected according to some predetermined range of specs.

With the fuzz face, people usually select Q1 to be ~70 hfe and Q2 around ~120 hfe. So in this case the hfe is obviously technically not matched but transistor selection is critical to the overall sound (not saying it's critical that the hfe be 70 and 120, just saying transistor selection is important for the FF)

The phase 90 is a specific case where it's important to actually MATCH the transistors (in this case JFETs). In the phase 90 the JFETs are used as variable resistors controlling the filtering and it is important that they are matched so that they sweep in unison resulting in the strongest phasing. If they are unmatched, just imagine that each transistor has a different sweep, and some of the effect is lost because they aren't all working together



To answer your question a little more.. If the transistor is set up where it's amplifying to the point of clipping, and that clipping is responsible for the TOANZ that you want to hear, you're most likely going to want to put some thought into your transistor selection. This goes for JFET overdrives as well

If you're getting the clipping from diodes like in the big muff, the transistor specs become slightly less critical

Then if you're using a transistor for buffering or switching, the specs may be even less critical



Overall this is something that varies on a case by case basis. A good circuit design should be flexible on what parts you can use, but clearly this isn't always the case.

Personally I can't think of anything that I've built in a long time where I didn't focus some degree of attention on semiconductor selection. It's pretty much always worth playing with, and I like to try and get the most out of every build

[Synsound]

Good thread! I have had this question floating around in the back of my head for a while and never addressed it.