Low Gain Silicon Transistors

[Ginsly]

It seems like most of the "standard" silicon transistors I have fall in the medium-to-higher gain range. That's mostly good so far, and they work well in the pedals I've used them in.

I'm noticing some schematics that call for a really low silicon transistor, like 60 hfe range.

Are there any specific silicons that generally fall into the lowest gain range?

 

[Zanshin]

I’m interested too. I went through my little trove the other day looking for transistors for a Super Fuzz and found I really didn’t have anything under a 100.

 

[PedalBuilder]

I got some 2N4123 from Tayda, which measured between 80 and 85 on my DCA 55.

 

[Coda]

Seems higher gain NPN is most common. I bought about a hundred 2n5088’s a while ago, and they all measure at the higher end of the scale. Same with BC109C…

 

[Ginsly]

I got some 2N4123 from Tayda, which measured between 80 and 85 on my DCA 55.

Yep, those look pretty good @PedalBuilder . Rats, it'll be a while till I order from Tayda again... Should have asked this earlier! Doh

 

[benny_profane]

2N2221 and 2N3903 are good candidates. You may get devices that measure a bit higher than 60 though.

 

[jessenator]

In my BJT addiction collecting almost specifically for the Super-Fuzz, these are ones that measure around 100 and below on my T7 and have been used in my Super-Fuzz builds:

part num	type	mat	min	mostly	max
A5T2243	NPN	Si	30	50	70
2N2369A	NPN	Si	30	90	90
MPS3394	NPN	Si	60	70	90
MPS4274	NPN	Si	70		90
MPS6512	NPN	Si	30	50-80	90
2N2369A	NPN	Si	60	90	100
MPS5131	NPN	Si	20		100

Occasionally I'll get lucky with NOS 2N3903s, but the ones I have still hover over 100.

If you want some unsolicited combinations I've tried and a one-word comment

Q1—Q3 should have the highest current gain (anywhere from 140-200 is approximately OE); some builds suggest these be in descending order of gain.
Q4 & Q5 are sort of the """secret""" to this pedal's tone, and are typically matched as closely as possible (anywhere from 60-140). However, the bias trimmer is meant for you to tune them to get the desired effect (more on that later).
Q6 should be as low as possible, around 50 being typical for original units. Some older silicon can get down this low (e.g. MPS3394, 5AT2243) but you can piggyback if necessary/desired.

Your project schematic might be drawn differently, so your mileage may vary.

 

[Ginsly]

In my BJT addiction collecting almost specifically for the Super-Fuzz, these are ones that measure around 100 and below on my T7 and have been used in my Super-Fuzz builds:

"NO. This is dumb ->" is the best thing I've seen today... Hey, if ya don't write it down ya don't remember! Ha... Great info all around.

Where do you get most of your low-power cheapo Si's from? Tayda?

 

[jessenator]

Where do you get most of your low-power cheapo Si's from? Tayda?

I got mine by trolling through places like Circuit Specialists —mostly their closeout items. I just kinda went through all of their NPNs and looked up their datasheets if I didn't recognize it. Some I scored on, others …well I'll find something for them eventually.

I think I bought out most of what they had which were lowest-gain on that list.

But who knows, they might still have some. Occasionally I'd buy what stock number was listed and then a couple days after my order was complete it would go from "sold out" to "21 in stock" or some random number. Probably poked around and found more. *shrug*

PM me (I can't PM you )

 

[Ginsly]

PM me (I can't PM you )

Ha, my apologies! I didn't realize that was the case... fixed!

Huh, I've never heard of Circuit Specialists, but that's not surprising as I'm really, really new to all of this.

I'd think that finding cheap, low-power silicons wouldn't be that hard..?

 

[kristopher]

I love those one word comments.
Anemic Tiger. Hahaha.
They sound like punk band names.

 

[jessenator]

Another solution, if quite clunky space-wise, is to piggyback transistors to get lower gain. I haven't messed with it much, so more experienced folks can chime in. I'm not sure if it's a perfect 50% of the original gain, but it definitely gets you lower. It's meant to "emulate" a germanium transistor for NPN fuzz faces, IIRC.

Again, experienced ones, correct me here…



I made a micro pcb for this, but never had it fabbed.

 

[giovanni]

I have some old BJTs I found at work (some in metal cans package). I’ll test them and if they are low enough I’m happy to mail them to CONUS. I’m not planning to build any fuzzes that requires low gain BJTs.

 

[szukalski]

If you can find them, 2N2218A are 80-90 and do really well in Fuzz Faces and other applications (to my ears).

 

[Ginsly]

If you can find them, 2N2218A are 80-90 and do really well in Fuzz Faces and other applications (to my ears).

Holy cow, those are ten bucks a pop at Mouser!! I wonder why...? Under a buck at "electrical.com", which I've never heard of... hmm

 

[Bucksears]

Great timing - I got the itch to try some lower (than typical) gain transistors for my Big Muff builds.
My main one is a GGG-tuned BMP (VRH variant), which was running 2N5089s. Just a ridiculous 'thick wall of lightning' fuzz.

I binge-bought some BC109Bs (Smallbear) and BC550Bs (Tayda); the former measured between 200 and 350-ish, while the latter were almost ALL 400-450. I tried the 200 hfe in my BMP and I'm hooked. It can still get that big fuzz sound with the sustain maxed, but everything lower is more articulate.
I have some BC549As and BC550As en route, and will be sorting those out ASAP.

 

[VanWhy]

I second the 2N3903. They are generally lower hfe and cheap. I just got a bunch from electronic goldmine measuring around 60-80 hfe

 

[szukalski]

Holy cow, those are ten bucks a pop at Mouser!! I wonder why...? Under a buck at "electrical.com", which I've never heard of... hmm

Find yourself an old school electronics outlet, they'll have some for cheaper. I think I got mine at €0.50 each. There are others which also work just as well..

 

[finebyfine]

I forget which suffix is the lowest gain of the Soviet KT315 (I believe КТ315И, but I'll double check when I'm home) but it's an awesome and cheap low hfe transistor. Weird pins but easy enough to finagle. I have a big ol' section of my drawer bins for low Hfe SI and I'll check to see if any I have haven't already been mentioned here.

 

[derevaun]

Small Bear has some silicon "dot" transistors sorted by gain. I got some of the low-gain ones for Sziklai pairs and they tested in the advertised range on the TC-1. Searching for "silicon dots" should turn them up.