MobyOctopad
Active member
Maybe look into something like the 2N3705s, gain between 50-150 hfe according to this Mouser datasheet
Low Gain Silicon Transistors
- Thread starter Ginsly
- Start date
MobyOctopad
Active member
I picked up a small batch of these from one of the forum's esteemed Ukrainian eBay sellers but stashed them because I thought they'd be difficult to use on a PCB. Was it too much of an issue dealing with their leads?
finebyfine
Well-known member
I checked and it is the yellow КТ315И (sometimes has the suffix “D” in latin). Mine measure from 50-80. The J suffix (orange) measure around 140.
Also in my bins are KSP06TAs from Tayda that measure around 95. Most others I have on hand have been mentioned
I’ve had the best luck with them by using rectangular female header pins and socketing them. I’ve tried to slim the leads down enough to fit in round sip sockets with flush cutters but it didn’t work and wasn’t easy to boot. Might work to just slam them with pliers too now that I think of it.
Chuck D. Bones
Circuit Wizard
Look for high-voltage transistors. They tend to have lower HFE. I picked up some 2N6517's at Electronic Goldmine. Mouser has 'em for about the same price.
finebyfine
Well-known member
Here's some more part numbers that are binned by Hfe, ranges pulled from datasheets. last letter here is the bin
- 2SC1815-O 70-140
- S9013-D 64-91
- S8050-B 64-91
- 2SA1020-O 70-140
- 2SC1384-Q 85-170
- KTC3202-O 70-140
- A44-A 80-100
- A42-A 80-100
- 2SC945R 80-100
- 2SC1815-O 70-140
- S9013-D 64-91
- S8050-B 64-91
- 2SA1020-O 70-140
- 2SC1384-Q 85-170
- KTC3202-O 70-140
- A44-A 80-100
- A42-A 80-100
- 2SC945R 80-100
Chuck D. Bones
Circuit Wizard
The datasheet values indicate the extreme bounds for every part that rolls off of the manufacturing line. Even the "typical" values may not reflect the HFE in a pedal circuit unless the datasheet HFE is measured at the same Ic as the transistor will see in-circuit.
The datasheets can provide some rough guidance on which parts might work well in a given pedal circuit. Ultimately, the builder will need to audition parts.
You can also try the power transistors in TO-39 packages. 2N5154 is a goodie, but apparently everyone selling them on eBay has figured that out.
The datasheets can provide some rough guidance on which parts might work well in a given pedal circuit. Ultimately, the builder will need to audition parts.
You can also try the power transistors in TO-39 packages. 2N5154 is a goodie, but apparently everyone selling them on eBay has figured that out.
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finebyfine
Well-known member
I'd say I'm always surprised at the Hfe ranges that sound good to my ears when I'm socketing transistors, even in circuits that are more dependent on variations. Honestly, it's such a fun thing about pedal building to me.
t1redhands
Active member
I LOVE using low-HFE transistors in a Big Muff. It gets the thick wall of doom sound I'm a sucker for as well as actually usable low gain tones. Try giving it only 5V.
The KT*** silicon transistors make great partners with the plentiful low-gain Soviet germanium PNPs for Sziklai pairs.
CR0SSBL4DE
Member
Take into consideration that the Bipolar transistor hFE (current gain) it's not the actual gain of the amplification stage in the circuit. That will be determined by the topology and the feedback used. Is that feedback the one that makes the huge variations in hFE usable in real world products.
For example, the first stage of a big muff pi is a common emitter and has 2 FB resistors. One is 470K between base and collector, and the other is 100ohm, between emitter and ground.
In that stage, if you place a BJT with hFE=100, the voltage gain of the stage will be about -4.66 (13,37dB). But if you place a BJT with hFE=400, the voltage gain of the stage is now -6 (15,5dB).
So a transistor with 300% more AC current gain, will only result in a 29% AC voltage gain increase on the circuit.
(you can play with values here, if want to check http://guitarscience.net/calcs/cecbemf.htm)
So that's why low gain bipolar transistors are not common. When adding feedback to get consistent results (and also to make it's response a bit more lineal), you actually get a lot less gain in the circuit.
For example, the first stage of a big muff pi is a common emitter and has 2 FB resistors. One is 470K between base and collector, and the other is 100ohm, between emitter and ground.
In that stage, if you place a BJT with hFE=100, the voltage gain of the stage will be about -4.66 (13,37dB). But if you place a BJT with hFE=400, the voltage gain of the stage is now -6 (15,5dB).
So a transistor with 300% more AC current gain, will only result in a 29% AC voltage gain increase on the circuit.
(you can play with values here, if want to check http://guitarscience.net/calcs/cecbemf.htm)
So that's why low gain bipolar transistors are not common. When adding feedback to get consistent results (and also to make it's response a bit more lineal), you actually get a lot less gain in the circuit.
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CR0SSBL4DE
Member
That said, if I were to play with a big muff to modify it's sound, instead of using low gain transistors to modify the gain staging of the circuit, I would modify the resistors values around the transistors to reduce each stage gain, but keeping the DC bias the same.
Chuck D. Bones
Circuit Wizard
Increasing the emitter resistors is a good way to mellow-out a BMP.
Changing HFE or any of the feedback resistors changes the input impedance of a given stage, which affects freq response, linearity and how it loads the previous stage. Bias point affects all of that as well. It gets complicated.
Changing HFE or any of the feedback resistors changes the input impedance of a given stage, which affects freq response, linearity and how it loads the previous stage. Bias point affects all of that as well. It gets complicated.
Very, very glad I posted this - lots of great info, thanks everybody! As a VERY new builder I sometimes feel pretty dumb posting these questions, but once in a while it's nice to see that it's something others have been wondering about.
I can't afford much at the moment, but I'll eventually have to check out some of the places I'm less familiar with for these low-gainers...
So Electronics Goldmine is generally worthwhile? They been mentioned a couple times here. Do people still go through Futurlec at all?
Antique Electronic Supply seems to be in the same realm as Small Bear and Stomp Box Parts, but mostly for tested/curated transistors. I'm sure it's worth it, but I kind of need to find some low-gain Si's on the cheap. Lots of leads in this thread, but I'll have to see about sourcing...
I can't afford much at the moment, but I'll eventually have to check out some of the places I'm less familiar with for these low-gainers...
So Electronics Goldmine is generally worthwhile? They been mentioned a couple times here. Do people still go through Futurlec at all?
Antique Electronic Supply seems to be in the same realm as Small Bear and Stomp Box Parts, but mostly for tested/curated transistors. I'm sure it's worth it, but I kind of need to find some low-gain Si's on the cheap. Lots of leads in this thread, but I'll have to see about sourcing...
jessenator
Well-known member
I've got to retract one recommendation here:In my BJTaddictioncollecting 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:
Occasionally I'll get lucky with NOS 2N3903s, but the ones I have still hover over 100.
part num type mat min mostly max MPS6548 NPN Si 30 50 60 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
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.
The MPS6548 is a VHF/UHF specialty application type and has a weird pinout of B E C—yes, the emitter pin is in the middle. So, don't buy it unless you want to bend pins for funsies.
Thanks for the heads up! Ha, I also checked out the KT315 @finebyfine and @MobyOctopad mentioned... yeesh! Thing looks like a thumb piano!
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Chuck D. Bones
Circuit Wizard
EG has 2N3903s on sale. Get 'em before the sale expires or they run out.
Antique Electronic Supply is very pricey IMO. Same goes for SB. Gotta shop around. There are deals to be found on eBay, but the usual caveats apply.
Antique Electronic Supply is very pricey IMO. Same goes for SB. Gotta shop around. There are deals to be found on eBay, but the usual caveats apply.
Right on! Yeah... I was thinking about AES because they have a couple pots that Tayda was recently out of, and a couple other specialty items. The basic transistors didn't seem too pricey, other than NOS stuff... I'll take another look around, though - thanks for the advice. Gonna be a minute till I can make any moves anyways.
I picked up some 2N3903s from EG (thanks @Chuck D. Bones !) and some MPS6548s - I don’t mind a little twisting…
The KT315 is intriguing. Is it possible to twist them to fit TO-92 shape?
The KT315 is intriguing. Is it possible to twist them to fit TO-92 shape?
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Guilherme Collateral
Well-known member
2N2369 is a pretty low gain silicon transistor, and so is 2SC828
