Germanium Transistors, Noise and Leakage

[Beaker]

"Unless I'm still wrong (which I could easily be) the transistor gain can cause noise, not leakage."

No. Sorry Squirrels but you are wrong. Gain does not cause noise, and neither does leakage. Transistors are amplifiers and will do just that - amplify the signal and any noise present- you've heard it before, it's called signal to noise ratio. So the higher the gain, the louder the signal and the louder the noise that may be present. That's why some high gain pedals like Devi Ever's that use ultra high gain Darlington transistors with HFEs of over 1000, are howling screeching monsters.

Fuzz Faces and most vintage fuzzes are noisy, as they are simple primitive circuits from the electronics stone age, with little or no noise filtering. That's why they can be noisy. But it's not the circuit itself that is noisy - it's just picking up noise from other sources and amplifying it.

More modern pedals tend to have more noise prevention and elimination measures built in.

Power supplies, flourescent lights, dodgy wiring in your house, fridges and freezers and a whole host of other culprits are the primary cause of the noise.

In your pedal, a wall wart power supply, dodgy components, voltage inverters and doublers, some ICs, dodgy solder joints and poor cable routing can cause noise.

That's why shielded wiring and careful wire routing in your pedal can do wonders in quitening down some pedals.

Take a look at the one knob fuzz bonanza layouts - they taught me a huge amount about what you can do with a Fuzz Face. Most feature the small pF value caps on the transistors that help tame high end hiss. Build and mess around with component values on some of these, and you get an idea of what makes a difference - both in a bad way as well as in a good way.

[squirrels]

Ok, I now realize that I have a lot of reading and research to do since there are many variables at play. Anything worth doing is worth doing right I guess. Thanks everyone. I hope this wasn't a waste of time for anyone,I appreciate it.

[Travis]

I think what's more important than any reading is just getting a tester, some Ge transistors, and making a bunch of fuzzes! It's more fun that way and you'll get better information.

I can't stress enough that leakage will have a different sonic effect on different circuits, so you're wasting your time looking for one answer there. It is possible to use math to see how leakage will affect bias in a given circuit, but most builders use a transistor tester and their ears

Also consider the fact that when these effects were designed, the engineer already knew about leakage and designed the circuit to sound good with the typical part he/she planned on using. It is foolish to design a circuit that simply sounds like crap with any leakage, because the average transistor at the time would be leaky. So hint hint, leakage is ok. You will naturally get the handle of when there isn't enough, too much, just by trying different transistors in different circuits.

[Travis]

squirrels wrote

I didn't mean switching the caps and connections for noise reasons, I meant as opposed to using an inverter or a battery, like the Oracle and Silicon Fuzz Master. The transistors are random, which is why I wanted to know about testing and all. I just read that reversing the connections could make it noisy. I'll try adding caps to my Oracle and Sunface. Thanks for the tip.

Unless I'm still wrong (which I could easily be) the transistor gain can cause noise, not leakage. So lower gain, lower noise. It's no different than a silicon circuit. I'm going to read up on what RG says about it.

Sorry for the confusion, I didn't think you meant that you were trying to daisy chain this for noise reasons. You are right that you can do the mods you mentioned to daisy chain this. Powering the fuzz face on a wall wart can be pretty problematic, so be watch out to make sure that it isn't deteriorating your sound quality in one way or another. I don't even like to put a cap from the supply to ground because that usually takes a little something away from the sound and doesn't help with noise much either (this is specifically in the fuzz face mind you)

I meant to basically say that any further modification to reduce noise should come after a more thorough transistor selection process. It sounds like the foundation of your endeavor here is a little shaky, and piling more stuff on to try and make it work in my opinion is much less effective than going back to the start and doing your best job possible there.

Once you've settled on some transistors with a sound that you like, then the modifications can begin. At least that is how I see it.

[rocket88]

keep in mind that when it comes to getting Ge transistors unsorted in bulk you're going to get a wide range of gains, and from batch to batch you'll see a lot of differences in gain due to the production lot, which you will definitely see from seller to seller. for instance, i have a rather large stock of MP38As, i'm kinda the reason they keep disappearing from evilbay cause i buy 500-1000 at a time and have completely bought out some sellers stock, but anyways, the last 2 orders i got from 2 different reliable sellers i've dealt with before. one had gains from 40-100hfe with most in the 60hfe range, the other had gains from 60-150hfe with most in the in the 90-110hfe range. it's really the luck of the draw, and luckily i can use every single transistor.

also, keep in mind that if you're going for transistors that a lot of people are after, like the AC128/AC125 i would highly suggest that you get unopened NOS bags, because a lot of the open lots that are sold are majorly picked through and you get a lot of low gains and/or high leakage.

if you're looking to figure out what Ge transistors to get check out the Ge transistor and diode thread. there have been a lot of contributions about perceived tone and distortion, gain and leakage spreads a lot of us have experienced. it's a really great resource if you're looking at diving into Ge builds.

[squirrels]

I forgot about that thread. I definitely will check it out.

[squirrels]

Any advantage using PNP over NPN, not including polarity issues? My local store gave me a 2N1304 to try out and has a few in stock. I was thinking of picking another up and popping them into a Fuzz Face.

[rocket88]

typically, and this has been my experience, good PNP transistors are much cheaper then their NPN counterparts, and i've found that they are more reliable. it's hard to find good NPN Ge transistors, which is one of the reasons you'll notice most of us really use 2 different ones.

the reason being is PNPs were made longer, and were mcuh cheaper to manufacture. when Si transistors came onto the scheme they were cheap to produce the PNP Ge, more temp stable, and reliable. what's an interesting thing to think about is that we owe the cold war to us having such a good stock of reliable Ge transistors. since they cut themselves off from the world they ended up being able to make Ge transistors that reliable, since they were far behind tech wise.

[squirrels]

That's some pretty good info. Makes sense, almost like how Cuba has all those old cars still up and running, have to make due with what you have.

I pulled the transistors from my previous builds to measure with the Germanium Tester I built and unfortunately one leg on both TK3055s broke and the same with two of the 2N404s. I guess they've been twisted so many times they couldn't take it anymore. I did have one 2N404 left as well as few others I was able to get in the last few days. The 2N404 tested at .24 mA with a gain of 125 and the two 2N1304A came out at .14 mA/ 46 hFe and .11 mA/ 48 hFe. I plugged them into my silicon Fuzz Face and they were very underwhelming, more like a weak OD.

Any ideas on what I can do with the 2N1304A? Maybe the Germanium Giant or Red Rooster?

[squirrels]

I was also given a pair on LX126A. I couldn't get a reading on them in any way regardless of pinout. From what I saw, they looked like they are in a TO-1 package.

[Travis]

squirrels wrote

That's some pretty good info. Makes sense, almost like how Cuba has all those old cars still up and running, have to make due with what you have.

I pulled the transistors from my previous builds to measure with the Germanium Tester I built and unfortunately one leg on both TK3055s broke and the same with two of the 2N404s. I guess they've been twisted so many times they couldn't take it anymore. I did have one 2N404 left as well as few others I was able to get in the last few days. The 2N404 tested at .24 mA with a gain of 125 and the two 2N1304A came out at .14 mA/ 46 hFe and .11 mA/ 48 hFe. I plugged them into my silicon Fuzz Face and they were very underwhelming, more like a weak OD.

Any ideas on what I can do with the 2N1304A? Maybe the Germanium Giant or Red Rooster?

How are you handling the transistors for testing? Since germanium transistors are temperature sensitive, it's important not to handle them much during testing. The heat from your fingers will heat up the transistor and cause you to get a reading with higher leakage and hfe.

I usually hold the transistor by the legs rather than by the body because this has less surface area to transfer heat. I only handle the transistor for a couple seconds while hooking it up to my tester.

Not all 2N404 are equal, but your leakage reading is much higher than any of the RCA or Texas Instruments 2N404 that I have (mostly 0 leakage)

That's a bummer about the broken legs. Gotta be gentle with the legs and try not to ever bend them back and forth multiple times

The 2N1304A with 46 hfe is gonna be too weak for most circuits. There are a few circuits where the low hfe stuff is perfect, like for Q2 in a Fuzzrite, or a Darlington pair. Mark suggests using low hfe or very leaky germanium as a buffer or diode if you can't find another use

The LX126 may be a sub for the AC126 which is NPN

[squirrels]

I've been holding them with needle nose pliers for the most part but I have had to use my hands on the body to get them in the socket. I'll try again later. I did some research and found that whole thing interesting, especially that people would refrigerate or freeze Fuzz Faces because they sound better. The 404 is an NTE and the 1304s are TI. I know nothing about the LX126As. The remaining 404 is staying in the Oracle for now with a 2N2907A 179 hFe in Q2, doesn't sound too bad.

[Travis]

Ahh yeah the NTE stuff is usually pretty out of spec in my experience. I'm not a fan.

The TI 2N1304 is a good tranny but you need a lot more than 2 if you're buying them untested.

The NKT275s which were used in the original fuzz face are pretty temp sensitive. When they get warm the leakage goes up and the sound gets weak and farty. They sound amazing but there are other germanium transistors which have better temp stability. The TI 2N404 is one of my preferred alternatives for sound quality and temp stability. The Russian transistors that you ordered will have nice temp stability.

[Beaker]

I don't worry too much about how I handle them, or what with, but I try to just glad the legs.
I will always give  them a minute to cool down before testing though.

And yeah, try to buy in as large quantities as you are comfortable with paying for, unless you are prepared to pay the premium for tested and matched pairs/sets.

[squirrels]

I tested them again, same results. I'm a little disappointed that I can't do much with the 2N1304s but at least I didn't pay for them.

[squirrels]

I got the MP21A's and tested a few. Most seemed around the 50-60 range with one at 92 hFe. A little let down, I was hoping to get at least two decent pairs for my Oracle and a Fuzz Face. Also received two GT404Bs. Looked up the pinout a hooked them up to the tester and they just got very hot. I know they're NPN and the middle leg is the collector. Any ideas or was my info wrong? Thanks.

[Travis]

You don't need to use the RG keen hfe or bias voltages. They aren't actually accurate to vintage Fuzz Faces, it's just his personal preference. 50-90hfe is plenty for a fuzz face

[Beaker]

Travis is right, the Russian transistors measure low by accepted standards for a Fuzz Face, but work great and sound great in most vintage fuzzes.

I've used them in Fuzz Faces, Fuzzrites and a whole bunch of other circuits and they sound fantastic.
A 50-60 HFE Russian will work just as well as 90-110 "usual suspect".

Don't be disappointed and don't panic - try them and see. I'm sure they will work fine.

[Travis]

Beaker wrote

Travis is right, the Russian transistors measure low by accepted standards for a Fuzz Face, but work great and sound great in most vintage fuzzes.

Personally I don't buy the "russian germanium sounds higher hfe than it is" kinda thing. I have a lot of Russian stuff, a lot of British stuff, a lot of American stuff, and some Japanese stuff. I just don't get that result, YMMV.

The Fuzz Face simply does not need the hfe as high as RG Keen suggests regardless of the origin of the transistor. Some types will sound great, others not.

I have a breadboard set up to audition Fuzz Face transistor sets and another one set up to audition MKII transistor sets. I have tried countless trannies in each circuit, and I can't say the Russian stuff is any better or worse than anything else. There are so many types of Russian trannies, so many British ones, so many American ones etc, it's pointless to generalize the whole thing.

My opinion is this. Russian Ge transistors are the cheapest. Not the best, not the worst, the cheapest. For that reason it is easy to get thousands of them and find all the stuff that works great for you. It costs about 10x as much to get the same depth/variety in your American or British transistor stock, so few people spend enough to form a well based opinion.

[squirrels]

I popped a 67 in Q1 with a 96 in Q2 of my Oracle. Not bad but not nearly as aggressive as the untested (and now broken) 2N404 and TK3055s were. Stacks nicely with my Black Forest. Gonna build a Fuzz Face.