first Germanium experience, I am confused

deltafred · Post by **deltafred** » 09 May 2011, 19:01

I know it is nice to build the old circuits that have lots of mojo, but there were good reasons for developing silicon transistors. If germanium had been the ideal material they would still be in production today.

The trouble with having transistors self bias due to leakage is that they will be very temperature dependant. The higher the temperature the more the leakage so the collector current rises and alters where on the curve the operating point is, changing the sound. Fine if you are messing about at home but not so good if you need it to play gigs with where at one you could be cooking under spotlights and the next freezing your nuts off in the open air. (Give me the spotlights everytime. it's no fun trying to play when you are cold)

It's a long time since I used germanium transistors, I built a fuzz pedal back in the 60s and it sounded as though it ran on steam, it hissed so much (leakage). I then built a 60 watt power amp, all germanium, and it lasted about 20 seconds before the output transistors fried due to thermal runaway (lack of temperature stability (and poor design)). After that I went over to silicon as they were becoming more available and have had no more problems like these.

But don't let me put you off

allesz · Post by **allesz** » 10 May 2011, 07:58

I think you got it exactly: this is something only interesting from a DIY point of view, it will be impossible to pack it in a fancy case and sell it for a lot of money; but it makes a nice present for friends by the way

.

Personally I put one (with a 10k pot on the collector and a 1k pot on the emitter) in an old box... and I plan to build another with the last schemo (just because I am addicted

) and put it in 1590a enclosure (with led and only 9v battery alim.).
The use will be probably restricted to rehearsals, home and studio (every two or three years I get to a recording studio). Gigs are so limited (4 or five in a year) it won't be a problem really. By the way I think I landed to stompbox building just by frustration of not playing live enough.

The funny thing (and the evidence of being a complete geek) is to put a socket for the transistor so you can change it just like you do for tubes (another nerdie sport that robs a lot of my time). Hey it is funny...

try this...

it is sooo strong

(the black eye emoticon looks quite stoned to me).

deltafred · Post by **deltafred** » 10 May 2011, 08:58

allesz

Glad to hear you are having some success, and enjoying it, that is what it is all about.

I have spent quite a bit of time recently looking in my garage for my original germanium fuzz box, I am interested to hear it again after all these years (and put the circuit on FSB). I have found of lot of things that I have not seen for some time, but not the fuzz box. I maybe stripped it for parts, but somehow doubt it as I cannot find the transistors, they would be in the drawer marked Ge. It maybe isn't in my garage at all.

allesz · Post by **allesz** » 09 Jun 2011, 15:32

Ok, I just finished the thing: I went with just two caps (1uF) a resistor (100 Ohm) and a 100K linear pot. In the pictures you will see a cap that was connected between emitter and ground, after some test I removed it because the sound got too boomy and fuzzed.
This pedal make me rethink (in a good way) the concept of overdrive. As you c an see I am using an ac181 right now. Transistor with less gain (I tried some, but really liked an ac184) just work as "buffers" with the pot maxed giving unity gain (but the sounds gets really good).

allesz · Post by **allesz** » 05 Jul 2011, 10:27

Hallo.
Sunday an old friend, and ex band mate that now has a solo project, came to my house to try my germanium boosters.
I was really happy, it is the first time that someone takes it seriously. He has a gig next sunday and he wanted to try new sounds. In the end he choose the one with the two knobs (it gives a greater range of sounds) and we selected a couple of different transistor. He is in search of dirty and rootsy sounds and he found some, he seemed very interested and amused of what came out of the box .
He had a little hard time understanding that the pedal actually has not a proper volume control... I just hope that temperature will not play dirty tricks to his sound, and that the gig will be good for him.

RnFR · Post by **RnFR** » 05 Jul 2011, 10:55

you should seriously try at least putting a 470K - 1M resistor from base to collector. this is probably the best way to bias using only one more part. I think you'll be happy with the results, and it will be more stable.

if you go to my blog, and search for electronics calculators, there is one specifically for rangemaster style circuits linked there. that may help you find values if you want to take this further. the math is actually very simple, just a few multiplication and division problems, but the calc is handy.

allesz · Post by **allesz** » 05 Jul 2011, 11:40

Hey, thank you for the input.
Actually I plan to try a circuit like the one above: in order to have a volume control wile preserving the "boost factory" effect. The pedal my friend got has the pot on the collector wired just like a variable resistor.... time to take out my breadboard once again.
I will try the biasing resistor you suggested, on previous experiments I heard no effect at all, so I left it out; but I reckon that stability may be an important achievement.
By the way I suspect that adding this resistor I won't be able to flip the trannie upside down like I do now. Maybe I am wrong, sadly I am at work (lunch time) and I have no breadboard here, because it would be easyer to find it out by myself.
As usual I don't find the thank button, have this

instead.

allesz · Post by **allesz** » 05 Jul 2011, 11:42

I forgot the attachment

The calculators links are very interesting... I will investigate.

allesz · Post by **allesz** » 05 Jul 2011, 11:47

hey I think I can take out one resistor (just to compesate for the added biasing one)