More Muff Experimenting: The Hybrid Series

[trad3mark]

Hello all,
I'm working on a series of muffs, which i'm calling the Hybrid series. There will be 4; Alpha, Beta, Gamma and Delta. I'm planning on working through the 4 combinations of Germainum and Silicon, Transistors and diodes. I thought i'd post up my progress and findings for all of you to enjoy.

So first up, my plan is to get a sort of "base" model. I'm using standard transistors and diodes, so i can get things like the tonestack just right, and hopefuly get noise and hum to a minimum. Out of all the muffs, my favourite is the two rams head versions (standard and violet) so for now, i've build the standard one, and i'll compare the changes between the two versions. There's 18 differences, and i'll try out my own little changes too. When i've settled on details, i'll post up the relevant changes.

As far as diodes and transistors go, well i've a pretty big selection. In terms of Silicons, ive loads of the usual suspects; 2n3904, BC547, BC550, 2n2222a. I also have a cupple of odd ones, like C33716W (which have a cool white face!). Diodes, I've even more. again, the usual 1n400X series, 1n4148's etc. But, i've a collection of other odd ones, like the BZT series, which are a funny ball shape, and i've some other massive ones.

Germanium wise, i'm far more limited. The transistors i'll be using are russian ones, which i think are GT404B's (i cant read russian lol!). Its funny cos they're HUGE. The 4 i'll be working with have respective hfe's of 263, 270, 272 and 275. Low enough, but that should be interesting!! My diodes are D18 Germanium Pulse diodes, which are also pretty big, but look awesome.

Before i get cracking on testing combinations, i've to build it on breadboard first, which might take a while (i've to have lunch too ) but i've my new white stripes vinyl playing to keep me occupied.

In the mean time, a little taster perhaps? These are a selection of the transistors and diodes i'll be using, with the germanium stuff at the top, and silicons at the bottom. You can see the odd selection of parts i have! lol!



If anyone has any tips as far as increasing the gain (particularly when i move onto the germs!!) that would be great. i know it'll be the resistors around the transistors, but any suggestions would be awesome. To the kitchen! AWAY!!!

[trad3mark]

already this is proving more difficult than i thought.

I've just breadboarded about half of it, up to the first clipping stage, and im getting no signal through. i'm using an audio probe thing and starting at the start. signal goes into the base of the 1st transistor, but at the collector side, nothing.

any ideas?

[MikeH]

already this is proving more difficult than i thought.

I've just breadboarded about half of it, up to the first clipping stage, and im getting no signal through. i'm using an audio probe thing and starting at the start. signal goes into the base of the 1st transistor, but at the collector side, nothing.

any ideas?

Pinout?

[trad3mark]

checked it. nada. found that the dc jack was dodgy, so i switched to battery. still nothing. gonna head out for food, i'll work on it again later.

[trad3mark]

result! bad transistor. now replaced with 2n5551. so far its looking good. barely noticible hum.

[trad3mark]

Right. just built the Violet rams head version, except wtih 4 x GT404B's and 4 x germanium diodes, and the most perculiar thing is happening.

When i turn up the volume past say 20%, it cuts out completely. like the whole thing is muted...

when it does work, it sounds nice though.

any ideas?

[Derringer]

there's some good info here about what different diodes will sound like
http://rkerkhof.ruhosting.nl/Taas/Mods/Big%20Muff.htm

When I was putting my muff together I tried different combinations of germanium and silicon diodes, and just like the above referenced material indicates, you get some octave-up action going on with germanium diodes .. even when you I mixed germs and si.

I'm not sure why octove-up happens with the germs. How does the lower break-over point of the germs create octave up?


as for your build, if it were me, I'd put everything together first with silicon and get the buggs ironed out, then I'd start swapping in the ge transistors.

and as always, check your wiring ... and keep checking it until you find the problem

[Hupla]

Im sorry I just had to come in and congratulate on the title *claps* well done sir. Best title ever. 

Good luck with the experimenting though.

[trad3mark]

there's some good info here about what different diodes will sound like
http://rkerkhof.ruhosting.nl/Taas/Mods/Big%20Muff.htm

When I was putting my muff together I tried different combinations of germanium and silicon diodes, and just like the above referenced material indicates, you get some octave-up action going on with germanium diodes .. even when you I mixed germs and si.

I'm not sure why octove-up happens with the germs. How does the lower break-over point of the germs create octave up?


as for your build, if it were me, I'd put everything together first with silicon and get the buggs ironed out, then I'd start swapping in the ge transistors.

and as always, check your wiring ... and keep checking it until you find the problem

i had it working perfectly with a fully silicon setup. I was using 2n5551's for Q1 and Q4 and then 2n3904 for Q2 and Q3. then i tried changing the transistors to germs, with silicon diodes, and it worked similar, albeit smoother, particularly when let ring out. it was only when i changed the diodes that it started to cut out.

[Derringer]

I'm taking a wild stab in the dark here, but I'm going to suppose then that the lower voltage required to break-over the  germanium diodes is affecting the bias of the germanium transistors.

Try nestling the pair of germ diodes between a pair of identical coupling caps and see if that changes anything.

so like  collector to cap to diodes to cap to base

[trad3mark]

at the moment they're base to diode pair to cap to collector. Would i get away with just putting one cap in between the base and the diode pair? so it's base > cap > diode pair > cap > collector?

[Derringer]

yeah, that's what I was thinking .. give it a shot

will it work? not sure ..... but it's easy enough to test out


you know what though, I'm thinking now that the issue may lay in the gain recovery section. Try a silicon transistor in Q4 and see if you can get full volume or not. The germ may just not like how it's being biased

[trad3mark]

its not that the volume drops, it completely cuts out.

i tried the coupling cap, and it still cuts out at about 40% on the volume. i suspect its the diodes, cos when i replace them with silicons, it works fine without the coupling cap.

maybe i should try biasing the transistors? not a clue how i'd do that though.

Its annoying cos it sounds sooooo awesome when it works...

edit:
oh wait, its cutting with silicon diodes too. hmmm.... might try to bias the transistors. how would i do that?>

[Derringer]

So the extra coupling caps helped you turn the volume up a bit more than previous?

triple check your wiring around the gain recovery section, it almost sounds like the volume pot is misswired

and if that's not the case, try that si in Q4 and see if that changes anything

[trad3mark]

the wiring all looks good. im working off the rams head version, and there's a couple of differences between it and the other versions, particularly in the 2nd clipping stage and the recovery stage.

in terms of that output stage, would things like the output cap (just before the volume pot) or the resistors between the transistor and the Vcc have anything to do with it? like the output cap on the Rams head is a 10uF electrolyte. on the violet rams head version (and i think all the others) it's an 0.1uF normal cap.

edit:
win win win!!! noob mistake, it's a 1uF output electrolyte, not 10uf. and it's certainly not the 100uF i had on my board! i don't think there's a facepalm big enough for that.

[trad3mark]

question.

if i want a bit more gain out of this, particularly when using the germs, am i correct in saying i just make the value of the resistors between the emitter and the ground bigger? at present they're 150R, so what about a 220R or a 330R?

[joegagan]

smaller resistors from emitter to ground will increase gain.

[trad3mark]

ok cool. only need it with germanium.

cheers! I'll put up pics and relevant changes tomorrow.

[trad3mark]

almost done with this!

My silicon transistors currently are:
Q1 2n3904
Q2 bc558b
Q3 bc558b
Q4 2n3905

And i've only made a couple of little resistor and cap changes. nothing major (like 120R to 100R etc).

I was planning on doing some drilling tomorrow, but, before i do that, i've a little pot problem. My stock of pots is quite low, i've three of the following:
100k, 1M and 470k.

As far as i can see it, i've two options:
Option 1: Use what i have.
Could i use the 1M in place of the Sustain pot, and the 470k in place of the tone pot?

Option 2: change the values of the pots.
So, i know i can use resistors to change the values of the pots. Great. Sounds good for tone and volume, cos there wont be any other resistors in series, and then i could use the 100k for sustain. Is this more hassle than it's worth compared to the above option?