Ge transistos in a muff

[RobA]

I've been doing some playing with Ge transistors in a Big Muff like circuit on breadboard. I like it. I just flipped the middle two transistors to PNP configuration and it works well. In the schematic below, I've added some switching in the clipping sections and changed the tone control to be what I used in the Scramjet tone control and then followed by what's essentially a Rat high cut control. The standard Muff TC works perfectly well too, I just wanted to do some playing with this idea.

The diode switching is fairly critical though and needs an on/off/on switch so that you can get a fuzz purely out of the Ge transistors overdriving. I've been playing with some AC125 transistors in the approximately 100 hfe range.

Before I start laying this out for a PCB, I was wondering if anyone had suggestions for improvement or had seen something similar that I should check out first.

Schematic: http://rock.it-frog.com/Downloads/Graphics/ge_muff.pdf 

[jtn191]

Nice, does it sounds smoother? Did you try it with germanium diodes?

[juansolo]

PNP transistors has been done in muffs in the past, there are even a couple in the spreadsheet: http://juansolo.co.uk/stompage/Muffsv2.htm

[RobA]

Nice, does it sounds smoother? Did you try it with germanium diodes?

Hmm, don't know if I'd describe it as smoother. With the diodes switched in, the diode selection still dominates the overall sound. There is a difference though. It's got a somewhat fluffier edge if that makes any sense. It's also darker, but I countered that a bit by changing the feedback capacitor value. (I also changed these so the high cut would have more to work with.) With the clipping diodes completely switched out, the Ge transistors give you pretty much what you'd guess you are going to get by using Ge transistors.

I did try Ge diodes. I didn't really like what they did. I was trying to get the output levels of the two stages to be closer to what they would be with the diodes switched out. (They are still very different, but at least they are within controllable range.) That means that you either need to combine the Ge diodes with Si or use a pretty long chain (4) of them. I liked the 1n4148 and red LED's better anyway so I went with them as it would take a lot less space on the PCB.

PNP transistors has been done in muffs in the past, there are even a couple in the spreadsheet: http://juansolo.co.uk/stompage/Muffsv2.htm

Interesting. I tested with BC560's in the PNP positions after I converted them from BC550's so I could get an idea if the circuit were working OK before I went to the Ge transistors. I couldn't tell any difference with just the change to PNP.

[GrindCustoms]

PNP transistors has been done in muffs in the past, there are even a couple in the spreadsheet: http://juansolo.co.uk/stompage/Muffsv2.htm

Interesting. I tested with BC560's in the PNP positions after I converted them from BC550's so I could get an idea if the circuit were working OK before I went to the Ge transistors. I couldn't tell any difference with just the change to PNP.

In that case, i think it's normal that you could'nt hear any difference as the compound of the semi-conductor remains the same aswell as the hFe range.

Well setup Ge's in Q1 through Q4 yields stunning grunty/raunchy results

[RobA]

[...]
In that case, i think it's normal that you could'nt hear any difference as the compound of the semi-conductor remains the same aswell as the hFe range.

Yeah, that's what I was hoping for with the BC550 to BC560 move. That way, all of the change in sound would be down to the Ge transistors. I was surprised to learn that PNP Si transistors had been used in commercial variants and I'm wondering why they made the move. Was it just because of availability and cost?

Well setup Ge's in Q1 through Q4 yields stunning grunty/raunchy results

I kinda wanted to keep Q1 and Q4 as Si. That's because I was focused on the distortion from what's usually the clipping sources. But, I could flip those to PNP too and test with both the BC560's and the AC125's in there easily enough.

You've got me intrigued now, so what's involved in well setup? Bias points, Hfe selection?

Thanks,
Rob

[raulduke]

The earthquaker hoof uses ge transistors and it's a great muff variant.

[RobA]

The earthquaker hoof uses ge transistors and it's a great muff variant.

Excellent! I'll check that one out. Thanks!

[GrindCustoms]

[...]
In that case, i think it's normal that you could'nt hear any difference as the compound of the semi-conductor remains the same aswell as the hFe range.

Yeah, that's what I was hoping for with the BC550 to BC560 move. That way, all of the change in sound would be down to the Ge transistors. I was surprised to learn that PNP Si transistors had been used in commercial variants and I'm wondering why they made the move. Was it just because of availability and cost?

Well setup Ge's in Q1 through Q4 yields stunning grunty/raunchy results

I kinda wanted to keep Q1 and Q4 as Si. That's because I was focused on the distortion from what's usually the clipping sources. But, I could flip those to PNP too and test with both the BC560's and the AC125's in there easily enough.

You've got me intrigued now, so what's involved in well setup? Bias points, Hfe selection?

Thanks,
Rob

It's forumate Dcountry13 on BYOC that had made me understand that whole thing correctly when that idea passed through my mind. It's all about preserviing the gain factors between the stages.

This article/page will explain way better than anything i could write about the matter.

http://sovtek.webs.com/bmpgainfactor.htm

[RobA]

I've done a bit more playing with this on the breadboard. I converted the Q1 and Q4 stages over to PNP as well so that I could test out using the Ge transistors in those locations. I actually preferred Si transistors in these two spots. And since I've got plenty of BC550C's and only a few BC560C's, I think I'll leave those as NPN on the layout.

I tried using a chain of two 1n4148 and one D9b in the clipping sections again. After a direct comparison to only the two 1n4148's, I think it's interesting enough that I'll make space on the PCB to make it possible to use that configuration of clipping diodes.

I found the Earthquaker Hoof on Tagboardeffects and traced that to get the part values for it. I think it will be possible to build that circuit on this PCB with a couple of off board mods for the tone control section and a couple of jumpers. The only real difference would be that this layout uses PNP Ge transistors.

Thanks for the input on this. I'll probably give it another day or so and then the PCB and send it off to OSH Park.

[raulduke]

The Hoof schematic (along with a shed load of other muffs) can be found on the Kitrae Big Muff website.

[thesameage]

Can you just "add" the ge trannies to a muff in the hoof locations? Or do you need to compensate elsewhere?

[RobA]

The Hoof schematic (along with a shed load of other muffs) can be found on the Kitrae Big Muff website.

My search skills are lacking. I can't find the schematic on their site. I couldn't even find it using Google restricted to their site, but that's not too surprising anymore.

It's not that important though because I'm pretty sure I've got the trace through the tagboard version right.

Can you just "add" the ge trannies to a muff in the hoof locations? Or do you need to compensate elsewhere?

If you've got some NPN Ge transistors, you can just drop them straight in the Big Muff circuit. The Hoof does use particular values for passives in their Muff version, but nothing outside the bounds of other Muff variants.

If you need to use PNP Ge transistors, then you just need to invert the power and ground to the Q2 and Q3 transistors' resistor networks. It would be difficult on an existing PCB, but it's trivial on a breadboard.

[selfdestroyer]

The Hoof schematic (along with a shed load of other muffs) can be found on the Kitrae Big Muff website.

My search skills are lacking. I can't find the schematic on their site. I couldn't even find it using Google restricted to their site, but that's not too surprising anymore.

It's not that important though because I'm pretty sure I've got the trace through the tagboard version right.

Can you just "add" the ge trannies to a muff in the hoof locations? Or do you need to compensate elsewhere?

If you've got some NPN Ge transistors, you can just drop them straight in the Big Muff circuit. The Hoof does use particular values for passives in their Muff version, but nothing outside the bounds of other Muff variants.

If you need to use PNP Ge transistors, then you just need to invert the power and ground to the Q2 and Q3 transistors' resistor networks. It would be difficult on an existing PCB, but it's trivial on a breadboard.

Hoof schematic in question:
http://www.bigmuffpage.com/Big_Muff_Pi_versions_schematics_part4.html

Cody

[RobA]

[...]
Hoof schematic in question:
http://www.bigmuffpage.com/Big_Muff_Pi_versions_schematics_part4.html

Cody

Thanks! It does verify that I got the parts right. This sounds nice with the AC125's in it. I tried a couple of AC187's in the Q2 and Q3 positions of a different muff I built a while ago and, although it did sound good, it wasn't as good as it is with the AC125's. I attribute that to the nature of the AC187's, but I don't have any other NPN Ge transistors to test with. Is there anything special about 2n1308's?