Breadboarding Germanium Big Muff Pi

[digi2t]

No, no, the second stage. Releasing the third stage clipping is just too much IMO. The second stage I find is just right. Nice volume boost to cut through, without drawing any "WTF!!!!?" looks.

I might add some small caps, parallel to the clipping diodes, to kill some of the fizziness. Somewhere between 1n, and 2n, I haven't decided yet. Vero is almost done.

[duck_arse]

orright lee, I don't think anyone has arksed yet, so I'll be the first: "what transistor types did you settle on, and what gains and leaks are in what positions?" please.

I haven't muffed yet, so I might make a "cod pie" named after/honouring lee ....

[digi2t]

orright lee, I don't think anyone has arksed yet, so I'll be the first: "what transistor types did you settle on, and what gains and leaks are in what positions?" please.

I haven't muffed yet, so I might make a "cod pie" named after/honouring lee ....

I've measured everything, and written it down. I'll list everything tonight. (At work right now)

[lmorse]

I went for the high-gain Russian transistors - ATES SGS 11113's I believe. I have just started work again, so won't be home until the end of next week. I'll check when I get back, but I went low to high, starting at around hfe320 with the last one being around hfe395.

I'll let you know more when I can check.

[digi2t]

OK, here's the low down...

Transistors are 2SB176, and supply voltage is 8.96v. All gains and leakages are courtesy of the Peak Atlas meter.

Q1 - gain 154, leakage 0.06mA
E = -0.547V
B = -0.684V
C = -4.82V

Q2 - gain 122, leakage 0.06mA
E = -0.547V
B = -0.679V
C = -4.93V

Q3 - gain 159, leakage 0.08mA
E = -0.544V
B = -0.684V
C = -4.53V

Q4 - gain 132, leakage 0.08mA
E = -1.347V
B = -1.465V
C = -5.52V (with a 4.7K emitter resistor)

I'm using 1N695 diodes for the clipping. Vero is almost done. Just picked up some 11113's off eBay, going to try them when they get here.

EDIT;

Here's the vero. It's a modified Muffarray layout, but it's not verified yet. You can play around with Q4E resistor value to tweak the collector voltage.

[mac]

Transistors are 2SB176,

My favourite germs

mac

[duck_arse]

thanks, digit. I've got 324's and 175's around those gains (we won't speak of their leaks). might be a goer ......

apropos of nothing, why are people happy to do standing resistors on their vero layouts, but they seem completely blind to the space savings to be had by rotating them, flat or standing, so they run east-west? and caps that come with 5mm spacing, why not just turn them and let them fall into the board, stead of jambing them nth-sth? rant over.

[digi2t]

duck, probably me being dense, but I'm not catching your drift on the resistors. Could you demonstrate graphically?

As for the caps, the vero pitch is 0.1 inch, so 3 rows, or 3 holes, is 5mm, which is what I generally adhere to (in most cases).

[duck_arse]

oh, I wasn't meaning to be rude to your layout. I took the "modified" to mean someone else's layout, now I realise it's your's.

well, you have an "east-west" at R25 (and C13). all the rest are "north-south". and I get confused by the 0.2" spacing diylc has drawn for caps on 0.3" placements.

graphically .....

..... I try and keep all the empty space to a minimum, by bridging cuts with components where I can. this was my first all-flat, some of the standing resistor layouts I've done end up in a blizzard of flying links. but small.

[digi2t]

OK, gotcha. Yeah, it's a tough call sometimes, but in the end, I always have to balance between board size, enclosure space required, and the amount of off board wiring. I don't like wire tapping that's not on the edge, although there are some rare exceptions. Some veros can be real Medusa's, like the PLL for instance. In the end, the amount of wires will dictate whether I care about component orientation, or not.

Also, I've found that if I try to align my cuts into groups as much as possible, it leads to less count errors, and speeds up the cutting process. I try to run jumpers over rows of cuts as well. I find it's just easier on my failing eye sight. I can trade some room for that.

All in all, if it fits into a 1590BB, and I don't bodge it up, I'm happy with it.

[deafbutpicky]

digi2t,
now you got me curious and while you're at it, as you are using GE diodes, would it make a difference soundwise to change the transistors to silicon types and lower the input impedance (with let's say 68k) in front of the input cap ?

[digi2t]

I'm not bright enough to give you an educated answer to that, so I would just have to try it, and listen to what it sounds like.

One thing that I have noticed, compared to any of the silicon Muffs I've build so far, this one seems to tame better when rolling down the guitar volume. I'm using mostly all the same values in the Ge version, but it's not as harsh, and the sound has a much softer overdrive feel than the silicon versions. It's not Fuzz Face clean, but cleaner than the silicon versions. More pleasant to my ears.

As for the clipping diodes, that was a whim. I figured "Ge transistors, OK...", then "Ge diodes as well".

Just a duffer trying different things.

[lmorse]

Releasing the third stage clipping is just too much IMO. The second stage I find is just right. Nice volume boost to cut through

Ha ha. No-one accused the Big Muff of being subtle. 
You have got me thinking though. I might also play around with adding a switch to the first clipping stage as well before I box up. I've been reading the DIY Russian Mid Knob post too ( http://www.diystompboxes.com/smfforum/index.php?topic=109298.0).

Looks like I might not be ready to box up yet. A bit more tinkering. Probably save it for the Chrimbo holidays so I have plenty of time... unless I can't resist the temptation, then I might have to build another version over Christmas with these mods.... and perhaps a charge pump for reversing polarity of a Walwart....

[deafbutpicky]

I'm not bright enough to give you an educated answer to that, so I would just have to try it, and listen to what it sounds like.

One thing that I have noticed, compared to any of the silicon Muffs I've build so far, this one seems to tame better when rolling down the guitar volume. I'm using mostly all the same values in the Ge version, but it's not as harsh, and the sound has a much softer overdrive feel than the silicon versions. It's not Fuzz Face clean, but cleaner than the silicon versions. More pleasant to my ears.

As for the clipping diodes, that was a whim. I figured "Ge transistors, OK...", then "Ge diodes as well".

Just a duffer trying different things.

we're far off educated guesses here I guess , as different transistors would shape the sound anyway.
I'm just curious to how much of this gets overruled by being simply clipped by diodes, as I have the "feeling"
much of the altered response is due to input impedance, as Bmuffs aren't prone to subtlety anyways.
So if you have some  time to swap components I'd be glad to hear about it.

[duck_arse]

failing eyes, digit? with the 200% zoom on diylc, I've stopped worrying about cuts or links. until recently, I've been saying I'm soldering by touch. yesterday it seemed I was just throwing the solder at the joints. oh-well .....

as for layouts, I think I've picked a bad circuit example to rail against, as all the resistors string the transistor between the supplies, and they are always above and below anyway, right? I've just gotten some X x 10 holes perfs, so I'm challenging myself to build everything on them, now. as if we need another muff layout. (we do, don't we?) I look at vero now, even for something as simple as 3 pots and the tone caps between, and just groan inwardly.

and, one last thing to get this post a bit more topic centered; IS there a circuit diagram to match ..... whatever it is everyone is building here that layout you posted? what with the extra pots and switches and all. and the funny diodes. I'd swear I saw a muff diagram last night I hadn't seen before, no idea where today.

chrimbo, lee? is that a queensland thing? (get any hail?)

[digi2t]

failing eyes, digit? with the 200% zoom on diylc, I've stopped worrying about cuts or links. until recently, I've been saying I'm soldering by touch. yesterday it seemed I was just throwing the solder at the joints. oh-well .....

as for layouts, I think I've picked a bad circuit example to rail against, as all the resistors string the transistor between the supplies, and they are always above and below anyway, right? I've just gotten some X x 10 holes perfs, so I'm challenging myself to build everything on them, now. as if we need another muff layout. (we do, don't we?) I look at vero now, even for something as simple as 3 pots and the tone caps between, and just groan inwardly.

and, one last thing to get this post a bit more topic centered; IS there a circuit diagram to match ..... whatever it is everyone is building here that layout you posted? what with the extra pots and switches and all. and the funny diodes. I'd swear I saw a muff diagram last night I hadn't seen before, no idea where today.

chrimbo, lee? is that a queensland thing? (get any hail?)

I had a feeling that you were going to take me to task on it, so I started on a schematic that matches my vero. I should be able to get it out tonight. 

Throwing the solder at the joints, eh? Your Kung-Fu is strong Sir!

[lmorse]

I have drawn up a schematic if anyone is interested (Eagle Cad). Just let me know.

Chrimbo? It's a UK thing. Born in Aus - lived in the UK for nearly 40 years - escaped back to Aus.

[duck_arse]

the uk? like they have sarnies instead of sangers. I guess we can excuse you, seeing as you came back. I'll happily take a look at that schem, lee. I'm about 100% sure I'll end up drawing the schem myself anyway, at the moment I'm just working from a drawing of a single stage.

[digi2t]

This is what I have so far. You can add a reverse voltage protection diode if you wish.



The 820p caps marked "optional" can be anywhere between 500p, all the way to 2n. I find that it helps trim out some of the very high end frequencies. YMMV.

The 4K7 resistor on Q4E is tweakable. Depending on what collector voltage you're getting, it can work with anything between 3K3, to 5K1. If your collector voltage is sitting between 5v and 5.5v, you're pretty well in the BMP territory. Mine is sitting at 5.52v with the 4K7. If you're really anal about it, the a 10K trimmer will do it.

If you want a really "IN YOUR FACE" boost, then move the Boost switch from the second stage to the third. Then, just before you hit it, you better sit down, shut up, and hang on.

@deafbutpicky: I tried your silicon/lower impedance idea, but my ears are telling me, "No, this has that silicon edge to it", even with the lower impedance. The Ge version sounds.... I dunno, rounder? (for lack of a better word at the moment). Think along the lines of a silicon FF versus a germanium FF, but more subtle. You'll just have to breadboard it to hear it yourself. One thing for sure, the Ge version is much more pleasing to my ears when I roll down the guitar volume.

[mac]

A word about the resistance of the diode used to raise the voltage across the 100k resistor.

As you know the diode is not linear. The diode's current is related to its voltage by

I = Is.[exp(Vd/n.Vt) - 1]

where I is the diode's current, Vd the voltage, Is is the saturation current, typically a few pico amperes, Vt the thermal voltage, 25mV at room tempereature, and n is an ideality factor between 1 and 2.

The dynamic resistance is Rd = dV/dI = n.Vt/(I+Is)

Taking n=1 and ignoring Is, Rd is Vt/I

In a Big Muff, I is the collector current, about 0.5ma, so Rd is 50 ohm, a bit lower than the 100 ohm of the silicon version.

mac