Muff driver - Big Muff Pi modified for a smoother taste

Nocentelli · Post by **Nocentelli** » 07 May 2013, 18:12

I had a bit of time this weekend, and a strong desire to breadboard, so decided to see if I could a make BMP I actually liked (as I am wont to do every few months).

I really like the simplicity of the clipping diodes and the idiot-proof biasing arrangement of the big muff, but I seriously dislike the tonestack and the way the pedal only sounds really good when the sustain is cranked (and therefore too distorted).
Probably a fool's errand, but I was aiming for a more versatile high gain overdrive/fuzz sound than just the usual chainsaw buzz.

To get some more useful lower gain sounds, I used the "focus" cap blend control from the Musket: I also tried out, but discarded a second sustain control between the two clipping stages. I settled instead for a large inter-stage resistor with a treble bypass cap: This might be useful as a trimmer set to suit. The tonestack and Q4 went completely, replaced by a simple treble roll off, and I used two back-to-back diode pairs in series (Timmy-style) for both clipping stages.

Muff Drive MD1_schem_nocentelli.bmp

beedotman · Post by **beedotman** » 07 May 2013, 18:29

Nice!

sinner · Post by **sinner** » 07 May 2013, 19:30

looks weird

MoonWatcher · Post by **MoonWatcher** » 07 May 2013, 19:37

Nocentelli wrote:Probably a fool's errand, but I was aiming for a more versatile high gain overdrive/fuzz sound than just the usual chainsaw buzz.

I think it's the kind of fool's errand that I end up periodically doing myself.

I do like dropping the gain with the Russian resistor values of 12K to the collectors and 390R for the emitters.

I have myself convinced that there's got to be a better method than the original sustain control for some reason.

I've also kind of come to an endpoint with playing around with the stock stye tone stack, but don't know where to take it from here. I think your idea is food for thought though.

So how does it sound to you?

Nocentelli · Post by **Nocentelli** » 07 May 2013, 20:11

MoonWatcher wrote:I have myself convinced that there's got to be a better method than the original sustain control for some reason.

I feel the same about the sustain control. I actually started out by trying mictester's suggestion of using a dual-ganged pot to control the clipping section collector voltages; I had a 100k dual with 100k resistors in parallel to give 0k-50k in series with 4k7 fixed resistors to each collector. I was rather hoping this could act as a decent alternative gain control, and i could maybe do away with the sustain control altogether, but it didn't work out like that. It's great for getting even higher gain, clipping and filth, but doesn't help with the lower gain end of things.

MoonWatcher wrote:So how does it sound to you?

I like it better than a standard big muff: The lower gain sounds are not exactly classic tube overdrive, more like a convincing solid-state amp emulating overdrive, but still way better than a muff with the sustain turned down. Nice and crunchy, I suppose. The "timmy" diode arrangement seems to lower the compression and make it a bit more dynamic, and the high-pass on the input helps for more subtle gain levels - It still goes pretty filthy at full whack, however.

The idea of adjusting bass levels before the clipping, and rolling off excess treble after clipping is something common to many dirt pedals, including the Timmy and Skreddy's Lunar Module, which are both pedals I really like. You can cut some bass and roll back the gain for a lighter drive sound, then set the final treble level to suit.

I find the bmp tonestack sounds good in only one position, and you are always forced into a compromise so it has enough bass but is not too muffled at the treble end.

juanro · Post by **juanro** » 07 May 2013, 21:36

I note that you left out the cap that isolates the clipping diodes from the collector DC to base; so collector will never sit more than two diodes drop above base, wich in turn is one diode drop above ground (much alike the bazzfuss). Is that intentional or a typo on the transcribed schematic?

Juanro

Nocentelli · Post by **Nocentelli** » 07 May 2013, 23:05

Crap, that's a typo - 100n on both.

juanro · Post by **juanro** » 08 May 2013, 00:46

And about the trimmer, you can use a regular pot, label it "Bass" or "Lows"....

bato001 · Post by **bato001** » 08 May 2013, 00:56

The big muff circuit can be modified so many ways it is mind boggling. Real nice spin on an old circuit.

bato001 · Post by **bato001** » 08 May 2013, 00:56

The big muff circuit can be modified so many ways it is mind boggling. Real nice spin on an old circuit.

Nocentelli · Post by **Nocentelli** » 08 May 2013, 17:44

Corrected schem:

: Muff Drive MD1_schem_nocentelli.bmp (1.07 MiB) Viewed 3702 times

Cub · Post by **Cub** » 07 Nov 2013, 09:34

What's the value of the cap between the collector of Q2 and the trimmer ?

Nocentelli · Post by **Nocentelli** » 07 Nov 2013, 11:08

220n, and I also ended up using a 500k trimmer instead of the 100k shown.

Cub · Post by **Cub** » 07 Nov 2013, 12:59

Thank you ! As Bato said, a real nice spin on an old circuit.

mictester · Post by **mictester** » 07 Nov 2013, 18:26

Nocentelli wrote:
MoonWatcher wrote:I have myself convinced that there's got to be a better method than the original sustain control for some reason.
I feel the same about the sustain control. I actually started out by trying mictester's suggestion of using a dual-ganged pot to control the clipping section collector voltages; I had a 100k dual with 100k resistors in parallel to give 0k-50k in series with 4k7 fixed resistors to each collector. I was rather hoping this could act as a decent alternative gain control, and i could maybe do away with the sustain control altogether, but it didn't work out like that. It's great for getting even higher gain, clipping and filth, but doesn't help with the lower gain end of things.

You have to increase the emitter resistors to 1k or even more. My version (on my pedalboard) has 1k8 in each emitter and 10k base coupling resistors. It goes from a slightly distorted, quite tightly focussed sound to a massive, insane, screaming, howling monster.....

Nocentelli · Post by **Nocentelli** » 07 Nov 2013, 18:46

Might try that again, then. Do you mean 10ks between stages or between B-C (surely not)?

Cannibal · Post by **Cannibal** » 11 Nov 2013, 13:14

Hey Nocentelli, have you tried using some negative feedback to tame the beast? bet you can get some low gain smooth tone if you filter some high end and super low end in the feedback network.

Nocentelli · Post by **Nocentelli** » 11 Nov 2013, 17:04

Cannibal wrote:Hey Nocentelli, have you tried using some negative feedback to tame the beast? bet you can get some low gain smooth tone if you filter some high end and super low end in the feedback network.

Now this sounds interesting. When you talk about negative feedback, do you mean the base-collector cap and resistor pairs?

I'm just heading home now to try out a couple of ideas on this circuit. First is a dual-gang pot acting as a pair of emitter resistor AC bypass pots on the two clipping stages (i.e. like the fuzzface gain control, but two of them simulataneously controlling the two clipping stages). Second idea is a BMP gain control arrangement outlined by Gus Smalley over th DIYSB, where he has a 500k pot AC coupled across the Q1 base-collector in this thread -

https://www.diystompboxes.com/smfforum/ ... c=104029.0

Cannibal · Post by **Cannibal** » 13 Nov 2013, 11:51

Nocentelli wrote:Now this sounds interesting. When you talk about negative feedback, do you mean the base-collector cap and resistor pairs?

I'm just heading home now to try out a couple of ideas on this circuit. First is a dual-gang pot acting as a pair of emitter resistor AC bypass pots on the two clipping stages (i.e. like the fuzzface gain control, but two of them simulataneously controlling the two clipping stages). Second idea is a BMP gain control arrangement outlined by Gus Smalley over th DIYSB, where he has a 500k pot AC coupled across the Q1 base-collector in this thread -

https://www.diystompboxes.com/smfforum/ ... c=104029.0

sorry for the late reply, when i said negative feedback i was thinking about the "honeybee-style" feedback. Something like this:

: bmp feedback.jpg (16.28 KiB) Viewed 3199 times

Use C2 value to filter some low end, C1 and R2 for the high end and R1 to determine the amount of feedback.