Bassifying a Muff

[BuddytheReow]

Edit: Take a look at post #18 for my final mods.

I've got a "stock" Green Russian muffin board that I want to tune it for my bass. Don't get me wrong: it keeps some low end for, say, a downtuned guitar, but it needs more bottom end. The stock coupling capacitors that I've circled are 100nf. I'll be swapping those out for 220n or greater. I'm not 100% sure if I need to swap out C5 and C8 here for something bigger. Green Russian specs call for 47n so I may up it to 100n. I would rather give something back to the community here rather than take all the glory for myself. Any other suggestions let me know.

 

[hamerfan]

I would opt for the c12 and c13 for the first attempt. I guess the other coupling caps should prevent the trannies from farting out. You could always put it in a parallel loop and mix it with a clear signal.

 

[BuddytheReow]

I would also increase the value of C3.

I attempted this on my lunch break today and pulled 2 trace pads up entirely. Pretty sure the board is shot, so I ordered a new one. Good thing these boards are relatively inexpensive. If I really wanted to cut costs I could make a vero layout of it, but not really in the mood...

 

[eh là bas ma]

I'd try to add a Dry/Wet blend knob, to restore a bit of clean signal in there. This always allows more bass to get through in the signal. You can use a Blend circuit, but honnestly a knob on your stompbox is much easier to use, with less patch cables involved.

Here is an exemple of how it has been done on an other circuit, with an extra buffer :

GuitarPCB's Bass Overdriver : Blend control and bass boost toggle mods.

I built the GuitarPCB Bass Overdrive a couple of years ago, never really could enjoy it because of some kind of bass cut. Compared to other Bass dirt circuits, it felt like it was missing some depth or something. I always liked something about it though, it sounds quite convincing as a Bass...

forum.pedalpcb.com

Edit : I would also have a good look at the Bass Big Muff, looks like 100n is a good choice :

Electro Harmonix Bass Big Muff

I haven't seen this one here already, so I gave it a trace both for personal fun and curiosity: Some values aren't there because they weren't marked on the silkscreen like the others, and I'm not going to pull them out to check. You get the gist of it

www.freestompboxes.org

 

[jimilee]

I would also increase the value of C3.

I attempted this on my lunch break today and pulled 2 trace pads up entirely. Pretty sure the board is shot, so I ordered a new one. Good thing these boards are relatively inexpensive. If I really wanted to cut costs I could make a vero layout of it, but not really in the mood...

Naaa, jumpers are the way to fix that.

 

[mdc]

I'd suggest pulling the first pair of clipping diodes altogether.
Also, I'm pretty sure increasing the values of C5 and C8 will do the opposite of what you want - the larger the cap, the more lows get clipped.

Adding a parallel blend circuit would be a good move too.

 

[RetiredUnit1]

Bassifying a Muff, or Muff-ling a Bass???

 

[GizzWizzKing]

I have a friend with the actual EHX bass big muff and it is really bad. Creates insane awful noise and there is no dynamic range to it at all. Maybe his unit is bad but I would steer clear of copying whatever they did in that without playing through one to determine its value in helping to address your needs.

 

[eh là bas ma]

Bass Big Muff deluxe !

 

[Feral Feline]

@BuddytheReow I think you're on the right track replacing the 100n with 220n, IMO. You should get a lot more lows with 220n but without farting out, but I've yet to try this myself.

Also based on my Muff research, making C5 & C8 bigger would be an error, as MDC already indicated.
I'd keep them at 47n.

Those two caps control the clipping frequencies and every Muff I've researched that's good on bass has small caps here. Using small caps constricts the clipping to mids and highs, letting more clean lows sneak through the circuit. Hence the reason why Russian muffs with their small 47n caps are preferred by bass players where 100n and greater caps in this position clip more lows, thus introducing extra harmonic content cluttering up the entire freq band.

Keep C6 and C9 large; typically they're 470pF, I recommend trying 560pF or even 680pF (both of which have been found in EHX Muffs). These caps let clean signal flow through bypassing the clipping diodes and blocking the highs, if I understand the circuit correctly — so in conjunction they work well with what clipping-caps C5 & C8 are doing.

When I was too lazy to breadboard, I socketed two (2) Muff PCBs just to compare circuits, here's one of 'em:

I've posted that pic before in the forums.

You could always just socket the coupling caps, clipping caps and any other components you wish to experiment with, instead of the whole board as I've done. Then once you've sorted out what you like, add a dribble of solder to the socketed component to keep it from dislodging.


Looking forward to reading about your findings...

 

[mdc]

The HMv3 is a great-sounding/bass-friendly BMP variant that you could easily build on any generic BMP PCB:

 

[KR Sound]

The HMv3 is a great-sounding/bass-friendly BMP variant that you could easily build on any generic BMP PCB:

I think I’ll try that when I do my next muff.

 

[Feral Feline]

Better still, build the Haunting Mids on a regular BMP PCB with a Footswitchable tone&recovery stage for a "dual-channel" effect.

 

[jwin615]

I'm doing something similar. Using IR LEDs in the first clipping stage(1.1Vf, so lower than regular LEDs, but higher than standard diodes), increased the filter caps to 200/220(I forget) and replaced the input cap with a cap blend pot. Still sorting the values on this as the current config is only sweeping 200-420. Need to lower the smaller cap to get it around 100-400. I think this was employed as a Focus control on some variants.
It's 90% built but I haven't circled back around to the Focus control yet to get it tested.

 

[jimilee]

There is a bass muff schematic over on FSB

 

[Feral Feline]

Thanks for that @jimilee, I've always been curious what's under the hood of the Bass Muff.

Thanks also to G.Bisson for tracing it. In addition to FSB, Bisson's over on Talk Bass with some cool builds, too, but I don't know about here.

 

[HamishR]

You may even want to skip one of the clipping stages. I don't know how doomy/sludgy you need it to sound but I often build a Muff with only one set of clipping diodes. Still sounds like a Muff but you get a bit more pick attack and sensitivity. So for example (using the schematic at the top of the page) you could leave out D3 & 4 and C5...

 

[BuddytheReow]

I should have replied back to this sooner. I replaced all the caps in the below schematic from 100n to 220n and kept everything else stock to green russian specs. Much more low end comes through now which is what I wanted considering this was for bass. Now I have a different "problem" where I have the BJTs "farting out" when I play on the E string around the 8-11 fret range. This only happens when I have the gain dialed up past 2 oclock or so. Signal passes through, but no clipping and it's only this one area where this problem occurs. It's not that big of a deal for me since a lot of clipping is already happening before this occurs.

In "Bassifying" this muff I need to dial the tone knob CW past the noon position in order to hear the clipping. C5 and C8 (both 47n) select what frequencies get clipped so it makes sense that I need to dial up my tone knob. Plenty of low end still comes through and is sufficient for what I wanted it to do. I will call this mod "conditionally successful".

 

[HamishR]

FWIW I have built a Muff using 1µF caps in the positions you have marked. With guitar it sounded great - in fact one of my faves. With bass maybe keeping C1 and C3 lower might help? If I want clarity in an OD I try to start off the circuit with not too much low end and build it up as the circuit goes. You want to keep the lows out of clipping stages and add them back in afterwards. I don't know if this applies to Big Muffs though. Often my favourite fuzzes have a huge cap on the input!

 

[jwin615]

This is pretty much what I've done with a madbean board except I swapped C1 with a cap blend pot. Problem is I wasn't getting enough sweep on it. Shelved it because...

I also wired a double rocker switch to alter both clipping sections independently between Si, UVLED(almost no clipping to nonclipping, depending on settings), and series germanium. Except I forgot to series the germs so I'm m assuming output would be too low there. I melted one switch already and didn't want to fight reworking the second only to melt it. They're auto style dual rocker on-off-on. Looks cool. Robust, once the soldering is done, and low profile. But I also have to hollow out a square hole in the side of the enclosure for them.

Maybe I'll go back to it tonight and breakout the breadboard and figure out what cap values will work.
Then melt a plastic switch. Then shelve if until fall.