Big Experimental Pi

[Fleetdog]

I've had an NYC reissue big muff for years and I love it.  I don't really need 2 though. I also have a BYOC Large Beaver PCB.  I want to see how far I can twist the BMP foundation into something different.  I'm definitely going to play with switching out diodes and transistors and the "creamy dreamer" mod (replacing a couple of resistors with jumpers, which I would guess you could do in reverse by making those resistors bigger as well).  I'd also like to do something different with the tone control (this may be value changes or a completely different tone shaping section). 

Are there any other changes that will give a big bang for the buck that I haven't listed?  Are there any particular tone circuits that would give vastly different results than the usual BMP tone knob with a relatively low parts count?   

[petemoore]

Are there any other changes that will give a big bang for the buck that I haven't listed?  Are there any particular tone circuits that would give vastly different results than the usual BMP tone knob with a relatively low parts count?
  See 'AMZ Labs Notebook'
  and 'Duncans Tone Stack Calculator'.
  ..maybe try a Mosfet instead of the bipolar 1rst stage..

[dano12]

If you want to go really crazy, run a pot between the Q3 emitter and the Q1 base for some wild feedback sounds.

[Elektrojänis]

One thing that might be interesting would be moving the tone control earlier in the signal path. It should sound different.

[Fleetdog]

Maybe I can use a Darlington pair or two in there.  It will be a little late for the January FX-X deadline by the time I get this up and running, but it's worth a try I suppose.

[Fleetdog]

I've got the board ready for some serious tweaking. 


Socket City.

I'm set for switching out transistors, diodes, and feedback caps as well as combining the gain stages and tone section in any combination.  I didn't populate the tone section at all so I can work with other tone shaping circuits and possibly just put the tone on a separate board. and I also socketed the emitter to ground resistors so I can play with jumpering them  (so called creamy dreamer mod) or possibly increasing them for an anti-dreamer mod.

If anyone else is familiar with this BYOC board and could tell me he purpose of the 2 pads at the top center of this picture I would appreciate it.  one is connected between the output of the 1st clipping stage and the start of the 2nd (on the 1st stage side of the coupling cap) and the other is connected between the 2nd clipping stage and the tone section.  My first thought was that you could put in a variable resistor there to have feedback on the 2nd clipping stage.  The only thing I could find on their forum was that it "moved the clipping stages".  I suppose you could remove the coupling cap between the 2 clipping stage and with a couple of jumpers put the 2 clipping stages in parallel.  I don't really think parallel clipping would be too advantageous though.

I'm going to do the onboard stuff first, but I'm also seriously looking into putting a low pass filter before the circuit to try and make it more of a synthy square wave fuzz.

[jefe]

Very cool Ben. Keep us posted on what you like / don't like. I've got the BMP Triangle on the breadboard right now, so I'm interested to see what you come up with. So far, I've only had a chance to play around with the tone stack (very fun), and some feedback stuff (so-so results thus far). Sorry I can't help you with the BYOC board, but without looking at the schematic, it sounds like you may be on the right track with those extra pads - could be for feedback.

[Mark Hammer]

 In some guitar amps, you have some option to attenuate the signal before it passes to the next gain stage.  So, your guitar (which may or may not already be boosted) hits the first tube, adds a bit of grit, then goes through a tonestack and maybe another gain stage before having another volume control, before going on to the output and adding more grind there. The general idea is that it is a normal aspect of producing distortion that one has multiple cascaded gain stges and produces different qualities of distortion by adjusting how much of the signal hits this gain stage at this point in the sequence.

The BMP is a dual clipper.  That means the signal is boosted and clipped, then boosted and clipped again. There is some attenuation between the first gain stage (Q1) and the first clipping stage, which we know as the "Sustain" control, but there is no padding whatsoever between the first and 2nd clipping stages.  You will note that each of the two clipping stages is preceded by the same cap/resistor pair, whether it is .1uf/8k2, 1uf/10k, or whatever.  The difference is that the first clipping stage has a cap and pot preceding that CR pair, where the second stage goes directly from the collector of the preceding transistor to the CR pair.

Why don't you consider inserting a cap and pot between the 1st and 2nd clipping stages, just like you see before the 1st clipping stage.  That way you can adjust how much clipping is produced in stage 1, and how much of that is fed to stage 2 for additional clipping there.  Think of the pedal as being like an amp with two cascaded gain controls and a master volume.

That will allow you to produce both gentler forms of distortion, as well as the wild stuff.

[Fleetdog]

jefe, here is a kind of nice schematic from the BYOC board. 
 
The 2 mystery pads connect to exactly where the signal path crosses into and out of the yellow Clipping (B) section of the schematic.  These 2 pads are in addition to all the connections shown above. 

Mark, I like the idea of a second sustain pot  I will definitely try that. If I did that while also making the 2 clipping stages less similar to one another I could make this a very versatile box. 

On the other hand, I hope I can avoid being the proud owner of a 24 knob BMP when all is said and done.  If I can get one really great sound out of this, I'll be thrilled.  I'd love it if it ended up with only a volume.

[Mark Hammer]

Mark, I like the idea of a second sustain pot  I will definitely try that. If I did that while also making the 2 clipping stages less similar to one another I could make this a very versatile box. 

In fact, that is what I was going to suggest, but figured I'd keep it simple and not throw too much at you at once. That's a nice stage diagram, BTW.  Good for thinking with.

You will note that at least one version of the Supa Tonebender was essentially a BMP without diodes in Clipping A..made for a stronger signal going to Clipping B, but with less harmonic content in it already.  You should be able to do some of that with the dual gain-pot arrangement I suggested.

[mac]

Use Ge transistors

mac

[paperhouse]

Try out a bunch of different diodes such as Ge's and various LED's (3mm/5mm/red/blue...) and play around with a bunch of different transistors. I'd love to experiment with some FET's, the multiple gain stages might sound really good. I'm gonna do the same soon.