excited about a tweaked opamp Big Muff

[Derringer]

so I breadboarded an opamp big muff per Gaussmarkov's schem
http://gaussmarkov.net/layouts/opbmp/opbmp-schem.png

It had the Billy Corgan thing going but I decided to start playing with it to see what other tones I could get out of it.

here's what I've changed
buffered 2n5457 input and a clean blend
2N7000 + Germanium Diodes for the clippers instead of the 2 X 3 1n914
decreased the gain in the second stage a hair (470K instead of 560k) and 68K instead of the 62K in the same stage (didn't have any 62K's anyway)
5K pot as variable resistor between a 1K resistor and ground (mids) for the high-pass portion of the tone control
C8 and C9 caps now 56n in the tone control
6.8K for r11
tone control pot changed to 100K
a bass blend where the 4.7uf cap comes from the wiper of the sustain pot (10n in place of the 4.7 uf and 100K pot between the two caps to add/cut bass)

and that brings the knob count to SIX .... so this is a new challenge, I've only done 5 knobs before 


I like the low gain sounds the best and with all the controls it works for every guitar I have .. at least it does on the breadboard

I started a PCB layout tonight based on this layout
http://www.fredric.co.uk/misc/opamp_muff_verified.gif

[tubesimmer]

I'm working on some Opamp BMP mods myself.
This question goes out to everyone, not just Derringer...

That 4.7uF cap off the wiper... it's way too large for any seemingly good reason (response would still be flat with a cap 1/10 that value).
(It could easily be a 470nF non-polarized.)
And to top it off, it's electrolytic - with the polarity possibly reversed with some mods!

See:  http://gaussmarkov.net/layouts/opbmp/opbmp-schem.png

I smell trouble, if you know what I mean 

There are some theories floating around...
1] It's large & backwards to create some sort of saturation distortion effect.
2] Most of the schematics are missing a cap - i.e., there should be another 10uF (properly polarized) between the opamp O/P and leg 3 of the Sustain wiper.

Either way, the cap(s) are still seemingly unnecessarily huge.

Anyone have any theories as to why C5 is a whopping 4.7uF?

[PRR]

5uFd electro is pennies cheaper than 0.5uFd film.

The polarity shown is correct. VB is 4.5V and VC is 4.9V.

[tubesimmer]

Wow, cost the only factor.... you'd expect to see a lot more large electros in circuits, no?
C5 polarity winds up only being reversed when there's a mod to VB or VC.
As-is shown in the schematic, polarity is correct for C5 - confirmed, thanks.

[Derringer]

holy thread from the grave

fwiw, I think my bass blend idea would work much better on the input cap to the BMP circuit rather than where I installed it.

It is useful where I have it, but you lose a lot of drive as the bass is reigned in and it looses the oomph that makes the circuit what it is.


And yeah, 4.7 uf is huge for that spot, but does give it that flooded&fuzzed-low-end sound

[Derringer]

I also tacked the octave-up section of a tone machine into the circuit

aaaaand, here's what it sounds like
https://www.4shared.com/mp3/Qcj-PzVRce/160828_obmpoct.html

I'm not even strumming the guitar much here, just standing close to the amp, letting it feed back, and sliding chords around

[tubesimmer]

And yeah, 4.7 uf is huge for that spot, but does give it that flooded&fuzzed-low-end sound

Hmmm... I'm now skeptical that it's purely a cost factor.
There's a 1uF cap in the power supply (C11) - and in my BMP, it's an electro 1uF.
So C5 could easily be 1uF (duplicate, cheaper part I imagine?) and retain bass response well below anything a guitar puts out, unless you're drop-tuning to like, lower F or something.
It's gotta be 4.7uf for some other reason - logical or not.

... actually it might make sense to swap C5 & C11 if faced with those two part values!

Anyway, I'll give the ultra-humongous C5 a try and see if I get a "flooded&fuzzed-low-end sound".