Op-Amp Big Muff. Wrong schematics?

[zosotone]

I found this page where several errors are mentioned about the EH Op-Amp Big Muff. In theory, all the schemes on the web have errors (also de Kitrae scheme).

https://tornadoalleyfx.wordpress.com/2015/05/20/project-cherub-rock-the-op-amp-big-muff-part-1/

I built the EHX IC Big Muff V5 '78 that Javi mentioned with 2 IC's and sounds ok for me but I'm worried about the changes on the values.

Corrections:

- volume pot 100K Log > 100K Lineal
- C9 150-330p > 15pf
- C1 150nF > 68nF
- C7 4u7 > 1uF
- C14 150nF > 220nF

R17 unknown it's ok 47R.

He also recommends removing C6 capacitor and R9 to ground (J1 and J2 on the scheme).

What do you think?

[zosotone]

For any reason the link does not work well.

This is the link:

https://tornadoalleyfx.wordpress.com/2015/05/20/project-cherub-rock-the-op-amp-big-muff-part-1/

[zosotone]

This is the layout with corrections for the original model.

[Ciaran Haslett]

My understanding is this...

Volume Pot taper will only affect the sweep of volume in relation to the turn of the pot.  The sound will not change, just the position of the pot to achieve the same volume.

C9 changed to a smaller value will filter less high end from the clipping stage.  That will be entirely a matter of taste.

C1 Input cap changed to a lower value will filter out low end at the very beginning of the circuit.  Again a matter of taste.

C7's typical value in the BMP is 100n!.  I wouldn't expect you'd hear much of a difference changing it from 4.7u to 1u.  Maybe in the really low end.

C14 alters the corner frequency of the fixed filter during tone bypass.  Taste again.

In the original BMP, C6 was used to decouple the sustain pot from any DC on Q1's collector.  Since we are now using an IC this isn't a problem so it could be removed.  But as the value is so high, I don't expect you to be able to hear a difference anyway.

R9 to ground is a limiting resistor for the sustain pot.  Basically it sets the CCW rotation of the pot just above ground so it doesn't dump all your signal and go quiet.  This voltage divider setup is standard in all BMP schematics and I see no reason to change it (other than for authenticates sake, based on Colins comments in your link).  It will still do the same thing regardless

It seems to me that every correction will make your IC Big Muff shave bass and add treble.  Not particularly something I would want in an IC based fuzz pedal.

[zosotone]

Thanks for your comment.

Well, I have rebuilt the sustain connections (C6, R9), the volume pot and I have changed the caps for 15pF and 68nF, sounds a little bit better now. Less bottom end and the gain it's less piercing for my ears.

I've noticed that the most important change it's around the sustain connection (without AnalogGuru’s suggested changes) and the caps C1 and C9.

I agree with you, the other changes are almost imperceptible.

We now that EH have changed the components constantly even in the same models.

[al_deckabrist]

Perhaps this is not a version bug, but another version ..
Your changes are very similar to the “Op-Amp Little Bif Muff” scheme, it remains to change R1 to 68K and C9 to 150pF

[al_deckabrist]

sorry for my "Microsoft paint" version
with additional changes it will look something like this

[Travis]

I wouldn’t say “wrong” schematic but EHX are well known for often changing component values

I’ve built Mirosol’s IC muff layout and thought it sounded great

This version seems worth a layout/try