Op Amp Big Muff not working.

[farwest1]

I just finished up putting this in the enclosure and—bummer, it doesn’t work. I get full guitar sound in bypass, but barely any sound when engaged. Just very faint (and doesn't sound distorted.)

The build is actually an Aion Electronics Muff—PedalPCB version was sold out. It allows for either single or dual second stage op amp. I'm showing the TL072 as a single. That empty op amp slot would take a dual 4558 as an alternate.

In addition, it includes a modification that I didn't install, which would have included CX1.

Any errors stand out to anyone? When I've made mistakes in the past, it's almost always been in the off-board wiring. Is my grounding ok? Do I need to ground the output jack?

 

[benny_profane]

I think you may need to actually jumper CX1.

 

[farwest1]

I think you may need to actually jumper CX1.

Yes! You win a prize—this solved my problem. Thank you so much. The build docs said to omit CX1 if not doing the modified tone stack. In other docs, this has meant leave it out altogether.

 

[benny_profane]

Yes! You win a prize—this solved my problem. Thank you so much. The build docs said to omit CX1 if not doing the modified tone stack. In other docs, this has meant leave it out altogether.

Glad you got it sorted. I think that documentation is a little misleading: the modification really alters the gain stage, not the tone stack. That capacitor is a holdover from the transistor BMPs that have decoupling caps between each stage. I'm not really sure what impact that has on tone (since it's so big), but you need to have a connection with the output of the non-inverting op amp stage in order to pass signal.