Question about op amp function

[brightlight]

So I've built both a Van Pelt Drive and a Thermionic distortion. I put them on the Auditorium test board yesterday and discovered something new to me (there's lots new to me, I'm fairly new to this still).

I tired the Van Pelt first and thought it sounded great. Then I tried the Thermionic - turns on but no signal. Oops, I forgot to the put the TL072's in it. Worked like a charm, sounds awesome.

Then I double check the Van Pelt and realized I forgot to put the TL072 in that one as well, yet it worked and sounded good.

So what is the difference between these 2 pedals that would explain one working without the opamp and one not passing signal without them? Does the opamp in these circuits simply supply volume? I know the Thermionic is an LED clipper and the Van Pelt seems to be cascaded transistors, but other than that I'm not sure exactly what's going on that would cause this difference in performance.

Thanks for the education and continued enabling of this addiction!

 

[BuddytheReow]

You are right about the Van Pelt. It’s primarily transistor based. The op amp is only used for the active EQ section and you can see in the schematic because of the feedback loop (input connected to output). This means that the signal doesn’t HAVE to go through the opamp in order to pass through. Try the EQ knobs both with and without the opamp in there. You’ll see what I mean.

 

[Erik S]

I didn't know the answer to your question, but I also tend to try my pedals without the ICs first. I just get so excited when that last jack gets soldered in!

 

[jesuscrisp]

TIL the JHS Charlie Brown is just a Zvex Box of Rock/Distortron with the gain knob not crackling and a tacked on 3 band Baxandall EQ.

 

[KR Sound]

TIL the JHS Charlie Brown is just a Zvex Box of Rock/Distortron with the gain knob not crackling and a tacked on 3 band Baxandall EQ.

Surprised?

 

[jesuscrisp]

Surprised?

About JHS being very creative once again? I guess no.

 

[spi]

I don't think that's a baxandall, it's looks like a straightforward 3 band active eq.