Informant OD - TL072 substitutions?

[mdc]

Hi folks—long-time listener, first-time caller here,

I'm just curious if anyone has tried out different ICs in the Informant Overdrive. I'm planning on socketing the two TL072s to see if anything else works or sounds different/cool/interesting in there. I know the TL072 is a dual op-amp, but is the circuit using both channels? Could I drop in a CA3130EZ or LM308N or any of the other go-to rat chips?

Thanks in advance!

 

[Chuck D. Bones]

Single & dual opamps have different pinouts, so you can't just "drop in" a single in place of a dual. The Informant, like the Rat (and so many others), drives the opamp into saturation. The opamp's saturation characteristic is one of the things that gives the Rat its distinctive tone. Different opamps will sound different.

Here are some options:
1. Build it on a breadboard. You can easily wire in singles or duals.
2. See if someone makes a dual-to-single adapter board. You will undoubtedly have to contend with clearances from surrounding parts.
3. The CA3240 is a dual that is similar to a CA3130. Not identical, but might be worth a try.
4. Try any duals you have, you might find something you like.

 

[phi1]

Good advice from chuck. The only thing I would add is, the circuit uses both op amps of that tl072, so you’d need a conversion pcb that has two single op amps that fits to one op amp spot on the board. That’s probably assumed, just making sure you know what to look for.

I heard an interview with the designer, he said he was hoping to stay away from old parts like the Lm308 chip for the purpose of easier sourcing. So he attempted to tune the response of the tl072 to sound similar to the 308 (with some consulting help from the guy from bondi effects). I believe that just means the 3n3 cap on the op amp feedback loop in the gain stage to dull the highs, And maybe a little extra help from the 3n3 on the output stage op amp.

Here’s another idea to try. Strap red leds on the gain stage op amp in soft clipping configuration. This limits the gain and basically eliminates the op amp saturation chuck referred to, so that you just hear the diode hard clipping. I went back and put this mod in my build recently. It’s probably farther away from an actual rat sound, but interesting to me... smoother, tighter, and clearer at high gain, but still rippin’. At this point the 18v seems not to make any difference, because even at 9v the leds keep the op amp from saturating, as far as I could tell.

 

[Chuck D. Bones]

Once you put diodes of any kind in the feedback path, you have a whole different pedal. Not saying it's better or worse, just different.

 

[mdc]

Thanks - I appreciate the responses!