What would you do with an unused opamp?

[Ripthorn]

I just did up a dirt box that uses three opamp stages and feel it is a waste to leave the one unused one just hanging there. I breadboarded it up and made the unused opamp an MXR micro amp, but running that into the dirt box input just makes it spluttery and nasty. Straight into the amp, the micro amp sounds quite nice.

Anyway, if you had a spare opamp stage, what would you use it for? Boost? Filtering? Treble boost? Something else? Come on, not like we don't have time to play with the idea, right?! Thanks!

[EBK]

My very first post to this forum asked the same question. 

https://www.diystompboxes.com/smfforum/index.php?topic=115935.msg1071746#msg1071746

[Kipper4]

Was one of the suggestions? Use it as a buffer for Vbias. @EBK?

[Ripthorn]

Beautiful! Turns out I wasn't very active on the forum back then. I like the idea of either a clean/dirty blend or a tunable filter. I'll have to tinker more!

[EBK]

Was one of the suggestions? Use it as a buffer for Vbias. @EBK?

The very first suggestion, in fact.

[Nitefly182]

Buffer VREF
Add an output buffer
Switchable active filter
Run the unused one in parallel with another to double current.

[Ice-9]

I would get the Dremel out and grind it out of the DIL package, thus saving power so the battery will last longer. and the pedal will weigh less. 

Sorry I couldn't resist just having a joke, I would most likely use it for VRef.

[swamphorn]

I rent out my spare op amps for use by other pedals and audio electronics in general. That combined with ad support allows me to sell my pedals for much cheaper than other manufacturers. I'm still trying to figure out how to charge for the last 10% of a drive knob; do you think I can fit a card reader into a 1590A?

In all seriousness, if I have a spare op amp I'm more likely to get rid of another op amp so I can, say, use a dual instead of a quad package. V_REF buffering can be nice, but if my V_REF has to source or sink enough current to throw a resistor divider off I tend to rethink my design. That's just my design philosophy though; I certainly don't have a problem with buffered V_REF in other people's designs.

[Rob Strand]

I'm not fond of buffered Vref because it can add unnecessary noise.

I like swamphorn's idea of getting rid of an opamp but that's not always going to work.
Putting a single opamp on a board full of duals would be a silly way to (not) solve the problem.

[Ripthorn]

Interesting thoughts on the buffered VREF, Rob. I was thinking I might go that route, as I breadboarded a wet/dry mix and, by the time I put in the buffer on the clean signal, add the blend pot, and some supporting components, I decided it wasn't the right fit for this pedal. I could just leave it unused, but I do use VREF extensively, as it saves me from doing a bipolar voltage supply. I don't want to use two charge pumps, that's just crazy talk . So I have one charge pump to do +15V, but my entire signal path uses VREF. It sounds great, so I'm thinking I might just buffer it.

I really appreciate the conversation around here, though, lots of food for thought.

[Sooner Boomer]

What would you do with an unused opamp?

Trade it for toilet paper?

[iainpunk]

Interesting thoughts on the buffered VREF, Rob. I was thinking I might go that route, as I breadboarded a wet/dry mix and, by the time I put in the buffer on the clean signal, add the blend pot, and some supporting components, I decided it wasn't the right fit for this pedal. I could just leave it unused, but I do use VREF extensively, as it saves me from doing a bipolar voltage supply. I don't want to use two charge pumps, that's just crazy talk . So I have one charge pump to do +15V, but my entire signal path uses VREF. It sounds great, so I'm thinking I might just buffer it.

I really appreciate the conversation around here, though, lots of food for thought.

what kind of dirt pedal are we talking about? if you won't mind asymmetric powering of the opamps, you could just use the 9v as the vref, and use the opamp for a summer circuit, which is a "cleaner" way of mixing two signals