Danelectro PB&J voltage question

[Dimitree]

in your opinion, why the input/output opamp of this stompox is supplied with 5V instead of 9V?

schematic:
https://www.experimentalistsanonymous.com/diy/Schematics/Delay%20Echo%20and%20Samplers/Danelectro%20PBJ%20DJ-17.PDF

[anotherjim]

It's an easy way to constrain the signal swings within 5v to suit the echo chip. Think I would use an opamp that clips nicer than the TL072 though. TLC2272 perhaps.

[Dimitree]

thank you.
what if the echo chip gets a signal >5V, i.e. 9V?
it clips, or it gets damaged?

[swamphorn]

ICs have protection networks on their inputs which are basically two diodes between the input and power rails. In normal operation these diodes are reverse-biased but if the input goes above about V₊+0.6 V or below V_--0.6 V these diodes will be forward-based. Now, the input generally clips well before this stage anyway so the real danger is that an excessive amount of current flows through these diodes, overheating and destroying the chip. With a sufficiently large series resistor (such as R₁₀₂ in the schematic) this isn't really an issue. Instead, I suspect the circuit runs off 5 V because Danelectro is cheap and they can use the V_ref pin from the delay chip to bias the rest of the circuit.

[bushidov]

Also, there are two versions of that PB&J. The newer one (by newer I mean, it still is over a decade old), uses an ATMEGA48, a DAC, and SDRAM, so it had some real serious 5V and 3.3V style circuits going on there.

[anotherjim]

You should look at adding input clamping diodes. They do the same job of the built-in ones in IC's but can handle greater currents and act before the IC ones can. Many solid-state amps do and their IC's might be running on /-12v or higher supplies.