Opa2134ua equiv

[Pav]

Re Euro vca needing opa2164ua, I'm not seeing availability, so is tl072acn ok as equivalent or is there better available audio chip ?

[Synthbuilder]

Re Euro vca needing opa2164ua, I'm not seeing availability, so is tl072acn ok as equivalent or is there better available audio chip ?

The OPA2134? It does seem to be hard to come by in surface mount. Mouser will have stock this time next year... The DILs are currently available thankfully.

For the VCA, I would try a OPA1678 in there first. That's a good all round chip and my go to these days. A TL072A will work too.

[Synthbuilder]

One thing to note when changing op-amps - just check the output doesn't oscillate at some really high frequency. A proper scope is essential here. If it does oscillate then increase C4 just a bit, perhaps to 15pF. If that doesn't work try 22pF and so on.

[Pav]

Oops mixed up the two chips , as I still need ssi2164 which Thonk may have. Thanks for the guidance.
Edit, do I place probes across c4 for testing.?

[Synthbuilder]

do I place probes across c4 for testing?

A scope probe will typically have a 'ground' clip and the pointy probe itself. The ground clip should go on the module's 0V connection somewhere, and the probe should go on to the output pin of the chip. The tip connection of the output socket of the module is also sufficient. You're basically checking the output of the module is not honking away at something like 1MHz.

With a single scope probe it is not possible to monitor the voltage across C4 directly as neither of its terminals are connected to 0V. This would require a differential voltage measurement which most dual input scopes can do when you select the correct mode on your scope and use both inputs and both probes. However, the probe's own internal capacitance would be too big to make this particular measurement viable.

Fortunately in this case, you don't need to measure the voltage across C4 as the output voltage of the op-amp with respect to 0V is what you really want to see.

You can't use a multimeter for this task as most cannot measure AC voltage above 1kHz and the capacitance of the input too large.