1975 MXR Phase 90 - Clock noise?

[Helmholtz]

This might be interesting regarding the bias: https://barbarach.com/simple-phaser-playing-with-lfo/

Also the cicuit analysis here: https://www.electrosmash.com/mxr-phase90

[clarisso11]

Is C8 good and well connected?

Does the unit apart from ticking work as it should?

Hi Helmholtz,

I have no idea how you managed to isolate C8 as the problem, but that was it!! I had a look at the capacitor and noticed that it was a little sideways, so I pulled at one of the legs, and it wasn't soldered in properly! Clearly an oversight when this was first put together. I mentioned that this was a spare part that was never installed, so I suspect it never went through quality control checks.

It now works perfectly, with no more audible clock noise.

Thanks to everyone chipping in with advice!

[Helmholtz]

Great!

I think the purpose of C8 is rounding off the peaks of the triangular LFO signal, thus reducing the HF content which can cause ticking.

[clarisso11]

Thanks for the explanation - make sense!