Tim/Timmy Pedal

[tubesimmer]

In theory, that diode junction does nothing, but he claims a small audible difference. Same with the off-center bias (that would matter if the opamp clipped but shouldn't matter in a diode-clipped arrangement).

I've simulated the circuit in LTspice for both the diode junction and the off-centre bias.

1] The junction between the back to back diodes indeed conducts no current other than a few fA of noise (normal wire).

2] The off-centre bias would work if the negative I/P was not left DC floating. When it's set, some VERY interesting asymmetry results... second harmonics galore. This can be approached at least two different ways.

I can post a screen capture of circuits & O/P if anyone's interested.

-- Edited --

Screen capture of 2 off-centre biasing schemes & resulting asymmetry:

[dbp512]

Oh please post screenshots of everything!

[Mark Hammer]

A local member of a different forum brought his Timmy over to my place because he had read that swapping op-amps improved the tone.  In particular, a 1458 dual op-amp - normally a less-preferred chip - was dubbed as the ideal replacement for the 4560 or whatever that the pedal comes with.  I was sceptical, but we installed a socket and subbed a variety of alternatives - TL072, JRC4558, CA3240, CA3260, OP275, etc. - and darn if a 1458 didn't sound sweeter and less harsh than the original and any of the alternatives tried.

Live and learn.  I forget which brand of 1458 it was.

[aron]

So fun and easy to swap out IC op amps! Also discrete versions.