"DRIVE UP" meet (yet another) Green Ringer Style freak

[Steben]

Here you go, my DRIVE UP concept:


Green Ringer style effect with opamp driver in front and adaptation of JD's Null carrier mod.

I made some sim examples and I'll try to share them (these are NOT true pedal sounds, but LTsim outputs, thanks to Vivek for technical education):
base file: https://sndup.net/448c/333245__alexnekita__bbking.wav
octave (much lower output sorry): https://sndup.net/2sdb/oct3.wav
octave with drive: https://sndup.net/7ms5/oct3drive.wav

[Vivek]

Nice !

Do you wish to cut Bass before clipper ?

[Steben]

Nice !

Do you wish to cut Bass before clipper ?

Classic "Octavers" rather like cutting treble. The drive section is there for some compression and sustain to bring out some "octave bloom", not as a main drive tone. The feedback cap deliberately cuts lots of treble with higher gain settings. You can experiment with any drive in front of a green ringer.

[antonis]

Shouldn't be a cap in series with 1k5 resistor and another cap on +4.5V node..??

As it is, op-amp output biases BJT with a Gain setting dependent DC voltage and op-amp gain is 1 + 47k/(1k5 + 22k//22k)..
(the later might be taken into account in your design but the former should create a serious issue..)

[Steben]

Shouldn't be a cap in series with 1k5 resistor and another cap on +4.5V node..??

As it is, op-amp output biases BJT with a Gain setting dependent DC voltage and op-amp gain is 1 + 47k/(1k5 + 22k//22k)..
(the later might be taken into account in your design but the former should create a serious issue..)

Afaik all nodes on the opamp are biased at vref, being 4,5volts. There is no dc diff.
It could be i am missing something, but the sim gives the same numbers.

[Mark Hammer]

Sounds good.

[antonis]

Afaik all nodes on the opamp are biased at vref, being 4,5volts. There is no dc diff.

Strange, indeed..

+4.5V on non-inverting input should be taken into account on output by 1 + Rf/Rg voltage divider..
(I mean, it works also as DC amp..)

[Steben]

Afaik all nodes on the opamp are biased at vref, being 4,5volts. There is no dc diff.

Strange, indeed..

+4.5V on non-inverting input should be taken into account on output by 1 + Rf/Rg voltage divider..
(I mean, it works also as DC amp..)

I might be wrong, but the virtual ground principle is just as useful here.... as long as the inputs have same bias (virtual ground), the signal is low enough (linear operation).
Mind you there is SOME deviation, it is not exact 4.5V, but somewhat lower. At the same time, the output current is a mere 1µA.

If the - input would go to GROUND seen in the single supply it could definitely go nuts.

[anotherjim]

I think you can get away with this for a single amp. Any signal ripple imposed on Vref is to an extent common-moded out?
A blocking cap on the inverting input would only be useful for high-pass frequency response of the gain.
I do have a feeling it could benefit from a bypass cap on Vref, since that is also used to bias the rectifier mix - you don't want fundamental carried forward to the output do you?

[Steben]

Blocking sneaky fundamental can be done as well by adding caps to the supply circuit divider adding a true gnd route for AC and which is the better move if using an external supply anyway.