VVR (cathode bias) suitable for preamp fixed bias amp

[guile]

Hi all,
I just dicovered the wonderful technique of VVR.
I'm wondering if a VVR pcb for a cathode biased amp would be suitable to regulate the voltage of the preamp of a fixed biased amp.

[martin manning]

Sure. Preamp stages are almost universally cathode biased.

[guile]

Sure. Preamp stages are almost universally cathode biased.

Thanks for reply. Will go and install it then!

If I understand right, just interrupt the current to the preamp or to one of the pins of the preamp-tube?

[martin manning]

I don't know what circuit you are applying this to, but I would say insert it in the power string after the screen node so you are scaling the PI voltage along with the preamp.

[guile]

I don't know what circuit you are applying this to, but I would say insert it in the power string after the screen node so you are scaling the PI voltage along with the preamp.

It's a Fender Deluxe reverb clone.

[martin manning]

Ok, I think between the B node and the 10k resistor on the AB763 schematic. This way the output of the VVR feeds the 10k, and the reverb driver and tremolo are still running at full voltage, but you may want to try moving the reverb driver to the VVR's output.

[guile]

Ok, I think between the B node and the 10k resistor on the AB763 schematic. This way the output of the VVR feeds the 10k, and the reverb driver and tremolo are still running at full voltage, but you may want to try moving the reverb driver to the VVR's output.

Wow, thanks!
Could you explain what you by screen node an b node? I'm Dutch and I try to understand.

[martin manning]

See below.

[guile]

Thank you so much!

My Deluxe Reberb only has the normal channel btw. So no reverb etc.
Would that change anything?

[martin manning]

Thank you so much!

My Deluxe Reberb only has the normal channel btw. So no reverb etc.
Would that change anything?

No, I'd insert it in the same place.

[guile]

Again, thank you very much Martin.

[guile]

Would installing the VVR after the 10k be good also?

[martin manning]

Yes, you could put it after the C node, and just scale the preamp (and not the PI). I suppose the difference would be similar to a pre-PI vs. a post-PI master volume.

[guile]

And what would that difference be tone-wise?

[martin manning]

I think you might want to try it both ways. Basically the difference will be PI distortion vs. effect on the negative feedback loop.