negitave feedback loop

[dmartn149]

Thanks Tom. I probably will mount the switch in the ex sp hole, just to keep everything close, short leads, etc.
That princeton NFB is interesting. Does the cathode bypass cap have an effect on the nfb at certain freq. or is that a dead end for the negative feedback due to the polarity of the cap?

[Enzo]

Doesn't work against the NFB. The cap keeps the voltage stable across the 1500 ohm cathode resistor. The 2700 ohm and 47 ohm resistors form a voltage divider. They sample off that small portion of the voltage signal at the speaker, and use it as the floor for that cathode resistor with cap. So the NFB signal acts as a moving ground point or reference point for that cathode circuit.

[dmartn149]

That Princeton NFB would be just a little more complicated than the circuit I was planning. What would be the sonic difference between them?

[S a m]

I put the Robinette NFB switch on my 5E3. I'm a clean-oriented player so it's a help: It lowers the noise floor and provides more clean headroom.

Putting it in the standby hole makes sense. Drilling into stainless is a pain the neck -- I burned out several bits making the extra hole on mine, but once you get started you might as well finish!

[Tom Phillips]

Nice build photo Sam.

...Drilling into stainless is a pain the neck -- I burned out several bits making the extra hole on mine, but once you get started you might as well finish!

That's one reason that I recommend using the external speaker jack hole for the added switch. It's in a good location to allow the wiring placement and we don't find people using an extension speaker with a 5E3 Deluxe anyway. That also makes it a reversible mod with no leftover hole.
Cheers,
Tom

[dmartn149]

Thanks for the input guys. I don't know yet if I'll actually use the amp in the NFB mode, but I doubt if I would ever reverse the mod. The stock circuit is always available at the switch, and this amp is not meant to be a "clone" anyway.