Best way to install Adjustable NFB control pot?

[joey]

Rip,

I just got done with the installation. It really makes the amp flexible. Definitely feels looser softer on the plexi 47K setting and more modern/raw s tighter feeling as you go up. I'm using the 8 ohm tap on the Output transformer.
The depth mod becomes much less effective as your NFB is reduced when using above a 100K NFB value.

Looking at your picture, you will need to use just the two lugs on the right. I used the middle wiper lug as the input and the lug to the right as the output that feeds my depth mod. You leave the far left lug unused then the pot acts like a varistor.

THANKS for your help Roe and Flemingras! Works like a CHAMP!

here's one thing you can do if you want to be a little different, and if you feel that less feedback sounds harsh. put a small capacitor from where the feedback resistor connects to the speaker tap, to the wiper of the pot. start with 20pf, and then move higher to get the result you want. this will smooth some of the highs in conjunction with higher pot settings. If you want to know why this happens I will tell you, but for now it is one more thing to add to your bag of tricks.

[harddriver]

Thanks for the tip Joey! I will have to try it down the road on this build. I struggled a little with this amp as it was built for my brother who wanted the best of all worlds a 2203 amp, with a High gain channel option but he also at times wanted a plexi feel and modern high gain. Kind of a tall order to fill but I think this feedback control does the trick he wanted the best.

I think he may like the harshness in a rude good kind of way, I really didn't hear it as harsh.

To say the least it was cool to hear how the amp responds as you decrease the Negative Feedback, I was amazed myself!

After I tweaked the amp the last time to more of a plexi NFB he asked for me to put it back to modern. He came over tonight and we played the amp and as I turned the feeback pot up he finally smiled and said that's what he was looking for!

The amp sounds really wicked, also gave him two zener diodes on a push pull master for added nastiness.

[sinkdrummer]

After a couple of years lurking around I finally joined! First I would like to thank my Bro (Harddriver) for building and tweaking me a wicked sounding amp! And second, thanks for being able to produce what I hear in my head...other than rattles. And thanks to all the metro brotherhood who suggest ideas. Thanks again!

[rip]

Rip,

I just got done with the installation. It really makes the amp flexible. Definitely feels looser softer on the plexi 47K setting and more modern/raw s tighter feeling as you go up. I'm using the 8 ohm tap on the Output transformer.
The depth mod becomes much less effective as your NFB is reduced when using above a 100K NFB value.

Looking at your picture, you will need to use just the two lugs on the right. I used the middle wiper lug as the input and the lug to the right as the output that feeds my depth mod. You leave the far left lug unused then the pot acts like a varistor.

THANKS for your help Roe and Flemingras! Works like a CHAMP!

Thanks for the help, oh and if you have the NFB control before the resonance and presence you will lose control as you lessen the NFB. But if you have the NFB after the presence and resonance then it will act more like a master volume because you are just setting the over all level and not limiting whats available to the presence/resonance.

Rip

[Roe]

I'm glad it turned out well. the NFB on the el34 amps varied from 27k at 8ohms to 100k at 4ohms, something which is equivalent to 27k-140k at 8 ohms or 19k-100k at 4 ohms

[lidesnowi]

Why not change the stock to a lower value, like 27k, so you have even more adjustment.

Thanks!