Variable feedback?

[PlinytheWelder]

Has anyone here tried bridging the typically 100k variable feedback resistor with a pot or maybe just substituting a pot for it to make a variable feedback control?

I have My Laney AOR 100/2 opened up and thought I might try it....

How 'bout on a wreck? My next build.

[greiswig]

I did this on a D'Lite build. It is not as useful as I had hoped. But that may just be because of the particular topology of this amp.

[Andy Le Blanc]

It depends on the inverter , and you need to find the right range for the control.
Its a bit of balancing act to get an effect that you can "hear" without going
too far and destabilizing the amp. Use the search on the forum, theres been
some past discussion.

[Normster]

I seem to recall a thread that referred to the variable feedback resistor as a "soul control." I've used it in bluesmaster circuits using a 47k resistor and a 100k trimmer. Pretty subtle actually, and very interactive with the presence control (as expected). The less feedback you inject into the PI, the less effective the presence is.

[Firestorm]

I did this on a 2xEL84 amp once. The effect was very noticeable. I think I cut the pot's carbon track at one end so you could turn the feedback completely off. Not something to do in an amp that needs it for stability.

[selloutrr]

i've tried it on a couple fender amps with bland results it's neat but not as useful as it's hyped up to be. It's worth trying just not worth drilling a hole, or cutting a wire for. If you do it try to use a hole you can live without. I put a 5K pot on the fender princeton reverb to help it distort a bit more for studio use. The amp had a Speaker and an Ext. speaker out jack since it's a combo I used the Ext. speaker jack hole to mount the pot. unsoldered the wire to the jack soldered it to the pot and made a jumper so it's 100% non destructive!!!

[gldtp99]

I think this is a useful feature in some amps--- i recently built two lo-watt Marshall 2204 clones (25 and 14/7 watters) with variable NFB pots on the front panel.
I used a 500k lin pot for the 25 watt/ JJ 6V6S amp and a 250k lin for the 14/7-- EL84 amp.
Both amps are stable with the pot dimed and the NFB practically eliminated.
The 25 watt 6V6 amp with the NFB pot dimed sounds like a Tweed Fender Deluxe when using the Lo guitar input--- not a tone one usually expects from a JCM 800-type amp.
On the Hi guitar input the NFB adds more Vol, Bandwidth, and Distortion.
The effect is very noticable....................gldtp99

[David Root]

Andy, would you elaborate on your comment that "it depends on the inverter". I've only done this in circuits with a LTP PI. What about cathodyne, paraphase inverters?