Sir Bob Posted July 10, 2001 Share Posted July 10, 2001 I have reissue Fender Bassman amp with a negative feedback knob. I have yet to figure out what to do with it. Gerald Weber says that it basically evens out your tone as you increase your volume. In other words, as you increase the volume of your amp, certain frequencies are being increase while others are not. To compensate for this you increase the negative feedback loop so that those frequencies that are getting increased will be feed back at 180 degree out of phased. Bottom line is if I want raw tone (who doesn't) shouldn't I be refraining from using the negative feedback dial? Please help me understand this. Link to comment Share on other sites More sharing options...
Chip McDonald Posted July 10, 2001 Share Posted July 10, 2001 Originally posted by Sir Bob: I have reissue Fender Bassman amp with a negative feedback knob. I have yet to figure out what to do with it. Well, once it happens your car blows it's water pump on the way to the shop to get the starter fixed, then insane people bother you at restaurants, people think you're playing air guitar and you can't find pants sized 31 30 anywhere. OH WAIT, negative feedback.. Hmm.. I've not seen that, but that's what goes on in the presence circuit of an amp if I'm not mistaken. Theoretically it decreases distortion while adding high end; but changes the slew rate in the process I believe? Presence knobs on Marshalls I think of as "how much harshness do I want?"; I would assume a Bassman you're talking about the same deal. Perhaps Weber is suggesting that as the amp gets louder the high end response gets squashed and that brings it back....? I'm half asleep tired and depressed so I may be talking about proton decay and pining for the fiords for all I know, I'm pretty sure I missed something obvious in the above. ------------------ New and Improved Music Soon: http://www.mp3.com/chipmcdonald Guitar Lessons in Augusta Georgia: www.chipmcdonald.com Eccentric blog: https://chipmcdonaldblog.blogspot.com/ / "big ass windbag" - Bruce Swedien Link to comment Share on other sites More sharing options...
DC Posted July 11, 2001 Share Posted July 11, 2001 I've got a Fender Bassman and I don't remember a negative feedback knob on it?! Where is it? -David http://www.garageband.com/artist/MichaelangelosMuse Link to comment Share on other sites More sharing options...
Submersible Posted July 11, 2001 Share Posted July 11, 2001 It's basically a presence control, and it can be quite useful at lower volumes. It'll give you some highs, and a looser, more ragged tone. Installing a pot or switch in the negative feedback loop is a common and easily reversed mod for SF and BF Fenders. Another common Fender mod is to replace the tremelo intensity control with a switching pot to take it completely out of the circuit when off. The tremelo mod is the more useful of the two, IMHO. Link to comment Share on other sites More sharing options...
Lee Flier Posted July 12, 2001 Share Posted July 12, 2001 Negative feedback? Is that like, you crank up the amp and it tells you that you suck? http://www.musicplayer.com/ubb/smile.gif --Lee Link to comment Share on other sites More sharing options...
stanner Posted July 12, 2001 Share Posted July 12, 2001 (hehe) i guess i would call that "feedback" 'cause then at least you know where you stand w/ your amp... AMPSSOUNDBETTERLOUDER Link to comment Share on other sites More sharing options...
Sir Bob Posted July 12, 2001 Author Share Posted July 12, 2001 I have learned that the "presence" knob on the reissue Bassman is a negative feedback circuit for the very high freequencies. How to use it? Keep moving it until the amp sounds good. Link to comment Share on other sites More sharing options...
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