pauln Posted September 9, 2005 Share Posted September 9, 2005 I just was reading about guitar amps and came across something interesting. The Fender amps introduced a new feature back in the early days and it has been included on many of them since (my 1990 Super 112 has it). Its called brightness. This is described as a circuit that takes "negative energy" from the output transformer and inserts it back into the signal path. Sounds like negative feedback, to me. The purpose of this is to give the tone a brighter sound, but in a completely different way than using the treble control. It sounds to me like maybe negative feedback circuits by nature brighten up the sound of an amp. Is this known and do feedback amp circuits account (compensate) for this? Just wondering, NF Paul Quote Link to comment Share on other sites More sharing options...
MrMcGoo Posted September 9, 2005 Share Posted September 9, 2005 Negative feedback can add distortion as well as reduce it. Paul Klipsch called the negative feedback distortion Otellini (sp?) distortion after the person that first described it. There is information in the Dope from Hope about it. Most amps use some negative feedback, but there is an art in its best use. Bill Quote Link to comment Share on other sites More sharing options...
Deang Posted September 10, 2005 Share Posted September 10, 2005 You're thinking of Matti Otala who discovered TIM distortion in solid state amps. As far as negative feedback goes, I think there are too many variables involved to allow for any specific description of the sound resulting from its use. Quote Link to comment Share on other sites More sharing options...
Frzninvt Posted September 10, 2005 Share Posted September 10, 2005 ALL amplifiers use negative feedback in some form and to some degree. Those that say they don't are lying! An amplifier should not sound like anything! It should amplify and add nothing to the sound at all! A good amplifier should sound good with any speaker that you hook to it and sound the same. Quote Link to comment Share on other sites More sharing options...
sunnysal Posted September 10, 2005 Share Posted September 10, 2005 no, negative feedback in a tube amplifier does not brighten the sound from the amp. there are many ways to implement feedback in audio tube amp ciruit designs and I can think of none that could be classified as brightening measures, they can increase bandwidth, lower distortion, etc. there are dozens of ways to play with the signal in a tube amp to change the sound, especially if you are looking for huge, exaggerated changes like in guitar amp (distortion, brightness). this fender brightness one happens to include a loop from the trannie back into the circuit at some point, you can´t generalize based on that one case in that one circuit. warm regards, tony Quote Link to comment Share on other sites More sharing options...
NOSValves Posted September 10, 2005 Share Posted September 10, 2005 You can tune feedback to boost high's, lows, broaden frequency response, lower distortion, raise distortion and so on. The trick is getting it just right. Craig Quote Link to comment Share on other sites More sharing options...
Duke Spinner Posted September 11, 2005 Share Posted September 11, 2005 the Fender circut causes a bass roll off in the output Quote Link to comment Share on other sites More sharing options...
Gilbert Posted September 11, 2005 Share Posted September 11, 2005 APL offers a 300+watt amp (?) that they claim has ZERO neg. feedback. The only reason I remember this, is because I was considering their CD player. Anyone heard of them? http://www.aplhifi.com/ Quote Link to comment Share on other sites More sharing options...
Deang Posted September 11, 2005 Share Posted September 11, 2005 Sure, but I love my kids and don't really want to sell any of them off on the black market to buy their product. Quote Link to comment Share on other sites More sharing options...
Gilbert Posted September 12, 2005 Share Posted September 12, 2005 Sure, but I love my kids and don't really want to sell any of them off on the black market to buy their product. You don't have to sell'em,...... you lease'em man, lease'em![], Quote Link to comment Share on other sites More sharing options...
3dzapper Posted September 12, 2005 Share Posted September 12, 2005 I have an adjustable feedback circuit in my ST-35 EL-84 amp that Shannon Sparks designed. and am putting a similiar circiut in the amps that I am s l o w l y building now. The proper way to adjust it is to inject a 500Hz square wave and set the scope pattern for best response. however, in his instruction booklet, shannon says "let your ear be the final judge". Paul G at Busy Bee Audio has designed an adjustable brilliance control into his new line of amps that alters feedback. I don't know if his circuit is the same though. Rick Quote Link to comment Share on other sites More sharing options...
WMcD Posted September 12, 2005 Share Posted September 12, 2005 I was browsing a book about the Beach Boys. There was a behind the scenes picture which was showing the back of the tube amps. Gee, the the chassis is mounted upside down with the tubes extending downward. How come that hasn't be recognized as a tweek for other designs? D-Man, we may have missed something in our discussion of physical factors affecting audio. Smile. Gil Quote Link to comment Share on other sites More sharing options...
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