Disconnect Neg feedback, vibrato, snubber caps on 71 Fender SFSR?

jcs

Member
Messages
8,065
What about these mods?

My amp already has a SS rectifier mod and is too bassy for the most part (which I addressed in another thread)...but how are these mods in terms of fidelity and harmonics?

Any fans of these?

Thanks in advance!
 

enorbet

Member
Messages
46
Perhaps you should rephrase your question or better, just try them because you will never learn anything useful by discussing "fidelity and harmonics" for a guitar amp. Not only do most players not realize they are technically playing distorted until it exceeds 30% or so, guitar amps are not sound reinforcement devices. They are musical instruments unto themselves. Whether or not you like these mods is solely up to your ears and playing style. I happen to like tweaking (not just disconnecting) the negative feedback resistor and a well-designed snubber becomes essential then but should have absolute minimal effect on tone other than to be better to most ears since the frequencies they snub are above human hearing but they beat on audible frequencies.

The Vibrato Mod I prefer doing with a switch because for some songs I like Fender Vibrato and don't wish to permanently disable it. Seriously, you can achieve these mods in an afternoon with decent tools and preparation so why guess? Hear them for yourself. They are easily undone.
 

jcs

Member
Messages
8,065
Perhaps you should rephrase your question or better, just try them because you will never learn anything useful by discussing "fidelity and harmonics" for a guitar amp. Not only do most players not realize they are technically playing distorted until it exceeds 30% or so, guitar amps are not sound reinforcement devices. They are musical instruments unto themselves. Whether or not you like these mods is solely up to your ears and playing style. I happen to like tweaking (not just disconnecting) the negative feedback resistor and a well-designed snubber becomes essential then but should have absolute minimal effect on tone other than to be better to most ears since the frequencies they snub are above human hearing but they beat on audible frequencies.

The Vibrato Mod I prefer doing with a switch because for some songs I like Fender Vibrato and don't wish to permanently disable it. Seriously, you can achieve these mods in an afternoon with decent tools and preparation so why guess? Hear them for yourself. They are easily undone.
Well, Black and Silverface Fenders are known as primarily clean machines.....as far as "trying them" I really don't want to mess around with the amp until I gather more opinions.....that's why I asked as the amp has not been tampered/modded with before other than a SS rectifier mod and BF bias.

The rest of the amp is basically stock with replaced electrolytics.

I will probably replace the PI cap from .01 to .001 as it is way too bassy.
 

enorbet

Member
Messages
46
Fair enough. My words are based on the unfortunate fact that most words to describe sounds are not anywhere near descriptive and exclusive. To some, for example, "glassy" means "smooth" while to others, "brittle". For your sound only your ears count.
 

jcs

Member
Messages
8,065
Good sounding harmonics....clarity.

I don't need more gain with this amp....clarity and good sounding harmonics would be a plus.

What does disconnecting the neg feedback do in general with this amp? Any way to describe it?
 

wyatt

Member
Messages
4,169
I don't need more gain with this amp....clarity and good sounding harmonics would be a plus.
Then don't do the Vibrato mod, that's all about adding gain.
What does disconnecting the neg feedback do in general with this amp? Any way to describe it?
Negative feedback is added to tame the aggressiveness of an amp and increase clean headroom. Most people find the amp opens up a lot with no (or decreased) negative feedback...becomes more lively, a lot more harmonic control, like using an Exciter effect...but it also becomes a lot more aggressive and overdrives quicker.
 

jcs

Member
Messages
8,065
Then don't do the Vibrato mod, that's all about adding gain.

Negative feedback is added to tame the aggressiveness of an amp and increase clean headroom. Most people find the amp opens up a lot with no (or decreased) negative feedback...becomes more lively, a lot more harmonic control, like using an Exciter effect...but it also becomes a lot more aggressive and overdrives quicker.
Thanks....that's kind of what I had gathered about the neg feedback being removed.

QUICKER overdrive I might be interested in....I don't necessarily want more gain overall.

I mean cmon, Super Reverbs are LOUD amps.....almost too loud these days.

I don't particularly care for adding a 12ax7 in the PI slot in place of a 12at7.....except for maybe very weak pickups
 

Baxtercat

Silver Supporting Member
Messages
12,661
What does disconnecting the neg feedback do in general with this amp? Any way to describe it?
Yes, a more 'raw' sound.
More mids...harsher imo.

Funny how 1st thing many want to do is disable NFB.
I find Fenders less annoying w/ it left in.

In fact, dial in the NFB by adding a small 1 mfd cap across the 100 ohm NFB resistor, kinda like the brown Fenders w/ Presence [a nice sweet top end].
 

jcs

Member
Messages
8,065
Yes, a more 'raw' sound.
More mids...harsher imo.

Funny how 1st thing many want to do is disable NFB.
I find Fenders less annoying w/ it left in.

In fact, dial in the NFB by adding a small 1 mfd cap across the 100 ohm NFB resistor, kinda like the brown Fenders w/ Presence [a nice sweet top end].
Like my 62 Bandmaster! The presence knob is way more useful in dialing in the top end sparkle.....which I have a presence on my 71 Marshall Smallbox 50 and 73 Carlsbro 60TC with the Carlsbro having a beautiful clean tone, sort of like a Hiwatt meets Vox.

Back to the 71 Super Reverb.....kind of my reference for beautiful Blackface Fender cleans is my 66 Princeton (non reverb).....but the 71 SFSR is way more versatile tonewise...the mid pot really does a LOT on the 71 SFSR.
 

GCKelloch

Member
Messages
537
Fender tone stacks are configured to boost the Bass & Treble, while cutting the Midrange when set flat. The impedance rise in guitar speakers will squelch the high end a bit. So, it should be OK to allow the high end of the amp section to be somewhat driven, as the rising impedance reduces clipping above ~1kHz. Just turn the amp Treble knob down a bit, and try boosting the Midrange. Engage the Bright switch to compensate. The Bright circuit is focused much higher than what the Treble knob generally boosts, so it won't sound harsh, but may be a bit glassy/brittle depending on guitar factors, how much the amp is driven, and how much ~5kHz range the speaker emphasizes. You should be able to get a nice harmonic sparkle. A low capacitance guitar cable will often smooth out and extend the high end into the first preamp stage. All these things together can make a big difference.
 

walterw

Platinum Supporting Member
Messages
38,246
i really like the trem bypass mod on both my early '70s silverface fenders, pro and deluxe reverbs.

yes more gain, but not so much "distortion" as just a hotter, livelier, fuller tone. i did the switching trem pot thing so i could eat my cake and have it too.

dunno about the extra little power tube bleed caps, i pulled them from the pro and it sounds good without them so i went with that.
 




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