NFB question

[iknowjohnny]

If possible, how would i go about reducing low end by doing so in the NFB? Is it possible? I know how to add it, but not reduce it. I don't want to do it in the preamp for reasons too longwinded to go into so the NFB seems the logical location.

[pdf64]

Consider a 5F6A presence control at some mid way setting; that results in more closed loop gain for higher frequencies than lower frequencies.
The cap value can be used to adjust the turnover frequency.
A much greater presence cap value (eg >1uF) will move the turnover frequency down and should result in an effect perceived as a bass cut rather than treble lift.

[iknowjohnny]

I tried that but no real joy. I did however find a solution, one i have tried uncountable times for various EQ changes and never seems to work. The tone stack. Changing caps there for bass or mids never has yielded good results in the past for me. Slope and treble cap changes, yes, but the slope didn't do it this time. What did was the bass cap which i tried after using the duncan TSC which also has never been much of a help to me in the past. But this time it was and i saw that using about a .0047 would help with exactly what i was after, a reduction in the very low end of the bass spectrum leaving the usable lows intact and what the graph showed was just what i heard.

[Stevem]

Can you detail what the issue is your having with the amp?

[iknowjohnny]

None now ! Just too much low end. I've reduced the bass cap in the past many times, but with this particular amp it was the first time it did exactly what i needed.

[ToneMerc]

None now ! Just too much low end. I've reduced the bass cap in the past many times, but with this particular amp it was the first time it did exactly what i needed.

Have you ever tried maybe different speakers?

TM

[iknowjohnny]

It's not a speaker thing and yes, i have but not because of this. There are some things you just know from experience and this wasn't a speaker thing. No matter, tho, as like i said the bass cap did the trick perfectly.

[tubeswell]

If you want to modify the NFB in order to reduce 'low-end' in the signal, you need to boost the amount of LF being fed back in the NFB loop so it feeds back more low end to the signal, which will cancel out the low frequencies in the signal - all other things being equal. (i.e. the NFB signal will need a low-pass R/C filter, with the C value being set to bleed out HF in the NFB loop. This amounts to putting a cap in parallel with the resistor in the 'lower leg' of the NFB voltage divider)