BF Super Reverb aa763 Normal Channel -- how to increase headroom?

[mort]

Without increasing headroom on the wet channel?

http://www.thevintagesound.com/ffg/s...a763_schem.gif

[pdf64]

Headroom is a funny word, has a precise definition in pro audio but guitarists use it to describe a variety of things; best to define exactly what you want to happen, eg I want the normal channel to generate less / more SPL when set to 3.

[mort]

With the volume set to 5, the amp stays clean and has a bit of OD when you dig in. I would like for that to happen at 6 or 7 instead, if possible.

[DRH1958]

I wonder what a 500k volume pot would do instead of the 1 Meg on the normal channel?

[Dave H]

You could remove the cathode bypass capacitor on the first stage of the Normal channel. If that's too much put a resistor (1k5?) in series with the capacitor.

[Leo_Gnardo]

I wonder what a 500k volume pot would do instead of the 1 Meg on the normal channel?

Darken the tone a bit. You could do a quick n dirty 'speriment, just wire a 1M resistor across the pot. Try a 330k to simulate a 250K volume pot, the difference should be obvious by that point.

[ThermionicScott]

Headroom is a funny word, has a precise definition in pro audio but guitarists use it to describe a variety of things; best to define exactly what you want to happen, eg I want the normal channel to generate less / more SPL when set to 3.

I hate it when people use "headroom" to talk about knob settings, but so many do that we might as well meet them where they are, huh?

What's so objectionable about having the knob on 5 rather than 6 or 7 anyway? One easy fix would just be to loosen the knob screw and turn it a little so it's on the equivalent setting at 6 or 7.

[mort]

I hate it when people use "headroom" to talk about knob settings, but so many do that we might as well meet them where they are, huh?

What's so objectionable about having the knob on 5 rather than 6 or 7 anyway? One easy fix would just be to loosen the knob screw and turn it a little so it's on the equivalent setting at 6 or 7.

The point is to get a bit of higher volume before it starts to break up. Maybe I was mistaken that the term headroom would communicate that intention precisely, and that's ok. I don't mind using a different explanation, so long as the point is communicated. That is the goal, right?

[loudthud]

If you want the amp to be louder before it starts to breakup, get some more efficient speakers or a more powerful amp.

[Malcolm Irving]

The point is to get a bit of higher volume before it starts to break up....

There are various ways to get break up at 7 on the volume control instead of at 5, but unfortunately the actual sound pressure level from the speaker(s) will be the same in both cases.
That's because the limiting factor in the sound pressure level is the power output stage. In any well designed amp the power output stage will 'break up' first, provided you have the master volume (on amps where there is one) set to max. If this was not the case the amp would not be able to achieve its rated output.

EDIT: more efficient speaker would do it though.

[ThermionicScott]

The point is to get a bit of higher volume before it starts to break up. Maybe I was mistaken that the term headroom would communicate that intention precisely, and that's ok. I don't mind using a different explanation, so long as the point is communicated. That is the goal, right?

Yep, sorry for the snark, but it's a pet peeve of mine. "Headroom" is more properly defined as reserve amp volume before clipping, and as LT and Malcolm point out, the output section and speaker(s) have way more control over that.

Is the goal to be able to switch between the normal and wet channels and have the same amount of dirt? It might be possible to tweak the wet channel for a little earlier preamp breakup if that's the case.

[mort]

"Headroom" is more properly defined as reserve amp volume before clipping

I ask this factually and not sarcastically, is that not what I was asking for? If clipping and distorting are the same thing I'm not sure I see how the word headroom was misused.


The amp in question is the one in this thread: http://music-electronics-forum.com/t40935/

And here is a clip from the clean channel on 5 w the guitar plugged straight in: https://m.soundcloud.com/mortatone/m...-clean-channel

When the player digs in a bit it starts to break up, and nicely I might add. Personally I would leave it, but the buyer asked me if it could have a smidge more clean volume. So here I am asking, as this is my first project that is not a straight stock copy(see signature below). I had someone privately help me on this from the onset, which I appreciated, but he has since dropped off the face of the planet so I'm once again at the mercy of all of your kindness. I do appreciate any help, this stuff doesn't come easy for me so I do rely on outside help.

[ThermionicScott]

I ask this factually and not sarcastically, is that not what I was asking for? If clipping and distorting are the same thing I'm not sure I see how the word headroom was misused.

When the player digs in a bit it starts to break up, and nicely I might add. Personally I would leave it, but the buyer asked me if it could have a smidge more clean volume.

Ah, there we go -- the player wants a little more clean volume. What the knob says when the amp breaks up isn't really important, and may stay the same after the mods, it'll just be louder at that point.

So, what speakers does the amp use? Since a Super has four of them, you could swap one or two to more efficient models and gain more volume without completely changing the character of the amp.

[octal]

I think what you were perhaps trying to communicate is "I would like the amp to play at the SPL (i.e. acoustic 'volume') I get when the volume control knob is set to 7 but as sound as clean as it does when the volume control is set to 5." What offends peoples sensibilities is expressing acoustic volume (SPL) in terms of numbers on a knob. (i.e. the old "Spinal Tap" joke about how an amplifier which has knobs which have numbers going up to 11 is one louder than an amplifier with knobs numbered up to 10) Obviously (I hope!) you know that the actual number you have to set a knob to in order to achieve a certain SPL is irrelevant unless you have a client who doesn't understand that the numbers don't matter. "I want the amp to stay clean up to a higher SPL" is an engineering goal. "I want the amp to play clean at knob position 7" is kind of a sloppy way of expressing it, and what SPL an amp achieves at any given knob setting depends on so many factors (speaker, gain in amp, volume control setting on guitar, type of pickups in guitar etc. etc) that knob settings are not considered a unit of measurement of SPL, gain, or anything else. The numbers are strictly relative.

To restate what others have said...since the breakup on the normal channel is presumably coming from the output stage overdriving , the only way to get the sound the client wants at a higher SPL is to get more power out of the amp somehow (raise the B+ with an SS rectifier?) or use more efficient speakers. That will change how it breaks up on the EF86 channel as well- unless the EF86 channel is designed for preamp overdrive (is it?)

[mort]

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.

I will never reference a knob position number on music-electronicsforum.com when referring to clean volume.







ok, now that my penance is complete, can we move on fro these semantics? I know that the actual number doesn't matter. Perhaps I should have said "for example" when referring to the volume being at 5. Sheesh.