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

[Jazz P Bass]

The amp is breaking up where it does because that is all of the 'clean' output that it can generate.

I like LT's speaker suggestion.

Or buy a more powerfull amp.

[mort]

I like the point made about the output breaking up before the preamp does, didn't realize that was more commonly the case. I suppose I had assumed it was the other way around. And if that's the case, does it stand to reason that I could get more overall volume by biasing the preamp a little hotter, since presumably it has some room left on it before it distorts. Is that What Dave H was getting at in his post?

[überfuzz]

I don't know exactly what you've tried so far, but buffing the anode resistors of that channel might give some extra volume. I take it you haven't scoped this amp... That said we have to guess that the break up is most prominent in the power section. I.e. you might squeeze some extra clean dB without any noticeable extra distortion, or 'headroom'.

[TimmyP1955]

Switch to JBLs or get a Twin Reverb (perhaps with JBLs).

[Dave H]

I like the point made about the output breaking up before the preamp does, didn't realize that was more commonly the case. I suppose I had assumed it was the other way around. And if that's the case, does it stand to reason that I could get more overall volume by biasing the preamp a little hotter, since presumably it has some room left on it before it distorts. Is that What Dave H was getting at in his post?

It's clean at volume settings below 5. That tells me the guitar signal isn't hot enough to drive the preamp to clipping so the clipping above 5 must be the power amp (as there is no master vol). That's the full clean volume it can produce. There's no point in tinkering with the preamp because the preamp isn't clipping.

I was replying to exactly what you said in post 3, not realising that you were using 'headroom' in the correct engineering sense in post 1, sorry about that. I just thought you wanted to move the onset of clipping from 5 to 7 to spread out the range of the pot. What I posted will do that but it won't have any more clean volume. It's as Pete said the way guitarists use 'headroom' just causes confusion. It should be banned.

[pdf64]

...the buyer asked me if it could have a smidge more clean volume...

My reading of that is that he wants more clean SPL; the only way to achieve that is to increase the max power output of the amp (very difficult) or to use more efficient speakers.
Assuming that the amp doesn't have any issues that are affecting its performance, the first point of a non master volume amp such as this to enter clipping (and last to leave clipping) is the power tube control grids.
It would be beneficial for you to verify this for yourself.
What is its power output at the onset of clipping, into a resistive dummy load? Ideally using a true rms meter to measure the voltage across the load.

I really can't see how headroom is appropriate to guitar amps?

[potatofarmer]

What speakers are in it now? Eminence makes some very efficient ones. If you have four 10s, the Ragin Cajun seems to be the winner as far as sensitivity goes.

Also this is a tube-rectified design, right? That's reducing your maximum SPL before distortion. Redesigning it for a solid-state rectified supply would be a pain, plus then you lose that tube rectified mojo.

Hey, there you go; it's not a bug, it's a feature. Tell him the power supply was designed to compress at high volume which give you that sweetness (what sweetness? who knows) of breakup and you've wrung every drop of volume you can out of the amp electrically. Tell your customer he has final control over the overall loudness (and tone! ooo!) by picking different speakers. You can even send him this little tidbit from Trace Elliot - about bass amps but still applicable to any amp:

[DRH1958]

Just to add to potatofermer's bit about having a tube rectifier, you do have a GZ34/5AR4, so you are getting the maximum B+ voltage to the amp with a tube rectifier. This is also a point you can make with your customer. If your amp can handle it, they do make a solid state plug in for the 5 volt series rectifiers. I don't know how much extra power this will generate but it might be worth a shot. https://www.tubesandmore.com/products/T-SSR01 Having the highest voltage will help to accomplish your goal. Just to be sure, is version 7 the as-built schematic in the earlier thread you referred to in post #12?

EDIT: This will will/might change how the EF86 channel sounds too, so evaluate both channels.

[mort]

Just to be sure, is version 7 the as-built schematic in the earlier thread you referred to in post #12?

I believe the only variations from version 7 are that I used a 10uF instead of 8uF as that last filter before the 86 plate, and the drawing does not show the input grid lead for the 86 being shielded, but it is.

As far as the clean volume goes, I think there's enough and when the owner of the amp finally does get it, I think he will agree. I think when asked, he was erring on the side of caution in wanting clean volume, as the other channel of the amp is versatile enough to go from clean to mean. In this case I'm going to leave well enough alone concerning clean output. I do have another small issue I may as for help with a bit later.

[mort]

And this amp is in head form. We recorded with a V12 loaded 2x12 cab. I'm not sure what the owner has for a cab but I'll be sure to mention the speaker selection.

[John_H]

And this amp is in head form. We recorded with a V12 loaded 2x12 cab. I'm not sure what the owner has for a cab but I'll be sure to mention the speaker selection.

This could be part of the problem. Super Reverb amps have a 2 ohm output.

[Leo_Gnardo]

This could be part of the problem. Super Reverb amps have a 2 ohm output.

All this faffing around... THERE'S your problem, unless your 2x12 is a pair of 4 ohm speakers in parallel.

[pdf64]

It would be helpful to include the current schematic in this thread.
The global feedback arrangement on the previous thread's schematic was unclear.
However, as the OT didn't seem to have a 2 ohm output, the negative feedback ratio will be greater than that of the original, which may lead to a harsher transition from clean to overdriven.
It might even affect the headroom

[mort]

Ok, I had cited the Super Reverb original circuit because I had thought we wouldn't be talkin about anything past the normal channel preamp which I left unchanged in my version. Here's what I built, using a 4/8/16 output OT. I'll doublecheck later but I'm pretty sure I connected the NFB to the 4 ohm output tap and there's a rotary impedance selector on it(not clearly denoted on the drawing)

[Dave H]

I'll doublecheck later but I'm pretty sure I connected the NFB to the 4 ohm output tap

If it's on the 4 ohm tap change the 820 ohm feedback resistor to 1k2 to give it the same feedback as the Super Reverb. Then it will start to clip even earlier (on the vol pot)