Power Scaling in General

[fiftynine]

I keep trying OD pedals and attenuators and just don't dig them. I've never tried power scaling and I'm thinking about London Powers SB-1 kit for my AB763 Deluxe Lite with 1-Tube Reverb.

Has anyone fitted it? Do you think it sounds better than pedals or attenuation at say half volume. In fact, what sort of volume reduction can I expect?

Cheers.

[samato]

I don't have any info on power scaling for you but rather a question. 

One thing I've always liked about the AB763 amps I've played is that they sound good at any volume.  Is that not the case with yours or are you just going for a more driven sound from the amp? 

I was going through all this with my Pro Jr. recently.  The Pro Jr., unlike an AB763, does not sound good at low volume to me so I was trying to figure out how to get it in the sweet spot with pedals and attenuators.  I did make a pretty cool attenuator that works well but it still wasn't working for me.

I've heard variable voltage regulator (VVR) is the way to go.  I never really looked into it though, I decided I need another amp to get the sound I really want.

[fiftynine]

No, samato. It's the sweetest amp I've ever had at any volume. I'm so glad I built it. The SB-1 is pretty intrusive though and I need to be sure it's for me. Skipz Circuits do the Vari-WattFX which looks like a clone with really nice pots.

[jojokeo]

I recently finished a SE amp w/ an EL34 & one 12a_7. I fitted a cathode biased VVR circuit copying Dana Hall's circuit (using one of many of Tubenit's schematics showing this) for use as a "master volume" control. It works really well but I find some interesting characteristics w/ it's use. Since the amp is pretty straight-forward, I think I've got a pretty good grasp on exactly what it's doing/how it responds and rules out possible bahaviors that might be associated w/ extra stages and/or controls.

1) it does a good job of controlling output power : power tube distortion
2) as B+ is lowered, the power tube's input sensitivity increases and overdrives more easily
3) the more it is lowered the more the treble control comes to a point to where it doesn't do much. There's highs in he signal but you only get so much into the speaker as it relates to output power.
4) it is better than an attenuator
5) it is more versitile than a "normal" master volume control
6) on smaller amps, having both a MV and VVR would seem redundant and unnecessary (unless you like or want the sound of preamp distortion also/instead)

Hope this helps, Joe

[fiftynine]

That sounds quite positive, Joe. What sort of volume drop do you get?

[jojokeo]

It goes down to well below "talking loudness" w/ the vol up full and the VVR down all of the way. In fact I only lower it down to "3" at certain times when I want to check it out as "1" seems too low. At this level of output, it's not necessary to drive the power tube as hard but at (preamp) 10 w/out the tone stack & in "Marshall biasing mode" it is as much signal as you can pump into the power tube. It can actually give unlimited sustain or feedback sustain at this lower output volume which says something about the coolness factor of having this type of amp volume control.

Describing it's functionality: when normally playing for overdrive at lower volume I'll keep it at "5" which is plenty and right in the sweet spot for the speaker to start being pushed a bit. Between 5 & 10 the loudness perception can be sneaky is the best way to describe it. It's not as "in your face" as a normal master volume but maybe it's because I'm only working w/ about 10 or 11 watts max? In working the amp btwn 5 & 10 and using the preamp's vol there's a wide range of "juicy" textures at any volume you like. For clean/country/jazz playing it's better to kick the VVR to 10 as the low gain biasing preamp setting doesn't kick out the signal output the same as the Fender & Marshall modes so you need that extra power on tap. The VVR makes your tone your own for any number of smaller venues or home playing and I'm really pleased with it.

[fiftynine]

That's a great help.