Standard Amp "body" and "Limit" controls - what the hell are they?

[Ptron]

Does anybody know what the practical effects are of the "body" and "limit" controls on a London Power Standard amp? These seem quite unique.

The "Limit" control is a 1M pot wired like a rheostat between the two output phases of the PI, so that when the control is maxed they are shorted together and when all the way down there is 1M between them. The "Body" control is 1M pot wired sort of like a volume control for the out-of-phase side so that when all the way down, the input to the out-of-phase power tube is grounded.

These controls seem like they would have drastic crazy effects on the output and balance of the power amp. In the sandard amp they are front panel controls, not internal adjustment pots.

[R ski]

Some amp builder kinda went over the holy tone grail edge. Altering
the load with a power rheostat, lowers the PI voltage impressed
into the power tubes, lowers the power tube drive.

The out of phase feedback also lowers the amplifier drive.

If moving air is your thing. That concept is a negative.

Some builders have gone through inovation configuration concepts
of simular attempts, Guitar Player mentioned about offerings some issues ago.

[Steve Conner]

I guess "Limit" is like a post-PI MV, and "Body" deliberately unbalances the PI to generate a different mix of harmonic distortion (which I guess makes it sound more bodied or something...) In the limit it would operate like a single ended amp with the opposite tube just providing DC balance.

Whatever floats your boat, but I wouldn't like the thought of losing a power tube's worth of output.

[carl gigun]

"What Steve said"

but to add a bit, the "body" control aims to give you a taste of single ended sound even though it's a push pull amp. It's been shown in KOC's books since the original TUT i believe. I tried it years ago but didn't find much use for it, might work better in other amps.

[Ptron]

Thanks folks. Have any of you tried a Post PI master volume like the aformentioned Limit control?

For some reason, KOC has givin the Standard a regular master volume and this "limit" control, as well as power scaling. I'm probably going to build a dumbed down version of this amp and that's 1 or 2 too many ways to get some disto at lower volumes.

The body control sounds interesting. I probably won't bother with it though. I want to get the number of knobs down to where I can still operate the amp drunk.

I have a few other questions about mods or de-mods for this amp but they probably belong in another thread.

[carl gigun]

I haven't played with post PI masters (I like low wattage amps you can crank) but there was a pretty long thread on the subject not that long ago. I don't remember if it was on the new or old board though.

I checked the london power page, it says "Limit is used to control power stage distortion at low Power Scale settings".

[Smitty]

Have any of you tried a Post PI master volume like the aformentioned Limit control?

Yes. I use the Matchless-style 'cross-cut' PPI-MV in my Bluetron Blueverb. Works pretty well in the upper range. In the lower settings it cancels the signals that are in common before attenuation cancels the distortion characteristics of the phase inverter (less oomph). This lower setting works well to understand by listening how much distortion the phase inverter is generating. At the lowest post pi mv settings, the level of phase inverter overdrive can be tuned with the standard Fender-style pre-Phase Inverter master volume.

Players ask me why I use two master volumes. That's why. I get this question a lot.

[Ptron]

Yes. I use the Matchless-style 'cross-cut' PPI-MV in my Bluetron Blueverb. Works pretty well in the upper range. In the lower settings it cancels the signals that are in common before attenuation cancels the distortion characteristics of the phase inverter (less oomph). This lower setting works well to understand by listening how much distortion the phase inverter is generating. At the lowest post pi mv settings, the level of phase inverter overdrive can be tuned with the standard Fender-style pre-Phase Inverter master volume.

Players ask me why I use two master volumes. That's why. I get this question a lot.

Ahh.That makes total sense. Thanks

[KevinOConnor]

Hi Guys

It always make sense not to ask the originator of a concept about it....

'Body' is there to provide altered harmonic balance.

'Limit' is used to limit the distortion of the output stage when the 'Power Scale' control is dialed down. 'Limit' is called 'Drive Compensation' in the kits. There are better ways to implement the 'Limit' function .

Having the traditional MV in place allows multiple operating modes for the preamp, splitter and power stage, where any/all can be clean or dirty.

Have fun
Kevin O'Connor

[DIY_Guy]

'Body' is there to provide altered harmonic balance.

Hey Kevin, that other thread about a PI as an input got me thinking about trying this. Can you explain what this sounds like for me before I try it? I'm sure it's explained in one of your books(I have them all) but trying to thumb through all the volumes to find something that small is nerve racking sometimes.