Power Scaling is Flawed?

[Jag]

Thanks Matt. I think I'll give Kevin a call and order one to try in my Marshall JMP.

[hasserl]

Would you have a link to that discussion ? I'd like to read that. I guess the discussion or debates would be over the sag issue. The supply is regulated and quite stiff so I don't see how you can get sag when the supply doesn't sag ?

No, but try a search on Power Scaling over at The Gear Page, or just search under Maven Peal or Kevin Oconnor and see what comes up. Kevin doesn't post much there, so any of his posts will likely be on the topic.

[Steve Conner]

I vaguely remember looking at the Maven Peal patents once. I think it has some kind of a circuit that adds adjustable sag.

[bob p]

that rings a bell, Steve. i also seem to remember adjustable sag being used in the Maven Peal approach, but i can't remember whether it was implemented with resistor selection or what.

[Ptron]

The K.O.C. version has adjustable sag too.

[Amp Kat]

Theres probably several ways to sag the supply all of which in the end create a low impedance high wattage resistance in series with the power supply to mimic the voltage drop of a tube rectifier. In term of sound it IMO acts more like a compressor than a true tube sag which of course we don't want to get into that sag/compression debacle again but it is different. Being the output is in series with the power supply the internal resistance depends on the transformer winding resistance and the Load resistance which can be calculated by dividing the voltage change by the current change. Sag after the power scaling is basically doing the same thing and that's dropping the plate voltage just making it variable at full load situations or at it's peak power point.

[Mickey_C]

I think power scaling could be flawed for two reasons: poor dynamic range and poor speaker performance.

I don't know what the noise floor is on the typical amp, but the dynamic range is the difference between the maximum output power the amp produces when it is amplifying a guitar signal and the amount of output power the amp produces when it is amplifying internal noise noise.

Reducing the output power brings the guitar signal closer to the noise floor and reduces dynamic range in the process.

From what I can tell, most guitar speakers stop perfoming well when power drops below about 1 watts or so.

The problems you speak to apply equally to any attenuation (except for the noise floor, which is erroneous, as the scaling also drops the noise level too, though indeed, there's not much dynamic range in a 10mw signal).

No matter if it's a master volume control, external attenuator, or power scaling, the speakers will not be driven as hard. More importantly, the dynamics of the ear change at low volumes too. But these issues apply to all forms of volume attenuation. So it's not per se a flaw with power scaling so much as a flaw in low volume playing.

What I will say is that your ears will be much more pleased with the results of power scaling than even the best of attenuators. It's a magnitude better in the correct direction!

We're starting a forum on Power Scaling, at PowerScaling.com, which will hopefully answer questions like this and much more, as well as review power scaling solutions, provide clips of power scaled amps, and get some talk back from the manufacturers implementing this technology.

Thanks,

Mickey C.
http://www.soultoneamps.com
http://www.powerscaling.com

[tbryanh]

I've got it bookmarked (Powerscaling.com).

Cheers

[mooreamps]

Well, as long as I don't see my P/S circuit displayed, then I have no problem with it.

-g

[tbryanh]

Well, as long as I don't see my P/S circuit displayed, then I have no problem with it.

-g

Its probably not your P/S circuit or anybody elses for that matter fool.

[Amp Kat]

You know that is quite funny tbryann that there are so many circuits that have been done by our forefathers and have been forgotten. Someone rediscovers it and all of the sudden it's theirs. Everything that is possible with tubes has allready been done before. Power scaling has been done before just the circuit was a tube circuit not a Mosfet. Unbelievable !

[mooreamps]

I am aware PS has been done before. I am aware of how the other circuits are built, including Kevins. I was considering giving S2 my P/S circuit as a kit for eval over on 18 watt.com before it got shut down. In the meantime, I'm not willing to release it into the public domain. It will only be for those few guitarists who contract me to build their equipment.

-g

[Steve Conner]

I've offered to collaborate on a free open-source design for a power scaling unit before, but I never got any credible offers of help. The offer still stands if anyone would like to help me develop something that just works with no hype, BS or patent hassles. All I ask is that you actually have a clue about electronics and make a contribution instead of just yelling omgplanz4me.

[mooreamps]

do you want to design one, or just have a working circuit for your own personal use ??

-g

[Steve Conner]

I want to see power scaling done as an open-source project, for the pure fun of annoying all the people who developed proprietary designs and patented them.

If I just wanted one for myself, I'd have made it about 7 years ago when I was experimenting with MOSFET regulators for B+. I have designed a whole range of stuff from DSP-based industrial instruments through to Tesla coils for science museums, so it's not like I'm stuck and needing help. (Except maybe with assessing the reliability of MOSFETs used in the linear mode when they were designed for switching power supplies and not specified for linear use.)

But I've been more than happy with the tones I'm getting from my experimental amps without scaling. I realised that the main thing I like about cranked tone is in fact the volume