Power Scaling question

[Ian Price]

I'm a complete novice when it comes to understanding amps. My question is if I had loads of amp heads all with power scaling but different wattage (lets say 5w, 10w and 50w) would the power scaling give you the ability to make all of the amps sound the same at lower volumes?

The context of my question is if I had only one amp that was used for gigging and home use would a power scaled higher wattage amp make more sense or would it limit the cranked sound I could get at bedroom level?

[martinw]

Choose the amp you like the sound of best, and Power Scale it.

When executed properly, Power Scaling will maintain the tonal character of the amp, whilst allowing you to take the volume down to bedroom levels.
There's no advantage in starting off at a lower power level, unless you prefer the sound of that amp.

[Twinfan]

Power scaling has limits Ian - you can only go so low on the voltage before the tone gets fizzy.

A Power Scaled lower wattage amp will sound a bit better at bedroom volumes than a Power Scaled larger output amp.

If you need a gigging amp, I'd got for that and use Power Scaling and a pedal to get nicer drive at lower volumes.  For example, a Power Scaled JTM45 and your OCD would be a good match  :)

[indysmith]

Can somebody explain to me how Power Scaling works electronically please? I've been reading thru the "London Power" site, and can't seem to squeeze any useful information out of it.

[martinw]

A Power Scaled lower wattage amp will sound a bit better at bedroom volumes than a Power Scaled larger output amp.

I'd have to say I don't agree with that.

[martinw]

Can somebody explain to me how Power Scaling works electronically please? I've been reading thru the "London Power" site, and can't seem to squeeze any useful information out of it.

It varies the HT rail voltage downwards, and in the case of fixed bias amps, employs a tracking bias regulator which means that the bias voltage decreases in proportion to the anode and screen voltage.
Cathode bias amps don't need the bias regulator part.

The effect is that the output valves produce less power, and yet maintain their transfer characteristics (i.e. tone) to the point where they are almost 'off'.

A 'drive compensation' control is employed to reduce the size of the signal from the unscaled part of the amp at more extreme settings. This is basically a master volume, which many amps would already have.

[Ian Price]

Choose the amp you like the sound of best, and Power Scale it.

When executed properly, Power Scaling will maintain the tonal character of the amp, whilst allowing you to take the volume down to bedroom levels.
There's no advantage in starting off at a lower power level, unless you prefer the sound of that amp.

Cheers Martin - my favourite amp sounds have aways been Hendrix and Frusciante, both Marshall based but I do prefer Frusciantes cleaner/slight break up sounds. I think he uses combinations of Jubilee, Major and JTMs.

[Twinfan]

A Power Scaled lower wattage amp will sound a bit better at bedroom volumes than a Power Scaled larger output amp.

I'd have to say I don't agree with that.

Fair enough - you know a bit more about it than me!

[dave_mc]

interesting thread, thanks for posting it, i've always wondered about this kind of thing too, as a home player who suspects he doesn't necessarily "like" the tone of single-enders.

How about an attenuator versus power scaling?

[martinw]

Fair enough - you know a bit more about it than me!

Sorry, don't mean to be brusque!  The 50W marshalls, and JTM45s I've done sound great at practise levels. Deluxes and Roadstars have the same issues with requiring drive compensation, and because of the logarythmic volume thingy, don't really seem to benefit from having a 30W head start.

A Power Scaled 5W single ended amp can sound great, but it's not going to sound like a small Marshall.

How about an attenuator versus power scaling?

Power Scaling is far better than any attenuator I've ever tried.

[Philly Q]

So is there any disadvantage to having power scaling?

It seems like a feature that would be worth having in any amp, although I guess cost might be an issue.

[martinw]

Cost is the only issue.
When the PS control is fully up, the system is invisible, so if you don't want to use it you don't have to.

[Philly Q]

Thanks Martin, that's what I was hoping you'd say.  :)

[Twinfan]

So is there any disadvantage to having power scaling?

Power scaling has limits Ian - you can only go so low on the voltage before the tone gets fizzy.

This is the only issue I've found.  If you go really low on the scaling control, you do get a bit of fizz creeping in.  Other than that, it's the best solution to reducing volume that I've heard.

[dave_mc]

thanks, martin. Just out of interest, how much does it cost to add powerscaling (either to an existing amp, or to a build-from-scratch amp)? Maybe it varies depending on the amp, but a rough ballpark figure would be cool.