Your thoughts on Power Scaling.

[Structo]

So John, are you speaking of the O'Connor power scaling or the VVR
method?
EDIT: I looked up the Badger and it does use Power Scaling from London Power.

I think the VVR is attractive to so many because it is so much cheaper to implement.

[Structo]

By the way there is a link to five of Guthrie Govan's live cuts on the Badger page.

http://www.suhrguitars.com/badger.aspx#30

You can link to high quality M4a files here.
http://www.mediafire.com/?zvuwicncssf46

[Decko]

Cool thread! I have a Dana VVR purchased some time back but was hesitant to install. For me, too many unknowns on how the overall tone would be affected. Power tube distortion is what I was looking for in amps design that I built. So if it sounds great why mess with it. Shove the cabinet in an isolation cab and rock on. But that said, you never know until you try! Right?

It would be cool to see an audio/video demonstration of power scaling. Any of you gents have a link that really demonstrates the benefits of scaling?

Danny

[gary]

Pete Thorn demoing the Suhr Badger

http://www.youtube.com/watch?v=HBUxUB-6qjw

the power scaling demo is near the end.

[leadfootdriver]

Thanks for the replies thus far!

My understanding to this point was that you're only altering the powertube voltages. I don't know why you'd want to alter the PI. As I've been reading on, it seems that you can get crazy, and alter the voltages of the whole amp.

If I'd were to do a power scale, it would be for a fixed bias amp. I'm not a cathode biased guy. I's be interested in scaling the power section only.

I found this kit on another message board. Has anyone had experience with this company? Anyone have a power section only kit to recommend?

http://skipzcircuits.com/FX100.html

[pablogt]

I have installed 4 Power Scale and will install another in my next build. Regarding drive compensation, I have a 36w amp in which I tried several different flavors of MV:

- Traditional MV, with scaled PI: big loss of treble when set below half. Not good
- PPIMV (both cross line and ganged pot) since NFB is reduced when the PA is scaled down, gain increases and it becomes fizzy
- "atenuated" PI, that is, using a pot in place of the bias resistor in the PI's cathode. Worked fine for distortion, but won't clean up at high attenuation levels
- Bootstrapped MV, called London Power MV by Kevin O'Connor. Very nice and neutral, this is the one that stayed.


I also installed power scaling in my Rocket. Since it does not have NFB, it does not suffer because of the reduced NFB at high attenuation levels. So I installed PPIMV and it works like a charm.

So, in my amps, the ones that get a PA only scaling in the future will get bootstrapped MV if they have NFB and PPIMV if they don't.

Pablo

[Structo]

Thanks for the replies thus far!

My understanding to this point was that you're only altering the powertube voltages. I don't know why you'd want to alter the PI. As I've been reading on, it seems that you can get crazy, and alter the voltages of the whole amp.

If I'd were to do a power scale, it would be for a fixed bias amp. I'm not a cathode biased guy. I's be interested in scaling the power section only.

I found this kit on another message board. Has anyone had experience with this company? Anyone have a power section only kit to recommend?

http://skipzcircuits.com/FX100.html

I believe the VVR and Vari-Watt are public domain circuits therefore you can source and build them as you like.

The London Power Scaling is copyrighted and you can only buy it one place (as I recall).

The trouble with any of these devices is, as you go up in power you have to dissipate that energy somehow, and that is by taking the heat out of the circuit.
And as you might well imagine, a 100w amp is gonna throw a lot of heat.

Heat + Electronics = Bad

So you have to isolate or "heat sink" the heat away from the more sensitive components.
Be that by bolting the hot device to the chassis or by the use of a Heat Sink bolted to the device.

[John_P_WI]

The London Power Scaling is copyrighted and you can only buy it one place (as I recall).

Tom,

KOC's TUT6 has his DC power scaling schematics detailed in full, and possible modifications. His kits have a bias tracking regulator (for fixed bias application) and dual mosfet regulators for the B+ and screen nodes. Plus the kits are rated for 100 watts-all of these are reasons that his kits are more expensive.

As I said previously, his designs are very flexible and can easily be tailored to channel switching amps. Sorry, I don't have any personal experience with the other guys circuits as I have followed KOC's designs since the late 90's.

KOC's "improved" bootstrapped master works well in most applications.

John

[Richie]

Thanks for the replies thus far!

My understanding to this point was that you're only altering the powertube voltages. I don't know why you'd want to alter the PI. As I've been reading on, it seems that you can get crazy, and alter the voltages of the whole amp.

If I'd were to do a power scale, it would be for a fixed bias amp. I'm not a cathode biased guy. I's be interested in scaling the power section only.

I found this kit on another message board. Has anyone had experience with this company? Anyone have a power section only kit to recommend?

http://skipzcircuits.com/FX100.html

I believe the VVR and Vari-Watt are public domain circuits therefore you can source and build them as you like.

The London Power Scaling is copyrighted and you can only buy it one place (as I recall).

The trouble with any of these devices is, as you go up in power you have to dissipate that energy somehow, and that is by taking the heat out of the circuit.
And as you might well imagine, a 100w amp is gonna throw a lot of heat.

Heat + Electronics = Bad

So you have to isolate or "heat sink" the heat away from the more sensitive components.
Be that by bolting the hot device to the chassis or by the use of a Heat Sink bolted to the device.

As with anything it may all depend on how its installed in an amp. or where you have room to fit it. And type chassis. Aluminum vs steel or whatever you use. As for the heat, only at certian settings does it have much heat in the VVR. Just saying, i've had some where it really didn't seem hot at all.

I've also used one and had a small heat sink and small PC fan. I put that in a 50 watt marshall. Yes, Dana has his own boards,and posted on many forums of it being public domain. But his VVR that has the bias tracking is not that i know of. Dana has built an amp that you could dial in voltages for every tube in the amp. I really can't speak for Dana, but i think looking around he does his thing,and others do theirs. I know hes helped others that were having problems and they were not even his boards.

As its all good. Just gives people more options. If you are building a new amp, you can design the section to install the scaling. Some take alot more space to install than others. Its when you have a built amp,and want to try and find room to add a scaling device is where it gets tricky.

[John_P_WI]

I really can't speak for dana, but i think looking around he does his thing,and others do theirs. I know hes helped others that were having problems and they were not even his boards.

+1, very much agreed.