Power Scaling is Flawed?

[mooreamps]

O'Connor explains his position here:

http://www.powerscaling.com/community/index.php?page=9


Basically, if you're a boutique amp manufacturer, you learn to power scale from his work, and you make money including his circuits in your product, you have to buy him a pizza now and then, .

That's nice, except I have no access to this board. Therefore, I can't be held responsible for it's content. Also, I did not learn to power scale from Kevins work. I actually come up with my circuit before TUT4 was released, and before it was brought to my attention that others had used the same approach using a solid state design. But, I would no problem having a pizza with KOC.


-g

[Chuck H]

This is my own personal opinion. I think that the only difference between power tube distortion and preamp distortion is that power tube distortion happens at thrilling volume levels that shake your whole body. If we scale power tube distortion down to half a watt, no matter whether we do it by reducing B+ or using a power brake, it just becomes another kind of cheesy fuzz box.

The only thing that it does that preamp tubes don't is the compression and pumping effect that comes from sagging B+, grid blocking, and cathode bias pumping up. But a savvy designer could easily simulate these in the preamp. I'm sure I remember seeing Marshall added a pair of diodes to a post-PI MV, to tick most of these boxes.

Great post. And mostly accurate

The only thing I would argue is that different tubes (be it a 12AX7, EF86, 807 or an EL34) distort differently. It is even subject to brand. But the interaction of the specific tube with where the sagging occures, it's response at different primary loads, where the top and bottom end rolls off, blah blah blah, is specific. Power tubes distort differently from preamp tubes because they are different tubes operated under different conditions. So it seems fine to surrender to the fact that if you want the distortion of an overdriven power tube, you should design with that in mind. Not try to emulate it with a preamp tube, who's tone and operating conditions are entirely different.

Other than that I fully agree that if what you want is power tube distortion of a certain character, you can't dramatically alter the operating conditions and get the same thing. But, for now at least, power scaling seems to be the compromise of choice.

Chuck

[hasserl]

I don't think most people could differentiate what they hear as being power tube distortion or preamp tube distortion (what category does PI distortion fall into anyway?) All they know is a type of sound they hear from certain amps, and they've been told that sound is due to power tube distortion; and the sound of different amps is due to preamp tube distortion; so that seems to be the concensus across the internet. Certain amps have power tube distortion and that's why some people like them; other amps have preamp tube distortion and that's why other people like them. When in reality there are very few amps with only power tube distortion, because by the time you turn the amp up high enough to get the power tubes to distort (if they do at all) the preamp and phase inverter will be distorting like crazy.

[Alf]

Have a look at this Suhr 18 watt amp that be be turned down to 1/2 a watt with their "power dampening control" , it sure convinces me !

It starts around 7.53

Whatever you call it , bringing down the wattage is imho a very good feature for an amp.


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


Alf

[hasserl]

Have a look at this Suhr 18 watt amp that be be turned down to 1/2 a watt with their "power dampening control" , it sure convinces me !

It starts around 7.53

Whatever you call it , bringing down the wattage is imho a very good feature for an amp.


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


Alf

I've seen that video plenty of times, there is a clear effect on the tone of the amp as the PS is engaged and the volume is brought down, and IMO the results are no better than just using a decent attenuator (or even a not so decent one).

And since a Master Volume is also required in order to get the best performance out of power scaling, doesn't that make power scaling kind of redundant?

I'm just not convinced that it's the best alternative out there, considering the added cost and complexity. Of course, it's easier on the power tubes than driving them full blast into an attenuator, but an attenuator has portability as it can be moved easily from amp to amp. It seems like a personal preference situation, and it's good to have choices. I just don't think the supposed clear advantage of power scaling vs. attenuation is as clear as PS proponents would have you believe. Since I can build a decent attenuator for less than the cost of a KOC book, or one of his kits, I'll just stick to them for now.

[Chuck H]

I don't think most people could differentiate what they hear as being power tube distortion or preamp tube distortion (what category does PI distortion fall into anyway?) All they know is a type of sound they hear from certain amps, and they've been told that sound is due to power tube distortion; and the sound of different amps is due to preamp tube distortion; so that seems to be the concensus across the internet. Certain amps have power tube distortion and that's why some people like them; other amps have preamp tube distortion and that's why other people like them. When in reality there are very few amps with only power tube distortion, because by the time you turn the amp up high enough to get the power tubes to distort (if they do at all) the preamp and phase inverter will be distorting like crazy.

Thats true enough. But for some of "us" (Ampage geeks) it can become a quest to find the magic formula between preamp AND power amp distortion (someone asked where the PI fits in all this ). And IMHO it's a valid quest. Every amp is like a recipe. We get to choose the ingredients and spices because we are the cooks. The general buying public only gets to choose from whats on the menu.

FWIW I try to get all the gain stages dancing to the same tune (starting to overdrive at the same time). Including the PI (just so you know that someone is considering it). That seems to bring out the most touch sensitivity and alows for a loud clean tone in an amp that is also capable of generous overdrive and distortion without getting much louder. It becomes very controllable with the volume knob on the guitar (provided the guitar has a "bright" cap on the volume pot) and is great for stage use. Thats "MY" recipe. Others surely differ in concept and implementation.

Chuck

[Chuck H]

I would have no problem having a pizza with KOC.
-g

Yeh, but what about us "common" folk...It would have to be dutch, wouldn't it?

Chuck

[mooreamps]

Yeh, but what about us "common" folk...It would have to be dutch, wouldn't it?

Chuck

If you're a guy, ya it's dutch....

-g

[Mickey_C]

Power Scaling is just one more tool for building amps. It's not an all-or-nothing thing. For a manufacturer building new amps, it is merely a handful of components at worst, and there are quite a number of different circuits to use to achieve it. For the DIY, it usually means a retrofit of some type, using some canned circuit, and I can see the hassles - but it can be a fun project, if that's the goal. In either case, it's not an end onto itself. It can add some additional flexibility to a great amp. To a crappy amp, it's no more than polishing a turd; it won't get any better, and it will probably just flake apart, and you'll be covered in specks!

Should Power Scaling be the only level/volume/power method employed on an amp? Of course not, it's just one of many. When properly integrated it adds some control to the player for changing more aspects of the amps performance, namely the power tube clipping, or when dialed out has no negative effect on the amplifier, so what's the issue? You can use it with a PPIMV, normal master, or attenuator, or any number of other options. There's nothing mutually exclusive about it. And therefore, for that very reason, there is nothing flawed about it.

Just add it to the growing list of circuit options when building an amp, and don't expect it to make a turd sing like a nightingale.

[booj]

My 2204 clone has variable plate voltage/screen voltage. I adjust the plate and screen voltage simultaneously without changing the driver or preamp supplies.
>The "Dynamic Window" as I call it changes as I reduce power.
>The noise floor stays the same
>As power is reduced, the Master needs turned down to maintain the clean to dirty feel with the guitars volume control.
>The tone is not appreciably changed, except to give it a fatter tone. There may be some slight high end loss, but it's not noticable.
>I think it's a useable feature. I use two JBL 12"s. A D120 and a K120. I don't think low power to the speakers is an issue.
It uses a Fender Bandmaster power tranny and a Marshall 50 watt output.
The Regulator tube is a 6550, and has its own filiment transformer.
Right now the outputs are 6550's. Lots of Glass

[jamez]

Phew... long thread. Very interesting stuff though.
I "power scaled" my amp with this circuit:

Tube Amplifier Attenuation

It is much simpler than K O'Cs complete circuit and I would assume its less capable - No sag controls etc, but it works a treat for just lowering the volume of a dimed amp be it fixed or cathode biased and keeps the tone roughly true.
I know speaker compression disappears and there are slight tone changes with heavy attenuation, but for under $30 for parts it beats the pants of any resistive attenuator or THD box (which I have owned,but just add a certain cover sound as well as unwanted squishyness.)

[daz]

I think saying that PS is flawed for the resons stated in the original post id akin to saying the new Yamaha 200HP Vmax motorcycle is flawed because it's not as fast as a 600HP Boss Hoss. In other words, so what if it cannot be perfect because of the fact it cannot change the loss of what a speaker contributes at higher volumes and loses at lower ones. The fact is a lot of people are raving about how much better it is than any other method to date at retaining inspiring tone at low volumes. If it's flawed, well, then so is every thing man has ever devised because the original post can only be seen as saying it's flawed because it isn't perfect. there are a lot of things in this world that aren't perfect but are f***ing awesome compared to others of thier type whatever it may be!

[jamez]

Absolutely.
If you dont need the walls to shake as you play, and have done the long expensive quest through drive type pedals (which I think try to give you a similar result at less Db's). Being able to turn down the output of a dimed amp without spending $$$ and without changing the essential tone is a godsend.

[Steve Conner]

Phew... long thread. Very interesting stuff though.
I "power scaled" my amp with this circuit:
Tube Amplifier Attenuation

I think the above circuit is rather nice actually. The simplicity is a big plus. I'd be careful using it on really high-powered amps, though, as the voltage might be getting uncomfortably close to the rating of the MOSFET. It'll be pushing the rating of any pot too, for that matter: I think they're all rated 350V DC or something.

Also, the MOSFET needs a decent sized heatsink, and the drain tab will be live with the full B+, so you need an insulator kit.

Got to love the "Power Sliding" name too :-)

[Mickey_C]

Has anybody noticed that this thread is still one of the top google hits on searches for the words "power scaling"? And it comes up bold: "Power Scaling is Flawed?".