VVR or Power Scaling

[tubesornothing]

Hey all, I have a client who wants his King EL84 20W amp modified for power scaling/vvr.  I notice KoCs power scaling has an option specific for EL84 to keep the screens 20V below the plates.  VVR does not. Not sure if this is a big deal or not, since darn near everyone at 18W has been using VVR, including 65 amps.  Cheaper too.

Anyhoo, y'all have any preference?  VVR or power scaling?

thanks a ToN

[kagliostro]

As I know

VVR and power scaling are not different

only VVR (as we usually call it here in the forum) have not a fixed bias control section

but I think that power scaling is something like a commercial name

and that VVR and power scaling are near the same thing

Kagliostro

[Merlin]

Hey all, I have a client who wants his King EL84 20W amp modified for power scaling/vvr.  I notice KoCs power scaling has an option specific for EL84 to keep the screens 20V below the plates.  VVR does not. 

If the difference is only 20V then the VVR is fine. In fact, allowing the difference between anode and screen voltage to shrink as the power is reduced is actually better than a tracking screen voltage, because it maintains a more constant operating point. (Although if the voltage differenceis very large, say 50V or more, then this relationship may fall apart, in which case KoCs tracking supply would be better).

[tubesornothing]

As I know

VVR and power scaling are not different

only VVR (as we usually call it here in the forum) have not a fixed bias control section

but I think that power scaling is something like a commercial name

and that VVR and power scaling are near the same thing

Kagliostro

Yes, they are near the same thing, but they are different.  They are names for two subtly different designs/products from two different people. However, there are some small differences:

"VVR" is a design by Dana Hall.  He also builds a product. He has both a cathode biased and a fixed bias version

"Power Scaling" is a design by Kevin O'Connor.  He also builds a product. He has both a cathode biased version and a fixed biased version. He has more components in his product.  He also has some other features, like a sag control as well as the EL84 feature I mentioned above.

If the difference is only 20V then the VVR is fine. In fact, allowing the difference between anode and screen voltage to shrink as the power is reduced is actually better than a tracking screen voltage, because it maintains a more constant operating point. (Although if the voltage differenceis very large, say 50V or more, then this relationship may fall apart, in which case KoCs tracking supply would be better).

OK, that's cool - thanks Merlin.

[FYL]

Anyhoo, y'all have any preference?  VVR or power scaling?

Dana's VVR is more or less based on the PSK-2, a first generation Power Scaling board for cathode-biased amps working on pulsating DC - the PSK-2 was mounted between the rectifier and the first filtering node. Very efficient but quite noisy with less than perfect layout and grounding.

The VVR works on filtered DC - it's mounted between two filtering nodes - and works very nicely in small amps with nearly identical plate and screen voltages. Not very efficient - dissipation in the pass Mosfet can be up to 43% of total power, quite crude when it comes to current limiting but cheap and effective.

KOC has since developed DC power scaling, with one module inserted between a filtering node and the tube(s) plate(s) or screen(s) thus allowing for very fast response - no time constants because of charging/discharging caps.

Different boards, different applications: VVR is fine for small cathode-biased amps, real Power Scaling is much better when it comes to large fixed bias amps.

 

[Merlin]

"VVR" is a design by Dana Hall.  He also builds a product. He has both a cathode biased and a fixed bias version

"Power Scaling" is a design by Kevin O'Connor.  He also builds a product. He has both a cathode biased version and a fixed biased version. He has more components in his product.  He also has some other features,

Power Scaling is a trademark name for a method, not a circuit. Both Dana and KoCs circuits are power scaling. Power scaling is simply proportional voltage adjustment, and for cathode biased amps you only need to vary the supply voltage- the rest will proportion themselves naturally. For fixed bias you need to force the bias voltage to track the screen, and sometimes you need to force the screen to track the anode too, but it's the same principle; all are power scaling.

[conger]

Dana's VVR is more or less based on the PSK-2, a first generation Power Scaling board for cathode-biased amps working on pulsating DC - the PSK-2 was mounted between the rectifier and the first filtering node. Very efficient but quite noisy with less than perfect layout and grounding.

The VVR works on filtered DC - it's mounted between two filtering nodes - and works very nicely in small amps with nearly identical plate and screen voltages. Not very efficient - dissipation in the pass Mosfet can be up to 43% of total power, quite crude when it comes to current limiting but cheap and effective.

KOC has since developed DC power scaling, with one module inserted between a filtering node and the tube(s) plate(s) or screen(s) thus allowing for very fast response - no time constants because of charging/discharging caps.

Different boards, different applications: VVR is fine for small cathode-biased amps, real Power Scaling is much better when it comes to large fixed bias amps.

Dana's VVR works on Cathode or Fixed Bias amps up to 50W.  The VVR board can be inserted before the first filter cap or after it.  It doesn't add noise.

There are many VVR implementations out there since Dana very kindly made his circuit available into the amp building community.

A bigger decision is what to scale, i.e. the whole amp, just PA or PA & PI? In my experience scaling the PA & PI works very well in an 18Watt amp.

[FYL]

Dana's VVR works on Cathode or Fixed Bias amps up to 50W.

VVR is for cathode bias, VVR3 for fixed bias, with a very primitive bias tracking section - KOC's original bias tracker was better, his new designs are way ahead.

  The VVR board can be inserted before the first filter cap or after it.  It doesn't add noise.

Pulsating DC is noisy by nature. This was a big problem for first generation Power Scaling boards, this is still a problem with *any* board working on pulsating DC.

There are many VVR implementations out there since Dana very kindly made his circuit available into the amp building community.

Let's be serious: VRM (voltage regulation modules) have been around for eons, Mosfet-based high voltage versions have been used for the last 30 years or so.

Dana got 99.9% of his inspiration from Kevin O'Connor designs. And he hasn't released the schematics for his take on the PSK-1 with tracking bias - wonder why.

[phsyconoodler]

Because the bias tracking is crude at best.
   For cathode biased amps the VVR works extremely well.Kevin O'Connor's version may be superior,but so is the price tag.
 I think he's trying to recover all his R & D money from a few customers.20 bucks worth of parts and very poor installation instructions do not add up to his selling prices.
  If he gave proper instructions and wasn't so reclusive and hard to talk to he'd sell lots of the kits.More than enough to pay the bills.
 As it is,he's rude,reclusive and overpriced.
   I guess genius has it's drawbacks.

[FYL]

Because the bias tracking is crude at best.

 

For cathode biased amps the VVR works extremely well.

Agreed, it's a fine entry level solution - just use a decent RV4 pot and add a 22n 600V cap across it.

Kevin O'Connor's version may be superior,but so is the price tag.

KOC's cathode bias basic DC scaling kit, the SB-2, is priced at CAD50 (USD50 at today's exchange rate). It comes in kit form, includes *two* complete DC Power Scaling boards (two Vin, two Vout tracking or not, for instance one board for plates, the other for screens, or roll your own), and all components including a PEC RV4 Mil-spec 2 W 1ML pot rated at 900 V RMS continuous dielectric strength and 500 V continuous operating voltage, as well as a dual-ganged Alpha (Taiwan) 16mm compact pot for "drive compensation", KOC's parlance for master volume.

http://www.londonpower.com/catalog/product_info.php?cPath=7&products_id=28

Dana's VVR kit is priced at USD30. It's preassembled, includes one board - one Vin, one Vout only - and all components, with a basic Alpha (Taiwan) RV24 0.5 W 1ML pot rated at 500 V dielectric strength for 1 minute.

So which one is less expensive?

If he gave proper instructions and wasn't so reclusive and hard to talk to he'd sell lots of the kits.

The instructions supplied with his kits are short, but perfectly adequate for techies who know what a mosfet is and how to use it.

KOC is always available for customers by email or thru the Power Scaling web site (http://www.powerscaling.com/community/index.php). He answers questions real fast and offers excellent customer support if you don't behave like a spoiled brat or a know-it-all Bozo.

[phsyconoodler]

"if you don't behave like a spoiled brat or a know-it-all Bozo."

Hmm...what are you saying?

[FYL]

In these days of instant gratification and global irresponsibility some people with more money than neurons don't read the instructions and don't properly build/mount/use/... what they've bought, they then believe that others are responsible. Others don't accept well-founded technical advice because they believe that they know everything. And when they're stuck it's never their fault.

KOC doesn't like to deal with such time-wasters. Maybe he's harsh at times but I can understand that.

[phsyconoodler]

I'm referring to my own interaction and a friend who called Mr O.

   I never received a response at all to an E-Mail and my friend who is anything but a know it all,called him and got a rude response on the phone.
   His prices have dropped considerably from where they used to be a few years ago.
And the website to answer questions is also new.

  We both know what a mosfet is and are not rude in return.
It's like dealing with Mr. Fulltone about his pedals.We had one that had faulty footswitches and he sent a message that basically said we were crazy and to stop bothering him.We can't order those switches from any supplier we know of and he could of at least told us where we could get them or even offered to send us some.
  So Mr O'connor is a good guy now.Well it wasn't always that way.

[Geezer]

We can't order those switches from any supplier we know of

Are you referring to the 3PDT's, like this?>>

If so, Doug has them...... http://www.hoffmanamps.com/MyStore/perlshop.cgi?ORDER_ID=264770201&ACTION=CONTINUE+SHOPPING&thispage=parts7.htm

If something else..nevermind.....  

[FYL]

I'm referring to my own interaction and a friend who called Mr O.

Sorry to hear about these two bad experiences. Mine have been very positive.



 

[tubesornothing]

Yeah I get mixed replies from KoC.  In all cases, he has been quick to respond, but sometimes he is somewhat rude and condescending.   I just chalked it up to him having a big head complex or something that requires him to pick at other people.  There are a lot of guys like that kicking around.  I just take what I need and leave them to there own stuff.

Thanks for the info on the two options. 

[phsyconoodler]

Thanks Geezer.We are limited where i work to using suppliers that we have accounts with so we can't order from Doug.Those switches are common in many pedals but not to our electronics suppliers.
  Fulltone is a nasty,bitter man.