London Power power scaling technology

[Champ_49]

Hi everyone,

I thought I'd chime in to talk about a technology called power scaling by Kevin O'conner which I think people already know.  And it is also explained in detail in one of his TUT books.  I am not working for Kevin nor am affiliated with him in any way as you will see in my other posts I am just a guy that likes to build amps.

I ended up installing this into my modified high gain amp and I have to say this is the best thing I have come across when it comes to playing at lower volumes with that cranked sound.  I will be installing this into my other amp since I was really impressed at how this works.  I have tried a multiple number of "attenutators (Ultimate, Hot plate, etc."  and quite frankly I can't say the power scaling even fits into this category now as it works as a single unit together with the amp rather than a standalone unit so in a way this is more integrated.

I ended up installing three of his kits into my amp.  For my fixed bias amp the power scaling unit (called SV1, which stands for super value/versatility) works in conjunction with a raw bias supply called the RBX. Unless the amp has a dedicated winding for the bias voltage the raw bias is recommended by him to supply sufficient voltage for proper biasing.
The other kit is the Bfx which is always integrated into the amp and I have to say I am quite pleased.

Initially my amp was designed with one bias pot where you have to get matched tubes all the time since both power tubes are biased together.  With the SV1 it incorporates a separate bias network for each power tube, so now I don't have to worry about matched power tubes.  And according to Kevin it is also now able to use different tube types not only el34's.

All in all this is the best investment I made in terms of amp building.  As this achieves the cranked tones at low volumes but also allows for a whole new different pallet of tones beyond that with the addition of a drive compensation circuit, power scaling and a master volume.  This came out awhile ago but I guess I had never heard of it since back then I was still looking at standalone attenuation units.  But then again back then I was still a novice at building amps so it would have been close to impossible for me to install something like this.  There are however other big amp builders out there that use this technology, which I found out later.
 

[Willabe]

but also allows for a whole new different pallet of tones beyond that with the addition of a drive compensation circuit, power scaling and a master volume. 

Drive compensation circuit? (A PPIMV will control the drive to the power tube grids  ~or~  you can use a pre PIMV to do the same but you won't get any distortion from the PI tubes then.) 

So you have a pre PIMV and a PPIMV?

What did you PS, just the output tubes or the output tubes and the PI or everything?

[Champ_49]

Hi Willabe.

Quite frankly I am still a newbie with building amps. So i might be wrong and I don't want to give misinformation.  But my drive comp is situated after the preamp.  so I should say post.  It is called the London Power master volume.  So LP master volume.  If you go here:  http://www.londonpower.com/
and look under various tech articles at the bottom there is a great deal of information there pretty much about everything.
You can also wire it with the drive comp before as well I believe. But I chose the LP.

All I did was follow the notes provided to me with the kits in which I learned a great deal about how it works as well as talk and exchanged a few emails with kevin.  But for more information and with a cup of coffee the idea is here:
http://www.londonpower.com/power-scaling-faq

I have to say for anyone who doesn't know Kevin's work. He knows his SH&T.  And I have only had good results with ALL the things he suggested. 

I will be implementing all his kits into my other amp and possibly future builds.

[torren61]

I've looked at the London Power site awhile back for power scaling.  I wish they had a better web site designer.  The power scaling promises quite a bit but a lot of amp companies use LP power scaling on their amps so there must be something to it.  It does seem like things are not as straight forward as you might think they are with additional kits that need to be purchased other than the main one you're looking at, unless I'm mistaken.

I'd be willing to try it if I knew i could install the ps myself.  It doesn't seem like a whole lot of money compared to an attenuator.

[HotBluePlates]

but also allows for a whole new different pallet of tones beyond that with the addition of a drive compensation circuit, power scaling and a master volume. 

Drive compensation circuit? (A PPIMV will control the drive to the power tube grids  ~or~  you can use a pre PIMV to do the same but you won't get any distortion from the PI tubes then.) 

So you have a pre PIMV and a PPIMV?

What did you PS, just the output tubes or the output tubes and the PI or everything?

In the London Power scheme, the "Drive Compensation" is a master volume which sits ahead of the power-scaled portion of the amp. So if you power-scale just the output tubes, the Drive Comp would be after the phase inverter (PPIMV you mentioned). If you power-scale the output tubes and phase inverter, you insert the drive compensation after the preamp but before the phase inverter (pre-PIMV you mentioned).

Drive Compensation is about reducing the distortion. When you drop the supply voltage with the power scale, the scaled-down portion's bias voltage also gets smaller (in absolute terms); this also means a smaller driving signal into the scaled circuit causes that circuit to distort. If you didn't have a master-volume of some kind to reduce the non-scaled signal, then large reductions of supply voltage in the power scaled circuit would tend to a situation where the scaled circuit distorts all the time and you can't get cleans (or lesser degrees of distortion).

The most-relevant situation to think of is power-scale reduction of supply voltage to, say, the output tubes to the lowest voltage/volume levels. Bias is also reduced to that circuit and might only be a few volts. When your preamp or phase inverter is throwing 25-55v peak of signal into the power-scaled stage whose bias is now down to a few-volts, you almost can't turn guitar/preamp volumes low enough to get the amp's normal clean tone, or the normal drive levels and reaction from non-scaled stages. So you use a master volume ("Drive Compensation") right before the signal goes into the scaled portion of the circuit to allow stock interactions between the 2 sections of the amp, if you want that.

Or you turn that drive control way up and hit the scaled circuit harder than it can ever normally be driven.

It does seem like things are not as straight forward as you might think they are with additional kits that need to be purchased other than the main one you're looking at, unless I'm mistaken.

There are many different amp topologies, with respect to amp voltage levels, bias method (fixed- or cathode/self-bias), power supply setups, methods of deriving a fixed bias supply (tap on high voltage winding, capacitive coupling of a.c. from PT winding to bias supply, independent bias winding, etc). Big powerful amps need power scale devices which can withstand more voltage across solid-state components and can dissipate more heat. Small cathode-biased amps can use lighter-duty power scale components and don't need an additional tracking bias supply.

Instead of making a unique kit for every amp out there, LP achieves versatility and universality by dividing sub-circuits of the overall power scaling circuit, so you just pick the group of sub-circuits needed for your particular amp. It might look like he's luring you in with 1 kit and selling you 3 other kits, but really he's just trying to sell you only the sub-circuit kits you need for your application. And you might choose to go whole-hog and include every bell & whistle, or keep it to the minimum.

If it were me, I'd simply email and ask the question about which elements are the right ones for my particular amp. Of course, the whole process assumes you know enough about your amp to make sense of which items are applicable, because if you install it yourself you're going to be working with high-voltage parts of your amp and you could wind up with a non-functional amp with incorrect installation.

[torren61]

Some of that made sense to me, lol.  Thanks!

[Fresh_Start]

HBP thanks as always for the simple and excellent explanation of what "drive compensation" is and how it would be useful.

I think we all have a tendency at times to think about portions of an amp's circuit as discreet units without considering all of the ways they interact with preceding and following parts of the overall circuit. For me, this was another example of "ah ha!  That's why _____ matters."

Cheers,

Chip

[HotBluePlates]

Even simpler:

Your stock amp is designed to put 10lbs of s#$t in a 10lbs bag. When you power scale to reduce output, you now have an 8lbs or 5lbs or 2lbs bag.

Drive compensation allows you to turn the 10lbs of s#^t from the non-scaled section down to just the 8lbs or 5lbs or 2lbs (or less) of s#^t so it doesn't overwhelm the scaled section, if you don't want it super-overdriven.

[Champ_49]

I've looked at the London Power site awhile back for power scaling.  I wish they had a better web site designer.  The power scaling promises quite a bit but a lot of amp companies use LP power scaling on their amps so there must be something to it.  It does seem like things are not as straight forward as you might think they are with additional kits that need to be purchased other than the main one you're looking at, unless I'm mistaken.

I'd be willing to try it if I knew i could install the ps myself.  It doesn't seem like a whole lot of money compared to an attenuator.

You are definitely right in that the cost of the kit is really low compared to let's say an ultimate attenuator that can cost upwards if  $700 with the extra features.
I have to be honest but the worst thing I did was decide to get an UA.  I ended up blowing a couple of OT on a reissue plexi amp . And no. Not becuase of negligence as I had followed to the T everything that was in the instructions.  Also you're running the amp at full load and in fact because the volume is so low at cranked volumes you can Play for hours with the amp just screaming for mercy. Maybe that was it. I didn't know how to resell this thing and ended up selling it to my amp tech.
the SV1 is I believe on a whole different level.  The output tubes actually run cooler. And other attenuators don't even come close to this in terms of tone. I can get a whole different pallet of tones as well as maintain the tone when dialing up the volume.  I have heard you have to dial the ps and the power scale pot together to maintain the tone at higher volume. It works great like this. I am still experimenting with it.

Yes. You do need to get separate kits for this.  Since my PT didn't have a separate dedicated bias winding I needed the raw bias supply kit as well.
This is so you will have sufficient voltage for your seaparate bias supply. 
The bfx loop is separate so up to you if you want the fx loop. Although the fx loop I'd recommend highly as it sounds very transparent.
All in all for power scaling you'd need one of the power scaling kits depending on whether your amp is cathode or fixed bias and the the raw bias supply (rbx) kit.
Overall the cost altogether is really low.  Considering what you are getting
Kevin is not a money hog as I've only known him to be passionate about this kind of stuff.  Although it is installed in many different amp companies the cost is more than reasonable. 
And it is really the BEST for playing your amp at low volumes. Better than the $300 to $800 attenuators which are not so ultimate but dangerous. 

As for installing. It is actually not that simple. Unless you know your stuff. For someone like me it took some help to understand proper installation as well as biasing methods. So you have to know your amp and all the appropriate points in the amp to install this. Or you can get a licensed tech to install it.  The more experienced builders will know how to install it easily I believe.  But for me it was not that simple.  It took me about a month to get it all working plus me gutting my original jcm800 completely and rebuilding from scratch
 Plus all the additional mods like the extra gain stage, galactic grounding method, and split filtering.  All discussed in the TUT books. I have two of them so far :)  this amp project must have taken me a couple of months in total


The kits themselves took me about a month or a bit more to completr. .  I had to figure out what to do before doing anything.  Now that I am familiar with the installation Im not soo scared to add these to my other amp (s).  Which I will be doing so shortly. 

Another thing to note is you MUST follow correct biasing procedures which is also explained in TUT2. I ended up frying the sv1 once because I just swapped in a new pair of tubes without biasing properly. Stupid I know.  If you don't know then you should ask Kevin or follow it to the T on the instructions provided with the kit.

Also I believe ay one point Kevin had a powerscaling kit which included both the raw bias supply and the sv1.  But he realized some people probably already had the sufficient voltage supply probably from a separate winding.  So hence he divides these up into separate circuits.  He is right. Sv 1 is really super value if you ask me.