Master Volume, Attenuator, Or Power Scaling?

Every amp I've ever owned had a master so I don't know squat about power scaling or attenuation. I found this cool article trying to educate myself so I'll put it up.......

What is Power Scaling?

Power Scale ControlPower Scaling's goal is to achieve the same tone as one's preferred "loud sound," but at a much lower volume. The method can be one of over sixty distinct approaches, each with many variations. There are many was to reduce power, but most do not achieve the full benefit of Power Scaling.

Earlier designers made attempts to achieve effective scaling of power, but never quite got there. London Power refined and fully developed the technology to allow the maximum power of an amplifier to be dialed down to whatever level a player needs. It was first used on the amazing London Power STUDIO amp.

Power Scaling™ is a methodology developed by Kevin O'Connor of London Power.


Isn't this just like a speaker load box?

• Not at all. Speaker load boxes, speaker emulators, and speaker attenuators are all forms of attenuation that are interposed between the output of a power amp and the speaker. They work for some people but are notorious for sounding "buzzy" at high attenuations.

A speaker attenuator forces your amp to be run flat out, producing its full power all the time. The power that is not needed is thrown away as heat, with the required power going to the speaker. It is quieter than full-tilt, but now the speaker is isolated from the amp and cannot interact with it, so some tone is lost.

The key to Power Scaling is that it is applied to the power output tube stage itself, and so comes before the output transformer. Power Scaling allows a dynamic power range of 40dB. Most speaker attenuators alter the tone before they reach 8dB reduction. Minus 8dB is just a little bit quieter than full blast; minus 40dB is literally a whisper.


Wouldn't a master volume do the same thing?

• Only in specific situations. If you only play clean or you only use preamp overdrive or distortion tones, then a master volume will satisfy you.

Power Scaling is the best solution for those players who incorporate some amount of output stage "effect" in their sound. This effect can be some clipping, heavy clipping, or just that cusp of compression you get in a tube power amp approaching clipping. Power Scaling allows you to live at that cusp or beyond, but at ANY loudness you need.


So Power Scaling will help my overdrive sounds. How clean will a Power Scaled amp play?

• All London Power Power Scaling amps are designed to provide smooth, sweet, clean sounds up to their limit of power.


How does Power Scaling affect tube life?

• With the POWER SCALE dial set to any setting less than maximum, tube life will actually be extended. In accelerated tests, power tube life is as long as that of a preamp tube ... up to 100,000 hours if the tube is not mechanically upset.

This is one of the benefits of the full Power Scaling effect, referred to above. Output transformer life is also extended, since it is subject to much lower voltage stress even with fully squared output signals and unexpected load disconnection.


Can I run a Power Scaled amp without a load right into a mixer?

• Yes. It is perfectly safe to do this, although you lose the benefit of frequency shaping provided by the speaker and the interaction of the output stage with the speaker.

The POWER SCALE control reduces voltage and current stress on the output tube, so even at a fully saturated distortion output, the tube is under less stress than it would be subject to in, say, a 3W amp.


Couldn't a low-power tube amp do the same thing?

• No. A low-watt amp only has one compression point, one cusp of distortion and one loudness level through a speaker.

Power Scaling amps can play both louder and quieter than amps of less nominal power. And, the compression point stays in the same position relative to the cusp point for all settings, allowing the touch responsiveness to remain consistent.


How is this possible? Is the circuitry complex or expensive?

• In technical terms, all that must be accomplished is to keep the "transfer curve" of the amplifier the same. The transfer curve is simply the relationship between the input and output signals, but as we know, tube amps respond differently to different-size signals. This is because the transfer is not straight and not uniformly curved.

Think of the transfer curve as a mirror. A flat mirror that is parallel to you will reflect your image perfectly and full size. If you move the mirror away, the image is smaller but still perfect. A tube's transfer curve is like a slightly curved or rippled mirror. In this case the image is slightly distorted, but this is exactly what we want - it is why we have chosen a tube amp in the first place. So, moving the mirror farther away reduces the size of the image, but it is still perfectly imperfect.

Electronically, it is very simple and inexpensive to achieve this goal. The diversity of electronic circuits allows countless circuit approaches to be implemented by different designers, with greater expense added or bulkier components used. In the end, it is all Power Scaling.


Does that affect the output impedance of the amplifier? People on the web say Power Scaling changes the tube plate resistance.

• Because the shape of the transfer curve is maintained, the plate resistance of the output tubes is maintained as well. So, the output impedance of the amp does not change even though much less power is available once you dial down.


Can Power Scaling be added to any tube amp? Is the circuitry large?

• The circuits are simple and small, and are easily retrofitted into existing tube amps. But... the tech doing this installation must be very good at mods and not just a good repair tech - as these are two different skills.

Depending on the amp, some heatsinking or a fan might be required to cool the Power Scale circuit.


Does that mean that the Power Scale circuit is just converting the unwanted audio power into heat?

• No. If you only need 3W of power then only 3W is produced; if you need 29W, then you get 29W. The simplest Power Scale circuits are soft regulators, and as such, they divide the voltage available from the raw power supply between the amplifier and itself. In that voltage sharing, there will be some waste heat.

At POWER SCALE control settings between fully clockwise and about 12-o'clock, there will be waste heat from the Power Scale regulator. At settings between minimum (counter-clockwise) and 12-o'clock, the regulator runs cool. Meanwhile, as audio power is reduced, waste power in the power tubes goes down in direct proportion, which increases their reliability.

Amplifire.

I am actually seriously considering forgetting about the Fuchs and grabbing a YBA1 Mod1 instead since those have a built in attenuator (as you obviously know having owned one). There is one available through L&M for about $400ish, and there might be more elsewhere in the chain for even less. I could use my Marshall as a cab and wouldn't have to go to the extra expense of buying a cab until later.

Hotplate, Rockcrusher, Power (shite) Break, Ultimate Attenuator... I think Dr. Z sells something or other... Air Brake, right? There are a bunch of options, all are simple to use. Attenuators are the best. If you're not sold, watch some Johan Segeborn videos.

Yeah man, but a set of old celestions blasting at your knees is something special.

Don't listen to me, though. My hearing is fucked.

I don't doubt it, but he's trying to get knee-blasting tones at non-knee-blasting volumes. Once I get my XiTone cab, I bet I'll be able to blast the shit out of things should I so desire.

+1
I do use an attenuator to keep the level down when needed. I don't feel it robs anything tonewise, but like any other method to keep the volume down, it sucks for the reason Snoop mentioned

Slamming an old tube amp with a turned up boost is my gain creation method of choice. It adds a freaking ton of overdrive, without adding much volume.

I like my Digitech RP500... Main reason is the individual kick buttons for COmp, Dist, Chorus, DDL, Rev, and the expression pedal for volume...

In my three patches I use (Lester, Single Coils, Bass), NONE of the individual kicks are on... I have to kick to engage em... The only thing true on patch when powered up is the overall output is jacked a bit to puch the preamp of the amp (same as a boost)...

I also have the modeling turned off so I hear MY amp.


No matter WHICH multi-effects box, DON'T expect the canned patches to be righteous for you... They aren't... Regardless of brand and model#, I think the same drunk ass cab driver hires out to the different companies to write factory patches.... 99% sound like dog shit on a good day.

You have to jump in there with it and tweak it to fit YOUR guitar and amp....

I'd still like to kick his ass for all that star trek bullshit on multi effects boxes...

I only use three patches. Eash patch though has the effects tweaked for that type instrument which pretty much like several stomps ready to go on each.

Also, read the manual on resetting to factory, editing and saving, backing up, restoring. Get the cable, hook it to your computer and back up and restore a couple of times before you change anything just so you know how to do it without smoking all those custom patches you're gonna smoke down the road if you dick up the process...

Pick a star trek bullshit user patch and start editing. Who cares if you dick that up... Go through every single edit area, including EQ... Build some real world tones on it. FInd out what every single knob/setting does... You'll find some cool shit possible that way. When you scratch build a patch, set eq to flat to begin with. I like flat. My guitars are usally dime-toned. I don't much like most tone knobs on guitars. My amps are usually pretty flat. If I have to crank any amp eq knob to ten, that amp is a gone ass...

Ok, nuff blathering... Just some things to consider if you snag a multi effects box...