The 5100 Project has been kicked off, and the original version schematic has been posted for group discussion in the PS Projects Forum - so come join the fun!

About the PowerScaling.com online community:

We are The Power Scaling User's Group; a coalition of manufacturers, amateur builders, and end-user Musician, Sound, and Recording Engineers, who are rallying about this incredible technology, with the blessings of Kevin O'Connor from London Power, who is himself a founding member, contributor, mentor, and guide. If you are building, considering to build, or even just shopping for, an amp, this is the place to be. We welcome you to join this coalition.

This website provides forums for amplifier manufacturers who have licensed Power Scaling methodologies from London Power, as well as those using similar technologies which are in effect a form of Power Scaling, and it will be used to share information, promote improvement and enhancement, educate, and provide general support for Power Scaling in widespread use by manufacturers and DIY users alike.

"The Aural benefits are too great for us not to do this..." - Kevin O'Connor, in reference to this website.

POWER SCALING and LONDON POWER:

Power Scaling is a methodology whereby amplifier tube voltages are adjusted proportionally to achieve volume attenuation without change of tone. This methodology was first proposed by Kevin O'Connor, author of the series The Ultimate Tone, and proprietor of London Power, Ontario, Canada, who licenses this as a technology to amplifier manufacturers, has been building amplifiers utilizing Power Scaling since 1995, and sells kits for the DIY community. Visit the MotherShip for the best information on Power Scaling, right from the Source!

Adminstrated by:

Let us not forget the hard labor of our Volunteers, Randyone (Randy) and Voodooman (John), the moderators, who keep the ball rolling in the right direction, along with Drew (Andrew Schur), the uber-man who makes this place look so amazing, keeping it well oiled behind the scenes. It should be known that Drew's presence here as a volunteer can only be a testament to his belief in what we are doing, being he has the lion's share of responsibility. It's hard work, and the more thankful we are for it, the more we will visit him at Gearpedia, with the link above, to get the scoop on the latest boutique and top-shelf guitars, amps, pedals, and pickups - along with some really bad G.A.S. (Gear Acquisition Syndrome)! It is our volunteers that make this site keep going, and we need more! If you have the time and interest to help, please let us know.

BROUGHT TO YOU BY:

 

This site is sponsored by Michael Corrieri (Mickey C.) of Soultone Amplification. Soultone is a premier manufacturer of vintage styled amplifiers of exceptional quality that utilize Power Scaling. Mike conceived of this website and the Power Scaling User's Group, and with, Kevin's approval, provided the funding and resources (including our very own private server), to make it all happen. He is also the UNIX admin for this site.
Visit Soultone online, and find out why he is so committed to our cause...

 

MORE TO COME...

[KevinOConnor]

There are many instances where we need a raw bias supply that is higher in magnitude or more capable in current delivery than the existing bias supply. Bias supplies are grouped as being either "low impedance" or "high impedance".

"Low impedance" supplies are either a tap or dedicated winding, with a rectifier and filter cap. Minimal or zero resistance is present between the winding and the cap. This type of supply can usually provide many tens of milliamps.

"High impedance" supplies are characterized as having high resistances between the winding and the filter cap. An example is the use of the plate supply with grounded center-tap, with a 100-220k resistor in series with a diode feeding the bias filter cap. To keep the filter cap voltage from rising to the same magnitude as the B+, but negative, a resistor or zener is placed across the cap. The zener is preferred as it gives a constant voltage clamping action at a specified value.

A second form of high-impedance supply is the type that is capacitively-coupled from the plate winding. In this case, the winding uses a full bridge to generate B+. A cap, resistor and diode feed the bias filter cap. The coupling cap "scoops" charge into the bias filter cap on a half-cycle basis. The cap impedance is very high, so maximum current from this supply is limited, as is maximum output voltage.

If your amp has a capacitively-coupled bias supply and you are thinking about adding Power Scaling - or merely wish to add a tracking bias regulator for other purposes - then you will have to add an auxiliary transformer to generate the bias supply. This will provide a low impedance that can support multiple bias pots, etc, and have sufficiently high voltage over-all to let the regulator function properly.

The resistively-coupled high-impedance supply can be modified to provide more voltage and more current. We simply parallel a few resistors to decrease the impedance between the winding and the final filter cap. Typically, three 100k-1Ws are paralleled to make a 33k-3W. We add 80-100V worth of zeners across the cap to clamp the voltage and protect the cap. Now, we have a -80V to -100V "moderate" impedance supply.

We should also make a distinction between the "raw bias voltage" and the "applied bias voltage"

"Raw" bias is the value of the supply at the first filter cap and prior to regulation. This voltage should be fairly constant regardless of the loading of a bias-set network or not.

"Applied" bias voltage is the voltage actually applied to the tube control grid to set its plate current In most resistive and capacitively coupled bias supplies, the "raw" and "applied" voltages are the same. This is an economic choice made by the manufacturer. Marshall, Fender, Peavey, Traynor, Hiwatt, Mesa, Trace Elliott, and all the other builders have done this and still do this. For our own builds, we do not have to pinch pennies in such an important part of the amp.

Have fun
Kevin O'Connor

268 Views | Rating: (1 rates)

[KevinOConnor]

Electronics allows any goal to be achieved in many ways. For guitar amp users, the ability to control how loud or quiet their amp is to achieve a "cranked" sound has always been difficult. Attenuators placed between the speaker and amplifier provided some means of control, but tended to alter the sound and shortened tube life. The amp would be clipping its output continuously at its full rating.

Power control methods have been around longer than electronics itself, but electronic control of power provides the greatest versatility of control attributes combined with low cost and fine resolution of control. These electronic methods have been around as long as we have had active gain elements, such as vacuum tubes. With semi-conductor technology, power control is much easier to implement, with extremely low-cost devices and small space requirements.

Back to our guitar player with cranked tone. His goal is to get that same sound in the same way but at reduced volume BUT without having to get a whole new smaller -quieter amp. The goal, then, is to "Power Scale the amp" and "Power Scale the sound". That means the goal is Power Scaling.

How we get there is _also_ Power Scaling.

If we maintain the "sound" of the amp while reducing its power output, we have Power scaled it. So, Power Scaling is the "methodology" of how we attain the sonic goal of Power Scaling. It is not just semantics to say that both the goal and how we got there is the same thing - Power Scaling - it is just that both are intertwined: the goal defines the method; the method achieves the goal.

The amplifier has a specific "response" to the input signal. It produces a specific output with unique characteristics to the amplifier design and component choice. If we swap tube types, it sounds a little different, because now it is effectively a different amp with a new response. That response is referred to as a "transfer curve". This is just a way of relating the output to the input. If we maintain the shape of the transfer curve, then we will maintain the sound, even if we make that curve "look" smaller. That is what Power Scaling achieves.

Transfer curves are generally considered on a single stage basis in traditional tube electronic analysis, but I have extended the definition here. An entire block of circuitry has a net transfer curve, as does the entire amplifier. For the most part, when we implement Power Scaling, it is not necessary to alter or control the entire amplifier circuit, rather, just a portion of it. Usually, this control is confined to just the output stage, or possibly the whole power amp. This is the circuit area where the greatest signal dynamics occur, and where signal processing from preceding stages is "swamped" by, say, hard clipping of the power stage.

To reduce the power output of the power stage without altering how it handles signals is quite simple, and any approach used to achieve this IS Power Scaling.

There are also simple ways to control power output which result in alternate tones as we dial down, and these are simply "Variable Power".

There are yet other methods that achieve variable output power and are labeled as such, but have nothing to do with either Power Scale nor variable-power methods.

Examples of Power Scaled products and approaches: The techniques presented in "The Ultimate Tone" volumes - particularly volumes 4,5 and 6; London Power's amplifiers, and its PSK-, DCPSK- and SB- kits representing preferred methods. There are countless circuit variations that will achieve this goal. The licensed amp products using the Power Scale trade names, of course, are Power Scaled amps and achieve the desired sonic goal. Unlicensed implementations are also plentiful, and those companies choose to call the control something else, like "Voltage", "Power", "Variac", and others. Claret's and Trentino's approaches can be implemented well or poorly, achieving either Power Scaling or just variable power. Zimmerman's approach achieves Power Scaling down to a still too-loud level.

Examples of "variable power" include: any implementations where the sound changes as one dials down but reduced loudness is nonetheless achieved; Mesa's D-180 Limit control using a variable current-source for the splitter, and Mojave's copy of it; Carvin's power reduction switches; Marshall's "virtual" power reduction; Moore Amplification's Power control; and many others.

Things that are neither include all master volumes. Seymour-Duncan's "Juice" control is an electronic post-splitter MV. Viking Amps' "Power" control is also a post-PI MV. Most controls labeled "variac" are simply variable current sources for the splitter. The use of light bulbs to restrict power gives limited effect while "browning" the sound.

One of the benefits of the preferred Power Scale approach is extended tube life. One can still achieve the sonic goal of Power Scaling without this benefit - but why would you want to?

Note that a "trade mark" and a "trade name" do not have to be registered to be recognized and protected. "Power Scale" and "Power Scaling" are trade names and trade marks of London Power and Kevin O'Connor, despite not being registered with the USPTO. That organization would like for you to believe that unregistered marks are without merit and protection. The only mark that is not legal to use is the circle-R for "registered". The "TM" symbol can be used for both registered and nonregistered marks alike.

Guitar amps are built to have fun, and we should have fun building them, too!
Kevin O'Connor

1062 Views | Rating: (1 rates)