What is Super Scaling?
• Super Scaling is a technique that allows the power output of a small amplifier to be boosted to a higher level to drive a speaker without changing the sound.
Doesn’t a regular power amplifier do this?
• No. Conventional power amplifiers monitor the input voltage only and scale this voltage to drive a load to a higher power level. The final load is fully isolated from the signal source.
What about a Guytron amp? It has a small amp driving a large amp.
• The large amp in the Guytron is like any other conventional power amplifier: it monitors the voltage across the load for the small amp, then boosts the voltage only. This produces an increased output, but the characteristics of the large amp dominate the final tone and interaction with the speaker. Besides, the player has no access to the output of the small amp, and thus has no way to know that the boosted sound is true to the small amp’s tone.
So, how does a Super Scaling amp monitor input power?
• Super Scalers are essentially just the final power stage of a type of power amplifier in which a driver stage would provide some amount of drive power to achieve output power. The difference is that the driver stage is missing, so this drive power must be obtained from an external source. Common tube output stages require no power to drive them, and so cannot be used as Super Scalers.
How does this retain the sound of the driving amp?
• In a Super Scaling amp, no output power can be produced unless input power is provided. The two quantities are intimately related. As you drive the Super Scaler harder, the speaker is driven harder. The speaker’s back-EMF tries to buck the signal from the Super Scaler, which then bucks back at the source. The driving amplifier can then ‘feel’ the speaker and interacts with it.
The Super Scaler is still a big amp, so doesn’t it provide better damping to the speaker than the small driving amp would?
• The Super Scaler is transparent. Its inherent damping is low – in the same range as a typical tube amp or less. However, the driving amp is able to ‘see’ and ‘feel’ the speaker through the Super Scaler, so that the sound is the same as if the small amp itself was driving the speaker directly, but to the new, higher power level.
How much boost does a Super Scaler provide?
• The boost for a typical tube Super Scaler is 4-100, with most in the 4-20 range. Nested Super Scalers can provide further boosts up to 1,000 times. The boost for a solid-state Super Scaler is anywhere from 4-1,000.
Can the boosts be varied?
• Not easily. Solid-state circuit are more easily adapted to variable boost ratios, but the circuits become much more complex. Nested tube Super Scalers can be made variable more readily than simpler tube Super Scalers.
Won’t a solid-state Super Scaler change the sound of a tube amp driving it?
• Not if it is properly designed. Our solid-state Super Scalers use special mosfets with characteristics approximating tube performance, in a circuit optimized for drive by a tube amp. The bulk of mosfets on the market are not suitable in this application. Solid-state Super Scalers can be made with multiple selectable boost ratios for different performance situations, while still retaining tone.
What is a Nested Super Scaler?
• This is a unit with two or more cascaded Super Scaling circuits for very high boost ratios. A half-watt input might produce 700W of output, but with the tone of the half-watt source amplifier.
What is tube life like in a Super Scaler?
• The simplest Super Scalers use conventional receiving-type power tubes in pure class-B circuits. Tube life is longer than in a conventional amplifier even though the internal voltages are somewhat higher.
Do I need matched tubes in a Super Scaler? Can I mix tubes like I can in London Power’s Power Scaling amps?
• Matched tubes are not required in the simplest Super Scalers, but they should be the same type. The circuit itself assures ‘matched’ performance by taking advantage of some of the tube characteristics that cannot be fully utilized in conventional amplifiers. See the Super Scaler project in TUT5, which uses standard common pin-out octal tubes.
In Super Scalers using filamentary triodes such as the 811A, SV572-160 or 572B, the tubes should be similar, and there is a benefit if matched pairs are installed.
Can I drive a Super Scaling amp with a Power Scaling amp and still have power amplifier distortion at any level?
• Yes. The Super Scaler will shift all the power levels up by six times typically, for a simple tube Super Scaler. Most players find this to be an ideal situation because they can use the same “quiet” home settings on their Power Scaling amp when they are on stage or playing with a full band. See the SV572 chapter in TUT5 for a Super Scaler project using these tubes.
Using a Super Scaler with a Power Scaling amp gives a modular system where you can bring along only as much power as you need.