ShortScale.org

Zaphod wrote:i don't know the answer but if it was just a simple pot why would people need attenuators?
i'm sure it's more complicated.

i'll get some gutshots of the champ 600 if you like though, i haven't screwed it all back together since it broke.

Power-tube distortion

Power-tube distortion is required for amp sounds in some genres. In a standard master-volume guitar amp, as the amp's final or master volume is increased, more power tube distortion is produced. This is slow-onset distortion. As such a tube (or valve) power amp rated at 50 watts produces 50 clean watts or, when pushed harder, twice as many distorted watts. To make the amount of power-tube distortion independent from the volume heard at the guitar speaker, several approaches are used:

The "power soak" approach places the attenuation between the power tubes and the guitar speaker. This pushes the power tubes to full power and then drains away the unwanted excess power by sending it to a mostly resistive dummy load and allowing only a portion through to the guitar speaker. Some power soak products include the Rockman Power Soak, the THD Hot Plate, the Weber MASS, and the Marshall Power Brake. The power-supply approach places the attenuation in the power supply and power amp; it runs the power tubes at a lower plate voltage and lets the full resulting power through to the guitar speaker. This prevents wearing-out the tubes or blowing the output transformer, and obviates purchasing and transporting a separate, bulky power attenuator. Some power supply attenuation circuits include London Power's Power Scaling and Mojave's Power Dampening circuit.

The Maven Peal Sag Circuit is the only patented power-supply that applies nonlinear analysis to power-supply design instead of the tradition attenuation approach. As a result, the Sag Circuit offers power tube distortion and response control at reasonable volumes, along with other features such as a built-in power conditioner and zero power supply hum. Unlike other attenuation approaches, the Sag Circuit adds power amp distortion and response control to transistor amps as well as tube-based amps.

In the re-amped dummy load approach, the tube power amp drives a mostly resistive dummy load rather than a guitar speaker. The dummy load is typically the internal dummy load inside a power attenuator, with the load selector switched all the way to internal load rather than a mix of internal load and guitar speaker. A line-level signal is tapped from the dummy load, optional signal processing (such as equalization and reverb) is applied, and then the signal is sent through the final amplifier, typically solid-state run only in the linear region, which finally drives a guitar speaker. The guitar speaker contributes complex physical transducer dynamics at a quiet listening level controlled by the final amp, or even more complex dynamics if the speaker is pushed into distortion.

In the isolation box approach, the guitar amplifier is used with a guitar speaker in a separate cabinet. A soundproofed isolation cabinet, isolation box, isolation booth, or isolation room can be used. The guitar speaker and microphones are placed inside a soundproofed space separate from the control room or listening area, such as in a double-walled isolation room in a different floor of a house. A speaker cable runs from the tube guitar amplifier in the control room out to the miked guitar speaker cabinet out in the separate isolated area. The microphone cables then run back from the isolated area back into the control room. Professional recording studios often use this approach to obtain power-tube distortion independently of the listening volume.

~ http://en.wikipedia.org/wiki/Guitar_amplifier

Mike wrote:Everyone here has covered it pretty much. A Master Volume can give you gain in the form of preamp breakup, but it's not simple to install, particularly into a PCB amp, and working on them is very dangerous. I would consider myself competant to do it after a degree in electronics and a lot of pedal experience but I would still have a large amount of trepidation in doing it since I don't want to die. I am a clumsy person.

william wrote: sounds like an attenuator would be much more useful than a master volume. is the difference just where you put the pot? or is an attenuator actually more complex hardware?

blacktaxi wrote:how much do these champions go for new? here in Ukraine they're greatly overpriced, and for the money you can get a much more useful practice amp.