An interesting topic came up in the forum over at Harmony Central:
Which has more influence on sound, the power amp or the preamp?.
Some good questions and we found some good answers. Doug Roccaforte, an amp builder and frequent HC poster, said that the preamp takes the tiny guitar signal, and drives it to the power amp. The power section then takes the the signal, makes it large enough to drive to the speakers. We agree.
Generally, our basic take is this (which is debatable):
The power section can help how early your sound brakes up in the volume controls.
The preamp section helps you dial in the EQ's of an amp.
Everything makes a difference from the speakers you use to the pick you are playing with.
What do you think?
Matt
Thursday, February 7, 2008
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5 comments:
I am fairly new to the tube scene so I hope my comments don't seem completely ignorant. I do believe however that preamp has more influence on the sound or tone of the amp than the power amp. I discovered this when I plugged my Tonelab LE into the effects loop of my Hot Rod Deluxe bypassing the preamp and got a more neutral tone which is what I needed for the Tonelab. My belief is that all 6L6 driven amps, for example, would all sound alike for the most part if not for the different preamps from amp to amp. The other thing that comes to mind is how much the tone of an amp is affected by changing any/all of the preamp tubes more than changing the power tubes...or am I way off base?!
I have found that, while the preamp tubes offer a much wider latitude of distortion depth or intensity, they never match the complexity that the power tubes' nonlinearity can accomplish. I can only get so far in getting a really satisfying 'growl' out of my old Marshall plexi or my Fender Hot Rod unless I operate the power tubes somewhat into their nonlinear range. I can particularly hear this difference while remixing my recorded guitar later. I get a much bigger, for lack of a better term, sound for a given volume when I'm getting a good amount of it in the power stage. I attribute this to more low-order harmonics.
A preamp prepares a signal to be amplified. A power amp simply amplifies that signal. It could be argued that either piece of equipment could be built with features that allow the sound to be augmented by the user, however when speaking of the most basic functions of these components, the preamp has much more influence over the sound as a good power amp's primary function is to magnify the signal provided by the preamp as clean and accurate as possible.
The fundamental difference between what we call a 'preamp' and a 'power amp' is that the preamp supplies virtually all of the voltage gain while operating at low current and low power, and the power amp supplies all the current gain with just a little voltage gain. There's nothing restraining a designer from giving either section a 'sound'. But tone mods are typically done in the low current, low power section (preamp) for the sake of efficiency, and the power amp is typically designed with a very predictable curve and safety in mind.
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