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Old 30th December 2006, 04:16 PM   #1
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Question high gain 12ax7 preamp from scratch?

Hi there
im looking to build a preamp with 12ax7's for a thick, crunchy sound like a mesa boogie or marshall.
i will be running it through a torque 100w power amp for the clean tight edge.
im wondering if anybody has any schematics for something like this utilising two to four ax7's for some massive metal gain.
the only other answer i can find is to reconstruct a mesa dual rectifier.
if anybody knows where i can get the transformers for the dual rec (to work on 230-240v) could you please tell me.
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Old 30th December 2006, 05:01 PM   #2
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Default Use a cascode topology if you want gain

or a pentode will give you more crunch! Once you get the gain up then you can play around with EQ and crunch all you want but first you've got to get the signal out of the noise. Les Paul used a 5879 pentode.
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Old 30th December 2006, 06:56 PM   #3
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many modern high gain amps (recto, 515o, Sl0, etc) share the same topology, and the schematics are redily available online. they are very simple... no magic there. You'll need three 12ax7 tubes for the high gain channel (more if you want a clean channel too)... four sections for gain stages, and one section for the cathode follower/buffer to the tone controlls and then another section as an output buffer.

Each stage draws around 1mA@ 350-400v for the high voltage supply, so you only need to be able to source about a dozen mA, but you'll need 900mA for the 6v heaters or 450mA for 12v heaters.

This is not the best place to ask about guitar amps. Click on my profile and drop me a message with your e mail address and I'll help you out.
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