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Old 5th November 2021 | Show parent
Lives for gear
kludgeaudio's Avatar
Originally Posted by M50k ➡️
Any thoughts on the two 12AX7 gain stages with feedback used in the Pultec MB1?
That's another attempt to split the gain among two stages so you can run them with reasonable linearity but not run into noise problems. You could make things cleaner than that, but given the output stage and the input transformer colorations, you probably wouldn't affect the sound any if you did. The input stage is pretty much blameless given the environment that it's in.

Today we can get much cleaner input transformers, we can get frame grid tubes that are quieter and more linear than 12AX7s, and even when that design was made you could get a bigger tube with more current drive than the 12AU7 for that output follower. We could add a tertiary feedback winding to that output transformer, get the transformer inside a feedback loop, and reduce that distortion too. Given all these things, the input stage is the least thing that I'd put more engineering effort into.

The Pultec was an excellent design given what was available at the time and what the demands of the market were. It was designed to be as clean as possible, but today what people like about it is the coloration. Go figure. It's a weird world.