I am a big fan of low wattage tube amps, after getting one of them, the famous Cream Machine produced by
Hughes&Kettner, playing it for over a year i decided to completely rebuild the amp and make a full
featured two channel mini guitar amplifier. The only original parts i used are the transformers (power and output)
and a few axial 15uF/450V electrolytic caps.
The original circuit is hybrid solid state / tube using NE5532 dual opamp, one ECC83 and a half of ECC82 tube in the
preamp section. The power amp is made as Single Ended triode stage using the 2nd half of the ECC82 tube. The lack of
any kind of EQ, besides one fixed Speaker Simulator output is limiting the number of possible uses. There's enough
space for more knobs on the front panel, so, the descision was simple. The Scream Machine was born.
Design goals:
Because there was not enough space for an additional tube and adding one would exceed the power transformer
capabilities i decided to use a solid state stages for some secondary tasks. A MOSFET and FET transistors are used
as tone stack diver and linear gain stage after the effects loop. The overall gain of the effects loop recovery
stage is set, so the circuit will work in his linear region. One dual opamp TL072 works in the effects loop, too.
The second one is used to buffer the Line Outputs.
The channel switching is realised using DPDT relays.
Output transformer technical data measured on my unit:
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SCHEMATIC (pdf)
Sound samples and video:
