Inside The Universal Audio M610 Vacuum Tube PreampThe M610 preamp is the same tube preamp used in the LA610, LA610 MKII and 2-610. The preamp is made up of two separate feedback gain stages that are cascaded one after another.
The UA M610 CircuitThe first feedback gain stage can be adjusted with the "GAIN" switch on the upper left of the front panel. This switch selects a feedback resistor that can add or subtract gain to the circuit. The first tube in the circuit (left tube) is a 12AX7 dual triode.
The following feedback gain stage uses a 6072 (right tube). The 6072 is similar to the 12AT7 dual triode. Notice that the big knob says "LEVEL". This is because it acts like a volume knob and not a gain knob in the circuit.
The first feedback gain stage feeds the 250k ohm "LEVEL" potentiometer and you adjust the input level to the following 6072 feedback gain stage.
More info and measurements coming soon.
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