Poor Man's Tube Mixer
If you just want a few rugged, quiet tube mic pres in a box then the Lunch Box is for you. But it is not a mixer. As soon as you need faders and mixing capabilities you need the Poor Man's Tube Mixer (PMTM). In construction, the PMTM is basically a 3U lunch box minus the rack mounting ears, with an added fader front section. But that is where the similarities end. The PMTM is intended as much as a DIY project as a finished product. As such, keeping materials costs to a minimum is a primary objective. To this end, a number of design simplifications are available:
Use a single EZTubeMixer twin line amp PCB to provide two mic pres
Replace stepped gain switches with potentiometers
Replace expensive input and output transformers with more economical alternatives
Replace expensive extruded aluminium module enclosures with the much more economic Mark 3 mixer mechanical design
Use a single bus amp to mix both balanced and unbalanced signals
All the above techniques help to significantly reduce the cost of the PMTM.
The base level product shown here provides:
two mic pres with phase, phantom, 20dB pad and HPF switches, a gain pot with a range of 26dB to 60dB, a pan pot and TDK slider fader and direct outs.
Four balanced line inputs with pan pot and slider fader
24 balanced stem inputs (12 routed to R bus and 12 to L)
A pair of balanced bus expansion inputs for daisy chaining with other mixers
The master bus has either a pair of slider faders which can be mechanically linked or a single stereo fader. A monitor output with level control is also provided along with a trim control for the stems. The direct and master outputs are impedance balanced.
Optional extras include output transformers, replacing line inputs with mic inputs and metering.