The Unbalancer is a tube-based, balanced-to-unbalanced converter that accepts a balanced input signal and puts out a single-ended, unbalanced signal, much like a Broskie cathode follower, but with gain. (In fact, a Broskie cathode follower is the output stage in the Unbalancer circuit.) The input stage is a differential amplifier with a constant-current source load on the coupled cathodes. Besides performing its unbalancing conversion, the Unbalancer circuit provides voltage gain and exhibits a fine CMRR (Common Mode Rejection Ratio), which means that the Unbalancer largely ignores common-mode signals. In other words, it delivers what a good balanced circuit should deliver.
The Unbalancer can also accept an unbalanced input signal, but at the cost of half the voltage gain.
The GlassWare Unbalancer 9-pin stereo PCB: This FR-4 PCB is extra thick, 0.094 inches (inserting and pulling tubes from their sockets won’t bend or break this board), double-sided, with plated-through heavy 2oz copper traces. In addition, the PCB is lovingly and expensively made in the USA. The boards are 7 by 6 inches, with five mounting holes, which helps to prevent excessive PCB bending while inserting and pulling tubes from their sockets.
The JJ ECC802 and ECC99 tubes work quite well in the Unbalancer. The resulting gain is a little over +20dB. Other tubes that would work well are the 6AQ8, 6CG7, 6DJ8, 12BH7, 5963.
Redundant Solder Pads: The Unbalancer board holds two sets of differently-spaced solder pads for each critical resistor, so that radial and axial resistors can easily be used (radial bulk-foil resistors and axial film resistors, for example). In addition, most capacitor locations find many redundant solder pads, so wildly differing-sized coupling capacitors can be placed neatly on the board, without excessively bending their leads.
Power-Supply-Decoupling Capacitors: The Unbalancer PCB provides space for two sets of capacitors to decouple both Unbalancer gain stages from the B+ connection and each other. This arrangement allows a large-valued electrolytic capacitor and small-valued film capacitor to be used in parallel, while a series voltage-dropping resistor completes the RC filter. (As an option, in place of the series resistor, an off-board choke can be used for each channel.)
PCB includes 16-page user guide.