GlassWare Audio Design
Thanks for supporting the Tube CAD JournalThe Unbalancer
Product Description
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.
PCB Features
HV B+ and Heater Power Supplies: On the Unbalancer board, two power supplies reside, one for the high-voltage B+ for the tubes and a low-voltage power supply for the heaters. The high-voltage power supply uses an RC filter to smooth away ripple, while the low-voltage power supply uses a voltage regulator to provide a stable and noise-free voltage output. The heater regulator is adjustable and can be set to 6V or 12V. The power supplies require an external power transformer(s) with two secondary windings (120Vac to 260Vac and 6.3Vac to 12.6Vac).
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 20-page user guide.
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.
PCB Features
HV B+ and Heater Power Supplies: On the Unbalancer board, two power supplies reside, one for the high-voltage B+ for the tubes and a low-voltage power supply for the heaters. The high-voltage power supply uses an RC filter to smooth away ripple, while the low-voltage power supply uses a voltage regulator to provide a stable and noise-free voltage output. The heater regulator is adjustable and can be set to 6V or 12V. The power supplies require an external power transformer(s) with two secondary windings (120Vac to 260Vac and 6.3Vac to 12.6Vac).
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 20-page user guide.
Accessories
Balanced Attenuator Like its unbalanced predecessor, this balanced attenuator offers 36 steps of attenuation for two channels of signal. The center rotary switch controls both channels and presents coarse decrements, while the two flanking switches afford fine volume decrements for each channel. Two options are available: -2dB / -12dB steps for a maximum total attenuation of -70dB, which is perfect for active line stages; and -1dB / -6dB steps for a maximum total attenuation of -35dB, which is perfect for passive line stages or those setups that do not require lots of attenuation. PCBs are 1.4 inches tall and 9 inches long and will fit within a 1U rack-mount enclosure. Each resistor position holds a redundant set of pads, so that radial and axial resistors can be used. The input resistance is nominally 28k. The kit includes instructions and three high-quality, open-frame, rotary switches and one USA-made extra-thick, high-quality PCB, with 2oz copper traces and solder mask and silkscreen. |
