Due to popular demand, the SRPP+ is back, minus the power supplies. The new PCB is 6in by 5in and, like all GlassWare PCBs, is crazy overbuilt, with extra thick double-sided PCB material and heavy 2-ounce copper traces. Each channel gets its own large power supply RC filter, whose voltage rating can be a low 250Vdc, perfect for high idle current applications, such as headphone amplifiers; or, 400Vdc, perfect for line-amplifier use. The SRPP+ PCB holds pads for two sets of output coupling capacitors. All in all, it's a fun little board and I can imagine many different audio applications, from the input stage of single-ended amplifiers to headphone amplifiers for high-impedance cans, such as those offered by Beyer and Sennheiser.
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 6 by 6 inches, with five mounting holes, which helps to prevent excessive PCB bending while inserting and pulling tubes from their sockets. Each PCB holds two SRPP+ line-stage amplifiers; thus, one board is all that is needed for stereo unbalanced use (or one board for one channel of balanced line-stage amplification). The SRPP+ board makes building a line stage or headphone amplifier a breeze. This assembled board with a chassis, volume control, selector switch, power transformer, and a fistful of RCA jacks is all that is needed.
Redundant Solder Pads This 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 SRPP+ PCB provides space for two sets of capacitors to decouple both SRPP+ 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 resistors, an off-board chokes can be used.)
Dual Coupling Capacitors The boards hold two coupling capacitors, each finding its own 1M resistor to ground. Why? The idea here is that you can select (via a rotary switch) between C1 or C2 or both capacitors in parallel. Why again? One coupling capacitor can be Teflon and the other oil or polypropylene or bee’s wax or wet-slug tantalum…. Each type of capacitor has its virtues and failings. So use the one that best suits the music; for example, one type of coupling capacitors for old Frank Sinatra recordings and the other for Beethoven string quartets. Or the same flavor capacitor can fill both spots: one lower-valued capacitor would set a low-frequency cutoff of 80Hz for background or late night listening; the other higher-valued capacitor, 5Hz for full range listening. On the other hand, each coupling capacitor can feed its own output, for example, one for low-frequency-limited satellites and one for subwoofers
PCB includes 16-page user guide with schematics and instructions.