The input stage of the Ball and Buck Amp consists of a pair of 12AT7 tubes. One half of the 12AT7 is configured as an actively loaded voltage amplifier using our Camille Cascode Constant Current Source for super quiet, dynamic, linear performance. It is RC coupled to the output stage with a high quality film capacitor. The output stage uses a 2A3 tube and cathode bias. A plate choke loads the output tube and the output is via a high quality parallel feed coupling capacitor and parallel feed output transformer configurable to 4,8 and 16 ohm settings to work with a broad range of speakers. The amp uses zero global negative feedback. The unused halves of the 12AT7s will accomodate future upgrades. We have several cool upgrades for this kit coming down the pike.
THE POWER SUPPLY
A custom 110/120/220/230/240VAC power transformer supplies high voltage to the driver stage C4S load and output stage plate choke via smooth sounding ultrafast rectifiers and a conservatively designed dual mono CRCRC filter for quiet operation. The power supply components are point to point wired in such a manner as to allow for more cool future upgrades.
The chassis layout utilizes a 10″ x 12″ format. The random brushed laser cut aluminum plate is extra thick to accommodate the ample iron. The chassis plate sits in an attractive Pacific Northwest alder wood base that you assemble and finish to taste. Inputs, speaker binding posts and an IEC style power entry jack are at the top rear of the chassis plate. A easily accessible power switch sits at the top front of the chassis along with volume, balance and input selector controls, and equally easy to access hum balance pots resides next to each output tube.
Laser cut chassis plates and alder wood base kits are made for us here in the Pacific Northwest. Our custom Bottlehead power and output transformers and plate chokes come from Northern California. The universal power transformer has been designed by Bottlehead’s head of R&D, Paul Joppa. Rectifiers are ultrafast soft start types. Capacitors are a combination of polypropylene and low ESR electrolytic. Resistor compositions are carefully selected based on the requirements of the circuit, and all resistors are sized for conservative power dissipation. Hookup wire includes both Alpha teflon and Carolco insulated 22 ga. solid core copper wire for high voltage connections and shielded/solid core Cat-5 cable for easy to install, super quiet signal wiring.
SPECIFICATIONS TAKEN FROM THE PROTOTYPE PREVIOUSLY ILLUSTRATED
- Power: 3.5 Watts per channel
- Hum: Typically 1 mV on the 8 Ohm tap with an 8 Ohm load, depending upon the output tube used
- Bandwidth: -1dB at 20Hz, -3dB at 50kHz
- Sensitivity: Full power at about 0.4v (2A3)
- Gain: About 8 at the 8 ohm tap (21.5 dBV)
Input impedance is 50K ohms, output can be configured for 2,4,8, or 16 ohm speakers. We recommend speakers of 96+dB sensitivity for serious listening with all kinds of music. 93 db speakers are satisfactory for less stringent requirements (chamber music, soft jazz, acoustical) and smaller rooms, and Doc even uses Stereomour prototypes in his home theater with some 87 dB sensitivity monitors with very satisfying results. Sonics are hard to describe in print – suffice it to say that Stereomour sounds like the very good SE2A3 amp it is, and our customers have remained enthusiastic about the design amp for over 15 years now. The parafeed output and C4S active load give the amp a remarkable sense of realism, bandwidth and bass articulation, particularly considering the price.