β22 gallery - Page 3
loop_'s β22This 3-channel active-ground β22 by loop_ is mounted on a ε22 backplane board and housed in a ATI 737U enclosure. Ventilation holes were drilled on the top cover. The companion σ22 PSU is in a Hammond 1455T2201BK enclosure. The umbilical linking the two uses Amphenol circular connectors.The β22 features a DACT CT2 stepped attenuator, Neutrik RCA jacks and Schurter gold-plated 1/4" phone jacks. The σ22 uses a Hammond 182K30 80VA toroidal transformer. All boards are populated with the recommended parts, and 2" tall heatsinks.        
β22 by rilleRille's single-box 3-channel active ground β22 is housed in a Pesante 2U enclosure from Hifi2000, with a 10mm thick front panel, with custom milling by Front Panel Express. The volume knob is also from Hifi2000.Inside, a motorized Alps RK27 volume control pot works in tandem with a Dantimax remote control kit, which also controls power on/off and switching between two sets of inputs. The small blue transformer provides the standby power for the remote control circuit. The β22 boards are mounted on a ε22 backplane board, and a σ22 PSU supplies the amplifier power. An ε12 protection/delay/muting circuit is also used. The amplifier weights 9 kg (about 20 lbs).        
Balanced β22 by naamanfShowcased here is naamanf's tour de force rendition of the 4-channel β22 amplifier. It is a combination headphone amplifier, pre-amplifier and speaker power amplifier. The twin σ22 PSUs are located in a separate chassis. As of this writing, naamanf had built four of these, three of them with twin 3-pin XLR headphone output jacks, and one with a four-pin XLR.Par-Metal 20-series anodized aluminum cases are used, with front and rear panels custom fabricated and engraved by Front Panel Express. Inside, the build features Elna Silmic IIs and Nichicon Muse KZ, as well as Wima film and silver mica capacitors. The gain resistors and compensation capacitors are socketed and could be changed as needed. The volume control is a Twisted Pear Audio "Joshua Tree" relay-based stepped attenuator. The Joshua Tree boards are mounted on a special I/O board that naamanf designed, which also contains relays to select between the balanced and unbalanced inputs, as well as switch between headphone and preamp/speaker outputs. Bulgin vandal-resistant pushbuttons on the front panel activate these switching functions. The σ22 boards use off-board heatsinks from Conrad in Australia. Power is switched via a Omron 30A AC relay, which is also activated by a Bulgin switch. One of these amplifiers was featured at the 2008 CamJam national head-fi meet in Fort Lauderdale, Florida; where it made quite a sensation.        
wolf18t's β22This 3-channel active-ground β22 was built in a single chassis from DIY Enclosures LLC. To minimize potential hum and EMI noise, a custom-made encapsulated and shielded toroidal transformer from Richard Sumner Technology was used. The volume control potentiometer (TKD 2CP-2511) was mounted in the back of the chassis using an extension kit to minimize the input signal wiring. The potentiometer is very close to the IEC power entry module but wolf18t reports that no AC noise was audible.As wolf18t intends to use common headphones only, he chose to set the σ22 PSU output voltage at ±24V for reduced heat dissipation. For easy change of the amplifier's voltage gain, R3-R4/C2-C5 were installed on gold-plated SIP sockets. All electrolytic capacitors are either Nichicon FW or KZ "Muse"e; series. Multistranded 22AWG silver plated wires and gold plated Molex connectors were used in the signal path. An ε12 muting and DC offset protection circuit was also installed to safeguard the headphones. wolf18t says: "This amplifer sounds wonderful with no signifiant hiss or noise with either my high Z Beyerdynamics or the lower Z Grados. The sound is very neutral, transparent and smooth and the soundstage is terrific."        
β22 by edroc73rpThis β22 belongs to edroc73rp of the Philippines. The amplifier is a 3-channel active-ground configuration with separate amplifier and σ22 PSU enclosures. edroc73rp had to travel some distance to coordinate the work with another builder, who did the electronics, while edroc73rp took care of the casings. The casings are custom-made from 2mm thick aluminum sheets, powder coated black. Rectangular vent holes are machine punched on the top and bottom panels. The fascia is made from a local hardwood called Molave, which edroc73rp carved with Dremel and a drill press, and finished in satin polyurethane finish.Neutrik power connectors for the umbilical cord connecting the amplifier and PSU cases. The amplifier has pre-out connectors and speaker-out binding posts on the rear panel. It also has two sets of inputs, all using WBT-style connectors. All internal signal wiring are silver, sourced from Hong Kong. The front panel volume control is a stepped attenuator made by the builder. Input and output selector switches, as well as the headphone jack are also located at the front. edroc73rp says: "When used with my Frugel Horns, i use the pre-out to integrate a Velodyne subwoofer into the system. It works great and has enough power for the Fostex 126s.        
β22 by rolkerolke of Germany built this 3-channel active-ground β22 in a two-box configuration. The three β22 boards are mounted on a ε22 backplane board. The amplifier also features a Cirrus Logic CS3310 based volume control and relay based four-input selector board/kit from diyclub.biz. Modifications were made to this board to accept DC power. The front panel has a digital display showing the currently selected input and volume attenuator setting, as well as pushbuttons for selecting the input and incrementing or decrementing the volume. An infrared remote control also comes with this circuit. The cases are from elcal.de, with custom front panels by schaeffer-ag.de (the German branch of Front Panel Express). The unbilical cable between the amplifier and PSU cases use Neutrik 8-circuit Speakon connectors. KThe PSU contains two power supplies. There is the σ22 which provides power to the β22 boards, and there is a separate 7805/7905-based power supply with separate transformer for the digital section of the input select/volume control board. All resistors are 1% tolerance, capacitors C2-C5 have been matched for 5% tolerance and film capacitors are Wima. All Molex connectors that carry audio are gold-plated. Wires have been braided where necessary (audio as well as DC), audio wiring from the back/to the input relays/to the ε22 is RG-174. Output stage biased to 65mV. DC offset is very stable with temperature and less than 5mV across the channels. The Zobel network proved necessary to avoid oscillation with rolke's AKG K701 headphones.        
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