The β22 Stereo Amplifier

The β22 Stereo Amplifier

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β22 - group-build special gallery

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Group-build β22 and σ22

In 2008, members of www.head-fi.org donated parts and funds to build a "group-build" 4-channel balanced β22 amplifier and dual σ22 power supply, which was then awarded to krmathis of Norway. The project was spearheaded by amphead as a random act of kindness, and the recipient was also selected at random. The community responded and the following pictures showcase the result.

The β22 and σ22 were built by AMB, amphead, rockcod, Jrossel and ruZZ.il in several mini-meets. They were tested in November 2008 at AMB Laboratories and reconfigured for 230V AC mains prior to shipping to Norway. A framed certificate which lists all donors was also included.

The donors were: 04BluMach. aaron313, Afrikane, akabeth, amb, amphead, Beefy, Blutarsky, cAsE sEnSiTiVe, Cool_Torpedo, dbel84, digger945, DoubleEs, error401, fatcat28037, fordgtlover, gates_2, GeWa, gz76, HeadphoneAddict, Tyll Hertsens (HeadRoom), JamesL, Jrossel, Jude, Lynxkcg, Malldian, mark_h, MASantos, MisterX, MrMajestic2, mwofsi, n_maher, naamanf, NJ Head-fi Meet, NoPants, nor_spoon, omegaman, Pabbi1, penger, Ricey20, rockcod, ruZZ.il, samgotit, scompton, synaesthetic, tomb, torjeh, Uncle Erik, VeipaCray, Voltron, Wavoman, wnmnkh

See the following head-fi threads:

The σ22 PSU and the β22 amplifier are housed in separate 12"x12"x3" Par-Metal 20-series clear anodized aluminum cases, the front and rear panels are both custom milled by Front Panel Express. The two cases are connected by twin umbilical DC power cords, one per channel, both with Amphenol 4-pin circular connectors at each end.

The σ22 features a Bulgin illuminated pushbutton latching switch which operates an AC relay to switch the power. The Schurter IEC power entry module on its rear panel also has a master power switch and fuse. Each σ22 board is fed by a separate Avel-Lindberg Y23 series 80VA toroidal power transformer.

The β22 features balanced (XLR) and unbalanced (RCA) input jacks, selectable by a rear panel toggle switch. Dual Neutrik combo jacks and a Neutrik 4-pin XLR jacks on the front panel allow the use of balanced and unbalanced headphones (dual TRS 1/4" unbalanced or HeadRoom-style dual 3-pin XLR balanced, and AKG K1000-style 4-pin XLR). Binding posts on the rear panel allow the amplifier to drive speakers.

The volume control is a 4-gang stepped attenuator with SMD resistors. It is housed in an aluminum box and located at the rear, near the input jacks for the shortest possible wiring. The front panel knob operates the attenuator via a shaft extender and panel bearing. A frosted clear acrylic disc behind the volume knob is illuminated by four blue LEDs to accent the knob, and serve as the power on indicator. The amplifier gain was set to 8 per board, for a good match with krmathis' K1000 and other high-impedance headphones.