The β22 Stereo Amplifier
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β22 gallery - Page 1

Here is an area showcasing β22 amplifiers built by fellow DIYers from all around the world. If you want to see more β22 builds than those featured here, please also check the AMB DIY audio forum.

If you want to show your β22, post the photos in the forum and include some descriptions. The unusual, the exotic, even the mundane... As long as you like what you built, then why not show it off?

Click on any image to see a larger version.

Quick jump: AMB | steinchen | set300b | kklee | oj | alfie
tedro | ferrari | n_maher | rjkdivin | cotdt | Mazuki
loop_ | rille | naamanf | wolf18t | edroc73rp | rolke
johnwmclean | Gatsu
group-build

AMB's β22

Here are some pictures of AMB's own β22 amplifier and companion σ22 PSU, wrapped in custom home-built cases. The styling follows that of AMB's other headphone amplifiers, this time the case and internal layout puts a strong emphasis on symmetry to reflect the amplifier and PSU circuit topologies. The transparent top covers display the beauty of the circuitry in full glory. The dimensions of each case is designed to fit everything without wasted space, which results in a sleek, low profile.

The β22 amp is in 3-channel active-ground configuration, and the three amplifier boards are mounted on a ε22 backplane board to minimize internal wiring. An Alps RK40 "black beauty" stereo potentiometer is used as the volume control, and there are loop-out RCA jacks on the rear panel in addition to the usual input RCA jacks. There are two headphone jacks on the front panel and a set of speaker output binding posts at the rear. The headphone jacks are Switchcraft, the gold RCA jacks and binding posts were sourced from Parts Express.

The σ22 PSU features a Corcom AC line filter module (rated 10A) and a 80VA toroidal power transformer from Avel-Lindberg. The output voltage of the PSU is set to ±30V. The heavy-duty PSU-to-amplifier umbilical cable features 16 AWG wires, Techflex sleeving and are terminated on each end with Amphenol locking circular connectors.

All other parts used are as recommended in the Parts list section, which includes Vishay-Dale RN55D 1% metal film resistors, Vishay-Roederstein film capacitors and Panasonic FC and Nichicon UHE electrolytic capacitors for the power rails. 3mm blue LEDs provide power-on indication.


β22 by steinchen

Steinchen's beautifully-built β22 is a 2-channel passive-ground configuration, powered by a σ22 PSU. The power transformer is a potted and shielded unit from schuro.de. The amplifier case is also from schuro.de, its heatsinks are adapted to the β22 board MOSFETs with angle brackets, and the σ22 uses onboard heatsinks. An ε12 muting/delay and protection circuit is also used.

The front panel was fabricated by Front Panel Express. The illuminated volume control ring is a nice touch (see for the parts), as are the headphone jack logo LEDs.


set300b's β22

This β22, built by set300b, is housed in a Par-Metal 20 series case. In 3-channel active-ground configuration, the β22 boards are mounted on a ε22 backplane board. The companion σ22 PSU board is also housed in the same case, but the 100VA Avel-Lindberg toroidal power transformer is in a separate case from Context Engineering. The umbilical cord is terminated with Amphenol connectors.

Two input sources are selected by an Elma rotary switch, mounted near the rear panel jacks. The switch shaft is coupled to the front panel via an extender and panel bearing. The rear panel also has loop-out jacks, preamp output jacks and speaker output binding posts (the preamp and speaker outputs are selected by a front-mounted switch). The headphone jacks are Neutrik locking jacks, but the locking feature was removed.

All electrolytic capacitors are Elna Silmic II except for the large σ22 filter capacitors, which are Nichicon UPW. The film caps are Wima. All resistors are Vishay-Dale RN55D and all heatsinks are 2.5" tall.

High brightness amber LEDs are used inside to give an illusion of tube glow through the case vents when the lights are out, and the front panel has a violet LED.


β22 by kklee

kklee's β22 is also housed in a Par-Metal 20 series enclosure (16"x12"x4") with a 3/16" front panel and handles. In 3-channel active-ground configuration, the three β22 boards are mounted on a ε22 backplane board. An Alps RK27 "blue velvet" stereo potentiometer controls the volume. An ε12 circuit provides muting/delay and DC offset protection.

The front panel has a Neutrik locking headphone jack, a volume knob, and two LEDs. The red LED above the volume knob is the power-on indicator, while the blue LED above the headphone jack turns on when the ε12 enables the output. A pair of RCA input jacks and Schurter IEC power entry module (with integral power switch) completes the rear panel.

The σ22 power supply is housed in the same case as the amplifier, featuring a large 120VA toroidal transformer from Plitron.

As could be seen, kklee has built enough β22 and σ22 boards to make two complete 3-channel amplifiers.


oj's balanced β22

Here is a 4-channel fully-balanced β22 by oj. Four β22 boards are each powered by its own σ22 PSU. The amplifier and PSU are in 2U and 3U aluminum subracks, respectively, spray painted with automotive lacquers (1k epoxy primer, then all 2k standox products). The photos don't do the actual painting justice, oj noted.

All wiring is teflon insulated; 16AWG wires from the power supply to the amplifier boards are FEP insulated for a thinner loom. All case connectors are Neutrik X-series (gold plated for the signal connections), including the 6-wire connectors from the power supply to the amplifier.

There is a single balanced headphone output, and all volume control is done in the digital domain, thus there is no potentiometer or stepped attenuator. The gain of each β22 is set to 2, for an effective gain of 4. This is to minimize the amount of digital attenuation necessary. The input and gain resistors were selected to within 0.1%, and the CRDs were J201 matched to within 2% Idss.


β22 by alfie

Alfie from Italy built his β22 with separate amplifier and power supply enclosures (HiFi-2000 Galaxy Maggiorato GX288 and GX283, respectively). Binder 693 series connectors are used for the power umbilical cable. These are similar to the Amphenol units used by AMB and several others. All panel jacks are from Neutrik. Two headphone jacks are on the front panel, and the rear panel has a set of loop-out connection. The volume control potentiometer is an Alps RK27.

Inside the β22, alfie made a special power distribution board and a volume pot interface board. The σ22 PSU has an encapsulated 120VA 30V+30V toroidal power transformer.



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