This is a Beta 22 build that I just finished. It's a '3 channel' or so-called 'active ground' version. The power supply is completely isolated from chassis ground using rubber sheets, Delrin blocks, etc. This maintains safety (the AC "subchassis" is bonded to the safety earth ground of the line cord) while keeping any noise from the AC safety ground off the signal ground. The power transformer is inside a box of mild steel, which pretty effectively reduces it's radiated magnetic field, enough so that noise currents are not induced into the low level, high impedance circuits.
Other things I've done include rather heavy silver plated / Teflon wiring for the power rails - 12 gauge for the + and - rails, and 10 gauge for the common rail, in order to keep supply impedance at an absolute minimum, and noise rejection high. The front panel was milled from a billet of 3/4" aluminum- not for any performance reason, but just because I like thick metal.
A Goldpoint attenuator is fitted, as are better quality RCA input jacks, being gold-over-copper rather than the more common gold-over-nickel-over brass. The gold/copper jacks are said to be lower noise.
Side panels are made from selected "tiger" maple with a gloss finish (12 coats) for maximum depth and chatoyance.
This photo doesn't do justice to the 3-dimensional depth of the wood grain.
The wood sides can be removed if one prefers an all-aluminum look.
The front panel is milled from a single billet of aluminum.
Neutrik non-locking headphone jack. (I don't like locking jacks.)
Power supply is completely isolated, giving the circuit advantages of a 2-chassis build without the inconvenience and cost.
LED brightness was toned down to offer subtle white light indicating "ON" for the Bulgin-style on/off switch.
Front panel is bead-blasted natural aluminum for a frosted look, with the raised area along the bottom polished to high gloss.
Good quality input jacks
The Goldpoint attenuator is rear-mounted to keep signal leads as short as possible
Efforts were made to keep the attenuator mechanical action as silky and smooth as possible- the attenuator is mounted to a machined Derlin block for rigidity and the shaft extension uses a high-quality aluminum flex coupling. The bushing holding the shaft to the front panel is closely fitted to the shaft and lined with Teflon to eliminate play and maintain smooth action.
I will be making a foam-lined, fitted wood case for the amplifier next.
The amplifier will be offered for sale at some point. Since starting this build in 2013, I have (ironically) decided to concentrate on electrostatic 'phones and so don't need this Beta.
Gain is "medium" - 5? I think? Not 2 or 8. I forget exactly, 5 I think.
