This preamp is basically made up of a few separate parts: Case, input selector, attenuator (volume control), line stage, phono stage and soft power circuit.

Input Selector and Attenuator

The input selector uses relays and a rotary switch to control them. Its called Darwin and you can get one from Twisted Pear Audio.

The attenuator also uses relays but it is digitally controlled. It uses a pot to set the level but the audio signal does not actually go through the pot. The value of the pot is read by the control section which adjusts the level accordingly. Its a very neat way of controlling a relay based attenuator. Its called a Joshua Tree Attenuator and is also available from Twisted Pear Audio.

I thoroughly recommend the kits from Twisted Pear Audio, they are fantastic!

Phono Stage

I made this myself. The schematic is based on RJM's VSPS but designed my own layout. The power supply uses LM317/LM337 regs instead of the fixed voltage types. I used 2x OPA627s on a BrownDog adapter, Elna Cerifine caps after the LM317/LM337 regs, matched wima polyprop caps in the RIAA section, Rubycon BlackGate bipolar caps on the output and all resistors are matched to 0.1%. I tried OPA637s but could not get them stable. I really like the sound from this phono stage. I used this method for making the PCB.

Linestage

I wanted to make a linestage for it as definitley needs more gain but I haven't had time!

Soft-Power Circuit

This enables you to use a momentary switch to control a relay which turns on the main power. This is a much more professional way of controlling power IMHO as opposed to using a 220/110V power switch. Most commercial audio equipment uses a similar system. There is a much wider choice of switches which are low voltage and momentary too. I chose to use the Bulgin MP0037 vandal resistant switch.

I copied this design from a thread on DIYAudio.com and made the layout to suit the transformer I could get from Jaycar. It uses a 4013 flip flop IC to control a power relay. I used this method for making the PCB.

The Case

It took more work to finish the case than any other part of this preamp but I'm very happy with how it turned out.

I bought aluminium from a metal dealer and got them to cut it for me:

I used a wood router and bit to round the end edges of the front panel:

I used 12mm square aluminium for the corners, drill and tapped all the threads my self:

An engineer cut the large holes in the front panel for the volume and input control knobs:

The knobs and RCA sockets are from THLAudio in taiwan. I mounted the volume pot and input selector switch on a lexan panel behind the front panel to create a ring of light around each knob:

I made two cases, one for a preamp and one for a power amp.

But I never got around to making another power amp so that case is just empty:

I got the metal polished!! OMG it came up so shiny! Here is an HDR photo:

And here it is with my dual mono GCs: