I’ve been impressed by the ESP projects by Rod Elliott, they work well, are simple for novices but with plenty of scope for modifications. The projects come with extensive documentation, including construction advice if you buy the PCBs. I decided to try his well regarded Project 88 preamplifier to go with my Nelson Pass ACA. This is designed to be simple and flexible with configurable gain using DIP switches. It requires a +/-15V supply so I built another ESP P05 PSU, this time with a conventional toroidal transformer rated at 15VA.
The boards are very small with a correspondingly compact layout. The preamp has a low parts count and I used generic 1% metal film resistors, Wima polyester capacitors Panasonic electrolytics and Vishay ceramics. The opamps are my usual choice, Burr Brown OPA2134PA, although others can be used. The volume potentiometer is an Alps RK27 10K mounted on a PCB for easier wiring.
There are two gain stages, the first is ‘hard-wired’ to be either 0dB or 6dB and the second stage is highly configurable, using a 4 pole DIP switch module for each channel. The circuit component values in standard guise are set to accommodate a linear volume potentiometer and a balance pot. The omission of the balance pot in my build just requires a resistor change, as does the use of a log pot for volume.
I found a nice enclosure which mimics the design of Pass amplifiers for a very reasonable price. I was a little apprehensive about this as I’ve read quite a few negative comments about enclosures from China, but this particular example is of very high quality. It comes with an IEC power connector and switch and the back panel has been machined to accept these. There are no cutouts for line connectors so I drilled the rear panel to accept RCA jacks. The front panel has a very nice volume knob, and again the hole for the pot shaft is pre-drilled, although it had to be widened slightly to accept the Alps pot. All PCBs and the transformer are screwed to the enclosure and a safety earth connection is made to the chassis. Anodising is removed at all contact points so that all parts of the enclosure are earthed.
I’m extremely pleased with this build. I have it installed in-between my Amp Camp Amp and the Topping D30 DAC which is fed by the Raspberry Pi IQAudio streamer. The combination of amp and preamp is superb and I think they look excellent together. This was a relatively cheap build, well under £100 for everything!