Roughly four years ago I saw my first LDR, or opto-coupler pre-amplifier. I was intrigued by this unique approach to controlling the signal output to an amplifier, but at the time funds were limited, and I didn´t have time for another DIY project. Fast forward to the present and another DIY kit has come my way, the Stereo Coffee LDR pre-amplifier. This time both time and money were at hand, so I took the plunge and ordered the kit from eBay.
The kit comes as two pre-assembled PCB´s, the main preamp board, and a small regulator board. The stock kit comes with RCA plugs installed, but as I wanted to leave my options open,I asked for these to be left out. All the builder has to do is install the boards in a nice chassis, and provide power. In an effort to keep things as simple as possible I chose to go with a 12V battery power supply with a switch to select between ´play´ and ´charge´.
As the PCB´s are already assembled the build time was spent on preparing the chassis. Once all the cut-outs and holes had been made, assembly took very little time. In total, it took a couple of evenings to complete and test before installing in my main system.
Prior to completing this kit I had been using Khozmo passive preamp in in my main system. This is the modified version with Z-foil resistors, and is very neutral in presentation. When I swapped in the Stereo Coffee preamp I was really surprised at the difference. The presentation was clearer, and the soundstage slightly wider, with placement of instruments and vocalists more destinct. My gut feeling is that this pre-amplifier is very neutral adding little, if anything, to the source. To some this may be perceived as producing a ´clinical´ sound, but I would describe it as a lack of colouration.
The Stereo Coffee LDR pre-amplifier now has pride-of-place in my main system, and I can´t see it being replaced any time soon. If you are happy doing a bit of DIY this kit is a real bargain, and will surprise many when used in a well resolving system.