Compactron Preamplifier Prototype

 Hi!

In my previous post I teased the new preamplifier I am working on. Here some photos of the prototype build.

This is a full function preamplifier with phono section on board. In the moment I am only offering separate line and phono stages and these each have separate power supplies. So a 4 box set up. The Compactron preamplifier is all in one box including power supply.

Above the face plate design which still needs to be manufactured. While many people including myself like to see a landscape of tubes, transformer covers and capacitors on top of their amplifiers, others prefer a more discreet design which is easier to integrate into a living room. So the new preamp will have an enclosed chassis.

So far my D3a phono stages are MC only. The reason for that is that a MC step up transformer is already integrated in the unit and part of the biasing scheme of the input tube. Also the D3a tube is not too well suited for an input tube of an MM phono stage since it has a rather high miller capacitance. I also received requests for adjustability of the load impedance and the possibility to have multiply phono inputs. This new preamplifier has 2 each MC and MM inputs so can be connected to 4 tonearms at the same time. In addition the MC load resistance can be selected between 1000, 375, 150 and 50 ohm. And if that does not offer the desired impedance value, there is a 5th position on the selector which connects to a set of RCA jacks on the backside which can take plugs with a specific resistor to get another desired load impedance. MM load capacitance is selectable between 150, 200, 250, 300 and 470pF. In addition the prototype has 4 line inputs, two balanced (XLR) and 2 SE (RCA). Both XLR and RCA outputs will be available.

The prototype is completed and proofs the concept. The prototype only shows an example of possible configurations. This will be the first of a series of new preamplifiers which can be customised with various features. For example the possibility to change EQ for historic records. Even more phono inputs, or less. Different set of line inputs, tape monitor loop, mode switch, phase switch, etc. Also phono and line only units are planned.

I will show some possible configurations in an upcoming post and also share some photos of the build process. Once the prototype testing is complete a final version will be built which will have a much shorter chassis since a lot can be compacted compared to the first build. Stay tuned for updates on the Compactron Preamplifier series.

Best regards

Thomas