Trilith - Current Feedback Pre-Amplifier


As you might have noticed, my philosophy in audio design is usually based on the statement "the simpler the better". Therefore, the preamplifiers line stage could just be a passive preamp which goes between your CD player and power amplifier!

Unfortunately, the world is not that simple - a "passive preamp" cannot drive long cables! A 10 kohm passive volume control, for example, has a far too high source impedance for cables longer than a one meter, whereas 20 to 30 cm would be ideal! Having a long cable, you either put the volume control into the power amplifier or you definitely need a line stage capable of driving large capacitance.

On the one hand designing an excellent line stage may be a challenge, on the other hand it is easier to design a line stage than a MC/RIAA phono stage!

At 50 Hz and below, the MC circuit must amplify the input by approx. 1000 times, while a  line stage just 3 to 10 times. Also the input noise of the phono stage must be extremely small in comparison to the typical half a millivolt output of MC cartridges. According to this, for MC phono stages there are three main requirements: You need very high gain, very low noise and finally very precise frequency equalisation (RIAA).

Altogether, there are a lot requirements to rack one's brains!

Design Considerations

Amplifiers are much more variable in sound than often suspected. Knowing the sound of the power amplifier No. 2 Megalith, it has been obvious to use an identical topology for the line stage. Moreover, this circuit is perfectly suited for driving long cables and low impedances (I use about 6 meters without any problem).

Trilith - Line Amplifier No.3

Along with the effort of designing the Trilith Pre-Amplifier, I considered another topology.


MC/RIAA Amplifier Stage

Line Amplifier Stage

Battery Supply Unit