Trilith - Current Feedback Pre-Amplifier
Introduction
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.
Overview
MC/RIAA Amplifier Stage
- Complete Schematic Diagram 1a
- Printed Circuit Board 1a
- Bill of Materials 1a
- FFT Harmonic Spectra and RIAA Equalisation
Line Amplifier Stage
Battery Supply Unit
