The Modular Preamplifier, Part 1: Introduction

Hi!

During the holidays I spent some thoughts on a new preamplifier concept. The idea is to make the preamp (phono and line) completely modular so it can be approached step by step and enhanced with upgrades or modified to different requirements or tastes. For this I plan to break the preamp up into more individual chassis: MC transformer, phono input stage, EQ unit, phono output stage, passive TVC line control, line stage. This can be further augmented by passive line level crossovers or additional gain or buffer stages as needed.

I started with the passive line control unit and MC transformer chassis. The photo above shows the assembled line control unit which basically only consists of an input selector switch and a transformer volume control. The wooden enclosure is still missing. It is currently beeing made by my carpenter. As you may notice the design follows a more classic approach with the control knobs on the front and the connectors on the backside.

Here a photo of the metal plates of the line control unit before assembly:

A rather thick metal plate (10mm) was chosen for the front so that the knobs reach into cutouts in the plate when they are mounted to the switch shafts. Some might be frightened by the increased number of interconnects this approach requires. But the chassis are quite compact. The front plates are 10cm high and 25cm wide. Most of the chassis will be stackable. This keeps interconnects short. All outputs will be transformer coupled and low impedance which minimizes impact of cables.

The metal plates for the MC transformer:

As you may guess from the printing on the front this will become an adequate housing for Lundahls new silver MC step up, the LL1933Ag.

With this approach each stage can be chosen according to requirements for gain, input and output impedance. A separated EQ unit allows to start with a simpler RC based EQ unit and later upgrade to a LCR unit or swap a stereo LCR for an adjustable EQ for mono records.

Stay tuned for further posts about this approach as it progresses.

Best regards

Thomas