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Monday, January 9, 2012

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

4 comments:

  1. Brilliant concept I am looking forward to the series. I assume that concept (phono) can be used in conjunction with with your 801 Linestage (it sounds superb).
    Peter

    ReplyDelete
  2. Hi Peter,

    yes this concept can be used with the 801A linestage. I'm also planning a 801A linestage in the same chassis style

    Best regards

    Thomas

    ReplyDelete
  3. Is the passive line stage available for sale? Brilliant modular idea. Where can someone buy your products?

    ReplyDelete
    Replies
    1. Hi!
      Everything shown on my blog can be ordered. I build the components on order and can also adapt them to your requirements. For ordering simply drop me an email. My contact information can be found under the link Impressum / Contact on the top left of this site

      Best regards

      Thomas

      Delete