• Item: Line Preamplifier  
  • Type: Balanced Zen Line Stage  
  • Posted: 7 April 2011  
  • Builder: martin  
  • Country: Austria  
  • Comments: 3  

Balanced Zen Line Stage

This project is based on the article and schematic published by Nelson Pass back in 1997.

Layout and Construction
My Balanced Zen Line Stage includes a few modifications. It is a real dual-monaural version with two power supplies and stereo channels fully separated, with a remote input selector and volume control.

The volume control is built around an ATMEL Mega 8 microcontroller which drives a motorized Alps–Potentiometers. This circuit even has a pin connector delivering TTL signals for switching five reed input relays. This solution is perfect and elegantly solved the problem with the selector too. Thanks to Frank Link for the µController, the perfect software and kind support!

As the inputs relays can be switched via remote control only, there was a need to make an LED board for the front panel that indicates which input is selected at the moment. An additional 5V power supply was needed for operating the microcontroller, the relay- and the LED indicator board.

I designed all the circuit boards with “Target 3001” and milled the boards on a very precise CNC engraving machine with a high speed spindle and tungsten carbide bits. The benefit of onboard potentiometers is short signal paths. This solution created a lot more work due to the fabrication of additional parts like axis, coupling and bearing bushes etc.

The power supplies are separated from the input and gain stages by a vertical steel sheet. The laminated and toroidal transformers got shielded housings. Access to all the necessary machinery made the production of all the parts for the enclosure easy. After anodizing, I engraved the front and rear plates of the case.

With the glass top in place the unit gets too hot. For this I need to find another good looking solution that enables sufficient air circulation. I must say that this circuit sounds very good and that I am very pleased with the result. No noise, just music, reproduced at a very high quality. Channel separation is superb. My effort with a strict dual-mono concept that features separate signal grounds and two power supplies seemed to pay off.

This preamp is quite flexible in its use, as the gain can be set internally. Aside from the volume control there is a potentiometer for setting the input signal level. In my setup, I almost always use the balanced signal of an external DAC. My F5 power amplifiers need an unbalanced signal, so the Balanced Zen Line Stage acts as balanced to unbalanced converter. But of course it offers balanced outputs too.

I strongly encourage everyone who is interested in high end DIY audio to give one of these great projects on the Pass DIY website a try!


  • Wardsweb
  • 20 April 2011 at 03:04PM
  • Very clean execution. As to cooling, you could machine some slots in the top to allow for better ventilation and still maintain the visual appeal.
  • martin
  • 25 April 2011 at 04:29PM
  • Thanks. Luckily the MOSFet's run at the correct temperatures. The heat comes from the source resitors. This top cover is tinted glass...
  • Alex Tech
  • 19 May 2011 at 11:49AM
  • Looking at this wonderfull work being done on this pre- amplifier. It well design put togather. I do love it..

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