RelaiXed2 -- DIY balanced pre-amplifier

Introduction

The Relaixed2 is an audio pre-amplifier design, created for easy re-builing by DIY audio enthousiasts. Although inspired by the original RelaiXed design, it has been thoroughly updated in almost all aspects. It targets the high-end audio segment, and is characterized by:

A little sister is also available: a derived implementation using SMD components to achieve a smaller implementation.

With respect to the original Relaixed design, the main Relaixed2 improvements are a strong reduction in noise level and overall improved audio quality (mostly due to lowering the impedance of the attenuator circuit). Furthermore, relay switch transients in the audio output are now properly suppressed.

The original drive to create the RelaiXed was to provide a high-quality DIY pre-amplifier with balanced inputs/outputs, for which there were very few choices available. The RelaiXed combines with several available power amplifiers that benefit from balanced signals, such as the DIY PassLabs mosfet amplifiers, the Hypex amplifier modules such as their UcD400HG, and Holtom precision amplifiers such as their HPA_nxV300 R2.

Design information

The design is documented with an extensive set of on-line documents and fotos:

You might want to check some performance characteristics, which are listed in the page on the SMD version.
New of July 2014: Added distortion measurement.

Note: A new firmware release "RelaixedApp-20130701.hex" is available for download from the sourceforge site. See the user manual on how to install this release in your own Relaixed2 (standard board or SMD version):

PCB and microcontroller availability

Upon request (by email) I can send PCBs and preprogrammed microcontrollers.
NEW from Apr 25: with a new set of PCBs made, I can do a slight price reduction. A pair of PCBs now costs 72,=. The preprogrammed PIC18F24J50-I/P microcontroller costs 8,=. Packaging and mailing with a sign-on-receipt delivery service costs 13,= throughout Europe, and 18,= elsewhere.

Additionally, there is some support for creating a RelaiXed cabinet.

Design background

Obviously, this single page is not suited to explain all of the design background. Nevertheless I would like to mention some of my ideas that guided this design. In the past I did design and listening tests on vacuum tube amplifiers. That background and experience did lead me to:

One warning: when turning the volume, one can clearly hear the mechanical clicking sound of the relays. If that would really disturb you, relay-based attenuators are not your thing...

Foreseen extensions

I still plan some extension that are not yet part of the current design release. This is among others:

Thanks for your interest,
Jos van Eijndhoven

Dec. 11, 2013