RelaiXed2 -- DIY balanced pre-amplifier


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:

November 2016:The PCBs of this RelaiXed version with classic through-hole components and the pre-programmed microcontrollers are out of stock. Unfortunately, I cannot actively support this project anymore due to lack of time.

Note that there are two related alternative designs, documented on their own web pages:

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 such as this Aleph-X, 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. This shows among others a distortion measurement.

For some of my early customers, a new firmware release 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.
A pair of PCBs 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...

Recent extensions

New:Support was added for a 16x2 character OLED display, as alternative for the standard 2-digit 7-segment display. This particular display from ebay was selected. Obviously, such OLED displays have a great contrast. Its i2c interface is simply connected in parallel on the 4-wire communication bus between the front- and the main- (relay) PCB. To use this display, you would need to update the firmware inside the PIC microcontroller to -at least- the 20160910 revision, which can be downloaded from the project sourceforge site. This display has some issues in obtaining a reliable communication. See how to handle that in the User Manual.

Thanks for your interest,
Jos van Eijndhoven

Please note that although I (aim to) create professional-quality audio devices, these developments are just hobby for me, next to a very busy job. These web pages result in many emails to me, which I cannot always answer quickly. So, please, have some patience with me. I always try to answer within a week, otherwise feel free to ask again!
Dec. 04, 2016