For easy mounting of all components, I advise to start with the lowest profiles.
Original version of the PCB.
Two beautiful small 7VA toroid transformers for the power supply.
Detailled view on the front-PCB. The IR eye sits next to the displays. The 18-pin DIL IC is the PIC microcontroller. It decodes incoming IR signals, drives the display, and keeps track of the preamp operation mode. The two light-brown strips each contain 4 resistors in an 8-pin SIL package, needed to set the display current.
View on the power supply stabilization: 4 separately stabilized outputs (left-channel positive and negative, right-channel positive and negative). Extremely low-noise and low-impedance over a wide frequency spectrum.
Output spectrum of preamp, single-ended measurement (not differential). Input signal is 750Hz. Harmonics (2nd, 3rd, 4th) show at an attenuation of more than100dB below the base signal, which means <0.001% distortion. HOWEVER see next picture...
This is a similar measurement of just the input signal, no preamp involved. It shows that the harmonics that were seen on the preamp output were already present in its input signal. So, the preamp distortion is basically not visible.
Output of the preamp when the same input signal is provided as in the earlier pictures, but the preamp volume is turned down to 00. Indeed the output becomes silent. The remaining peak at 3kHz is part of my measuring device: It also shows up when no preamp is connected.
Preamp input/output signal with a 100kHz square-wave, 3Vt-t output voltage, as seen on my oscilloscope. Note the absence of dirty 'ringing' effects. -3dB bandwidth is about 370kHz.
The Dale resistors as I ordered came in their traditional 100-pc boxes. It seems that some of the E96-series values are rather unpopular and were delivered from amazingly old stock. Maybe the shop was glad to finally sell these after nearly 30 years...
Updated version of the RelaiXed PCB, still in one piece as I receive them. I will send them out with the left part (the front PCB) separated from the main (relay) PCB. The connector for the front-PCB was moved to the front side :-) The circuit around the audio opamps was modified, and the power supply was slightly adapted.
The specific XLR socket version which I received (left) did have a connection from the chassis (the screw hole) to the XLR ground pin. I did cut that (right picture) because I did not want that.
PCB mounted with components: right half. Still empty sockets for the four LM4562 dual-opamps. Only the 1uF capacitors on the power-supply output are still missing. I still want to do a listening test to find out if such are needed.
Left half of of PCB, mounted with components. The PIC microcontroller is labelled with a sticker to indicate its firmware revision.
I did order a personalized back-panel, 3mm thick black anodised aluminium. Holes and text are CNC machined. This was ordered at http://www.schaeffer-ag.de/en . They provide the drawing program to specify this on your own PC.
First check to see if everything fits together: The relaiXed preamp and my DAC-in-development. This is a black 'Slim Line' cabinet from http://www.hifi2000.it/ with the optional 10mm thick front. (Yes, the front really is straight. Only my camera makes it curved :-)
Lucky me, the XLRs mounted on the PCB fit exactly....
And, the DAC input connectors (3x BNC, 1x optic) fit as well...
