Valve DAC

[Thermionic Idler]

I managed to get hold of a PCB for this to make my own version of it, which arrived today all the way from Oz. I suspect it won't look as smart as Ray's.

I'll start my own thread for it when the actual build starts. That will probably be around winter time, as there's still a substantial amount to do on the 'Quad Style' line stage.

[Ray P]

Good to chat yesterday Mr. Idler - we'll sort out you and Mrs I having a listen to my Valve DAC once you have you 300B sorted out...

[Irene Idler]

A few years late, but apropos of the Pachelbel hilarity:

[Ray P]

I'm working on a commission build of another Valve DAC. Power supplies all installed and tested, reconstruction filters built. It'll soon be time to hook up the DAC board for testing and adjustment. It's being built into a 3U Modushop chassis.

[IslandPink]

Nice work. Quite shoddy, actually.

[Ray P]

Today I finished installing and testing the last of the supporting circuits so I'm now ready to hook-up the actual DAC board and start checking it out.

The final item today was to assemble and test the DSD rate indicator board, which will eventually find its way onto the front panel - checked it out and it works perfectly.The indicator board has four RGB LEDs for DSD64,128, 256 and 512 and they show 44.1K family recording by lighting red and 48K with yellow.

[Ray P]

I've been working on the second Valve DAC build for a friend over the weekend and I'm currently listening to it - it's sounding good.

The build basically replicates my original build with respect to power supplies, a Maida regulated supply for the B-, regulated filament suply and low-noise regulated supplies for the digital circuits, the exception is the use of a JLSounds USBoverI2S on the input (instead of a Beaglebone with Pavel's reclocker on my original build).

I just need to install the front plate on the chassis so I can button it up. The transformer primaries will be tidied up too, they need to be configured for 115VAC operation before I sent it across the pond.

[Ray P]

Nearly done with the second Valve DAC build. I just need to reconfigure the transformers for 115VAC supply and give it a test before the lid goes on ready for shipping to its owner.

The DSD rate indicators are yellow for 48KHz family data and red for 44.1KHz data.

[Nick]

Very nice. I do think you may be overusing thermal paste though. If you use too much it can reduce dissipation.

[Ray P]

Cheers Nick. I don't think there is as much paste as it looks like, it's just my clumsiness, managing to get it on my fingers when installing the device - maybe I'll clean it up a bit. As it happens I have measured the temperatures and the device and chassis warm up to almost the same temperature, which is around 36C.

[Ray P]

Somewhat disappointingly, especially given the proximity of Owston, the DAC has developed a low-level noise, like static, in one channel, though it still works and plays music through both channels. The noise can be heard in the background during quiet passages. The noise seems consistent and doesn't change when the trimpot is adjusted. I also noticed that it changes in level when I press on one of the valves (U3). There is also a change if I press on the adjustment knob of the trimpot but that may be about the internal mechanics of the pot? I have tried different valves in the socket and it makes no difference so I don't believe it is a valve problem. I'm guessing at the moment, but perhaps the thermal stresses from several power-up/down cycles have revealed a dry solder weld? Anyway, work to do.

[Ray P]

I managed to find the problem causing the noise - it was one of the valves - it took a bit of tracking down but swapping in a spare seems to have got rid of the noise and it's been behaving for an hour or so. I don't have time to tweak the presets to optimise the performance for the small amount of residual noise but I feel it's in a place where it is worth bringing tomorrow.