Valve DAC

[steve s]

I'm always searching for something better ray...

[Ray P]

Does it work with a plain vanilla SPDIF input Ray ?

It could do Phil but not by simply bolting on an SPDIF socket. The thing to remember is that its a valve based decoder for a sigma-delta modulated (SDM) (or delta-sigma modulated (DSM)) signal - in simple terms DSD instead of PCM - so in almost all instances you need to upsample a PCM stream to DSD so you could use an spdif input to your upsampling solution, which could be something like the AK4137 I've mentioned before.

[Ray P]

I had the Valve DAC working at DSD512 on the bench this evening - no dropouts, noises, artifacts or whatever. Tomorrow I'll hook it back up to my Noir HPA and do some critical listening to see if DSD512 gives me anything over DSD256.

[Ray P]

I've been listening for most of the morning with my headphones - this DAC is simply beguiling.

It works fine at DSD512 but the noise floor had some noticable 'static-like' noise on the silences, which prompted me to finally get round to trying to optimise its performance - it has some potentiometers that can be adjusted to balance the valve and flip flop sections. Some really concentrated listening and adjstment has bourn fruit this morning and I've got the noise floor at DSD512 down to where you have to really listen hard to hear anything and DSD256 now has a really inky black background. I think I'll leave it for now, just enjoy some music and maybe see if i can wring a little more out of it another day.

The process reminded me a little of the old days of tweaking cartridges for geometry and tracking, though turning potentiometers is a lot easier to execute.

[Ray P]

I've got the Valve DAC in the main system now playing through the 300B amps. First thing to do was further tweak the DAC to minimise the noise floor and I've now got it so that, at DSD256 rate, I can just hear a little noise with my ear right up against the drive units. It's necessary to make these adjustments in the main system because the amps are delivering more gain than the headphone amp I've been using until now.

To make the adjustment easier I downloaded and played a CD image of silence (i.e. zeroes) - the 32min long track was plenty long enough!

Anyway, the music sounds bloomin' marvellous.

[Nick]

I downloaded and played a CD image of silence (i.e. zeroes)

What, no dither?

[Ray P]

What, no dither?

It was played via HQ player, but the purpose of the exercise was just to "...set the balance between the DAC anode resistors... ...for minimum idle-channel noise"

[Ray P]

I got the lid on the Valve Dac yesterday. I'm a litle annoyed because I managed to get the holes cut slightly out of position so the valve sockets aren't perfectly centred below them - shoddy I say - I will have to have them re-worked with slightly larger holes, eccentrically placed with respect to the existing ones. That said, I'm quite pleased with how it looks as well as being delighted with how it sounds.

[Greg]

Really cool, Ray. I’m significantly impressed. You’ve done a very nice job there which leaves me in envy.

[Ray P]

Cheers Greg. I'm hoping the Bristol crew can get to hear it as soon as conditions are suitable.

Ray

[Dave the bass]

MEGA SHODDY!

[simon]

Very impressive Ray. It's not obvious to me the valves aren't concentric with the holes - perhaps it's the photos, or maybe it's obvious to you as the constructor as I always see every little imperfection in the things I make? It really does look professional.

Did you use Front Panel Express? I haven't looked at it for years; I found the software a bit frustrating as I'm used to the precision of AutoCAD, but it looks like they can handle DXF import now which would be a big step forward. Are the cylindrical "legs" from FPE too?

[Ray P]

Thank you Mr. Bass, no need to shout though!

Simon, the valves are slightly tilted! But you're right about I do see all the imperfections in my projects - it causes some of my slow progress because I find myself reworking stuff that is perfectly functional but the flaws nag at me.

Yes, the panel was done by FPE (or Schaeffer to be precise, I think FPE is the US outfit.) The software is really simple to use but is getting more sophisticated in what it can offer - DXF imports and exports are available! The chassis, with legs, is a Chinese ebay purchase - fine for what it is but they use cheap 'soft' alloy that doesn't machine as well as the Schaeffer provide material.

[Ray P]

This morning I've spent a couple of hours listening to the Valve DAC through the 13E1 amplifier (Which is now complete apart from the woodwork for the front panel and toroid collars).

I had two objectives, the easy one was to just run the 13E1 for a prolonged period to start burn it in and check for any problems. It gets nice and toasty, especially the chassis where the Current Sink mosfet is mounted (I'm using the chassis top plate as the heatsink) but all was well within the touching test parameters. The amp behaved impeccably, no misdemeanours or hums/buzzes. Sounds very good too.

The second objective was to continue tweaking the DAC to squeeze everything out of it. Having spent quite a bit of time listening to 'silence' in order to minimise noise by balancing the valves, today I moved onto listening to music and exploring the modulator and filter settings in HQ Player - I have noticed that with some SDM modulators there is some noise that correlates with the music but I've now got a modulator setting that eliminates the noise and sounds good with the filter options I've currently settled on. To all intents and purposes (i.e. measuring with my ears sitting in the listening seat) the only noise the DAC/Amp produces is the music.

I enjoyed the music too.

[simon]

Good info, thanks Ray