Valve DAC

[Ray P]

Spent a bit of time on this project today. I would have finished installing and testing the power supplies today but I can't find the current limit resitor for the Maida HV regulator

[Ray P]

It's been a productive couple of weeks. I now have both of my SE-OTL amplifiers playing music with just a few tidying up tasks to complete on them (now I know the effort and money for the cosmetics won't be wasted).

Anyway, having got those projects under my belt I spent some time on the Valve DAC today and reached a significant milestone.

I've connected up and tested (with dummy loads) the various power supplies - they all checked out.

I connected the Beaglebone Black and fired it up - visible on the network and to HQ Player.

Connected up the isolator/reclocker and checked that I could see tracks being played with the correct clock rates selected etc. within HQ Player - all OK.

Plugged in a simple LP filter 'decoder' to the isolator/reclocker (Data L & Data R) and listened to some music via my headphone amplifier - sounded pretty good too; I had forgotten how musical this approach can be - it's where I started this DSD playback journey.

So, I know I have a fully functional infrastructure into which I can insert the Valve DAC board. I have some parts still to buy/assemble to complete the Valve DAC board so I'll look to get them ordered over the weekend.

[Ray P]

I'm on the home straight with the Valve DAC project, hooking everything together ready for testing.

[Ray P]

Everything is now hooked up and ready for testing. All being well I will receive the six valves this week so next weekend...

In the meantime, I've done some very limited testing;

• I inserted a single valve and powered up the filament supply - it glows and I measure 6.24VDC.
• I've powered up the 5V power supply and DAC circuits - I measure 4.97VDC
• With just the filaments and 5VC circuits energised I connected the DAC to the network - it was 'seen' by HQ Player and I was able to 'play' a track (@DSD128) without any apparent glitches.

No magic smoke!

Nothing I can do now until I get the valves so a time for patience.

[Cressy Snr]

The Marineville DAC!

[Ray P]

Yep - 'anything could happen in the next half hour!'

I think we have similar childhood TV memories Steve.

[Ray P]

Well, first things first - it works and I've listened to some music, or more precisely, it worked and I listened to some music for a few minutes!

First though, last evening I had a big scare. Fairly late on the temptation to plug the valves in got the better of me so I reinstalled the main board and powered up the 5V and filament supplies - all OK. I was just about to flick the switch of the B+ when luckily I had this really scared feeling - turns out I had connected the B+ supply the wrong way round. Phew, a near miss - don't mess when you're tired!

Anyway, after a good nights sleep I resumed this morning.

Checked and double checked! Powered up the filaments and 5V sections and verified that HQ Player was seeing the device and I could 'play' tracks (DSD128) - all OK.

Powered down and hooked up the headphone amp set volume to mute and started powering up again and got music tracks 'playing'. Switched on B+, quickly checked the voltages and all seemed OK. Put on the headphones and gradually turned up the volume - music!

I listened for maybe 3 minutes (about a track's length) and then started to hear some noise, which gradually increased. Now no music just a loud buzzing noise.

I've powered everything off for now to have a think and get advice from the designer over on DIY Audio.

So, some trouble-shooting to do. I'm assuming a faulty component at this point.

[pre65]

That's a bummer Ray, hope you can get it sorted.

[Ray P]

Cheers Phil.

I pulled the valves out and did some basic measurements and everything was within a reasobable tolerance of the values on the schematic.

Next test...

I inserted the valves for just one half of the DAC and measured and listened - there was music, a bit longer this time, and then the noise gradually appeared again. Measurements were essentially the same as I saw previously without any valves.

Is the fact that it played longer with only half the valves a clue?

I'll do the exact same test, with the same valve trio, on the other channel after a coffee.

[Ray P]

It's working nicely now and sounding very good indeed.

The problem was to do with timing of the flipflops, not a problem component. First step to resolving it was to step down to DSD64 (previously DSD128) and I enjoyed an hour of listening via my headphone amp. Fortunately the designer included the ability to adjust the timing so adjusted as per his recommendation I've just listened to DSD128 for about half an hour with no problems. heading out on the bike now but later I'll try DSD256...

[Ray P]

So here it is...



I didn't mention earlier that my HQ player configuration was set for DSD512; using the lower 64 and 128 rates, I've done some experimenting with the HQP filters with noticable affect - its sounding really very good. I'm chuffed.

[Cressy Snr]

Great stuff!
Well done Ray.

[Ray P]

Thanks Steve.

I can't help thinking about how ridiculous it is using all those transformers and generating all that heat just to create a line level output; I think you made similar comments about your 13E1 build. However, I can now boast of being the owner of one of the world's few DACs that actually uses valves in the conversion process (as opposed to have a valve buffer on the output).

Tis a great hobby we pursue.

[Ray P]

This morning I've been playing music at DSD256 for an extended period with no issues, in fact it just keeps getting better and better.

The DAC has a silent background as far as my ears can tell. The music out of it has a fantastic richness but without any stodginess, every voice/instrument is clearly discernible and, to use an old cliche, I'm hearing things I hadn't picked up on before. I still have the fun of exploring the HQPlayer settings further to see if I can optimise the playback to my tastes even more.

I tried DSD512 too and it works except that the computer I'm using for the testing isn't powerful enough to do the HQplayer processing so there are lots of dropouts. I do have a more powerful, audio-dedicated, workstation available so I'll give DSD512 another try at some point.

Now I know that this project is a keeper I'll finalise the build and I've started to design a chassis top plate to close it up.

IMO this DAC deserves to be built by more people and it will be good, in due course, to expose some of you guys to it to see what you think as my opinion isn't necessarily objective! Downsides are that it's not cheap, it It needs to be fed a high quality SDM (DSD) datastream (no PCM) and it's ridiculously inefficient to power all those valves to just produce a line-level analogue signal but it is also, IMO, ridiculously good and so easy to listen to.

[IslandPink]

Good effort Ray - glad it's worked out so well.