This thread was going on in parallel with:
https://forum.psaudio.com/t/cost-no-object-edition-of-ds-dac/6066/3
Nice! Thanks
I guess youâd also use opto-couplers for the control interface on the front panel?
I was reading a Halcro technical document on the design philosophy of their dm reference amplifiers and the lengths they go to to reduce distortion. They donât have a LED electrically hardwired to the facia, instead the LED (on/off status) is mounted on a PCB internally and an optical fiber carries the light to the facia. Thus eliminating a wire that can act as an antenna and pickup unwanted RF. Same with the on/off switch, which is a rubber faced sealed pressure chamber and piping that carries the air pressure back to a pressure switch mounted on a PCB. Again, eliminating wires that can collect RF.
Love the optical link out of the digital box.
No leakage currents, no RF getting into the analogue box. If cables were sounding different before, this will really reduce this potential. Iâd like to say eliminate this potential (and thatâs what I believe inside).
What about any jitter at the optical receiver, before the flip flops?
Iâm not quite so paranoid about RF in the digital box. I want the option to have no explicit radios and Iâd like a shield between the display and the rest of the box, but the idea is to have the jitter cleaned very well in the analog box, and keep electrical noise in the digital box.
1 Like
Note that it would be a bidirectional optical link (âa zipcord optical cableâ). The clock would be in the analog box, it gets sent to the digital box, the digital box runs off of it and sends the DSD bits over optical back to the analog box. The analog box can phase delay the upgoing clock so that the deserializer receiver will be lined up with the local clock and then the DSD is reclocked to lower the jitter. Like the DS there would be an extremely short path from the clock to the final reclocker. The clock is split from there, buffered and goes to other places like the earlier reclockers and deserializer which receives the bits (and control) from the digital box. Donât ask how the whole thing bootstraps the round trip signal and, for example, mutes if either end stops (looses power, gets rebooted, etc.) 
2 Likes
Ha gee, complicated stuff.
The 2-box solution lengths the path from FPGA to output stage. But it sounds like youâve solved the challenge this brings.
Does this mean the new FPGA can/will now up-sample to even higher sample rates than the current DS?
Are you thinking 2 separate chassis that you can sit side-by-side or stack on each other. Or something like Halcro power amp which has 4 separate boxes incorporated into a single chassis?
If the latter, you could have your separate digital and analog boxes connected by uprights/legs that contain the guts of a power power plant. Something like thisâŚ
And regarding optical connections, CH Precision are using SFP modules and fiber to connect their components now (particularly, the transport to the DAC).
I wouldnât want the digital and analog box to share any power connections. Then the user can plug the âanalogâ analog box into clean power near the stereo and plug the âdigitalâ digital box somewhere more isolated from the rest of the stereo, like with the computer, streamer, etc.
The optical connection can be arbitrarily long so that, for example the analog box can be in the audio rack and the digital box can be next to the computer, transport, etc. (I like having my control screen (and knob(s)) right next to listening position.)
1 Like
The length of the path from the FPGA to the reclockers was never much of a problem - they are balanced high current connections so they arenât very susceptible to interference and the reclocker is right next to the clock - thatâs the connection that matters.
1 Like
I the multi-box single chassis concept, the power supply for the analog box would be in one leg, and the power supply for the digital box in the other leg. No sharing involved.
Thanks Ted. Planning to upsample to high sample rate than current DS, with the new FPGA?
Or no further benefit there?
Everything can handle a higher rate, the question is whether the additional (relative) jitter from a faster sample rate adds more noise than it lowers the S/N from the sample rate increase. That will take listening on a real box. In theory a higher sample rate is worse than the current rate because of jitter, but lowering the ultrasonic noise may more than make up for that.
1 Like
True. Thanks for sharing.
This high speed optical link solution (Playback Designs have been using one from source to DAC for a while of course) is cool. I canât see a new high speed optical interface becoming standard anytime soon for both DACs and sources, so this is a great solution.
Thanks for the reply. I wasnât suggesting analog EQ, but more like Dirac (or similar) processing in the DAC. Right now I run Dirac to good effect on a mac mini as my main audio source, but none of my other sources have this capability, and it is apparent in the sound when playing the same material on different sources (eg tidal played through mac with dirac vs tidal played via DS Jr bridge). If the DAC handled this EQ chore, each of my (digital) sources could be room corrected, and then I might be able to get the computer out of the stack of gear and just stream to the network bridge in the DAC.
If adding this functionality increases noise, then that would obviously be counter to your goals, so I understand if it doesnât make sense. Just wanted to clarify my situation and why that would be valuable for me.
PS - my DS Jr also runs HOT. It would be nice if my next DAC wasnât hotter than my amps. In a small/med room with no AC, this is a factor for me in the summer.
Thanks again for providing the forum for feedback
The thing is, in the target market for high-end DAC customer, very very few people would be using an EQ box of any sort.
that may be true. for me, room correction and a high end system are in no way mutually exclusive. dirac was a big upgrade for my main rig.
Sure. DEQX, Trinnov and others. But as I say, for the target audience for this product most would not be using EQ. The only EQ is likely to be whatâs built-in to their subwoofer.
IMHO there is no doubt about it speakers are the main component that determines system sound. Strangely I find DACâs second then even more strangely amps and cables about equal. Here is an interesting story. Took a Explorer 2, ran it through the iso regen connected by a good quality USB cable (a Curios made for the Explorer 2) and some expensive high quality audio cables using a little headphone to rca converter. The cables cost more than the DAC. I sat with a couple of Audiophiles expecting a bit of a laugh. We were shocked. We had to go back to the Direct Stream to confirm it was better - it was - but my god we didnât expect it to be this close. We tried some ordinary cables - nowhere near the same level of performance. It was really eye opening I can tell you. Since then I have sat with a cable maker down Brisbane way and checked out a number of cables and the differences have shocked me - they really have. Careful though, some cables are high capacitance and some amps will shut down with them. The technical consensus is this is because the amp is designed to be on the verge of instability, although one amp maker claimed it was his FET output stage. BTW the BHK has zero problems, but there was at least one other high end amp that had issues as well as some other good, but not quite in the class of BHK, amps that also had issues.
Hi Ted
Thatâs interesting - Rob Watts claims his up-sampling and filtering reduces jitter by 64 times:
http://www.the-ear.net/how-to/rob-watts-chord-mojo-tech
Yes all my DACâs up-sample to 2048 times that is at least 16 times more than typical. What does this do? Well its not just about up- sampling but filtering out the RF noise that is present on a digital signal. Its essential to do this, as it gets you closer to the original analogue signal in the ADC (and this is the DACâs job to recover the analogue signal not the digital data). This extensive filtering reduces jitter sensitivity by a factor of 64, and allows the DAC to eliminate noise floor modulation.
Am I missing something?
Just as an aside what do you think of his 1 million tap filter - he claims it was a revelation. Sounds way overkill to me - but audio, as you have noted, is a funny thing.
Thanks
Bill