The Best DAC is no DAC

I generally play digital audio from my computer via my EMU 1212M sound card. I prefer hi res, I've ripped a lot of my LPs @ 192k/24 bit, and I buy hi res down loads from HDTracks and ProStudioMasters (unfortunately I can't buy from the Pono store in Australia). I have also ripped my hi res DVDs and Blu Rays to hard disc. Recently my audio buddy has been ripping all of our SACDs with his PS3 and I also now have a collection of DSD tracks. Software is Foobar, and I use the sacd plug in to play DSD files. Sound is pretty good, not as good as my turntable but hi res beats the pants off red book.

Anyway you will know that Foobar converts DSD to PCM before it sends it to the sound card. Then recently I read that Delta Sigma DACs (including the CS4398 which is on the EMU sound card) convert PCM to single bit during conversion. So, when playing DSD files, FooBar converts bitstream DSD to PCM, then the sound card converts PCM back to bit stream. Wow, there has got to be a better way. So I started investigating USB DACs and my eye was captured by the DIYINHK USB receiver and Sabre DAC combo. Very reasonably priced if it all works!

ES9018K2M XMOS DSD DXD 384kHz USB DAC with Bit-perfect volume control and SPDIF input - DIYINHK

I received these components (very quick delivery from HK) and am very impressed with the build quality. As I was going through the admittedly sparse documentation I noted that the output pins on the USB board were putting out native DSD signal, left and right, on 2 of the pins. Then something that I read on Joe Rasmussen's site many many years ago came floating to the top of my mind - I recall he was talking about Sony SACD players, and that he was able to play SACD simply by finding the DSD signal on the Sony's circuit board and filtering it (3rd order at 90kHz IIRC) before a j-fet buffer sent the signal to his pre-amp. No DAC at all!! Well isn't this the way to go? Send the DSD files from my hard drive out through the USB and pick off the DSD from the USB board?

So far I have achieved partial but very promising success. I have connected my PC to the USB board, and set up FooBar as per instructions. And it plays! I am a minimalist designer, and I eschew buffering and any electronics whereever possible (especially op amps) and right now I am taking the DSD output off the USB board (single ended) to a pair of Lundahl LL1527XL trannies. Theses are configured 1+1:1+1. The balanced output from the transformers goes straight to my balanced attenuator which sits right atop my balanced power amps. I am relying on the transformers to filter the high feq DSD noise, and I have added a zobel across the secondary (15nF, 1kohm) as suggested by Joe Rasmussen in a thread about Sabre DACs and transformers. So I am not even using the DAC board.

How is the sound? A mixed bag. Highly transparent. I have never heard such extended treble from digital. And the sound is almost a 3D analog presentation - every instrument has its own space on the sound stage. Even the best digital has been 2D before (through my sound card or Cary multi-player). But the bass is a bit light. I need more inductance in my transformers. The LL1527 is rated at 10Hz with a 800 ohm source, so I am guessing that the output impedance of the USB board is several kohm. And of course the level is down. The USB board has a 3.3V supply, and as its single ended it will only be putting out 1.1V RMS at full output. My power amp (DIY) was designed for regular 2V input, so I can't get full output. And as this is still prototype, I am using a cheap 5V SMPS with a 3.3V LM3940 regulator - this is way too noisy.

So i need to do something about the bass and output level. There are 2 options spring to mind.
1. Build a jfet gain stage (2 x gain). This would be a LTP with the input on side grounded, and the LL1527XL across the drains of the jfets. And a resistor across the drains to knock down the gain to the right level (also reduces output impedance which gives better matching for the transformer).
2. buy a 1:2 transformer with enough primary inductance to provide full bass response. Note - I did try the LL1527 configured as 1:2, but this reduces the primary inductance - and as expected, bass just about disappears. Has anybody got a recommendation for a 1:2 transformer, capable of 2 v output, which as as transparent as the Lundahl but with more primary inductance? I imagine something like a 5kohm:20kohm transformer is required.

Regarding all my PCM files - the foobar sacd plug in will convert PCM to DSD on the fly. I am playing PCM files in this manner, ie convert them to DSD128 and play as above through the USB receiver. Only one small wrinkle - this works perfectly with 44.1k files (including 88.2k and 176.4k) but doesn't work with 48k files (including 96k and 192k). The work around I have implemented is to use the Foobar DSP re-sample function to resample all PCM files to 176.4k. This then converts nicely to DSD that will play through the USB board. Has anybody else come across this, and is there a better way to play 192k files?

So I really believe that this is the way to go. The best DAC is no DAC!!! There is more to be done, but the prototype is only one day old. I am sure that I can improve it given a bit more time. Any suggestions would be welcome.

UPDATE 10 September 2015.
I now have this working as described in later pages. My final solution is as follows:
Hardware. I have replaced the DIYINHK USB board with the board from JLSounds. The advantage is, I can run the JLSounds at DSD256 in Linux without a driver (in Windows, and Linux, DoP is limited to DSD128). See final circuit in post #335
http://www.diyaudio.com/forums/digital-line-level/273474-best-dac-no-dac-34.html#post4446944
Software. I bought a licence for HQPlayer Windows and Linux. In Windows 10, I convert everything (PCM and DSD) to DSD128 and send to the DAC board. Sounds excellent. In Linux I convert everything to DSD256. Does it sound better? Not that I can tell, but I can do it, so why not :)
Note - when using HQPlayer v3.7, the CPU load was 55% when upsampling to DSD256 and I was getting intermittent glitching. HQPlayer 3.8.1 was recently released, it seems to be more efficient and CPU load is rediuced to 42% when upsampling to DSD256, and no glitching.
 
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Here is a photo of my prototype.
1. LM3940 3.3V regulator is foreground RHS (5V SMPS is out of view, to the right of the reg)
2. DIYINHK USB board is foreground LHS.
3. Lundahl LL1527XL transformers are in background
 

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"Because it has been extremely difficult to carry out DSP operations (for example performing EQ, balance, panning and other changes in the digital domain) in a one-bit environment, and because of the prevalence of studio equipment such as Pro Tools, which is solely PCM-based, the vast majority of SACDs—especially rock and contemporary music which rely on multitrack techniques—are in fact mixed in PCM (or mixed analog and recorded on PCM recorders) and then converted to DSD for SACD mastering."

Direct Stream Digital - Wikipedia, the free encyclopedia
 
Member Stanic has sent me a link to a transformer supplier in Thailand. These look like the perfect fit:

SAC Thailand

Primary impedance is 1,100H!! This should be high enough to get decent bass response. They are also capable of 6dB gain, which is also one of my needs. However in this case, the primaries are parallel, and inductance will only be 275H - still respectable.

They are expensive though. I received a quote from SACThailand - USD $425, shipping USD $25. That will be about $600 in aussie currency!! I've got plenty of j-fets at home, I think I better try a j-fet buffer first because this won't cost me anything. Something to do on the weekend.
 
"Because it has been extremely difficult to carry out DSP operations (for example performing EQ, balance, panning and other changes in the digital domain) in a one-bit environment, and because of the prevalence of studio equipment such as Pro Tools, which is solely PCM-based, the vast majority of SACDs—especially rock and contemporary music which rely on multitrack techniques—are in fact mixed in PCM (or mixed analog and recorded on PCM recorders) and then converted to DSD for SACD mastering."

Direct Stream Digital - Wikipedia, the free encyclopedia
Yes, i understand that this is the case. SACD is best when converting old 2 track masters to digital. For example, the Rolling Stones master tapes were converted directly to DSD. I bought the Rolling Stones 64-69 box set when it came out but this is DSD files cut to vinyl. As much as I love vinyl, I don't believe that it is going to improve the DSD files mastered by Bob Ludwig. Much better to rip my SACDs and play them in native DSD. Well, that's the plan, lets get this working first before I can say its the best way to go.
 
We have discussed that in Italy for many weeks.....if you can..take a look to jlsounds usbi2s interface..with double proper power supply..(LT3080 based in most of our cases)..the results can be stunning (HQplayer as "engine")
Sorry for my english... :)
Yes had a look and this does look like a nice kit.

I2SoverUSB - I2S over USB Audio

I've already got my USB receiver but anyone else interested in this approach should be looking at this product.
 
Am I just being stupid, but why do you think there is no DAC involved? Where do you think the analogue audio you are listening to is coming from?
I'm not sure what you are getting at Gopher. I think that there is no DAC involved because I deliberately left out the DAC from my circuit. The USB receiver takes the digital signal from the PC and outputs digital data in I2S format (if PCM) or DSD (or DSD). This usually goes to a DAC. But I am feeding the DSD data straight into a transformer.

Are you suggesting that the transformer is the DAC? I guess technically you could say that the transformer is performing the function of a DAC but I don't think that anyone would describe a Lundahl LL1527XL transformer as a DAC. Would you?

Another way of thinking about this - if I did use a DAC I would still need an IV convertor and some other output circuitry at the end of the DAC. Some people even use a transformer for DAC output stage. In ths case the signal path would be

USB Receiver ---> DAC ---> transfomer (output stage).

But my signal path is this

USB Receiver ---> transformer. No DAC!!