DIY near SOTA Dacs.

I've probably got a problem with dacs, I think I own about a dozen dacs, but it could be more.
Despite a lifelong love of all things tube, I am fascinated by digital to analogue convertors, maybe because they are somewhat of a mystery to me, digital is a young mans sport, digital engineering is a long way removed from tube engineering.
Despite this I like to keep up to date with what is current , and like to think I'm aware of state of the art (SOTA), although I could well be delusional about this, it seems to progress so fast I doubt anyone is on top of everything digital.

So here is a story of 3 dacs, which are as far as I understand, are close to , or maybe SOTA, and available to the average audiophile without stupid hyper- prices because they are DIY . Two are restricted to those with good DIY skills, one to even the in-experienced.

Dac conversations often come down to arguments about delta-sigma v R2R ladder dacs, or newly designed Sabre 9018 v old style TDA1541, PCM1704 dac chips.
The argument often goes along the lines of delta-sigma being very accurate and detailed, monitor quality v the ladder dacs which are "musical" and "emotive" .
Superb technical measurement v not so great measurement  but good subjective sound.

Both camps get very hot under the collar about which is the "right" or "best" sound, but of course there is no correct answer as music reproduction is subjective and what you like is what you like.

Over the years I've been in both camps, I started out with 1541 dacs many years ago, ended up with 9018 dacs the last 5 years , and now have what I consider very good examples of both, in quite a few different configurations and guises.

One of the things I like about digital is the generosity of the young digital designers these days, unlike we old tube designers who like to keep our "secrets" to ourselves ( which is rubbish because there is very little new under the sun) 

There are some excellent digital designs which have been published in the DIY forums, and lately there have been some which are indeed very close to SOTA, and available to those with DIY capability.

On www.diyaudio.com a Canadian named simply as Ian has published some interesting and somewhat complex designs that are intended to bring out the very best of delta sigma dac chips and specifically the Sabre 9018 . 

Look here for the details, and here is a pix of his component designs complete in a prototype system, in this case based around the Twisted Pear Audio Buffalo 3 9018 dac kit, and the Amanero USB-i2S convertor.
No SPDIF or provision for cd players- sorry Luddites, the future and the now is computer audio , whether you like it or not.

5 digital/signal boards and 3 power supply boards make it a bit complex, but it worked first time I fired it up , and has been reliable since then. The line up is an Amanero USB-I2S convertor into  Ian's FIFO board/galvanic isolator/Si 570 super clock , into the Buffalo 3 9018 dac via its i2S inputs. Power supplies for the FIFO, the clock, the dac and the Amanero also has its own PSU.

The sound of any dac, whether it is delta-sigma or ladder is very much influenced by the current-voltage conversion ( unless internal) and the output stage. I have a lifelong dislike of op-amps, I can always hear the feedback employed by these nasty little devices, and anything is (usually) better than them IMO. Tubes are great, but unless they are very carefully designed for both input and output impedances , can be a bit hit and miss as to suitability for a particular dac chip. They always used to be my first choice , but I've gone back to trans conductance zero feedback opamps as the finest sounding outputs for just about any dac chip, delta-sigma or ladder. Respect to Pedja Rodjic for initial use of these devices. Delve into his website for interesting discussion on trans conductance op-amps.

For the 9018 I like the OPA861 op-amp , used  on one phase of the 9018's diff output. This is a bit controversial to some, who can't leave one phase unused, but in this case single- ended with an OPA861 is as good as I've heard a 9018 sound.
However I'm open-minded about outputs for Sabre dacs, and there are some other options I'm exploring. 

The total system is 384Khz  and DSD capable and it is ultra resolving, hi- rez is its forte , and as far as technical performance goes it is as good as it gets. You want to hear EXACTLY what is on the recording, then this is the device for you, it is quite ruthless to listen to.

Ian is quite prolific, and a little later he brought out a device to enable hi-res to be used with the older style  ladder dacs, which are usually restricted to 16 bit and 96 KHz. With his device the old 1541 and PCM1704 dac chips can be used at 24 bit and 384Khz, quite amazing really.

The methodology is complex and you need to wade through this page to get the gist of it. 
The promise of using the older "good" sounding ladder dacs with computer audio at the very high resolutions is very enticing , and something I couldn't resist.
 
Thanks to Chris alias "hochopeper" for helping me through  the complexities of getting it up and running.
A little less complex than the 9018 set up -5 digital/signal boards but only one dual power supply and the TDA1541's power supply on the dac board. 

The trans conductance op amp I/V conversion is a little different, it uses the older AD844 op-amp  in a "stacked" configuration with 4 op-amps positioned on top of and paralleled with each other.
Kudos to "george hi-fi" for promoting this idea the last few years.


So how does the old TDA 1541 dac chip sound when it is enabled with the very latest thinking and implementation of digital design?

Well it still sounds like the very musical and engaging  1541 of old, but with even more intensity and vividness, along with higher levels of resolution and transperancy. 
It's damn nice to listen to, it's at that lovely level of HIFI when you just forget about the system and listen to the music.

Absolutely the best way to listen to 44.1Khz and up to 96Khz , above that I think it maybe gets a little less convincing and if you are going to listen to the very best recording technology , then the 9018 is probably technically better, and maybe subjectively better at the higher resolutions. Personally I prefer this super version of the 1541, it may not be as technically proficient as the 9018, but it sure sounds wonderful, especially with Windows Server 2012 and AO.

It is worth noting that Ian's FIFO/isolater/clock/I2S-PCM components enable the 1541 to be used in simultaneous data mode , a different variation of I2S that uses a separate digital line for both Data right and Data left , rather than a single line for both channels. It is claimed to drastically lower jitter, and certainly changes the character of the 1541's tone for the better IMO.

And finally something of a surprise package that offers very good sound at a very reasonable price and something that would be possible for even an inexperienced diyer to build, noting the safety requirements that are essential and which I will emphasis again.

The www.jlsounds.com I2SoverPCM USB convertor/AK4396 dac combo is a tiny package that gives surprisingly excellent sound at a value price. Combine it with a couple of the optional power supplies and you have a remarkable dac capable of 384Khz and DSD capability.
Unfortunately it has negative feedback op-amp  outputs that do detract a little from the sound, curtailing the openness, "air"  and naturalness the more complex and expensive aforementioned dacs have.
I'd love to try it with transconductance op-amps but tiny SMD caps and resistors make this a tricky operation.
Nevertheless it's a bloody bargain and sounds almost 1541 like in it's presentation, I'm thinking about putting it in my preamps as an optional extra, it's that good.
If you do decide to build this little dac you must ensure that all mains wiring is completely covered and inaccessible to anything and everyone. Put it in a box, make sure it has a low amperage fuse, check , double check, triple check before you turn it on, did I say to make sure the mains wiring is completely inaccessible? Ok consider it said again.

Dacs auditioned with either a 4P1L or 801A/10Y DHT preamp. No matter how good your dac is it will always sound better with a good tube preamp.

                                                  Prototype 801A/10Y preamp. 

Other dacs I have built and listen to occasionally include Ackodacs best 9018 implementation with Exa U2I-USB convertor and a Lundahl output transformer on the differential outputs, but I'm not convinced that transformers are the best option for Sabre dacs- it will get an OPA861 output , or some other discrete output when I find the time. 

In a more conventional and traditional format is my old TDA1541 dac with the conventional resistor I/V conversion, with a tube output stage. It has been updated to the computer age with an Amanero USB convertor driving the I2S lines, in conventional I2S fashion, not simultaneous data mode. Only 16 bit and 96Khz capable but redbook is probably the 1541's best operating function.

This is the format that 1541 fans get quite passionate about- it has a nice easy sound that people find very enjoyable and "magical" but truth be known it does leave a lot of information out of the presentation. 
As much as I love tubes I'm not convinced that tube output stages are the best option for ladder dacs,  better left to delta-sigma dacs with a need for bit of nice tube harmonics. 

At the moment I'm quite happy with my TDA1541 dac in sim data mode for redbook 44.1Khz and the Sabre 9018 for hi-rez music, but things change so fast I expect there will be something quite different in a years time.

Please note that these dacs are in prototype form, once they are finalised they will be placed in suitable boxes and rewired optimally for best performance and safety.
Note that all the mains wiring is insulated, mains wiring can kill you. 

The CABERNET REFERENCE DHT Preamplifier

The CABERNET REFERENCE DHT Preamplifier is the new top of the line, and highest quality preamp ever built by Supratek.

It surpasses the 101D, 300B and 801A preamps in every way and represents a new standard in DHT preamp design.

Incredibly versatile, in addition to the optimally loaded 4P1L DHT gain stage it also has a switchable Lundahl input transformer , a switchable 6SN7 driver stage and a switchable  Magnequest output transformer.

All of these options can be used singly or in combination to give a variety of gain, input/output impedances and sonic signatures.

If you want low gain/low output impedance preamp to use with high sensitivity or difficult amplifiers use the 4P1L stage with output transformer switched in.

If you want the highest gain possible (and the resultant dynamics that comes with high gain) switch the input transformer in, the 6SN7 driver stage in and the output stage off.

With three stages, and with such versatility,  you are sure to find a combination that is just right for your system.

The heart of the preamp is the 4P1L DHT line stage . Optimally loaded with a v-fet/j-fet CCS and using filament bias it is supremely balanced and open sounding.
Deep strong bass, liquid midrange and shimmering treble it is the ultimate refinement of DHT sound.
Sophisticated design , using the famous Supratek tube shunt regulation and wonderfully complimented by the choice of high quality input and output transformers, which you may switch in or out to further refine the sound to your requirements.

The Lundahl input transformer suits all sources up to 1000 ohms (virtually all digital sources) and is wonderfully clean and transparent - it gives real "oomph" to the 4P1L line stage.

The 6SN7 tube driver stage is suitable for sources up to 100Kohms, tube phono stages etc, and adds a touch of tube euphonics and warmth to the sound, although it is most definitely a state of the art design that is very hi-tech.

The Magnequest output transformer is ideal when a low output impedance is required, it drops the output impedance of the 4P1L from around 1000 ohms ( which is already low enough to drive virtually anything) to around 250 ohms, for the most difficult amplifiers.
It also imparts a slightly different sonic signature that you may enjoy to have at the convenience of a switch.

This is a DHT preamp that does not limit you to the restrictions of a fixed and rigid sonic signature. You will enjoy learning how to get the sound you prefer , and having the ability to enjoy something a little different when the mood or source requires it.

Once again, being a Supratek it is at the forefront of audio design , and incredible value for money, easily besting designs costing 3, 5 and even 10 times the price.

Images soon.

Finally - Beautiful Digital Sound

I've been a champion of Computer Audio for quite a few years now, a little strange for someone who has built around 500 tube phono preamplifiers, and who still insists that a system without a tube preamp, preferably a DHT tube, is missing something.

I believe computer audio (CA) digital passed vinyl in terms of sound quality some years ago. Without the coloration of vinyl the accuracy and resolution of CA reveals exactly what is on the recording, and if it is a very well made recording, it simply gets more of the recording quality passed through . The atmosphere, the ambience ; good CA and good recordings let you hear this, especially in a good system that can do 3D imaging well (think DHT preamp).

Sure vinyl can sound excellent, but take a really good vinyl recording, say something recorded in the 60's , get hold of the master tapes, copy them in hi-rez digital and play back through a high quality CA system and you will be amazed at the fidelity.

BUT. There is still something to be said for vinyl/analog. Yes the CA will have better resolution, be way more accurate, closer to the recording, but the vinyl, despite its coloration and noise has a sense of realism, and "tone" that can be very nice sounding- the terms beautiful and beguiling are often used.

The audiophile world often gets divided into two camps- those that insist in truth and those that insist in tone. Accuracy versus musicality. Digital versus analog.

I dont think it is as clear cut as that, but sure, listening to really good digital is like listening to the recording. Listening to really good vinyl is like listening to a really nice, interesting INTERPRETATION of the recording.

And it sure can sound nice, however I'm the sort of guy that generally prefers things as they really are. I like to listen to vinyl, but its a retro thing, something for fun.

A few months ago, a CA program called AudiophileOptimizer was getting  rave reviews from the CA guys, just about without fail,  anyone who used it was convinced it was a significant increase in sound quality.

The AudiophileOptimizer (AO) basically optimises a computer so it becomes a digital audio transport only, it shuts down unused computing systems and maximises the audio quality.

Nothing new about that , other products do the same thing , with varying degrees of success. JPlay is another similar program, quite contentious with many claiming it did nothing for the sound, and the media player program JRiver even belittling it publicly.

Others loved it and claimed it was very good.

I tried JPlay and thought that it did provide a slight increase in sound quality, but the cost of using it- a level of bugginess that drove me crazy, was too high for me.

AudiophileOptimizer brought a new game to town. Although it is usually used with a single computer , it can also be used in a dual computer setup. One computer is the "control" - it handles the music files, and the playback process . A media program like JRiver selects the music and can be controlled remotely using iPad or phone or whatever you like.

The "control" computer is connected to a second "audio" computer , preferably by ethernet cable,  although wireless can be used.

The "audio" computer uses a different operating system. Instead of Windows 7 or 8 it uses a windows operating system named Windows Server 2012.
Its  more basic than 7 or 8 and is designed for specific applications, and it turns out that used as a platform for audio it is much better than the more general use Windows 7 or 8 and Mac OS.

The AO program further refines the operating system for audio use , optimising it to levels of your choice, through the use of different modes.

Highest sound quality is claimed to come from core mode , where the audio computer is completely shut down to all uses apart from passing the audio stream to a dac. Blank screen and controlled by DOS manual input.

Other modes are GUI mode ,which gives a screen and normal computer mouse operation.

The remaining mode is minimal server which is a cross between core and GUI.

Core and minimal-server require a fair bit of computer knowledge and being able to work in DOS language- with the help of a IT guy I was able to try all 3 options and was relieved to hear that GUI mode was my preferred sound. DOS is tricky, CA is hard enough without having to go there.

The dual computer system requires JPlay to be installed on both computers, not so much as for sound quality issues, but as a means of transferring the audio from one computer to another with lowest latency (I think) .

There is a lot of networking to be done. Its not simple and its not a job for the average computer user. I believe the AO program used in a single computer is much simpler, but you still need to know how to install Windows Server 2012 and set it up.
I was grateful to have help from an audiophile IT guy and would have been lost without him (Thanks Tuyen)

So instead of a single computer running Windows 7 and outputting via USB into a dac we have two computers, the control used for selecting the music files and connected to the audio computer which outputs pure audio via USB to a dac.

Seems like a lot of trouble, is it worthwhile?

This what AO claims for sound quality on the website:

   - Analog sound quality rarely heard before on computer audio systems
   - Bigger soundstage, holographic imaging, more 3D-effect
   - Very well defined bass, deeper and more powerful
   - Lifelike, fluid and very precise sound reproduction
   - Natural air, timbre and image density
   - Ability to fine-tune the final sound presentation (through Sound
     Signatures and Digital-Filter modes) to achieve outstanding balance
   - Sound Signatures and Digital-Filter modes are 100% bit perfect
   - Minimizes harshness in digital sound
   - Very low noise floor / blacker backgrounds

And its true!  Very rarely do claims as strong as this live up to the hype, but the moment I first heard the dual pc set up I was bowled over by the immediate and pronounced lack of "digital" sound. It sounded like vinyl, but even better. Amazing resolution, but sweet, a naturalness that made listening a pure pleasure. Now I had all the accuracy and resolution of a hi rez recording but the inviting, pleasurable experience of vinyl sound.
I've been listening to the dual pc for a while now and still amazed at the new experience of listening to my digital music collection as if for the first time. 16 bit, 24 bit, 44.1, Hi-rez , DSD , even mp3's sound significantly better

And there is the possibility of even better sound- there are a great number of fine-tunings possible with the dual pc system, the AO has Sound and Digital filter choices I haven't investigated yet, and  JPlay also has quite a few adjustments to try.

I was so impressed I convinced others to try it.

They heard the results immediately and commented:

"I took your advice and created a separate partition on my Toshiba laptop and installed Server 2012 with AudioOptimizer. Even though I have only the simple SinglePC setup running the Server 2012 GUI Edition, I heard the difference immediately. You're right, it is excellent and sounds just like analog, without the ticks and pops. My guess is that it reduces and/or changes the nature of the jitter. 

Now I need to get a second laptop so I can upgrade to the DualPC setup running in Core mode."

"Last night brought over my windows 7 jriver laptop to compare against  my friend's  dual pc jplay/jriver windows server 2012 core mode setup (similar to yours. but he hasn't got AO though).     Improvements with the later setup was quite pronounced.   More coherent, organic, natural, dynamic and less 'noise'."

      

This is without doubt the best digital transport available - I haven't heard the ridiculous priced digital ststems, the DCS etc, but I doubt they can compete with the sound of the dual pc, Audiophile Optimized Windows Server 2012 system.

It is incredible sounding, the biggest advance in digital I've heard. At last we can hear what digital really sounds like, and it is beautiful. And at the progress digital is making, hang on to your seat!

The unfortunate thing is that the installation and maybe even the operation of a dual pc is beyond the ability of the average audiophile- you need a certain amount of computer skill  or at least the help of someone who understands networking and OS installation.

I'm confident that, because the result is so profound, someone will bring out a music server that contains two operating systems in the one box and will be ready to go very soon.

My control pc is an ordinary late model Toshiba laptop, its used mostly for audio, but is also used for downloading music etc.

The audio PC is a bit special, its a fanless high speed, high power super-duper computer that was especially built for me as an audio only PC. But it only really came to life with Windows Server 2012 and AO.

There is some retro in this system, although I have very good 32 bit/384Khz dacs , with the dual pc I just love the sound of my "old" TDA1541 dac, although it has been modified for USB-I2S input and has the formidable AD844 I/V output.

                                                     Control screen

                                                      Audio screen

http://www.highend-audiopc.com/optimizer.html

( not involved in any way with highend-audiopc)

AMARRA Symphony with IRC

While I'm here I'd like to also tell you about my other digital system, which uses Amarra Symphony media player program, incorporating Dirac's IRC room/speaker correction system.

The Windows Server/AO system referred to above is used with a set of active monitor speakers, they are quite accurate and they couple well with the room, I found no real need for room or speaker correction with them, and they sound so good with the AO system that I'm loathe to change anything.

However my hybrid Martin Logan electrostatics are a different kettle of fish. They have had the passive crossovers removed (passive crossovers are very dynamic limiting) and are connected from  a DHT tube pre to a DEQX digital active crossover, and then into a high power Carver Sunfire 5 channel power amp. 2 channels for bass drivers, 2 for the stat panels.

Because the passive crossovers are gone there is no level adjustment for the bass driver/ stat panel combination, and as the bass drivers are higher efficiency they sound louder than the stats , giving an unequal bass heavy response. The obvious way to balance this is with DEQX's active crossover level adjustment.

And indeed doing this and using some DEQX equalisation very good sound can be produced. With the passive crossovers gone Martin Logans can be VERY dynamic, they can play very loud and very clean, great for recreating a live performance, with the electrostatic capabilities of detail and slam.

Electrostatics are quirky by nature and getting them to couple with a room well can be challenging. Stats really lend themselves to room/speaker correction. But the results are not always convincing and often the price to pay is too much to bear , with indifferent results.

The Ammara IRC room correction is one of the latest DSP room correction products and it is very good. Not only does it do frequency correction, it is phase linear and gives near perfect impulse response. Its a big step up from outdated digital correction.

I left the levels of bass and stat drivers unchanged and measured the combination of room and speaker.

On the image below the white lines are the measured response of left and right channels.

It looks a bit wobbly but this total response of speakers and room isn't actually too bad,

although it couldn't be called accurate.

The orange line is the target, what we want the speaker and room to sound like. Its not flat, with a falling response, but this is what gives the most realistic sound in this room, with this speaker.

Below 30Hz has been excluded as I use a separate sub-woofer with DSP EQ to control sub-bass room modes.

The difference in sound with target on and off is remarkable, not only is the frequency response much improved , but the imaging, sound-staging is also much better, no doubt due to the improved impulse response which is a result of the IRC's very sophisticated filters.

Again, its just closer to realism.

This system doesn't have the breathtaking resolution and fidelity of the Windows Server 2012/ Audiophile Optimizer but it has an immediacy and dynamic integration that is exciting to listen to. It really brings the best out of "difficult" and quirky speakers and lets them give of their best.

I have some horn speakers coming soon, and expect Amarra's IRC to work very well with them.

Supratek 2014

2014 will be the 27th year of Supratek , this year I'm changing direction a little and only building a limited number of DHT (directly heated triode) preamps.
I've been building DHT preamps longer than any other audio business- I built the worlds first commercially available 300B preamp, also was the first to release a 101D preamp, and as far as I know the first to release a commercial 4P1L based preamp.

I also built over a thousand 6SN7 based indirectly heated triode preamps, the older Syrah, Chardonnay, Sauvignon, Chenin and Cortese preamps are still going strong and most remain with the original owners, a sure sign of customer satisfaction, and reliabilty.

My true love has always been the DHT preamps, there is something about a DHT preamp that is magical, there is no other component that can take you further into the music than a good DHT preamp.
Even today , with digital taking more and more of analog's place in our systems, a DHT preamp always imparts a sense of "rightness" and musical bliss to any system.
There are good technical reasons for this, tubes are linear devices that require no feedback for distortion free playback, and my chosen DHT tubes have the lowest distortion spectrum of audio tubes.

I've become very involved in digital playback the last 3-4 years, it is the future of audio, and DSP (digital sound processing) will enable your stereo system to get closer to the sound of real music in your home.
I have an enormous amount of respect for today's digital designers, they are taking us closer to the sound of the recording than we have ever been.
I never thought I would say this, but I expect to be listening to vinyl digitally soon- I'm presently working on a tube phono/analog to digital convertor.
Why?
In order to take advantage of DSP's amazing capabilities to perfect the speaker/room interface. Done properly (and it's not easy) this can bring vastly superior performance to the very best system.

So does the ancient tube (or valve) still have a place in this new world?

Most definitely. There is still a place for the highly evolved and ultra performance tube preamp. A modern DHT preamp has something that is very hard to describe, it brings an extra sense of realism, enhances the ambience, throws a wider,  deeper soundstage and gives pin point imaging .
It's all about impedance conversion and phase performance, and its easy to confirm.
Just take the DHT tube preamp out of a digital system, and you will be connecting it back up again as fast as you can!

And for those still happy with the analog world and not using digital?
The famous Supratek phono preamps now come with DHT line stages.
I'm only making very limited amounts of preamps now, and DHT linestages are what I do best.

This year I will be building a range of DHT preamps using various selected NOS tubes -
please visit my web site www.supratek.biz for details.