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.
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.
