The Audio Note Kit 1.1 Tweaks Page

I have been interested in the Audio Note DAC Kit 1.1 for a long time since I became aware of its existence in the autumn of 1999. What made me interested was the simplicity of the design, the large case and the tube output stage. The large case makes it a perfect item for the tweak oriented person, the simplicity of the design is what makes this DAC different to others and also better in my opinion. The tube output stage finally makes my digital replay system free of sand components in the signal path apart from the D/A conversion where the transistors do what they are good at, switching on-off.

Now it is summer 2000 (northern hemisphere) and I am a happy owner of this DAC since three weeks. I mentioned my interest in the DAC to my Internet friend Wesley Fong in Hong Kong when I found it, and one day a couple of months ago Wesley informed me that he had actually ordered one and a couple of weeks later his first reactions arrived. Wesley was euphoric! He is not the only one, read this Internet review by Steven R. Rochlin on EnjoyTheMusic:
The Tale of Two DACs - Audio Note Kit 1.1 Meets MSB's Highly Raved Gold Link DAC... and kicks it's butt!

Another review here by Werner Ogiers on TNT Internet Magazine:
Audio Note DAC Kit 1.1

Soundstage review by Ian White:
Audio Note DAC 1.1 Kit

Article by Ryohei Kusunoki :
Non-oversampling, Digital-filter-less DAC Concept

Inspirational tweaks by Ken Schei:
Ken Schei's Home System

Some nice pics of Audio Note DAC 3 with DAC 5 digital PCB (text in Polish):
Maciej Parvi's DAC page

The DAC Kit 1.1 is derived from the Audio Note DAC 5 and share the major construction principles but the DAC 5 uses a lot more iron as can be seen in the pictures.

Audio Note DAC 5 interior


Martin Colloms DAC 5 review conclusion from HiFi News, February 2000:



Audio Note DAC 5 (Peter Qvortrup)
Audio Note DAC transformer conversion patent
HiFi Choice DAC 5 review


Audio Note DAC Kit 1.1 Construction

Adio Note DAC Kit 1.1

The assembly is quite straightforward and if you can use a soldering iron it is not difficult, just follow the instructions. It took me about 8-10 hours to assemble the two PCBs (PSU and analogue - the digital PCB comes assembled), finish the mechanical assembly and wiring the Kit. I was a bit surprised to find a Hammond transformer but there is nothing wrong with this. Note how much room there is in this DAC for extra transformers, chokes or other components that you wish to add in order to reach CD nirvana.

Via a transformer the input signal is taken to a Crystal CS8412 receiver chip and the D/A conversion is made by an AD1865 DAC. From the current outputs the signal is filtered by a third order passive circuit and taken to the tube output stage, a simple grounded cathode stage with a 12AU7/ECC82 tube (DC is used for the filament). No messing with the digital signal, just D/A conversion with passive filter and good output stage. The component quality is high with for instance paper in oil capacitors (the golden ones in the picture) in the output.

Audio Note calls the D/A conversion method 1 X OVERSAMPLING and I think this is where they have hit gold. I gave the idea a thought and indeed it makes sense, any oversampling method requires interpolation and this means in normal English guessing. The basic idea behind the interpolation is that the sampling frequency is moved into higher frequencies and therefore is simpler to filter, this may be true but you will not get more information out of the digital signal. The theory says that you can recreate a digitised signal perfectly if the sampling frequency is twice the highest needed, in the CD case the sampling is 44.1kHz and it is then possible to get a perfect 22.05kHz signal. This is the theory and to do this you need a PERFECT filter where ALL frequencies above 22.05kHz are cut off. Not possible of course and this is the main limitation of the CD media but how do we get close? Interpolation in the time domain (up-sampling) moves the cut-off frequency higher and the filter itself can be made better but the guesses are not perfect and there will be added high frequency information that has nothing to do with the music signal. Some manufacturers claim to make better guesses and use for instance a Bezier curve fitting method that according to them shall be able to predict the music signal, the result is probably only different. My guess (and Audio Notes) is that the closest approach to perfect D/A conversion is not to mess with the digital signal at all and make a decent filter that reduces the high frequency components to a level low enough to make it impossible to hear. The human ear is only capable of 15-20kHz so there is a good filter to begin with and if only the amplifier and speakers were perfect and did not induce intermodulation distortion (interference between high frequency components resulting in lower frequency components) this is the only filter we need. Unfortunately this is not the case but if the signal is reduced by some 20-40dB at 44kHz and the following amplifier is of decent quality this shall do the job. Audio Note has done just this!
 
Audio Note DAC Kit Upgrades

Wesley Fong informed me about the 'DAC Kit 1.1 Power Supply Upgrade Kit' and now Audio Note has also made a new output board. The news can be found following the link below:
Audio Note North America (What's New)

Wesley bought the PSU upgrade and he also changed the output tube into an ECC88 (possible with the new PSU). Wesley's own words describe best what he thinks about the upgrades.
The addition of the power supply upgrade gave me the following. The soundstage is now slightly deeper. There is an increase in resolution. The bass is now much more solid and goes deeper.  You will immediately notice more weight. The soundstage has widened at least 20%.  The imaging is now more 3-D.
I find the transition to a 6DJ8 a big jump from the 12AU7.  I will also try a 6SN7, but that will take some time since i will have to get the octal base, do some rewiring and also find some nice tubes in this type.  I am very satisfied for the time being.  I still have not done any tubes rolling with other tubes yet.  I am too happy!

Mats, this power supply is a great upgrade, but the change to a 6DJ8 is a must.  You will be amazed at how much better our 1.1 can get.  I definitely did not like the sound of the 12AU7 anymore and it was irritating me.

Black Gate Capacitors in the Power Supply

In addition to the PSU upgrade and output tube transition, Wesley also tried adding Black Gate capacitors and here is the result in his own words:
 
I just added Black Gate caps to the analogue PCB and power supply last night.  It's a real significant upgrade.  I couldn't believe it.  Here are some immediate noticeable differences:
The sound now makes Ella's voice sound grainy in the past.  No kidding.  We thought she was sounding good, but now her voice is much more smooth sounding. Cymbals sound like analogue.  No joke.  You will also find brush work on jazz remarkable.  Bells, tambourines, etc. Have mind blowing realism. More speed and power of attack.  Scary stuff! You will hear sounds you never heard of before on your CD's!
It is imperative that you add these caps.  You don't know what your DAC is capable of...
Unleash it's potential ASAP!!!

 The power supply upgrade is a must, but i think the caps made a even bigger difference.

 For your info, I put in the more expensive "FK" type on C1 and C2 of the (upgraded) power supply.  This was suggested by my parts shop. Total cost here for the caps was around $90.  Remember that does not include the caps on the digital PCB......I'll add these at a later date...I am right now too happy to make another upgrade.

 
My Own Audio Note DAC Kit 1.1 Tweaks
  1. Replacing the supplied tube.
    When I first tried the DAC I was not too impressed, the bass was sloppy and overweight and the treble rolled off. The midrange was nice though, the overall sound was classic tube sound. Not a hint of digital sound and I immediately noticed that there was something about the transient quality that made this DAC different. I missed some of the detail that my Meridian 606 DAC delivered but the Audio Note DAC sounded more analogue and overall I would have preferred it to the Meridian but with a close margin. Since Wesley had already informed me about what a tube switch makes I popped in a JJ ECC82 instead and now the DAC was really singing, the supplied Philips tube (6189W, a military spec. ECC82) was no good. With the JJ ECC82 in place the sound was totally different, wonderful bass with lots of weight and power, extended treble with attack and superb transient response. At first the midrange was a bit forward sounding and slightly raw, the JJ tube needs some running in. I used a CD de-magnifying track on repeat for a while and after that the midrange was very good indeed and is steadily improving and now after two weeks I have no complaints. Now I have replaced the JJ tube with an AEG ECC82 that I found on a close-out sale and this tube sounds even better. I have tried several other 12AU7/ECC82 and the results can be found further down on this page.
     
  2. Some silver wires
    Wesley supplied me with a silver wire kit and first I tried the four extra high quality (7N) fine gauge cables for the connection between the digital and analogue boards. The treble quality is now even better with metal sounding as metal and the transients are also very good.
     
  3. Some more silver wires
    Wesley has been experimenting a lot with silver wires lately and thought that if that tiny piece of silver did so much for the sound, why not replace ALL wires with silver. I did the same with the wires I had received, all the wires from the power supply to the analogue and digital boards except the filament supply were replaced. This is not a tweak I would have tried if Wesley had not reported such positive results and he was right! The silver wires really makes a difference, the treble quality improved furthermore and the sound of percussion and piano was more lifelike, a substantial improvement indeed.
     
  4. Choke in the power supply
    I had two 18H (30mA) chokes lying around and I installed one between the power supply board and analogue board. The choke DC resistance is around 380ohm, not the lowest but it works very well. I mailed the other choke to Wesley and here is his first reaction:
    I was just going out to dinner earlier when my security man told me he had a package for me.  It was your choke!  Immediately after dinner I popped it in.  Here's the first noticeable improvements I can immediately hear.  It's late now, so i could not crank it up. The highs are better, I can hear the shimmer of the cymbals, triangles, chimes, and tambourines much better.  You can clearly hear the distinguishable sound of each different note.  I didn't have to listen for the improvement, it was immediately noticeable! There is much better focus on everything, there is more air and things just sound more live and there is more presence there......ambient detail is pushed to an even higher level.  I can hear background noise and every little movement of Ella's mouth....now that's resolving power! All I can say is that we have a DAC that probably can knock the socks off another DAC in the many thousands of dollars range.
    We have used an Ella Fitzgerald recording (Clap Hands Charlie) for comparison, this is a very good live recording. I agree fully with Wesley, this tweak really improved the sound. EVERYTHING is better and more lifelike, particularly complicated large scale music has improved. When I looked at the power supply schematics I thought it looked quite good with an RCRCRC configuration, each C is 100uF and the last capacitor is on the analogue board. I knew that a choke would make a difference but I was not prepared for the magnitude of the improvement.
     
  5. Polypropylene capacitor as bypass in the power supply
    To make the power supply design complete I added a 2.2uF/630V polypropylene capacitor in parallel with the last 100uF capacitor, applied nicely on the choke. The power supply is now RCRCRLC with good bypass on the last C, a good design of modern standards. The improvement was not that large but the treble quality was improved slightly, with a larger value polypropylene capacitor the improvement may well be increased.
    Wesley Fongs comment on this tweak: Fantastic!!!  I added your cap tonight.  When i played the first cut of 'Clap Hands Here Comes Charlie', I could immediately hear more sparkle in the tambourine.  I also noticed more definition overall.  It's not a minor tweak.  It is of very significant value!  Actually, it is a must do tweak.
     
  6. Removing the electrolytic bypass capacitors in the tube output stage
    The ECC82 stands on 330ohm//47uF and the 47uF electrolytic capacitor is a good quality Elna Stargate but I have never liked the idea of having an electrolytic capacitor in series with the signal. With the bypass capacitor in place the output impedance is 5.3kohm and the amplification 21.3dB, without it the impedance is 7.5kohm and the amplification 19.4dB (TubeCad calculations). This means that we get 1.9dB feedback with the bypass removed and the output signal is lower, the already high output impedance is even higher and if you don't have a high impedance input like I have this tweak may not work well at all (I use the tape output as input with the selector switch set to an open input - the impedance is 500kohm!). Replacing the Elna Stargate with a 47uF polypropylene capacitor would have been a nice solution but it is hard to fit it onto the PCB. I was a bit surprised about the how the sound changed, first I had to set the volume control quite a lot higher (almost one mark) to get the normal listening level. The sound is much more relaxed and the detail is impressing as is the ability to handle crescendos, overall the sound is more laid back and seemingly less bright but when the treble is on the recording it comes out wonderfully. It is kind of Quad ESL-63 sound really.
     
  7. MT Audio Design cable from analogue board to RCA outputs
    The output cable attracted my interest for a design idea I have had for some time now. I decided to try it and the result is magnificent, the transient behaviour is very analogue-like, as is the rest of the sound but transient speed is the most difficult part of the sound to get right with a digital source. The cable is quite cheap but a bit difficult to make. I used three cables, two for the ground with only one of them connected to the RCA ground and one for the signal. All three wires are silver plated 32AWG (very thin) multi-stranded with PTFE isolation. The thin wires were chosen to prevent skinning and if some skinning occur anyway the surface is silver and conducts better, the higher resistance in thin wires is of no concern in this high impedance environment. To peel off the isolation you need a special tool and I am lucky enough to have access to such an item, if you use normal methods to remove the isolation the thin wires are broken. That's the tricky part of the construction besides the fact that such thin wires are fragile and need careful handling. I have used extra PTFE tubes (18AWG) on the wires and then I made a three-weave and installed them in the DAC. The extra PTFE isolation layer is used in order to increase the distance between the wires, this reduces the parallel capacitance and in a high impedance environment, such as the DAC, the capacitance must be kept as low as possible. The result of my effort is breathtaking, I had no idea that this little cable could have such an impact on the sound. Especially the transient behaviour improved and is now sounding as a very good analogue source. The treble quality is impressing with amazing detail and the correct shimmer and sparkle. When listening to familiar records I hear plenty of details I have never heard before and the dynamic impression is almost scary. At this stage I could state that the result is perfect but there are more improvements possible, meaning of course that the result is not perfect.
    Wesley Fongs comment on this tweak: Not bad but there is something wrong...The highs are better and there is more detail, however the imaging lacks realism.  There is definitely more focus and dimensionality with the original wire. My suggestion is this.  It is from my experiences of messing with wires lately. Just a single strand of wire is not enough.  You lose air and focus, which is just what your wire lacks.  I suggest you triple run the pos. and neg. wires.  Run 3 wires in parallel in PTFE tubing for both the pos. and neg.  A single drain wire should suffice.  Then braid like what you did.  I guarantee you there will be improvement.
    MT comment on WF comment: Wesley is probably right about how my cable sounds in his system, the difference from my system is that I have a VERY high input impedance (500 kohm) that loads the cable and with a normal 50 kohm load the current through the cable is increased 10 times and Wesleys experience with more parallel wires needed makes sense. The effect of a too small wire area may well be lack of imaging and dimensionality. My conclusion is: with thin wires, use high input impedance.
  8. More Tweaks
    As you have seen above there are some interesting tweaks I have not had the time to try yet, and when I have the reports will appear here.
     


Received Tweak Suggestions

From Bob Fitzgerald I have received these suggestions on improvements of the DAC:
A few things on the digital side I would consider:
- Eliminate relay connection for SP/DIF input (hard wire to CS8412)
- Tweak analog filter on CS8412 with larger capacitor values
- 100 Ohm resistors on data and bit clock lines before DAC

A larger modification would involve a 2 stage jitter filter and VCXO w/ reclocking of the data / clock lines.
This would be a somewhat ambitious project, and would perhaps not fit in the chassis.
Also, installation of either constant current sources, or plate chokes on the 12AU7 would also help. I think i would be tempted to try a 6CG7 as well, but it needs a larger filament.

Here is the philosophy behind them:
Eliminate relay - you want to keep signal clean and putting an RF signal across relay contacts may introduce some reflections and impedance problems. I would direct wire with a shielded twisted pair wire, direct from the digital transformer to the CS8412 input pins. 

CS8412  Analog Filter - people have been experimenting with different values of capacitors on this filter for some time, with good results. In general, you want to use the largest capacitor value that still allows the unit to lock in a repeatable manner.

100 ohm resistors - Slice the board traces and insert surface mount 100 ohm resistors on the non -timing digital lines, before the DAC. This decreases the bandwidth of these digital signals to lower the RF energy going into D/A processor and return currents on the ground plane. The critical clock line that controls the D/A process should not be slowed down too much.


Power Supply Simulation
I have simulated the original power supply with Duncan Amps PSU II and it looked quite good with 38uV ripple and good looking output, but not entirely free from high frequency components.
Original power supply simulated output

The modified power supply (tweak #4) with a 15H choke looks even better with 9uV ripple and pure sinusoidal output.
Modified power supply simulated output

It is hard to explain the increased sound quality with the ripple reduction but it is interesting to get the facts.

Tube Evaluation
I have tried the different ECC82/12AU7 in my possession and I have also ordered some more NOS tubes. The tests are initial and the results may change when some of the new tubes have been burned in properly. I have ranked the tubes and used a 10 grade scale where 5 is OK.

Some comments on the tube evaluation after some weeks of trial:

I have tried some more tubes, among them a couple of RCA 12AU7 (Black Plate and Clear-top), an Amperex 12AU7 (Orange Print, Holland), Radiotechnique 12AU7, RCA 8417 and a few other not mentioned here. All the tubes listed above are good, more information later. Right now I am using the RCA Black plate 12AU7, a natural sounding tube with an 'alive' quality.

More information on the tubes will appear in the near future (I hope...).

 

Score

Tube type

Comment

10

AEG ECC82
(Long Plate)

This is the best ECC82 I have heard, it sounds perfect and I have no complaints at all. The way this tube makes the sound become real is very impressing, the sound is smooth and warm but at the same time dynamic with excellent transient response and treble detail. Voices sound real and you can hear every detail without any veil. I found this tube on a close-out sale and paid $2.50 which makes this my cheapest ECC82. I walked around with it in my pocket for a day but now when I know how good it is I would be more careful, the most expensive ECC82 was $45 and this tube is worth much more to me. Unfortunately I don't know what kind of tube this is and it is probably very difficult to find another one. AEG-Telefunken is normally listed as one brand and I suppose it is some sort of Telefunken variety, it has long flat plates but is not identical to the Telefunken listed further down but pretty alike. Now I think I know, it looks EXACTLY as the EI ECC82. I tried the EI tube again and you can read my comments further down. The EI tube is a Telefunken copy and the AEG probably is a Telefunken tube. The Telefunken tube I have is not nearly as good as this one, there are many versions available and some are better than the others.

10

GE 5963
(Long Plate)

A very good tube, creating a stunning 3D 'audio hologram'. The treble is detailed and realistic, the midrange is clean with voices appearing with lots of realism and separating overdubs in a most impressive fashion. This is the tube I have been using for the past two weeks and I am very happy with its performance. I tried this tube several weeks ago and liked it a lot but replaced it since I thought the bass was too thin, a couple of weeks I tried it again and the bass is steadily improving and by now it is very good. The JJ ECC82 is still the bass reference but the GE 5963 comes pretty close, it is only below 30Hz or so it lacks some power. The bass is however still improving and with some more running in it may reach the JJ level. The RCA 5963 I have tried previously is also a good sounding tube and if it was not so microphonic it should have been in the 10 point level, the GE 5963 is not microphonic at all and share the RCA 5963 sonic character and is a clear 10 point tube. I bought this tube from Antique Electronic Supply and paid $4.50, a bargain!

10

JJ ECC82
(Long Plate)

The sound was a bit harsh at first but with some running in this is a top class tube with a nice, large soundstage and also impressive dynamic capabilities. The bass is the best of the ECC82s I have tried, it is however not quite as realistic sounding as the AEG or GE 5963 tubes but not far behind. It is well balanced and does not emphasize a particular frequency range like some of the very popular ECC82s like Telefunken or Mullard. A very good tube this too and with the availability and low price this is a tube I recommend, it costs less than $10 and I am very satisfied with this one too.

9

EI ECC82
(Long Plate)

I like this tube, it has a wonderful midrange, almost as good as the AEG but it lacks some detail and the treble is a bit rolled off.
This tube is probably the same as the AEG and the sound is very similar but lacks some detail and treble extension, this is because the EI tube has done service for a couple of years and probably is a bit worn out. I recommend this tube and it is still available at reasonable cost but maybe not much longer because the Yugoslavian factory was bombed in the war.

8

RCA 5963
(Long Ribbed Plate)

A nice sounding tube, good resolution and a musical sound. The lowest bass could be a little more firm. The soundstage is very good and it shares some of the treble qualities of the AEG. I was going to give this tube a score of 7 but the pins had some oxidation on them so I decided to clean them and after that the tube sound was improved substantially. Not quite up to the JJ standard yet, but some more breaking in may do the job. This NOS tube is still available at decent prices, I paid $17.
I have reduced the score from 9 to 8 because this tube is VERY microphonic, at low level it is probably the best of all my tubes but the microphonic behaviour makes it less interesting.

8

Mullard 12AU7LP
(Long Plate)

After some breaking in this tube started to sound really good with very good treble and good soundstaging. I think the treble is a little over-emphasized though and it does not sound as engaging as the two best tubes.

7

Telefunken ECC82/12AU7
(Long Plate)

I hoped this tube should sound as good as the AEG or better but it does not. Maybe it needs some running in but at the moment the sound is only good and slightly mechanical. It is not as smooth and alive sounding as the AEG tube. Telefunken has quite a reputation as one of the best manufacturers of tubes and I hope it will deliver the magic after some running in.

7

Sylvania 6189/12AU7WA
(Long Plate)

 

6

Philips 6189W
(Long Plate)

The deepest bass is not well defined and the treble is rolled off but the midrange is very good and also the ambient detail. A good tube for string quartets or small Jazz ensembles and it may also be perfect for mini-monitor speakers with metal dome tweeters.

6

Golden Dragon 12AU7/E82CC

Warm sounding, easy to listen to but it lacks some resolution.

6

Sovtek 12AU7A

Slightly mechanical sound but with good definition and a good soundstage.

 


Conclusion
I am very satisfied and the CD sound is now far better than I thought possible with no trace of digital sound, I could well stay the tweaking here but there is more to come. The DAC is highly recommended but the amplifier must be able to handle some high frequency information without sound degradation and the input impedance shall be at least 100kohm to get the most out of this DAC (the input resistor can often be substituted quite easily, I recommend 500kohm). To get the information out of the CD properly I also suggest a CD clock upgrade, it really makes a difference.

  

This site uses frames, but if you have found this page via a search engine and do not see a frame on the left side of this page, you can use the home button to get to the main frame of the MT Audio Design site.