New PCM1794A Kit – Balanced Mode Update – Good to Fantastic Sound! - diyAudio
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Old 5th September 2010, 08:01 AM   #1
TC Goh is offline TC Goh  Hong Kong
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Default New PCM1794A Kit – Balanced Mode Update – Good to Fantastic Sound!

Hi

I was looking for a DAC to replace my current DAC which I bought many years ago. It uses a Yamaha YM3623B chip feeding two PCM63s. The analog section is of a tube design using 2 6DJ8/6922. I felt that although it was sweet, it lacked transparency and clarity and tube rolling was incredibly expensive!

I have never put a kit together, let alone a DAC. Anyway, due to cost and wanting to get my hands ‘dirty’ I began looking for one. I read here that the DAC Chip is largely responsible for sound quality in a properly designed DAC. After some further research, I came to the conclusion that the TI PCM1794A chip may be the best chip out there. I began searching and stumbled upon a site called Fetaudio that just released a PCM1794A DAC in kit form. After an email inquiry I decided to give this a try. It appears that the DAC is decked out with audio grade parts and uses a discrete transistor IV analog output. To top it all up, Fetaudio is in Hong Kong, where I live. I thought if all else fails, I can at least make a trip to the company and have the kit fixed!

Anyway, after working on it for two full days, I got the DAC to work. However, that was not before some troubleshooting. I must commend Spencer, the owner of Fetaudio as he was always very thoughtful and prompt in his replies to questions. When the left channel didn’t work, he helped me trouble shoot. He asked me to take some MM readings and suggested, before anything else, that the issue might be a dry solder joint and asked me to touch up the left channel IV solder joints. That seemed to solve the problem and the DAC has been singing for about 2 weeks without any problems.

The experience has been very rewarding as the feeling of being able to put something together for the first time that works is indescribable. It is like winning a lottery!

Anyway, Spencer continued to keep tabs on my progress and sent me 4 Silmic 2 100uf caps with instructions on how to create a pair of bi-polar caps to upgrade the original Panasonic ones used for output decoupling. I also got 2 Russian 10uf boxed caps from him. I had a few Jensen 0.01uf PIO lying around and I put these in too.

I must say the improvement in clarity, transparency and musicality was stunning. It blew my old tube DAC away by a wide margin. For those thinking of trying out this DAC, don’t waste time on the Panasonics output decoupling, go for the SiImics BP. They give a more neutral and defined mid and high. Bass is also deeper and lower. If you can, try out the Jensen's too.

Although the DAC was not cheap compared to those on ebay, it does sound incredible.

BTW, Spencer offered to solder all the SMD parts, including the CS8416 and PCM1794. I think that was fantastic as I wouldn’t have been able to manage them. The parts are tiny and the pins are well, microscopic….. I think I would need to be a surgeon to manage that!

I must say I am surprised that even a first timer like me can do this. I never thought I could. Anyway I did and the DAC sounds like a million dollars. It is open, clear, dynamic and musical. With the Jensen’s, I think the overall sound is best as it smoothens out some of the edgyness in the highs and adds a touch ‘Jensen’ mellowness too. I am very happy with the DAC.

What next? Well, I can hook up another DAC to create a true full balanced DAC. There are some jumpers to set to configure the boards to mono L and R mode. This will double the analog output voltage which should improve performance even further. As my pre amp and power amp are balanced too, I ordered and have received a second kit. I am working on this right now and things are getting exciting. Apart from inhaling some more flux smoke (and more sleep deprivation), this DIY business is very exciting and fun and yes, I expect it to get 100% infectious!! I have to be careful.

Watch this space ……!

Best wishes

TC
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Old 8th September 2010, 12:24 PM   #2
TC Goh is offline TC Goh  Hong Kong
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Default New PCM1794A Kit – Balanced Mode Update – Good to Fantastic Sound!

Hello

As I mentioned in my initial post, after completing the first DAC, I proceeded to kit out the second so that I can run them in Balanced Mode using a digital I2S interface cable and configuring each board to mono L and R modes.

According to the 1794A specification sheet, the dynamic range in mono mode improves from 127db to 132db. In addition, Fetaudio’s manual lists other benefits, but the most important of all (to me, at least) is that sound quality will improve significantly. There were actually two choices available for the upgrade. I took the more expensive route by getting another full board. There was a cheaper alternative, which is offered as standard, which does away with the digital receiver section - Fetaudio calls this Slave Board. My logic was if this upgrade didn’t go according to plan, I can always run them as two DACs!! However, I don’t see why I would need two DACs but in DIY, logic often gets over-ridden!!!

Anyway, I must say I am very pleased that I managed to kit the second board without any problems and it worked beautifully right out of the gate. I was very careful with soldering to avoid dry joints. Yippie ….. What a relief! I finished assembly in about a day and the half, half a day faster! No bad, eh…. After all, this is my second ever DIY kit project!

The additional item to make was the I2S cable. This is actually a flat computer cable (10 wires, I think) with a 5 * 2 pin on the one side and a 8 * 2 pin on the other. This was easy to make despite not having a dedicated crimping tool. I just laid the connectors with the wires on the floor and pressed them in with the flat surface of one of my wrenches! Ha ha…. A very high tech solution to a high tech problem!

Fetaudio’s also sent me information on how to connect the analog outputs of both the boards in XLR Balanced mode.

I also bought another transformer. Although I could have used the same one, it just didn’t seem right. I thought I’d go all the way; Full Balanced ‘independent’ mode, period! No excuses if it doesn’t sound right.

Spencer was kind enough to make me an input selector switch, which is really great of him. This allows me to switch between the three digital inputs available, coaxial, optical and AES. I tried the optical and coaxial but I don’t have any source with an AES output.

Anyway, I got the Silmics BP and Russian MBO 10uf from him too.

So enough of this construction talk … how does it sound?

Hmmm…. In a word, FANTASTIC! From the onset, the Stereo SE version was already very good; sweet, clear, detailed and dynamic. In Balanced mode, the performance was ‘out of this world’. It felt like the hidden latent power of the DAC is unleashed with a vengence! The soundstage expanded way beyond the confines of my speakers. The height and depth of the soundstage improved significantly and the 3D effect became 4D, ha ha. At the same time, the music was dynamic and very life like. It was remarkable, and frankly, I am still a little stunned. I think I got a bigger bump moving from SE to Balanced Mode than from my previous (now in deep storage!!) tube output DAC to SE!

Of course, I had hours of fun playing with the output capacitors. The Silmics BP were good and the Russian MBOs from Fetaudio were excellent. However, I began thinking of what I can do to improve the sound even further and match it more to my taste in music, which are mainly vocals. I had some Russian 10uf KBG (as opposed to KGB!) so I decided to try them out as bypass for the ‘standard’ Silmic BP. I also put in my Jensens PIO 0.01uf. Wow ….. This combination actually blew all others away by a mile! This is by far the most natural sound I have ever heard!

Of course, as I said in my previous post, I am probably a little biased as ’I made these DACs’. In my mind, there is nothing better. Not very objective, I know. However, a friend came to my place yesterday and he was impressed by the new DAC too. So, I guess I am not completely dreaming in cloud cookoo land!

I think this is a remarkable sounding DAC. I have been in hi fi for a while since before the days of Sony CDP 337 ESD (still my transport) with its excellent KSS 190A mechanism and I have owned a modest amount hifi equipment during this time. This DAC probably gave me the ‘best bang for the buck’ in terms of sound quality improvement. It goes to show that you don’t need to spend an arm and a leg to get superior performance.

I feel I need to give Fetaudio and Spencer a plug here. He has designed a great product and I feel his attention to service to me has been exemplary. Although I am new to this, I never felt ‘alone’ during the project.

And now …. in response to Chris661 question on what is next, I think a pre amp may be on the drawing board. I see there may be some Pass designs here... Opps! I can see the missus looking over my shoulder now …..

A diyer’s life is never dull!!

Again, thanks for reading ….

Best wishes

TC

PS. Sorry about the picture of my dog. He decided to come see what I was doing .... What can I say, he is into hifi too! It runs in the family Click the image to open in full size.
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Last edited by TC Goh; 8th September 2010 at 12:47 PM. Reason: typos!!!
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Old 8th September 2010, 02:43 PM   #3
TC Goh is offline TC Goh  Hong Kong
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Default New PCM1794A Kit – Balanced Mode Update – Good to Fantastic Sound!

Hi

Here are some more pictures showing the best cap combination, Silmic BP 100uf, KBG Russian 10uf PIO and Jensen 0.01uf PIO.

Enjoy!

Best wishes

TC
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Old 10th September 2010, 10:07 AM   #4
TC Goh is offline TC Goh  Hong Kong
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Default Living Dangerously!

Hi

I was visiting the Fetaudio site and noticed that they have tried OCL (Output Capacitor Less). I think this is similar to OTL (Output Transformer Less) in some tube gear. Anyway, the idea was to remove completely the output decoupling caps so that the signal will travel unfiltered straight through, DC and all! As a result, Fetaudio warns that OCL does carry some risks.

However, what is life when you don’t take some risks? I thought that since my pre amp and power amps all have output decoupling devices, at least the damage can be contained to the pre-amp, or at least that is the theory.

Anyway, I gave this a try. I checked the output current again by adjusting the 4 VR and then removed all the output decoupling caps. I shorted the connections with pieces of wire. I plugged in the ‘naked’ DAC and powered it on! The usual click of the relay was heard and the digital locked light came on; a good sign … I then powered on the pre and power amp and waited. No smoke or pops or cracks. Speakers are still sitting there! I then hit play and the system began sing.

Whee … all appears to be well…. OCL here I come …..

I proceeded to listen as the system warmed up.

The Thiel CS2.4 was in for a shock! The clarity, transparency, soundstage and dynamism of the music improved in this configuration again. The whole music floor took on a new sense of new urgency! Wow. This DAC never ceases to deliver and amaze. The entire spectrum appears louder and more accentuated. Bass was even more extended. OCL does improve the musical experience significantly and offers yet another step-up, albeit one that entails some risks.

I am not sure what I will do next but the prospect of running the DAC permanently in OCL mode is very very appealing. The Manual does say that there may be some limited protection as there is a relay to shunt everything to ground (I think) in case of a failure.

Decisions, decisions, decisions…..

Best wishes

TC
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Old 15th September 2010, 10:58 AM   #5
TC Goh is offline TC Goh  Hong Kong
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Hi

After a few days, I think common sense prevailed. Although I had no problems with OCL, I felt it would be more advantageous in the long run with the coupling caps. It is more fun too. I bought some K75-10 Russian caps (ebayer claims this is the best Russian audio cap??) together with some Teflon insulated ones. They should get here in about 2 weeks.

The DAC is beginning to settle in after about 50 hours or so of burn in. Overall, it sounds more refined. The slight edginess I detected has disappeared. I guess this is to be expected.

One day, I had it on for 24 hours straight using a cheap transport ($30 DVD player!) feeding my portable stereo!! Ha ha …. No point using up the tubes in my pre and power ampClick the image to open in full size..

I think this DAC is turning out to be a real winner and I am getting a lot of enjoyment out of it.

Again, thanks for reading!

Best wishes

TC
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Old 17th September 2010, 04:57 PM   #6
spencer is offline spencer  Hong Kong
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Hi TC, Thank you for your great review on my new PCM1794A DAC. Here is another feedback from a user of the SE DAC below from Germany:

Hi Spencer,

Sorry for my late reply, but today I finally had the chance to test the dac. Hands down, I am very impressed! Thank you again for providing your great design! There really is lots of detail and room information in the sound. Instead of an r-core I used two (good quality) toroids from my drawer.. Compared to the UA2192 the sound is very different. The UA has a lot of "analogue warmth" (that's what it is famous for) but in comparison lacks detail and seems to smear a little. For monitoring I clearly prefer your design! However I will need some kind of passive attenuator for the final box. What would you use in order to reduce the output impedance so I can drive the power amplifier (Zin=33k) without any trouble? I have zero experience with FETs since I mostly built tube-based stuff, but I'd be interested in experimenting with them!
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Old 18th September 2010, 11:52 AM   #7
TC Goh is offline TC Goh  Hong Kong
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Hi Spencer

That is alright. I was only saying what I experienced.

I am glad that you have another happy buyer. I feel there would be many more in the future.

What is the UA2192? Is this a professional DAC? Frankly, I have not heard about it. What DAC Chip does it use?

Another one of my friends just left after listening to the set for about an hour. They said it was superb.

Again, thanks for all you have done.

Best wishes

TC
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Old 23rd September 2010, 04:34 PM   #8
akira is offline akira  France
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Quote:
Originally Posted by SY View Post
Since you're posting this in the noncommercial section of the forum, you certainly wouldn't mind giving full details, schematic, BOM, board layouts...?
.
Here you go :
http://www.fetaudio.com/wp-content/u...-Manual_R3.pdf
But I tend to agree that this post should be in the vendors section.

Cheers

Last edited by akira; 23rd September 2010 at 04:36 PM.
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Old 23rd September 2010, 05:26 PM   #9
sendler is offline sendler  United States
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Default Good thread

Quote:
Originally Posted by TC Goh View Post
Another one of my friends just left after listening to the set for about an hour. They said it was superb.
Thanks for posting about this kit. I may be interested in building one if my passive transformer I/V for the PCM1794a needs improvement. I wouldn't have known about it if not for this thread. There should be a surge of interest for the fet I/V since Pass recently published an article about his long time circuit. It is cool that the schematic and board layers are available for view right in the manual.
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Old 23rd September 2010, 06:32 PM   #10
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Gee,,,,I get a warning that this file is damaged and cannot be repaired,Any Idea????
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