New PCM1794A Kit – Balanced Mode Update – Good to Fantastic Sound! - Page 4 - diyAudio
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Old 26th September 2010, 11:14 AM   #31
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Default PCM1794a Kit - Another Field Report

Hi everybody,

let me short tell about my experience with the PCM1794a kit.

My listening experiences with digital sound many years ago (compact disc aera) were extremely frustrating and so I did not pay any more attention to digital technology.

Two years ago I started to explore the potential of hi-res digital audio. I went with an Apogee Rosetta feeded by a Ubuntu box with a realtime kernel and was more or less satisfied, means it was okay but still had not the live character that Vinyl has.

So I read a lot about different DAC chips, I/V conversion, amplification and all that stuff. I decided to build one of those diy kit and ordered the PCM1794a balance kit from Spencer 4 weeks ago. Although the parcel was immediately sent (I had the tracking number) I did wait a long 17 days until it finally arrived in Switzerland. The kit gave a good impression on me, gold-plated pcb, parts were complete and properly labelled and I got e-mailed the latest version of the manual.

Well, I soldered all the parts together which took some hours, made the calibration of the I/V supply voltage and the output dc offset which was not a problem at all and connected the kit to my Office PC to burn it in for an hour. Sound was there, everything looked fine. After that I recalibrated the output dc offset which hardly changed and connected the kit to my hi-fi system. Well - I was excited, that thing is in a different league. Music is vivid, sounds more natural, the sound stage is wide, details are here, and listening is a real pleasure, very very close to Vinyl or maybe even there ...

As a next step I will give different output caps a try. At the moment there are no output caps which is a small risk but since I have output transformers to connect the balanced output to the single ended input of my preamp latter is protected.

Last word: I can highly recommend the PCM1794 to everyone looking for a good-sounding DAC.
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Old 26th September 2010, 03:00 PM   #32
sendler is offline sendler  United States
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Default Mono mode

Hi Spencer,
I am glad to see you posting your advanced design here. I have a question about The PCM1794a in mono mode. I'm sure I will eventually want your dual boards to hear a cutting edge active I/V but for right now I have a versatile test sled in the "Big Dac Board" that I am using for experiments that sounds quite good with DIR9001 (sounds better than CS8416 in this application) and CS43122 (better than 4398 according to the designer so I didn't try that chip). The next thing I want to try is a passive transformer I/V using PCM1794a with it's outputs paralleled to take advantage of the increased current level. Would you recommend using a small series resistance on each output to isolate it from power hogging and offset currents or can I just parallel the identical outputs in mono mode to double the available current to the same I/V resistor which should get me all the way down to 10-20R with a 1:8 transformer.
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Old 26th September 2010, 03:26 PM   #33
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Quote:
DIR9001 (sounds better than CS8416 in this application)
-way better jitter rejection
Quote:
The next thing I want to try is a passive transformer I/V using PCM1794a
-if you care even a little bit about channel matching, you shouldn't
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Old 26th September 2010, 03:45 PM   #34
sendler is offline sendler  United States
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Default Channel matching

Quote:
Originally Posted by tritosine View Post
if you care even a little bit about channel matching, you shouldn't
What happens to channel matching?
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Old 26th September 2010, 03:54 PM   #35
spencer is offline spencer  Hong Kong
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Scott,

I have not try to parallel PCM1794A current output and thus I cannot comment much. But if you want to try, I think measurement is the only way to confirm if it is better or worse. A FFT scan is very important to see how the distortion changes. For the series resistor in the BJT I/V, it is used to supress some harmonics spike that I see from the FFT measurement and thus a small value resistor is added.
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Old 26th September 2010, 03:55 PM   #36
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Quote:
Originally Posted by sendler View Post
What happens to channel matching?
-without resistor IV , its goin to look bad, tolerance? Theres a commercial example somewhere with plots published, it was enough to deter one of my friends.

-with resistor IV you might exceed the output voltage compliance and the switches inside for current sources (diodes ) goin to suffer , introduce linearity errors in turn. ( I assume pcm1794 has r2r roots?)

Last edited by tritosine; 26th September 2010 at 04:01 PM.
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Old 27th September 2010, 05:18 AM   #37
skseah is offline skseah  Singapore
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Hi All,
I also got a Balance kit from Spencer. The kit came well packed and marked. I just finished soldering the components (except the output coupling caps) and now looking for some hookup wires. Attached is a photo of the layout, unfortunately there is not much space so the trans (maybe should look for smaller ones, but these were my spares) are very close to the PCB.
Regards
Victor
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File Type: jpg IMG_5153a.jpg (190.7 KB, 784 views)
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Old 27th September 2010, 06:09 AM   #38
TC Goh is offline TC Goh  Hong Kong
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Default Denon

Quote:
Originally Posted by anatech View Post
Hi Spencer,

The electronics are very good, the transport is a Sony KSS-240A type. Too bad this CD player didn't use those really nice NEC CD transports. This machine is very close to DCD-3000 and a few others with the centered

-Chris
Hi Chris

I have been looking for a good transport to eventually succeed my aging Sony ESD 337. This uses the KSS 190 drive mechanism. I really love it as the laser and tracking are magnetic. I had many years of enjoyment using it. About a year ago, the rubber belt controlling the loading tray gave way. I thought I had it but after minor surgery, I managed to replace it.

Does your Denon's 240A have the same magnetic laser head control? From what you have written, is seems like it is good as is without a DAC. I am sure I can find out easily but how many and what type of inputs does it have?

Best wishes

TC
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Old 27th September 2010, 10:54 PM   #39
anatech is offline anatech  Canada
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Hi TC,
The KSS-240A transport uses the same gear driven mechanism that most of that style transport uses. Nothing spectacular there, but it works well. I would rather have a better transport, but there just aren't any out there anymore.

The Sony ES machines are not something I would want either. They are overly complicated and suffer from the same problems that plagued Sony from the start. That company never seems to learn from their past mistakes and will often lie to cover up their own design problems. You have to watch silly things like lubricating grease becoming stiff, broken gears .... on and on. There is no excuse for that company. I hate to say it, but those KSS-210A and KSS-240A transports at least work and are repairable. That's pretty sad.

The base transport using a linear feed motor (magnetic head you referred to) is a KSS-151A. This is another excellent head, but didn't like warped CD's too much from what I've heard. Tascam and Denon both used these, and probably many others as well.

Technics uses a linear feed motor type head and it appears to be reliable. Too bad their audio section is so painful to listen to. Truly bad (another meaning for MASH technology? )

The Denon DCD-S10 was "blow me away" good when I first heard it in comparison to anything else I had heard. So this many years later, I still can't find anything that really sounds better. It has the D/A circuits that the Nakamichi OMS-7 should have had (had they existed yet!). The OMS-7 uses a Philips 14 bit chip set (TDA-1540). Nakamichi made it sound better than the 16 bit systems that were out then. It still sounds good, but the Denon kills it.

One thing everyone should understand is that the sound begins with the RF pattern coming off the CD. If this is compromised, it will not sound good. The one thing I saw decline over the years was the quality of the RF (Eye) Pattern.

-Chris
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Old 28th September 2010, 03:06 AM   #40
sendler is offline sendler  United States
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Default Transports

Transports are now completely obsolete for me since I started using my hard drive out through the spdif of a Firewire410. The sound is better than my best burns on Mitsui gold discs read by my EAD T1000 transport. I was a hold out for years but now realize what I was missing. Better sound and the convenience to play more music, more often.
.
.
Quote:
Originally Posted by anatech View Post
Hi TC,
The KSS-240A transport uses the same gear driven mechanism that most of that style transport uses. Nothing spectacular there, but it works well. I would rather have a better transport, but there just aren't any out there anymore.

The Sony ES machines are not something I would want either. They are overly complicated and suffer from the same problems that plagued Sony from the start. That company never seems to learn from their past mistakes and will often lie to cover up their own design problems. You have to watch silly things like lubricating grease becoming stiff, broken gears .... on and on. There is no excuse for that company. I hate to say it, but those KSS-210A and KSS-240A transports at least work and are repairable. That's pretty sad.

The base transport using a linear feed motor (magnetic head you referred to) is a KSS-151A. This is another excellent head, but didn't like warped CD's too much from what I've heard. Tascam and Denon both used these, and probably many others as well.

Technics uses a linear feed motor type head and it appears to be reliable. Too bad their audio section is so painful to listen to. Truly bad (another meaning for MASH technology? )

The Denon DCD-S10 was "blow me away" good when I first heard it in comparison to anything else I had heard. So this many years later, I still can't find anything that really sounds better. It has the D/A circuits that the Nakamichi OMS-7 should have had (had they existed yet!). The OMS-7 uses a Philips 14 bit chip set (TDA-1540). Nakamichi made it sound better than the 16 bit systems that were out then. It still sounds good, but the Denon kills it.

One thing everyone should understand is that the sound begins with the RF pattern coming off the CD. If this is compromised, it will not sound good. The one thing I saw decline over the years was the quality of the RF (Eye) Pattern.

-Chris
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