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Old 30th September 2010, 01:48 PM   #51
TC Goh is offline TC Goh  Hong Kong
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Hi Scott

Thanks for your reply. I will do more research on e transports.

Regards

TC


Does anyone have any suggestions on a balanced pre-amp a novice can build?

Thanks.

TC
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Old 30th September 2010, 03:01 PM   #52
sendler is offline sendler  United States
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Default Dac gain adjustable?

Quote:
Originally Posted by TC Goh View Post
Hi Scott
Thanks for your reply. I will do more research on e transports.
Regards
TC
Does anyone have any suggestions on a balanced pre-amp a novice can build?
TC
Can the gain of the I/V and buffer stage be adjusted? You may already have a great pre built in. I use passive stepped attenuators at the amp and or gain optimized digital volume control with the amps and dac gains matched to deliver my reference listening level at -0db volume control.
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Old 30th September 2010, 04:11 PM   #53
TC Goh is offline TC Goh  Hong Kong
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Quote:
Originally Posted by sendler View Post
Can the gain of the I/V and buffer stage be adjusted? You may already have a great pre built in. I use passive stepped attenuators at the amp and or gain optimized digital volume control with the amps and dac gains matched to deliver my reference listening level at -0db volume control.
Hi Scott

If that were the case, that would be superb ... However, I am not sure how easily the I/V gain can be adjusted. I think it can be but would require some work. Spencer said that there is a 4.99ohm resistor that links the DAC analog output to the I/V. Maybe something can be done here???

I guess the best person to answer whether this is possible would be Spencer...

Hello Spencer....

Best wishes

TC
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Old 30th September 2010, 07:00 PM   #54
anatech is offline anatech  Canada
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Hi TC,
Quote:
Hit a nerve, eh ha ha?
No, not in any way. Made a lot of money from damaged transports due to many off-spec CDROM blanks. While they are in spec for data cdroms, they certainly weren't for audio CD player use. I just hate to see people cost themselves money is all.

The actual issue was that their reflectivity was far too high. This threw off the expected RF pattern amplitude and many earlier CD servo sections had adjustable "slice" levels (a reference for determining what was a low and high). So when set for normal CDs, no problem. Stick one of these other types in and it might track, and it may just lose lock. Then the rotational velocity would go way up (All is lost now) and if you were very unlucky, the tracking servo would run the sled right into and beyond (well, it tries) the end. This often destroys the gears outright. Unfortunately for some people it wouldn't rip the teeth right out, but rather split or crack them. This resulted in many machines labeled as "not worth repair" simply because the white grease hid the damage, and unobservant technicians didn't check.

We had notices from most distributors that stated that the warranty was null and void if recordable CD blanks were being played. My concerns are simply that the gold coloured CD blanks were off spec as far as audio machines are concerned. Using these in an audio CD player will result in many more read errors as a result. Yes, they still play these days (servo controlled everything now), but I'm not sure about the error rate.

Hi Scott,
Quote:
I am sorry that apparently someone ruined your transport with a green ring?
No, not me. I have had to remove them (the rings) from CD player mechanisms on occasion. Just think, it cost some people real folding stuff to impair the performance of their machine. There was an entire industry built up out of lying to the public to sell useless crap. That industry is alive and well.

Just look at yourself. You gave up on CD players and use hard drives now. That's an intelligent choice I think, and I certainly can't fault you for it. A hard drive would probably be the best playback device for automotive use. I'd spring for that, none lossy storage of course.

Quote:
and burns always sound better than the original cd. This is well documented in other threads
No, it's not well documented. It's called anecdotal replies.

Sound quality is directly related to the BLER rate on the disc. So the fewer the errors, the better it should sound. The result of having varying error rates on a disc will depend greatly on both the mechanism, it's calibration/performance (or setup and how new is the head) and how much money went into the error correction area. That's it, that's all that will differ. The DAC simply converts what it is fed and the audio section remains constant for everything. Or it should, it's entirely possible that some manufacturers may play there to make disc errors less noticeable.

The one thing to remember too, the information coming off the original CD is the perfect standard as for as the information you are about to burn is considered. It doesn't get any better, only worse. However, the original CD may have disc errors that a machine has problems tracking. Taking the data over to another medium frees those issues, so for the case of a poor quality CD, the copies may sound better. But you can not say that blanks are better. All you can say is that some store bought CDs are of poor quality. On that, I completely agree with you.

The amount of mis-information about CDs and how the information comes off the disc is appalling. We can thank the self appointed experts, "white papers" and other marketing ploys. Once you know how stuff actually works, there are many products that you will know can not work, at least in the way they are promoted. I've been servicing CD players since the first ones were released (those were grim days), up to and including the present. The one thing I am grateful for are all the problems with the early machines, because we got an excellent education from the engineering departments. Most of todays machines are "continuous setup via servo" machines. They self correct until they can't anymore. This means that the average performance is probably better, but the extremely high performance that hand tuning can produce is no longer possible.

Give me the storage and I'll do the same. BTW, up-sampling on the way off is at least as good, and more efficient for storage (as you should know). The trick is to get the information off the original media without errors, so a good transport makes sense there.

Finally, I'm well aware that amplifiers, preamps, tape decks and everything else sounds different between various devices. I've never once said they sound the same, and I do a fair amount of work improving the performance and sound quality of amplifiers. You must be thinking of another "Chris". I also listen to my CD player for enjoyment, or a turntable. I also use both tube and solid state equipment. You're talking to another person who listens extensively.

-Chris
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Old 1st October 2010, 07:00 AM   #55
TC Goh is offline TC Goh  Hong Kong
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Quote:
Originally Posted by anatech View Post
Hi TC,

...Made a lot of money from damaged transports due to many off-spec CDROM blanks. While they are in spec for data cdroms, they certainly weren't for audio CD player use. I just hate to see people cost themselves money is all.

The actual issue was that their reflectivity was far too high......

-Chris
Hi Chris

Good for you! I remember those days of using these 'enhancers'. They were fun though. Frankly, I also bought those black 'audiophile' disc to record and I still have some.. he he.

If I am reading you correctly, the silver audio CDs have a lower reflectivity index than CDROM ones? Just from purely looking at surface, it seems to be the opposite. The silver ones seem to reflect light better. I always thought that was why some DVD players cannot read CDROMs.

So, any suggestions on a good transport other than the Denon?

Best wishes

TC
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Old 2nd October 2010, 11:19 AM   #56
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Default Some photos of the DAC without the final case

Hi,

just some pics of the DAC. The next two steps will be to install the output caps and to put all together into a nice case.

Sound is a dream, vital, and no fatigueness.

Daniel
Attached Images
File Type: jpg DSCN0327-small.JPG (465.8 KB, 634 views)
File Type: jpg DSCN0328-small.JPG (487.7 KB, 618 views)
File Type: jpg DSCN0336-small.JPG (393.5 KB, 592 views)
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Old 3rd October 2010, 01:31 PM   #57
TC Goh is offline TC Goh  Hong Kong
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Exclamation OCL Rules!

Hi

After a few weeks of rolling output coupling caps, I came to the conclusion that OCL gives the most accurate and hence best sound. My rationale was that the top of the chain should be as accurate and faithful as possible, leaving the personalization to the pre and power amps. As I have a complete tube setup, this is possible. That way, I can hopefully ensure that as little of the intricate nuances of the music is lost.

Although I do appreciate the risks involved in running the DAC in this mode, I think in my set up, these are minimal; well that is the theory anyway. Ah well, what is life without some excitement, right?


Tubes Died!Click the image to open in full size.

When I first configured the DAC to OCL, there was some harness in the highs. At first, I thought it was the DAC. I then tried the system with another pre amp and the harshness was not there. What gives?

It was then that I decided to test my preamp tubes with my trusty TV7 and hold and behold, 3 of the 4 6V6 GECs were testing marginal! Ouch! These were smoked coke bottled with black bases! I bought these about 8-9 years ago and they cost more than the whole DAC then!!! Ouch again….Fortunately, I still have four (NOS matched Quad) so I am fine but maybe I should just sell them for a tidy profit!! Ha ha… Open to offers ...ha ha ha ha!!Click the image to open in full size.

Anyway, I am now using Sovtek 6L6 as their temporary replacement. Of course, the Sovtek can’t come close to the finesse, smoothness and refinement of the GECs but they will have to do for now. Anyway, the edginess of the highs is gone and the soundstage is much more open.

So, after more tests, OCL vs non-OCL, I feel that with OCL the system is more detailed and open and with more punch. It continues to be very easy on the ears but much more dynamic and faster. The soundstage is larger and as quiet and the bass is fantastic; more in quantity and quality … lower and more extended. I feel the improvement in the bass is most pronounced.

With the GECs, I am sure these improvements will be even more apparent. I think I will eventually put these in ….. I also have some Tungsol Reissues to try too…. . Its going to be another fun week.Click the image to open in full size.

This little DAC continues to amaze. It is capable of reproducing incredible musical detail. Truly amazing ….

So, the conclusion is OCL for this 1794A DAC rules….

Thanks for reading.

TC

Ps. A picture of the DAC with the big K75-10 10uf, Jensen PIO and Silmic …
Attached Images
File Type: jpg IMG_7958.JPG (187.0 KB, 215 views)

Last edited by TC Goh; 3rd October 2010 at 01:47 PM. Reason: typos
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Old 3rd October 2010, 01:50 PM   #58
sendler is offline sendler  United States
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Default How much dc?

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Originally Posted by TC Goh View Post
So, the conclusion is OCL for this 1794A DAC rules….
How low can you get the dc offset on the output with the adjustment. Is it stable during warm up?
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Old 3rd October 2010, 02:42 PM   #59
TC Goh is offline TC Goh  Hong Kong
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Default DC Offset

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How low can you get the dc offset on the output with the adjustment. Is it stable during warm up?
Hi Scott

Hope you are having a good weekend.

The DC offset is set by 2 (5K, I think) variable resistors on each board. So far (touch wood), the offset is close to 0 with a variation of about +/- 2mV but hovers around +/- 1mV most of the time. It doesn’t vary much though, even during use (on my set, at least) but that could be because my Fluke can't detect it! Its resolution is only up to 1 mV.. Ha ha.

I think if it stays within this range, it should be ok, right? Anyway the speakers and amps are still functioning, which is always a good sign.

Oh, OCL is also slightly louder. I guess this is because this is the path of least resistance.

Best wishes

TC
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Old 3rd October 2010, 03:15 PM   #60
TC Goh is offline TC Goh  Hong Kong
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Default Output Line TXs?

Quote:
Originally Posted by c1cc1ccc1 View Post
Hi,

just some pics of the DAC. The next two steps will be to install the output caps and to put all together into a nice case.

Sound is a dream, vital, and no fatigueness.

Daniel
Hi Daniel

What are those two round devices connected to the output of each board? Are they line transformers?

How do they affect the sound?

Best wishes

TC
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