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Old 21st March 2012, 09:32 PM   #1911
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Exclamation pcm64 not pcm63

sorry ......

the dac is pcm 64 (denon dcd 3520) and not pcm 63

the question is same .
thanks luigi






Quote:
Originally Posted by luigilamarca View Post
Dear Gregg,
Many thanks for your last answer regarding the pcm56 cdp yamaha, but now I wanted to ask you for information instead PCM63 (denon dcd3520)
and 'can bypass this opamp dac?
or i 'can use an output transformer without opamp?
Luigi
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Old 13th April 2012, 02:27 PM   #1912
FOXYE is offline FOXYE  Israel
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I replaced the NE5532 with LME49720HA, the sound has improved in many ways.

What OPAMP s most highly recommended to try?

I have: LT1358, LT1364, LME49720NA, OPA2137P, LT1057
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Old 13th April 2012, 02:35 PM   #1913
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That is a great op amp, I have tried it and use it in a home made pre. The Burr-Brown OPA2134 is one that is at the top of my list. But often, it is more of how the op amp integrates into the circuit that matters rather than how good the op amp itself is. But op amp rolling is fun. Also tried the OPA2604, but not had good results with it.

Good luck.
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Old 14th April 2012, 09:54 PM   #1914
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Default help gregg for pcm 56

Hi Greeg thanks for your answer please but if use step-dawn transformer 4:1
2500 ohm / 600 ohm after the pcm56p
can good matched dac/imput preamplifier with low impedence ?
how you think ?
thanks luigi








Quote:
Originally Posted by auddoc View Post
Luigi,
I found the data sheet. It is attached here.
Read page 7 of the BB data sheet for the DAC- last two paragraphs.
What you may be hearing is most likely, your transformer saturating with RF from the DAC. The data sheet suggests that the DAC be followed with a high-order filter (a very steep slope 24-36db/oct-9th to 12th order LPF around 22-25kHz)which is probably what you bypassed in the Yamaha. If you have access to a scope you will see all kinds of HF artifacts mixed with the audio signal.
What do you mean by balanced? You only have +signal and GND as outputs. To feed a balanced transformer input with an unbalanced source means you are unbalancing the input. A true balanced signal is + signal, -signal and GND. The negative (or 180 DEG phase reverse) is produced, usually by an inverting op-amp/ driver. This is a separate topic from trying to get a DAC to work without a LPF of some kind.
I get the feeling that you can't really do what you want to, in this case. Perhaps the better way to go would be to optimize the output section of the Yamaha unit with the best parts money can buy. Also, get rid of any electrolytic caps in the audio path or design a "servo"-style output which eliminates DC and the need for caps in the audio path in the first place, etc, etc. Op amps are not that evil, if done correctly.
Ciao,
Gregg
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Old 15th April 2012, 03:43 AM   #1915
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Foxye,

The LME49720HA (metal can) is the best opamp of the group you listed! Be sure to use a good regulator though and run the device at 15-19VDC rails...with a clip-on heatsink on the device. Do not use any plastic package devices.

I just modified a D/A preamp last week (that I designed many years ago at National-now TI) by replacing all the plastic DIPs with metal cans. Several engineers who heard it were surprised that the same die in a metal can package could sound that different! (I actually did the same demo for Bob Pease during my first stint at National and he was shocked that he could hear the difference. Wish he was still with us!) The only plastic opamp I would play with right now is the LME49990. 0.9nV of noise!

Of course my favorite opamp is still the CFB LME49713HA...but since I did specify that part I am a bit biased! It is a Current Feedback Opamp though and requires a few special considerations when using it, like a 1.2k to 1.5k feedback resistor.

Best National...I mean TI regards,

Audioman54
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Old 15th April 2012, 06:44 AM   #1916
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Audioman

A lot of the so-called evidence for the sonic qualities of different op-amps comes from anecdotal sources or poorly designed comparisons. I think your example of swapping plastic case for metal can versions of the same op-amp comes into that category I'm afraid because it relies on your memory of what the DAC sounded like before you made the swap, and that's not 100% reliable. Are you aware of a properly designed and conducted double blind test where the basic circuit remains the same and only the op-amp is different e.g. two identical DACs using different op-amps switched blind while playing music in a reference system.

Did National carried out double-blind tests like this to evaluate their audio op-amps when you were there? If so, were any statistically significant differences between sonic qualities of the different op-amps tested found?

Last edited by Gopher; 15th April 2012 at 07:08 AM.
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Old 15th April 2012, 11:16 AM   #1917
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Quote:
Originally Posted by audioman54 View Post
I just modified a D/A preamp last week (that I designed many years ago at National-now TI) by replacing all the plastic DIPs with metal cans. Several engineers who heard it were surprised that the same die in a metal can package could sound that different! (I actually did the same demo for Bob Pease during my first stint at National and he was shocked that he could hear the difference. Wish he was still with us!)
I have a hypothesis for why there might be a sound quality difference between the devices in the metal can vs the plastic ones. Would you be able to describe what the differences sounded like to you? Also did Bob hear the same effects?
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Old 15th April 2012, 12:09 PM   #1918
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Thermal? Selection?
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Old 15th April 2012, 01:23 PM   #1919
Gopher is offline Gopher  United Kingdom
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I think abraxalito may be talking about mechanical stresses in the op-amp die being different in the two types of package. I may be wrong though.
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Old 15th April 2012, 01:26 PM   #1920
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Yeah - you are My notion is that the metal can acts like a faraday cage, improving immunity to RF-induced effects.
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