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Old 18th January 2012, 06:21 PM   #191
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by SoNic_real_one View Post
I choose the times at 0.01% for OpAmps and the time for the TDA is at 1LSB - like I said. For full swing I am sure is worse
Actually the datasheet very clearly says "Current settling time TO +/-1LSB - 0.5uS <emphasis by me>" in the TDA1541A one I am looking at (Feb 1991). While the "from" is not specified it is normally a full traverse of the output from silence, or in the case of the TDA1541 a 2mA step.

Quote:
Originally Posted by SoNic_real_one View Post
(albeit not published by Philips, I gave the PCM comparation, because BB cared to show both).

What matters in the end is Slew Rate, and again, albeit Philips didn't care to publish their SR, comparation with BB shows a SR of 12V/us for that generation of DAC's.
When BB are talking "Voltage Output" they are talking about the behaviour of the build in Op-Amp plus DAC, not that of the DAC alone (see block diagram), for the converter alone a 1mA (= 1MSB) Step has 0.25uS settling time to to 0.006% of FSR according to the datasheet. So you can see the build in Op-Amp of the DAC, if used degrades settling time sixfold...

Quote:
Originally Posted by SoNic_real_one View Post
Below 20V/us (or higher) of modern OpAmps.
You do not know, because no slew rate is given for the output current.

I'll do the measurement for the current rise time (30% - 70%) for a real TDA1541A when I get time.

I can tell you that using a 150MHz 'scope and running the DAC at quad speed (~5uS samples) you cannot see any rounding off of the steps at sensible zoom levels with a purely resistive I/V. And even that, by producing more outvoltage than the nominal 50mV compliance range will slow things down...

Quote:
Originally Posted by SoNic_real_one View Post
Sure, I see where the legend started - with OpMAps used in '90s having SR of 3-9V/us (LM833, NE5532)...
In the 90's we used OPA(2)604 which was 25V/uS and OPA627/637 (55/135V/uS) plus stuff like AD811 (2500V/uS) and LM6181 (1400V/uS). Well, i don't know the "we", certainly I DID.

The pedestrian stuff you mention above more properly belongs to the 80's.

As for the Legend, what Legend? I don't see any.

Ciao T
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Old 19th January 2012, 01:01 AM   #192
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I did try the video Opamps and their distortion level was too high. Speed is not everything. -74dB THD?
Sorry for the sidetrack.

Last edited by SoNic_real_one; 19th January 2012 at 01:04 AM.
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Old 19th January 2012, 02:06 AM   #193
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Quote:
Originally Posted by SoNic_real_one View Post
I did try the video Opamps
Listening, or just eyeballing the meter?
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Old 19th January 2012, 03:23 AM   #194
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Back then, I was working in a metrology lab (time/frequency), so I had "toys" around me to measure. My hearing was better than now also.
And yes, now I am eyballing the datasheets too...
I still have to hear a TDA1541 to sound above "well". SAA7220 doesn't do good in that direction, NOS is absolutelly horrid, tubes are noisy and distort (in a pleasant way, but still)...

PS: Looks like you put a lot of trust in "hearing". I didn't see your reply when it was that post here about listening two files posted here and saying which is the "uncompressed one". I did say public my oppinion then, and I was right. Did upset the OP because I did reveal the good answer (instead of PM like he wanted). And, even if I still hear distortions well, I trust measurements more.

Last edited by SoNic_real_one; 19th January 2012 at 03:33 AM.
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Old 19th January 2012, 06:36 AM   #195
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by SoNic_real_one View Post
I did try the video Opamps and their distortion level was too high. Speed is not everything. -74dB THD?
So, you know any audio Op-Amp's that do better at 2V peak-Peak into 100 Ohm at 10MHz? The AD811 for example at 2V P-P into 100 Ohm and at 30KHz is -110dB (0.0003%) 2nd HD and 3rd HD is at around -120dB (0.0001%) and remember, this is with 100 ohm load.

Again, I see few if any Audio Op-Amp's that compare well.

The LM4562 is shown as -105dB THD at 20KHz with 3V into 600 Ohm. For this the AD811 will be AT LEAST 6-10dB better.

The OPA134 offers 0.002% 2nd HD at 1V RMS into 600 Ohm, by 30KHz and if we reduce the load for the AD811 to 600 Ohm as well We will be looking at least at 30dB worse HD for OPA134.

The OPA627 does offer a 20KHz THD into 600 Ohm that is broadly comparable with that of the AD811 but the funny part is that it is actually emphatically NOT an Audio Op-Amp (though I like to use it for that job) and the AD797 driving 600 Ohm too offers a broadly comparable distortion performance to the AD811 driving 100 Ohm to 0.7V.

The AD8651 you mention is actually listed as video line driver, but with 0.0006% THD at 0.7 RMS into 600 Ohm it really compares to the AD811.

So, I am not sure what your purpose was with that little quip, however the facts do not bear out your contention in the least.

Ciao T
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Old 19th January 2012, 07:33 AM   #196
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Hi,

Quote:
Originally Posted by SoNic_real_one View Post
I did try the video Opamps and their distortion level was too high. Speed is not everything. -74dB THD?
Sorry for the sidetrack.
AD811 Datasheet figure 17.

Ciao T
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Old 19th January 2012, 08:55 AM   #197
erin is offline erin  Australia
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Quote:
Originally Posted by SoNic_real_one View Post
NOS is absolutelly horrid
I think that you feel that way because you have only heard circuits that don't do a good enough job of removing the ground noise which is generated by the current draw of the TDA1541, from the output stage power supply.
I'm not talking about aliasing, or the low pass filter, that is another issue.

All TDA1541 kits are plagued by this issue which causes an audible effect, which some would assume is aliasing, but actually is not. It is ground noise.
Glad I found out how to solve it.

Last edited by erin; 19th January 2012 at 08:59 AM.
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Old 19th January 2012, 10:24 AM   #198
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Quote:
Originally Posted by SoNic_real_one View Post
PS: Looks like you put a lot of trust in "hearing".
No, I trust my hearing but its not infallible. No senses are. So I cross check.

Quote:
I didn't see your reply when it was that post here about listening two files posted here and saying which is the "uncompressed one".
That would be because I was not interested in replying

Quote:
And, even if I still hear distortions well, I trust measurements more.
Which measurements do you trust? Relative humidity?
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Old 19th January 2012, 04:29 PM   #199
mekr is offline mekr  India
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Quote:
Originally Posted by abraxalito View Post
I'll make a mental note to PM you when there's something available to hear.



For whatever I send to you to listen to, based on some negotiations nearer the time about how it would need to slot into your system.



Well your input would be to ascertain in what respects it approaches (or exceeds) the sound quality of the CD-777. And then estimate the price accordingly.

@regal - no, not TDA1541A based. Still interested?
Count me also in if the DAC sounds better or nearer to AMR players
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Old 19th January 2012, 08:03 PM   #200
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Quote:
Originally Posted by erin View Post
I think that you feel that way because you have only heard circuits that don't do a good enough job of removing the ground noise which is generated by the current draw of the TDA1541, from the output stage power supply.
I don't deny that I didn't count that in... but I doubt that not-filtered aliasing products had nothing to do with the disturbing noises that I heard.
Too bad we cannot test your NOS against some of my OS DAC's
Quote:
Originally Posted by abraxalito View Post
That would be because I was not interested in replying
I was not interested in the test, but I wasn't scared to say what I hear. Of course if I was wrong, you would remaind me that

@thorsten:
PCM61 is rated for 8x OS and, to be able to do that, has CURRENT settling time listed as 350ns for 1mA step (has a max +/- 1mA range).
PCM63 is rated for 16x OS and, to be able to do that, has CURRENT settling times listed as 200ns for a 2mA step (max swing +/- 2mA).

You want to convince me that TDA1541 with max 4x OS capabilities will swing faster the outputs than the BB DAC's (rated at 8 and 16x) and the Phillips datasheet is wrong when it says the settling time is 1 micro second?
Well, to give you credit for something, I become curious to test the new, fast, low noise ADA4897-1 in my PCM61 DAC. I need an adaptor single-dual now...

Last edited by SoNic_real_one; 19th January 2012 at 08:29 PM.
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