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Old 5th March 2011, 02:32 PM   #1201
tmas is offline tmas  United States
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Headrott,

I would be very interested in your experience with the tubeizator boards.
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Old 5th March 2011, 03:04 PM   #1202
Marek is offline Marek  Poland
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Quote:
Originally Posted by BrianDonegan View Post
So, the loopback measurement was done SE?
Previously presented measurments was done balanced (PP). Whed I disconnect one balaanced output eg OUT- then 3rd harmonic stays and additionally 2nd harmonic shows up

BuffaloII SE (one complementary output) to EMU:

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Last edited by Marek; 5th March 2011 at 03:16 PM.
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Old 5th March 2011, 03:35 PM   #1203
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You should not be seeing that degree of 3rd harmonic, something is clearly wrong either with the setup or the measurement. It is not easy to obtain good measurements from a PC solution even from the EMU device. The problem is that the ADC itself can introduce some very nasty errors. This will not really be noticed in a loop-back situation. Also simple things like how you run the measurement cable etc can make very large differences.

Since you are using the DAC in an extremely bad setup (voltage out etc) I am not completely surprised. But your measurements are particularly off even compared with what others have posted here and other threads, but most of those people are measuring complete solutions.

We have had the Buf II tested several times with AP. And we easily achieve the results stated in the datasheet with IVY-III. Legato also comes very very close, but it has no global feedback, so THD is very slightly higher.
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Last edited by Russ White; 5th March 2011 at 03:45 PM.
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Old 5th March 2011, 03:42 PM   #1204
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Here is a recent measurement at 1khz with IVY
Attached Images
File Type: png Buf_Ivy_1K.PNG (75.0 KB, 313 views)
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Old 5th March 2011, 04:06 PM   #1205
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Marek, very nice. Keep them coming....
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Old 5th March 2011, 04:09 PM   #1206
Marek is offline Marek  Poland
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Quote:
Originally Posted by Russ White View Post
You should not be seeing that degree of 3rd harmonic, something is clearly wrong either with the setup or the measurement. It is not easy to obtain good measurements from a PC solution even from the EMU device. The problem is that the ADC itself can introduce some very nasty errors. This will not really be noticed in a loop-back situation. Also simple things like how you run the measurement cable etc can make very large differences.
If problem is in EMU's ADC is must be visible on loop test (physical cable from EMU DAC to EMU ADC) but it isn't. Both situations are the same, only different DAC
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Quote:
Originally Posted by Russ White View Post
Since you are using the DAC in an extremely bad setup (voltage out etc) I am not completely surprised. But you measurements are particularly off even compared with what others have posted here and other threads, but most of those people are measuring complete solutions.
Sabre32 DAC in voltage mode should have -108dB THD - its enough for me. I use this setup because of testing tube output stage (tube is voltage driven device).Before I do measure performance of tube stage I need to define source (BuffaloII) and meter (EMU ADC) performance. And I did, and my results are that the EMU DAC with OPAMP output stage has better THD performance that alone BufII (I'm suprised).
I know that datasheet THD is true for sure - I try to figure out what is the reson of my bad results.Maybe I made something wrong or my BufII is lightly broken...

I've just made a test using Jensen JT-11P-1 (1:1) as a simple passive output stage which provide galvanic isolation and BW limiting but THD results are the same..

Quote:
Originally Posted by Russ White View Post
We have had the Buf II tested several times with AP. And we easily achieve the results stated in the datasheet with IVY-III. Legato also comes very very close, but it has no global feedback, so THD is very slightly higher.
Have you measured BufII in voltage mode (no output stage) with AP? can you post result here?
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Old 5th March 2011, 04:12 PM   #1207
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No, I actually have not measured it like that (no output stage) , because I know the results would be far from ideal. Even in voltage mode you would want to do some form of output stage. Direct is never going to be an excellent option.
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Last edited by Russ White; 5th March 2011 at 04:18 PM.
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Old 5th March 2011, 04:29 PM   #1208
Marek is offline Marek  Poland
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Ok, got it, but what can I do to stay voltage out (for tubes) and heve better performance?

Anyway I'm wondering in what conditions ESS achieved those -108dB..
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Old 5th March 2011, 04:39 PM   #1209
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This is what they show on their site.
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File Type: png voltage_out.PNG (23.5 KB, 307 views)
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Old 5th March 2011, 04:45 PM   #1210
Marek is offline Marek  Poland
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Yeaa..I was there (in OPAMP world) and never come back again...
I definetaly prefer -90dB 3rd harmonic over -120dB from OPAMP output and I think I'm not alone.
Anyway, thanks for you help.
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