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Old 27th April 2010, 04:44 PM   #51
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Default -108 THD in Voltage mode

Hi Marek
I would be bit carefully firmly stating this nice numbers. -108 THD in Voltage mode is ESS Sabre number and no doubt this is true, but I'm afraid this is not necessary number at Trafo output(!!).
I did some measurements with my EMU202 and they doesn't looks like -108 THD at trafo output (!!!). I wouldn't call them reliable enough to post but
If anyone else did measurements of Buffalo with trafos and could share would be nice to confirm the numbers. My EMU could be wrong. .
As for not loading trafo output, again from my uncertified(!!) measurements seems that this influences specially low frequencies response (20-200Hz) of trafo . And at list 1Kohm trafo load is probably about minimum to have.

Rosendorfer
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Old 27th April 2010, 04:55 PM   #52
Marek is offline Marek  Poland
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I am curious how your measurments looks like. Please post theme and method you used (RMAA?)
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Old 27th April 2010, 07:36 PM   #53
glt is offline glt  United States
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Quote:
Originally Posted by Rosendorfer View Post
Hi Marek
I would be bit carefully firmly stating this nice numbers. -108 THD in Voltage mode is ESS Sabre number and no doubt this is true, but I'm afraid this is not necessary number at Trafo output(!!).
I did some measurements with my EMU202 and they doesn't looks like -108 THD at trafo output (!!!). I wouldn't call them reliable enough to post but
If anyone else did measurements of Buffalo with trafos and could share would be nice to confirm the numbers. My EMU could be wrong. .
As for not loading trafo output, again from my uncertified(!!) measurements seems that this influences specially low frequencies response (20-200Hz) of trafo . And at list 1Kohm trafo load is probably about minimum to have.

Rosendorfer
Hi Rosendorfer. You could compare the 3 configurations: straight from DAC, trafo and Ivy.
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Old 27th April 2010, 11:43 PM   #54
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Default It is technically possible but ....

Dear GLT

I'm afraid that measuring Buffalo+IVY with EMU202 isn't good idea. EMU is not able to do anything in the range of that parts and the results will tel more about my power supply than the IVY. So it is technically possible but posting this kind of measurement in TP thread wouldn't be at list "wise".
Regarding "straight from DAC" voltage out, EMU202 is simple SE stuff I would need something with balanced inputs, /maybe EMU404 I do not remember if it has balanced inputs/ to make any THD measurements. Basically we need something to convert differential to single ended. In theory I could try to modifie IVY for higher imput impedance but to be honest idea of desoldering resistors from my "presious" IVY is not realy tempting. The second option is nice Trafo from Lundahl .
I realy do not wish to sound negative but how in reliable way measure Bufalo in Voltage Output with EMU202 I'm puzled. Anyway in any idea I'm open. There will be "long weekend" this weekend so I could find some time.

All the best
Rosendorfer
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Old 28th April 2010, 12:02 AM   #55
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Marek

Yes I did use the RMAA v5.5 and 6.2.
During the wekend I can try to use ARTA to check if the measurments are the same and will see if they will get relliable enought to post if this is interesting to you.
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Old 28th April 2010, 03:15 AM   #56
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You would need something much better than any sound card FFT to get accurate enough measurements for the IVY III.

RMAA is good software, but the ADC will be the weak link.

You would need something like an Audio Precision or similar.

Otherwise the noise and THD of the measuring device itself will dominate and you won't have any very useful data.

Cheers!
Russ
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Last edited by Russ White; 28th April 2010 at 03:19 AM.
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Old 28th April 2010, 04:39 PM   #57
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Default In any case I will quote myself

Russ
In any case I will quote myself:

"measuring Buffalo+IVY with EMU202 isn't good idea. EMU is not able to do anything in the range of that parts and the results will tel more about my power supply than the IVY. So it is technically possible but posting this kind of measurement in TP thread wouldn't be at list "wise". "

OK

Just was thinking about way of making my distortion measurements bit more reliable, without need of buying AP. I did checked AP web but I decided to save some money for second Buffalo and Legato, if TP will still be kind to sell to me.

So

I have a look at Lundahl web page, there is LL1517 datasheat
http://lundahl.se/pdfs/datash/1517.pdf
and it is clearly stated that :
>>>>
Distortion (achieved with mixed feedback drive circuit, load 600 OHM.......... < 0.03 % @ 20 dBU, 30Hz
>>>>

Acording : http://www.sengpielaudio.com/calculator-thd.htm

0,03% is -70.4dB

Maybe that's why bas produced by trafos is so "big"; litle help from strong harmonics..??

30Hz (!!) is probably something like Worst Case Scenario.
Trafo THD depends on frequency so 30Hz THD is not the same as 1kHz THD.

But again this is the number with special Opamp based (!!!) mixed feedback(!!) circuit.

See: "mixed feedback drive circuit":
http://lundahl.se/pdfs/papers/feedbck.pdf

What is the real THD “number” will depend on trafo working conditions like input and output impedance and measured frequency, so I'm afraid “single number” THD is no go.

But we probably can agree /If there was any dispute on this/ that THD at trafo output is not the same as Sabre output and not even close to -108dB ( 0.0003981 % ).

I wouldn't like to sound like somebody that fights trafos, it is oposite.
I'm just trying to find the best possible way of connecting this two, with just lite bit of "know-how".

Russ
If You would be kind enough and have a look at the “mixed feedback circuit” from Lundahl web and post any comments about possibility of adapting this kind of circuit to be used with Buffalo, this could be very interesting.


All the best
Rosendorfer
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Old 6th May 2010, 01:17 PM   #58
io is offline io  Hungary
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Rosendorfer

best
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Old 7th May 2010, 06:40 AM   #59
io is offline io  Hungary
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I'm sorry, primary resistance, 100 ohms Delete
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Old 7th May 2010, 04:46 PM   #60
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Pleas repost the drawing with the correct values?

Thanks

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I'm sorry, primary resistance, 100 ohms Delete
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