John Curl's Blowtorch preamplifier part II - Page 3406 - diyAudio
Go Back   Home > Forums > Member Areas > The Lounge

The Lounge A place to talk about almost anything but politics and religion.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 2nd February 2013, 05:35 AM   #34051
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Quote:
Originally Posted by BV View Post
2SY
. No one presented (or I can not find anything..)better , measured results for realistic conditions - gain different (lower) than 0dB, about -20-30dB, what is the most used region in real use.
There you go! This needs to be done on every digital product, system and interface. S.O.P. No more thd and FFT numbers at 0 only, please... It is Very misleading. Thx-RNMarsh
  Reply With Quote
Old 2nd February 2013, 05:53 AM   #34052
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
Correct. Links to audio magazine tests are useless. No one knows at what volume settings they were performed. The level is controlled in the AP, not by volume control.
__________________
Pavel Macura
http://web.telecom.cz/macura/audiopage.html
  Reply With Quote
Old 2nd February 2013, 05:57 AM   #34053
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
I vote for manual rotary stepped attenuator or relay resistor network. And blue Alps 10k is also sonically better than any PGA.
__________________
Pavel Macura
http://web.telecom.cz/macura/audiopage.html
  Reply With Quote
Old 2nd February 2013, 07:09 AM   #34054
diyAudio Member
 
Esperado's Avatar
 
Join Date: Jul 2011
Location: France
Quote:
Originally Posted by BV View Post
this is very "primitive" task .
What was the previous stage and the following one ? No cap as a charge, like a cable ? No Caps in the signal path ? Separate grounds for command and signal ? Symmetrical or not ?
I bought a kit to evaluate, and i had to modify-it on several points to get it nice.
From Stereophile (ClasséCP-800 D:A preamplifier):
The volume control is implemented with two two-channel Burr-Brown PGA2310 programmable-gain chips, one per channel used as a differential volume control.
Tonally, the CP-800 fell into the camp of the clean and clear rather than the mellow and euphonically colored. In that respect it was somewhat similar to the Parasound Halo JC 2 ($4000), which I reviewed in March 2008: A wealth of recorded detail was laid bare without being spotlit. In level-matched comparisons with the Ayre Acoustics K-5xeMP ($3500; I reviewed it in June 2011), the Ayre sounded slightly veiled, though there was a robustness to its soundstaging that resulted in more fully fleshed-out images within that soundstage.
__________________
Ultimate Protection and more.The Only Source of Knowledge is experience, everything else is just information” ©A. Einstein

Last edited by Esperado; 2nd February 2013 at 07:12 AM.
  Reply With Quote
Old 2nd February 2013, 07:21 AM   #34055
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
He knows what he is doing, we have known each other for 10 years. No stupid mistakes. And remember that he measures distortion in front of and behind PGA and values differ in 2 orders (behind PGA it is 100x higher).

And please do not quote audiophile magazines impressions, they are useless.
__________________
Pavel Macura
http://web.telecom.cz/macura/audiopage.html

Last edited by PMA; 2nd February 2013 at 07:34 AM.
  Reply With Quote
Old 2nd February 2013, 07:22 AM   #34056
BV is offline BV  Slovakia
diyAudio Member
 
Join Date: Sep 2005
Location: Trnava, Slovakia
, Classé CP-800 D/A preamplifier Measurements | Stereophile.com , pictures 6 to 9..and 14
As i wrote, previous stage was buffer (OA with gain1) and series resistor 33R, distortion at this pont was 2 orders lower than at output. Output was also buffered with OA (LM4562) distortion figures at input/output the same..Grounds separated, conected according recomendations in one point (a "must" condition). Unbalanced in/out conection.

Last edited by BV; 2nd February 2013 at 07:30 AM.
  Reply With Quote
Old 2nd February 2013, 07:34 AM   #34057
diyAudio Member
 
Esperado's Avatar
 
Join Date: Jul 2011
Location: France
Quote:
Originally Posted by PMA View Post
He knows what he is doing, we have know each other for 10 years. No stupid mistakes. And remember that he measures distortion in front of and behind PGA and values differ in 2 orders (behind PGA it is 100x higher).
And please do not quote audiophile magazines impressions, they are useless.
I was amused by the reference to JC2. This said, their measurements (note the levels)
Mark Levinson No.38S preamplifier Measurements | Stereophile.com
__________________
Ultimate Protection and more.The Only Source of Knowledge is experience, everything else is just information” ©A. Einstein
  Reply With Quote
Old 2nd February 2013, 07:42 AM   #34058
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
Pretty poor this Classé, right?

Click the image to open in full size.

(volume = -10")
__________________
Pavel Macura
http://web.telecom.cz/macura/audiopage.html
  Reply With Quote
Old 2nd February 2013, 08:14 AM   #34059
diyAudio Member
 
Esperado's Avatar
 
Join Date: Jul 2011
Location: France
Mark Levinson No.38S preamplifier Measurements | Stereophile.com measurements are not at 0dB of the volume level.

About measured distortions of the Classé:
"Although the level of distortion with a full-scale digital input signal was low in absolute terms, it was higher than I expected, the third harmonic lying at –77dB, or 0.014% (fig.6). Reducing the output level by 10dB with the volume control preserved the level of the third and other harmonics (fig.7), whereas reducing the level of the signal data by the same 10dB dropped the third harmonic to –87dB, or 0.005% (fig.8). This suggests that the slight nonlinearity occurs in the D/A conversion circuitry ahead of the volume control.,"

Note that they made measurements at various volume control positions, and the distortion DECREASE with attenuation and levels (as expected and opposite to your remarks).
[edit] Not so sure about their analysis, may-be the switches are the responsible, but at least HD ratio does not increase.

Really, there is something strange in this story: two people, knowing each other, and feeling the same (BAD) about those volume controls, while so many people are satisfied with them, and prestigious manufacturers use them in some of their high end products.
Kind of -120dB distortion syndrome ?

Of course, we all agree a passive stepped attenuator is better, and, as i'm not paid to promote any Ci, i will stop here.
__________________
Ultimate Protection and more.The Only Source of Knowledge is experience, everything else is just information” ©A. Einstein

Last edited by Esperado; 2nd February 2013 at 08:24 AM.
  Reply With Quote
Old 2nd February 2013, 08:19 AM   #34060
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
I am not here to argue, I have read the review and I am able to make my own conclusions. The results of Classé preamp with PGA2310 are very poor and are similar to BV's measurement (-75dB of 2nd in both cases at certain volume setting).
__________________
Pavel Macura
http://web.telecom.cz/macura/audiopage.html
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 07:36 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2