John Curl's Blowtorch preamplifier part II - Page 3416 - 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 4th February 2013, 03:10 PM   #34151
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Few mfr will give thd spec below 0 dB. And, spec which only give an A weighted number is clearly suspect to begin with. No calc should be made with A weighted number as a beginning point.

As designers, we owe it to ourselves to measure against the claims under conditions of actual use. As a minimum, that would require thd at realistic levels... -20-30 db below max and it isnt asking too much to expect to have clean signal levels-30 below that level... Or -60dB. This should be done as S.O.P. here before debating. Using marketing numbers and conditions as a basis for arguement is foolish and misleading.

Thx-RNMarsh
  Reply With Quote
Old 4th February 2013, 03:49 PM   #34152
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
Quote:
Originally Posted by RNMarsh View Post
Few mfr will give thd spec below 0 dB. And, spec which only give an A weighted number is clearly suspect to begin with. No calc should be made with A weighted number as a beginning point.

As designers, we owe it to ourselves to measure against the claims under conditions of actual use. As a minimum, that would require thd at realistic levels... -20-30 db below max and it isnt asking too much to expect to have clean signal levels-30 below that level... Or -60dB. This should be done as S.O.P. here before debating. Using marketing numbers and conditions as a basis for arguement is foolish and misleading.

Thx-RNMarsh
For the reasons you have just described, I built a measuring amplifier with gain 40dB to be able to measure noise level of preamplifiers and make FFT analysis (noise level which is normally below common audio measuring system threshold) and to be able to measure at low output level. My SW computes unweighted integral noise in 20Hz - 20kHz band, so no tricky "noise bottom" like -150dB etc, which depends on bin width (number of samples in FFT, sampling frequency and possibly averaging as well). Noise of the measuring amp is attached. So I amplify the preamp output by 40dB, measure noise and ten subtract -40dB to get preamp's noise. I also measure distortion, at about 10 - 20mVrms of preamp output voltage. I have not measured any increase of harmonic distortion at low signal output level, but found differeces in noise of preamplifiers and its spectra.

With this method, I can measure noise level down to -126dB/ref 1Vrms (20Hz - 20kHz, unweighted). The best preamp I measured had noise -115dB/1Vrms unweighted, 20Hz - 20kHz. The gain of that preamp was 14dB.
Attached Images
File Type: png meas_amp40.PNG (59.1 KB, 153 views)
__________________
Pavel Macura
http://web.telecom.cz/macura/audiopage.html

Last edited by PMA; 4th February 2013 at 03:51 PM.
  Reply With Quote
Old 4th February 2013, 04:00 PM   #34153
a.wayne is offline a.wayne  United States
Sin Bin
 
Join Date: May 2008
Location: Front Row Center
Quote:
Originally Posted by jan.didden View Post
Indeed, analog volume control also worsens the S/N ratio (except maybe when you use a 1kW pot immediately before the speaker).
Taking a whitepaper from an analog volume control manufacturer as proof that digital is 'bad' - I don't know

jan
As oppose to white paper from digital manufacturer ...
  Reply With Quote
Old 4th February 2013, 04:29 PM   #34154
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Quote:
Originally Posted by a.wayne View Post
As oppose to white paper from digital manufacturer ...
Quite. Whitepapers are marketing instruments, whether from 'digital' or 'analog' manufacturers. You see the same trend in data sheets. You're not supposed to lie in data sheets, but nothing prevents you to emphasize the strong points and do the measurements at favourable conditions.

jan
__________________
If you don't change your beliefs, your life will be like this forever. Is that good news? - W. S. Maugham
Check out Linear Audio!
  Reply With Quote
Old 4th February 2013, 04:43 PM   #34155
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
One has to make his own measurements. Whitepapers do not help, I agree. Whitepaper is not the same as scientific paper.
__________________
Pavel Macura
http://web.telecom.cz/macura/audiopage.html
  Reply With Quote
Old 4th February 2013, 04:48 PM   #34156
diyAudio Member
 
Esperado's Avatar
 
Join Date: Jul 2011
Location: France
Quote:
Originally Posted by elektroj View Post
And what are you going to do about the front end due to fact that modulator runs off of a single +5V supply? Coupling caps?
OPA with offset.

I don't understand the matter of all this discussion about evil digital calculations.
As long as the errors (rounding) are under the noise floor, (that you can't hear) what the matter ?
With 32 bits, you can attenuate by 60db without any audible artifacts. What the hell ?
Don't you think that analog distortion+noise is not an error as well ?
__________________
Ultimate Protection and more.The Only Source of Knowledge is experience, everything else is just information” ©A. Einstein
  Reply With Quote
Old 4th February 2013, 05:02 PM   #34157
diyAudio Member
 
Kindhornman's Avatar
 
Join Date: Aug 2012
Location: Los Angeles, California
I think we would have to bring Scott into the discussion about data sheets but I don't completely agree with the disregard to a data sheet or white paper. If we did not have at least this basic information we would be completely in the dark about so many products. We need to start somewhere and the data sheets and white papers at least give us a basis to start our selection process. If you had neither of these what would you have to do, inspect and test every single device against every other device before you could even start to conceive of a design? Yes you will need to test and confirm the information, but you do need something to at least weed out the devices that the data sheets will at least tell you are inappropriate. From there of course you need to do your do diligence to make final selections.
  Reply With Quote
Old 4th February 2013, 05:22 PM   #34158
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Quote:
Originally Posted by PMA View Post
One has to make his own measurements. Whitepapers do not help, I agree. Whitepaper is not the same as scientific paper.
They do help, you can learn all kinds of interesting things from whitepapers. As an on-topic example, there was a Cirrus whitepaper on the Jeff Rowland site discussing the design of their CS3308-family of analog volume controllers. I found it facsinating how they contour the shape of the substrate underneath the cmos ladder switches to cancel the voltage coefficient, so they can get to 0.000xx % THD of the control.
That doesn't proof it is better than any other volume control, but it is an interesting insight.

Edit: it was the resistors that were linearised, not the switches.
Also, they switch the comp cap with gain changes.
See http://jeffrowlandgroup.com/kb/categ...categoryid=147

jan
__________________
If you don't change your beliefs, your life will be like this forever. Is that good news? - W. S. Maugham
Check out Linear Audio!

Last edited by jan.didden; 4th February 2013 at 05:31 PM.
  Reply With Quote
Old 4th February 2013, 05:23 PM   #34159
diyAudio Member
 
Esperado's Avatar
 
Join Date: Jul 2011
Location: France
If your system is able to produce 120dB spl (no need for more pain), and, considering that 30dB spl is the noise floor of your quiet listening room, 60dB is the max attenuation range needed for a full volume control.
That is the reason why CD used 16bits of definition (96dB). And, as far i'm concerned, it is enough.
With 24bits, you keep 48dB of margin for a attenuation (witch will be enough for HIFI listening at a correct level). Then, you can set an analog 30db attenuator to bring the max at your comfortable listening position and keep a huge margin of definition..
With 32bits, you have 192 dB of dynamic. it let -you 96dB of margin for the level attenuation...hum.
__________________
Ultimate Protection and more.The Only Source of Knowledge is experience, everything else is just information” ©A. Einstein
  Reply With Quote
Old 4th February 2013, 05:24 PM   #34160
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
Yes, you may rely on AD opamp datasheets.
__________________
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 02:09 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