Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Digital Line Level DACs, Digital Crossovers, Equalizers, etc.

NOS dac, 15KHz wave test Strange results
NOS dac, 15KHz wave test Strange results
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 25th September 2016, 03:56 AM   #1
erez1012 is offline erez1012
diyAudio Member
 
Join Date: Dec 2009
Default NOS dac, 15KHz wave test Strange results

hi
for year i use the ad1865 DAC, i build fine PS and i use current output.
decide to do some test with my new spectrum analyzer:

for 1KHz wave, the results are fine for NOS DAC (i think), but when i try 15KHz i get another frequency at 1.2KHz and 200Hz

i think of Nyquist, because for 44KHz sample, 20khz look like rectangular, so maybe 15hkz look close?

thanks
Attached Images
File Type: png image (1).png (161.1 KB, 178 views)
File Type: png image (2).png (172.7 KB, 175 views)
File Type: png image (3).png (188.7 KB, 172 views)
File Type: png image.png (190.3 KB, 170 views)
  Reply With Quote
Old 25th September 2016, 04:19 AM   #2
abraxalito is offline abraxalito  United Kingdom
diyAudio Member
 
abraxalito's Avatar
 
Join Date: Sep 2007
Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
Send a message via Yahoo to abraxalito
You're not filtering out the image frequencies so you may well be seeing aliasing artifacts from your analyser. The zero-order hold attenuates the images of 1kHz to a much greater extent than 15kHz.
__________________
I know you think you understand what you thought I said but I'm not sure you realize that what you heard is not what I meant - Alan Greenspan
  Reply With Quote
Old 25th September 2016, 06:48 AM   #3
erez1012 is offline erez1012
diyAudio Member
 
Join Date: Dec 2009
"You're not filtering out the image frequencies " you are right.
just to clear things: as i remember perfect 15Khz pulse not have aliasing in the audio BW, only 22KHz >>. but here the alising is from the 15KHz 2nd harmonic?

the solution for this is 2.2nf in parallel to R I/V ?

thanks
  Reply With Quote
Old 25th September 2016, 02:37 PM   #4
abraxalito is offline abraxalito  United Kingdom
diyAudio Member
 
abraxalito's Avatar
 
Join Date: Sep 2007
Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
Send a message via Yahoo to abraxalito
A first order filter will be of help, but only barely. I can only guess that your I/V resistor will be of the order of 1k so in parallel with 2n2 this'll give a corner frequency of 72kHz. So the first set of images (below 44k1) won't be affected at all.

There will be very little harmonic distortion as compared to the presence of image products.
__________________
I know you think you understand what you thought I said but I'm not sure you realize that what you heard is not what I meant - Alan Greenspan
  Reply With Quote
Old 25th September 2016, 04:20 PM   #5
erez1012 is offline erez1012
diyAudio Member
 
Join Date: Dec 2009
Quote:
Originally Posted by abraxalito View Post
A first order filter will be of help, but only barely. I can only guess that your I/V resistor will be of the order of 1k so in parallel with 2n2 this'll give a corner frequency of 72kHz. So the first set of images (below 44k1) won't be affected at all.

There will be very little harmonic distortion as compared to the presence of image products.
50 ohm R i/v
i add 40nf cap, help little bit, now the SNR in 1Khz is 60DB.
also the 10khz sin wave not look good, maybe its the sample rate?

so everyone live with the noise in high frequency? i dont see many in the NOS community that talk about that, maybe that’s the whey the DAC works.

thanks
  Reply With Quote
Old 25th September 2016, 06:58 PM   #6
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
If you don't filter the images away then they will be present; the level depends on frequency. NOS people either don't know this, or don't worry about it. If images are present then some test equipment may be confused, or the equipment user may be confused.
  Reply With Quote
Old 25th September 2016, 11:37 PM   #7
abraxalito is offline abraxalito  United Kingdom
diyAudio Member
 
abraxalito's Avatar
 
Join Date: Sep 2007
Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
Send a message via Yahoo to abraxalito
Quote:
Originally Posted by erez1012 View Post
50 ohm R i/v
i add 40nf cap, help little bit, now the SNR in 1Khz is 60DB.
With 42nF and 50ohm your corner frequency is 76kHz. Still inadequate to make an impression on the strongest image frequencies.

Quote:
also the 10khz sin wave not look good, maybe its the sample rate?
If you want your DAC's output to look good on the 'scope, consider a much sharper filter. I have several examples on my blog using inductors and capacitors.

Quote:
so everyone live with the noise in high frequency? i dont see many in the NOS community that talk about that, maybe thatís the whey the DAC works.
Pretty much all the NOS guys don't much care about the images, you're correct. Some even think that having 'perfect' squarewave pictures on the scope is a bonus point for NOS. I'd put this down to groupthink myself.
__________________
I know you think you understand what you thought I said but I'm not sure you realize that what you heard is not what I meant - Alan Greenspan
  Reply With Quote
Old 26th September 2016, 07:14 AM   #8
erez1012 is offline erez1012
diyAudio Member
 
Join Date: Dec 2009
Quote:
Originally Posted by DF96 View Post
If you don't filter the images away then they will be present; the level depends on frequency. NOS people either don't know this, or don't worry about it. If images are present then some test equipment may be confused, or the equipment user may be confused.
now im confuse, alising happen when we sample more then 2*f of fsample.
only the spectrum sample here.

the DAC receive PCM not more than 20KHz. (i think)

when i send 15KHz PCM to the DAC its play 15KHZ wave, in the F-domain it has 30K and 45K component etc. so this issue its only the spectrum sample rate?

investigate the noise in the circuit i learn more thing, the SPDIF with fine transformer make noise too in the audio domain ( or its alising too

so the solution its not on the DAC? the LPF need Should be kept at the probe entrance always?
  Reply With Quote
Old 26th September 2016, 07:46 AM   #9
erez1012 is offline erez1012
diyAudio Member
 
Join Date: Dec 2009
spectrum spec
Attached Images
File Type: png Capture.PNG (173.8 KB, 95 views)
  Reply With Quote
Old 26th September 2016, 10:07 AM   #10
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Quote:
Originally Posted by erez1012
now im confuse, alising happen when we sample more then 2*f of fsample.
only the spectrum sample here.
Yes, you are confused. You are confusing aliasing (happens if the low pass filter before the ADC is inadequate or missing) with imaging (happens if the low pass filter after the DAC is inadequate or missing). A common mistake. Filterless NOS DACs suffer from imaging. Aliasing, if present, happens at the recording or mastering stage so is outside your control.
  Reply With Quote

Reply


NOS dac, 15KHz wave test Strange resultsHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Blind DAC Public Listening Test Results RocketScientist Digital Line Level 168 15th March 2016 05:40 AM
LIMP strange results. Jonhny Subwoofers 5 22nd May 2014 10:24 PM
Strange transformer test results jerluwoo Solid State 7 14th May 2014 12:48 PM
dcx2496 strange results george a Digital Line Level 2 28th May 2005 03:01 AM
3Khz/3.15Khz Test LP WANTED GUILHERME Swap Meet 6 19th May 2004 10:05 AM


New To Site? Need Help?

All times are GMT. The time now is 01:30 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki