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

Equipment & Tools From test equipment to hand tools

DIY Audio Analyzer with AK5397/AK5394A and AK4490
DIY Audio Analyzer with AK5397/AK5394A and AK4490
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 20th February 2018, 09:24 PM   #1941
modmix is offline modmix  Germany
diyAudio Member
 
Join Date: Nov 2006
DIY Audio Analyzer with AK5397/AK5394A and AK4490
You are quite likely true with respect to the 50Hz peaks.

What is the causing the strange flucations of the noise level at the right channel?

Ulli
  Reply With Quote
Old 21st February 2018, 04:31 AM   #1942
diyaudnut is offline diyaudnut  United States
diyAudio Member
 
Join Date: Feb 2015
Quote:
Originally Posted by mbrennwa View Post
Does that noise change if you play some test signal through the USB/DAC?

Also, how is the USB interfaced to the DAC? For example, some USB-to-I2S converters output an I2S signal as soon as they are connected to USB. If the DAC chip has some internal processing of the I2S data stream, you may see the residual noise of this processing. For example, the DDDAC does this, I believe.
That is a good pointer. The noise does seem to go away when i play a test tone.
Interface to the DAC is I2S (i use exau2i).
Thanks. Will post some more pictures. Hopefully not too out of topic. Using the RTX6001 i'm able to get a much better insight into the performance of the DAC compared to sound cards i was using earlier.
  Reply With Quote
Old 21st February 2018, 05:04 PM   #1943
zfe is offline zfe
diyAudio Member
 
Join Date: Dec 2014
I finally found a Windows (7) desktop PC for upgrading the firmware. First I had no success (with any of the USB2 ports). Then in a whim I connected an unpowered USB Hub connected the RTX 6001 to that and now it worked.

P.S.
Quote:
Originally Posted by zfe View Post
Yes -140dB is 0.1 ppb ...
Ups, I went to far in diminishing billions for the use in English.
-140dB is 10^-7 (for voltage like units) so 0.1 ppm or 100 ppb.
  Reply With Quote
Old 21st February 2018, 05:53 PM   #1944
zfe is offline zfe
diyAudio Member
 
Join Date: Dec 2014
The mains hum in unbalanced cabling is quite sensitive to the quality of the connection.

To visualize this I have made several measurements of an Soekris DAM DAC, playing a 1kHz -100dBV signal, from its raw output (unbalanced and unbuffered connected to the DAM's switched resistor ladder). The DAM is floating AC powered. The RTX6001 input is set to 0dBV.

The comments on "quality" refer to the mains hum.

First the recommended pseudo balanced connection (cabling no 17 of ...). The quality depends on the point to which you connect the separate ground line from the dedicated RTX terminal. The first is the best way I found, the second a worse point.
1 DAM 1k-100 0; No13-Cabel G-Chas1.jpeg2 DAM 1k-100 0; No13-Cabel G-CinchG.jpeg
All the following pictures are connections where the pin 1 and 3 of the input are shorted at the RTX side. One thing they have in common is the much better overall noise floor.

In this row all pictures are taken by using a commercial Netric XLR-BNC adapter, a BNC cable and a commercial no-name BNC-RCA adapter. The connector on the RCA side connected "easily", also the BNC cable connectors were perhaps not the best. As a result the quality depended much on where you pushed to the cable (from best to worst result )
3 DAM 1k-100 0; Adap, BNC AdapC 3.jpeg4 DAM 1k-100 0; Adap, BNC AdapC 2.jpeg5 DAM 1k-100 0; Adap, BNC AdapC 1.jpeg
With the commercial Netric XLR-BNC adapter, a no-name BNC-RCA(female) adapter and a good RCA cable whose connectors had firm contact, I slightly improved the best above result. And here pushing the cable had no more influence.
6 DAM 1k-100 0; Adapc, Cinch 1.jpeg
With a custom made XLR to RCA cable with good connectors, a reliable, and slightly better result was obtained.
7 DAM 1k-100 0; Adapc, XLR_cinch1.jpeg
With the same cable as above, by cleaning all connectors with contact spray the 50Hz peak can be reduced by further 5dB. The peak is now below the noise floor of the pseudo balanced cabling.
8 DAM 1k-100 0; Adapc, XLR_cinch Contact spray.jpg
  Reply With Quote
Old 21st February 2018, 06:14 PM   #1945
zfe is offline zfe
diyAudio Member
 
Join Date: Dec 2014
A discovery of some monkey testing is that the overflow indicator is not always working reliable. RTX out set to 0dBV. The signal played is the ARTA jitter test signal.

First with input set to 0dBV - a clean signal with -10dBFS peak.
Jittertest 0,0.jpeg
When I set the input to -10dBV the overflow indicator on the RTX lights and the measurement looks ugly - as expected.

With input set to -20dBV the overflow indicator is OFF and most of the time (long enough to make a good average) the measurement looks like that.
Jittertest 0,-20 average.jpeg
From time to time it jumps to that, but still no overflow indicated.
Jittertest 0,-20 jump.jpeg
  Reply With Quote
Old 21st February 2018, 06:50 PM   #1946
zfe is offline zfe
diyAudio Member
 
Join Date: Dec 2014
Some more monkey testing. The low level high frequency artefacts of some signals of the DAC section.
Output was set to 0dBV, input to -20dBV, the signal level is always -40dB.

First some sine signals (100Hz, 500Hz, 1kHz, 10kHz, 12kHz)
Sine 100Hz -40dB 0,-20 .jpegSine 500Hz -40dB 0,-20.jpegSine 1kHz -40dB 0,-20.jpegsine 10k -40dB 0,-20.jpegsine 12k -40dB 0,-20.jpeg
Two simultaneous sines of 10kHz and 11kHz
Twosine 10k 11k -40dB 0,-10.jpeg
A 1kHz triangle.
Triangle 1k -40dB 0,-20.jpeg
Well, the only conclusion up to now - better to reduce the signal strength by analog attenuation than digital, if the low level HF part really is of importance.

Last edited by zfe; 21st February 2018 at 06:56 PM.
  Reply With Quote
Old 21st February 2018, 08:39 PM   #1947
mbrennwa is offline mbrennwa  Switzerland
diyAudio Member
 
mbrennwa's Avatar
 
Join Date: Mar 2005
Location: Zurich, Switzerland
Quote:
Originally Posted by zfe View Post
First the recommended pseudo balanced connection (cabling no 17 of ...)...

...the following pictures are connections where the pin 1 and 3 of the input are shorted at the RTX side. One thing they have in common is the much better overall noise floor.
I would've expected it the other way round. Why is the noise floor lower with the single ended connection?

Quote:
Originally Posted by zfe View Post
by cleaning all connectors with contact spray the 50Hz peak can be reduced by further 5dB. The peak is now below the noise floor of the pseudo balanced cabling.
Is it really the contact spray that does the trick? Or is it just the repeated make-and-break of the connection that cleans the connectors?
__________________
[ audioroot.net | hifibau.ch ]
  Reply With Quote
Old 22nd February 2018, 02:43 AM   #1948
DualTriode is offline DualTriode  United States
diyAudio Member
 
Join Date: Aug 2009
Location: Sacramento
Quote:
Originally Posted by mbrennwa View Post
I would've expected it the other way round. Why is the noise floor lower with the single ended connection?


This stuff is all over the page because noting is calibrated.

The reason the single end has "lower noise" is because it is half the voltage of balanced, (-6dB) less voltage.

Recommendation: start from something solid and build from something solid, something repeatable and build from there.

DT
  Reply With Quote
Old 22nd February 2018, 07:12 AM   #1949
zfe is offline zfe
diyAudio Member
 
Join Date: Dec 2014
Quote:
Originally Posted by mbrennwa View Post
I would've expected it the other way round. Why is the noise floor lower with the single ended connection?
Well, the source is single ended, so there is no "true" balanced connection. The different setups differ in at which point (at the source or analyzer side) and how "ground" is connected to the negative differential input.
As the RTX6001 dedicated ground terminal is "only" screwed to the front plate and probably the source's best ground terminal is its RCA connector, maybe the direct unbalanced connection is here just the better grounds connection.
But I am also a bit surprised that even the not so good "unbalanced" connections show consistently an other quality of the ground floor.


Quote:
Originally Posted by mbrennwa View Post
Is it really the contact spray that does the trick? Or is it just the repeated make-and-break of the connection that cleans the connectors?
No repeated make-and-break had only a slight effect, but gave me the hint that I should thoroughly clean the connectors. Especially the RCA-outputs of the DAC had already been in use for several years.
  Reply With Quote
Old 22nd February 2018, 08:51 AM   #1950
mbrennwa is offline mbrennwa  Switzerland
diyAudio Member
 
mbrennwa's Avatar
 
Join Date: Mar 2005
Location: Zurich, Switzerland
Quote:
Originally Posted by DualTriode View Post
This stuff is all over the page because noting is calibrated.
How do you know? The signal source was "an Soekris DAM DAC, playing a 1kHz -100dBV signal", and the 1 kHz peak always shows up at the same amplitude in the plots. That made me think that the 6 dB difference between balanced and single ended was compensated by the calibration in the software according to the different ways the RTX input was used in these tests.

I have only now realised that the levels shown in the plots are in dBFS, not in dBV. So the data were not calibrated in absolute terms, which isn't great.

Everyone: CALIBRATE YOUR DATA IN A MEANINGFUL WAY!!! PLEASE!!!

Quote:
Originally Posted by DualTriode View Post
The reason the single end has "lower noise" is because it is half the voltage of balanced, (-6dB) less voltage.
That explanation would work if the calibration would not account for the 6 dB difference between the balanced / single ended tests. But again, the test signal shows up a the same level in all tests, so I thought the software compensated for this difference somehow.

zfe:
  • How did you calibrate the data in these tests?
  • Can you provide absolute levels (in Volts or dBV, for example)?
__________________
[ audioroot.net | hifibau.ch ]
  Reply With Quote

Reply


DIY Audio Analyzer with AK5397/AK5394A and AK4490Hide 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
New AKM Stereo ADC AK5397 announced JensH Digital Source 20 24th December 2014 12:05 PM
New AKM Stereo ADC AK5397 ??? HpW Equipment & Tools 6 16th May 2014 04:26 PM
NTi Audio XL2 Handheld Audio Analyzer Fredenando Equipment & Tools 0 18th April 2010 03:04 AM
AKM AK5394a TobWen Digital Source 41 31st December 2003 06:18 PM


New To Site? Need Help?

All times are GMT. The time now is 08:39 PM.


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