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

QuantAsylum QA400 and QA401
QuantAsylum QA400 and QA401
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 2019, 07:53 PM   #2551
QAMAtt is offline QAMAtt
diyAudio Member
 
Join Date: Nov 2017
Location: Seattle, WA, USA
Quote:
Originally Posted by agdr View Post
Interesting you found/solved Jen's jitter discovery in the FPGA.
Yes, that bug report led to another side benefit too. There's an experimental mode on the QA400/QA401 that was released in 2013 or 2014 called "melt noise" based on an AKM paper Demian had sent long ago regarding using N converters to acquire a signal. Every time you double the number of converters used, your noise drops by 3 dB. In the paper they paralleled 8 converters.

The melt noise feature acquires the signal N times. And since the box has precise control of the samples going out and coming in, they are precisely lined up. And if you do 8 acquisitions, that's the same as having 8 converters. The N acquisitions are precise in time alignment, and then they are averaged in the time domain (squashing the noise) and then the FFT of that average is displayed.

And eventually, THD should equal THD+N because you've melted all the noise away. But it never quite got as close as expected and I couldn't understand why. But this was due to the jitter. And once the +1/-0 sample jitter issue got fixed, then it started to better match the simulations.

Below you see loopback in the experimental mode with "melt noise" turned on. MeltNoise2 needs several more minutes to run to match the THD (and it's already been running for several minutes). MeltNoise1 has already converged and you see the THD and THD+N are very close.

PS. To turn on the experimental menu, just place a file in the QA400 or QA401 data directory called "experimental" (no extension) and the menu will appear on next re-launch of the app. Melt only works on the left channel.

PPS. AKM published the technique to explain how to extend the dynamic range of a converter. It's primarily useful if you are looking to find harmonics in what you are measuring that might be below the noise floor of the converter. But as you can see, a lot of tones get uncovered that are likely sigma delta idle tones from either the DAC or ADC. Thus, the ultimate utility of the mode is limited IMO. Though still interesting. That's why it's buried in the experimental menu.
Attached Images
File Type: jpg MeltNoise1.jpg (254.2 KB, 507 views)
File Type: jpg meltnoise2.jpg (248.3 KB, 512 views)
__________________
www.QuantAsylum.com

Last edited by QAMAtt; 2nd February 2019 at 08:05 PM. Reason: Added PPS
  Reply With Quote
Old 3rd February 2019, 01:41 AM   #2552
agdr is offline agdr  United States
diyAudio Member
 
agdr's Avatar
 
Join Date: Sep 2010
QuantAsylum QA400 and QA401
Quote:
Originally Posted by QAMAtt View Post
Yes, that bug report led to another side benefit too.
Oops - I see a typo on my part - should be " Jens' ". Sorry Jens!

Ah very interesting about the experimental parallel conversion mode. I think that I can see that, in general. I know that paralleled op amps (with output current balancing resistors), used for higher headphone amplifier output current, increase S/N since the op-amp noise is uncorrelated.

In this case am I understanding correctly that essentially the effect would be paralleled uncorrelated converters? Here is a paper:

Correlation of Signals, Noise, and Harmonics in Parallel Analog-to-Digital Converter Arrays

Except instead of paralleled converters just the single converter taking multiple uncorrelated samples? Or maybe they would be considered correlated since the time intervals are known?

Cool that the jitter fixed made the "melt noise" math work! Impressive it converged within -0.8 dB of the THD. Love it when fixing one thing solves some other lingering issue in anything I'm working on.

Hey a question I've been meaning to ask. For measuring power supply noise (page 49 of the QA401 manual) I understand the resistive divider to keep the QA401 input DC below 5V (I'm measuring a 12Vdc switching wall wart in this case). I read more than 5V would turn on some protection diodes. Just wondering if you could share a bit more of what is going on there, since the inputs are capacitively coupled? The protection diodes must be between the inputs and coupling caps. Are the caps rated at 5Vdc? Would be especially nice if it were possible to hook higher DC voltages to the QA 401 input since >5Vdc is a real "accidental" possibility with headphone amps. The rails are typically +/- 12 Vdc or +/15 Vdc. if something internally goes wrong (DIY issues or part failure) the output can hit the positive or negative supply rail. There are 2 or 3 failure modes with the O2 headamp which can cause that to happen.

Last edited by agdr; 3rd February 2019 at 01:54 AM.
  Reply With Quote
Old 3rd February 2019, 05:40 AM   #2553
agdr is offline agdr  United States
diyAudio Member
 
agdr's Avatar
 
Join Date: Sep 2010
QuantAsylum QA400 and QA401
Default May have figured it out (QA401 5V DC input limit)

Matt ...thinking about it some more (I haven't looked at the QA401 circuitry) I think I may have figured it out (DC 5V input limit). There is probably a resistor to ground between the coupling cap and op-amp input(s) on the QA401 for op-amp input bias current ground sink/source. Since the coupling cap is initially a short at t0+ with charging current, the full applied front panel input voltage (AC and DC) would exist across that resistor for an instant, and hence at the op-amp input for an instant.

So the 5V clamp diode may have gone across that resistor to protect the op-amp input. Which works, but with repeated clamps, and/or high(er) voltage clamping, the diode might degrade?

Also the QA401 attenuator - the manual seems to indicate it won't help with the DC input issue, so must be an AC attenuator only?

What I really should do with the headphone amp testing, if I think there might be a DC output issue (sketchy unit), is use a 3/4 / 1/4 resistive divider on the QA 401 input (like the QA 401 manual page 49 mentions). So even if the headamp outputs +/-15Vdc at some point, the max going into the QA401 would be 15Vdc * 0.25 = 3.75. Although the resistive divider, the series resistor part anyway, will introduce a little bit of thermal noise.

Thanks for the help and information!

Last edited by agdr; 3rd February 2019 at 05:52 AM.
  Reply With Quote
Old 3rd February 2019, 02:06 PM   #2554
edechamps is offline edechamps  United Kingdom
diyAudio Member
 
Join Date: Sep 2013
Location: London, United Kingdom
Quote:
Originally Posted by edechamps View Post
I have created entries in the ASIO401 issue tracker to act as my to-do list and so that people are aware of these issues: channel swap issue and polarity reversal issue. I'll try to take a look at them over the next few days.
These issues are fixed in ASIO401 1.1. Starting from that version, ASIO401 sticks with the convention that a positive sample value represents a positive voltage on the + terminal.
  Reply With Quote
Old 3rd February 2019, 10:47 PM   #2555
agdr is offline agdr  United States
diyAudio Member
 
agdr's Avatar
 
Join Date: Sep 2010
QuantAsylum QA400 and QA401
Default "read the manual" :)

Matt - I found my answer about the DC input specifics on pg 9 of the User Manual just now. No need to post a reply to the above, but PM sent here in a minute.
  Reply With Quote
Old 4th February 2019, 02:56 PM   #2556
FdW is offline FdW  Netherlands
diyAudio Member
 
FdW's Avatar
 
Join Date: Feb 2009
Location: Both feet on the ground (near Gouda)
QuantAsylum QA400 and QA401
Quote:
Originally Posted by QAMAtt View Post
The QA400 is a very different animal. It uses the old Cypress USB stack, which had some serious problems for us once MSFT moved to Windows 1803 (A Win10 release about a year ago). At that time, we moved the QA401 to the WinUSB stack, which has been rock solid and a great move even though the migration was painful at the time.

-Matt
The USB issue was an oversight on my part sorry (what good is 40 years+ of IT experience?). So, actually, I'm better of switching to QA401.
  Reply With Quote
Old 8th February 2019, 02:09 AM   #2557
QAMAtt is offline QAMAtt
diyAudio Member
 
Join Date: Nov 2017
Location: Seattle, WA, USA
Some experiments in replacing the input/output OPA1612 bipolar opamps in the QA401 with some new OPA2156 CMOS opamps. I'd not recommend doing it without a lot more study. And there are some very easy pre-amps you can make if you want to measure high Z things. But this is an important opamp in the evolution of opamps.

OPA2156: HiFi in CMOS
__________________
www.QuantAsylum.com
  Reply With Quote
Old 8th February 2019, 06:10 AM   #2558
chris719 is offline chris719  United States
diyAudio Member
 
Join Date: Jun 2004
Location: Connecticut
QuantAsylum QA400 and QA401
Nice article! Does the distortion rise significantly with the 10k source impedance compared to OPA1612?
  Reply With Quote
Old 9th February 2019, 03:53 AM   #2559
johnc124 is offline johnc124  United States
diyAudio Member
 
Join Date: Jan 2006
Location: Tucson, AZ
Quote:
Originally Posted by QAMAtt View Post
Some experiments in replacing the input/output OPA1612 bipolar opamps in the QA401 with some new OPA2156 CMOS opamps. I'd not recommend doing it without a lot more study. And there are some very easy pre-amps you can make if you want to measure high Z things. But this is an important opamp in the evolution of opamps.

OPA2156: HiFi in CMOS
This is an awesome article! It makes me really proud of all the hard work that went into making the OPA2156. Thank you for writing it.
__________________
General Manager - TI Linear Amplifiers Business Unit
OPA1637: New Fully-Differential Amplifier for Audio
  Reply With Quote
Old 9th February 2019, 01:07 PM   #2560
Bob Cordell is offline Bob Cordell  United States
diyAudio Member
 
Join Date: Sep 2006
Quote:
Originally Posted by QAMAtt View Post
Some experiments in replacing the input/output OPA1612 bipolar opamps in the QA401 with some new OPA2156 CMOS opamps. I'd not recommend doing it without a lot more study. And there are some very easy pre-amps you can make if you want to measure high Z things. But this is an important opamp in the evolution of opamps.

OPA2156: HiFi in CMOS
Thanks, Matt.

I was unaware of this CMOS op amp part. Your article about it is a real eye-opener. I would never have believed that a CMOS op amp could get down to 4 nV/rt Hz.

Cheers,
Bob
  Reply With Quote

Reply


QuantAsylum QA400 and QA401Hide 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
QuantAsylum 401 & 405 B&W_arthur Equipment & Tools 5 22nd March 2016 04:27 PM
QA190 and QA400 Gains sgtnoah Equipment & Tools 4 17th July 2015 03:46 AM
Question on QA400 Alan0354 Equipment & Tools 7 10th July 2015 06:34 PM
FS QuantAsylum QA400 audio analyser jan.didden Swap Meet 3 29th September 2014 05:10 PM
New Quantasylum QA190 Differential Input Probe stellavox Equipment & Tools 3 20th March 2014 06:06 PM


New To Site? Need Help?

All times are GMT. The time now is 06:35 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright ©1999-2020 diyAudio
Wiki