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 25th March 2013, 03:59 AM   #41
1audio is online now 1audio  United States
diyAudio Member
 
Join Date: Mar 2004
Location: SF Bay Area
Default QA400 plus interface

I have started making the cables to test the QA400 with the interface board. Making proper shielded BNC to minijack cables (cheap stereo to cheesy bnc's) really got the noise down. Here are a few measurements of the QA400 plus the interface in loopback.

The first is in loopback with the gain switches at unity (+6 dB for the output because of the X2 nature of the device) The external differential voltage is approx 1.2V

The second with both at X10 and the drive from the QA400 reduced. The external voltage is around 7V

The third is as the second but one side of the diff output is grounded.

The driver and the receiver get in trouble when the voltage goes above 7V RMS. I will rescale things around that limit.
__________________
Demian Martin
Product Design Services
  Reply With Quote
Old 25th March 2013, 09:25 AM   #42
jan.didden is online now jan.didden  Europe
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Westende Resort, BE coast
Looks very, very good Demian!
I'm relieved that the 40kHz BW limit isn't - I'd hate to be able to see only harmonics up to a 10kHz fundamental or so.
I guess the droop above 60 or 70kHz could be corrected with a cal file.

I also got from the section on plugins that there's an automatic generation of the measurement data in a text file which is great for publication purposes, though it isn't clear whether that also occurs with 'regular' measurements.

jan
__________________
Cable: a potential source of trouble interconnecting two other potential sources of trouble - Erik Margan
Linear Audio pubs and articles . The SilentSwitcher now at diyaudio store SilentSwitcher. Keeping in touch with SY.
  Reply With Quote
Old 26th March 2013, 04:09 AM   #43
RNMarsh is online now RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Quote:
Originally Posted by 1audio View Post
I have started making the cables to test the QA400 with the interface board. Making proper shielded BNC to minijack cables (cheap stereo to cheesy bnc's) really got the noise down. .

1. Grounding and shielding.

Grounding and shielding -- done.
check
  Reply With Quote
Old 26th March 2013, 04:41 AM   #44
1audio is online now 1audio  United States
diyAudio Member
 
Join Date: Mar 2004
Location: SF Bay Area
OK, now that it all works and works OK there are some limitations that need to be resolved.

Both the input and the output circuits get distressed when the signal exceeds 8V RMS, even with 17V supplies. Originally I was expecting to get 10V RMS at each point but its not happening. So how to scale?
Option 1 (Current) input divide by 10 or unity, output X16 or X6: problem, both have overload issues withing the operating range of the codec. I could add a resistive divider to correct for the X2 of the output driver and the output won't be clipped when driving a balanced load at 10V but does clip on unbalanced load at 8V.

Option 2, rescale and fix both the output and input to 7V max. Operating range will all be OK but input sensitivity is compromised and the output will need significant attenuation to be linear, however both the DAC and the ADC are better at a reduced level.

Option 3, Rescale output to 7V max, leave fixed. Two settings for the input, unity (1V approx) and -10 dB (3V approx?) or -16 dB (round number near 7 V)?

Making external attenuator cables for input and output is simple and expected to deal with power amplifiers, high gain inputs etc. I want to make it easy to use and hard to get it too wrong with odd gains and different gains that make the on screen arithmetic difficult.

Any suggestions?
__________________
Demian Martin
Product Design Services
  Reply With Quote
Old 27th March 2013, 01:46 AM   #45
RNMarsh is online now RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
#3 --- BUT Which option best preserves the S/N and dynamic range of the test system?


-Richard
  Reply With Quote
Old 27th March 2013, 02:59 AM   #46
1audio is online now 1audio  United States
diyAudio Member
 
Join Date: Mar 2004
Location: SF Bay Area
its more of an issue of the device under test. If its output is low that you need gain to get it in range of the input of the QA400. if its high (power amp) you need attenuation. Same for the output buffer. The issue is more one of what are you testing? if all I was doing was testing iPods and other mobile stuff (what consumer electronics has become) no gain is needed. To test a traditional preamp or connect to a higher output DAC the output of the DAC is much too high for the QA400.

And then there is the scale factor issue. Its relatively easy to add scaling factors in the software but you need to remember to do it and put the right values in.

Have you gotten your QA400 running?
__________________
Demian Martin
Product Design Services
  Reply With Quote
Old 27th March 2013, 10:15 AM   #47
jan.didden is online now jan.didden  Europe
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Westende Resort, BE coast
Demian how about the age-old 1-2-5 step sequence?
You'll need some more steps but you could go like 50-20-10-5-2-1 V/V

So you would have atten steps 1/50, 1/20, 1/10, then 1/5, 1/2 and 1/1.

For low level sources add gain steps x2 (0.5V/V) and x5 (0.2V/V).

Then you would have an overload capability on each range of some 40% say +3dB.

My unit is still in SF at the USPS sort centre :-(

jan
__________________
Cable: a potential source of trouble interconnecting two other potential sources of trouble - Erik Margan
Linear Audio pubs and articles . The SilentSwitcher now at diyaudio store SilentSwitcher. Keeping in touch with SY.
  Reply With Quote
Old 27th March 2013, 04:02 PM   #48
1audio is online now 1audio  United States
diyAudio Member
 
Join Date: Mar 2004
Location: SF Bay Area
I was trying to avoid adding the necessary protection stuff and its performance compromises. Not to mention the complexity.

If I fix the output at 7V I get on loopback .0002% THD so the extra gain is not compromising anything. (see below image)

For the input, sticking with the original concept, external probe cables with appropriate connections, a few cables can handle pretty much any input requirements. If I stick with the original X1 input gain and external divide by 10 "probe" would be able to handle pretty much any line level source. If its terminated in RCA or XLR connectors it becomes a complete solution (no more collection of adapters). A separate cable with a divide by 100 ratio and fully balanced could handle almost any power amp. Since the input is fully balanced and the external probes would also be balanced ground loops are not an issue nor are balanced output amps.



If time permits I'll finish a set of cables for this today and try it.

I have also added two pictures showing the "melt noise" feature. It really removes random noise and leaves the deterministic stuff. I suspect the remaining noise is the limits of the 24 bit system. The peak level is about -7.5 dBFS. The signal is scaled, the peak is just below 7V.
Attached Images
File Type: png QA400 + QA interface loopback at 7V ext bal div 10.png (36.0 KB, 851 views)
File Type: png loopback melt noise disabled 6.3V.png (33.5 KB, 843 views)
File Type: png loopback melt noise 6.3V.png (51.7 KB, 260 views)
__________________
Demian Martin
Product Design Services
  Reply With Quote
Old 27th March 2013, 05:48 PM   #49
RNMarsh is online now RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Quote:
Originally Posted by 1audio View Post
its more of an issue of the device under test. If its output is low that you need gain to get it in range of the input of the QA400. if its high (power amp) you need attenuation. Same for the output buffer. The issue is more one of what are you testing? if all I was doing was testing iPods and other mobile stuff (what consumer electronics has become) no gain is needed. To test a traditional preamp or connect to a higher output DAC the output of the DAC is much too high for the QA400.

And then there is the scale factor issue. Its relatively easy to add scaling factors in the software but you need to remember to do it and put the right values in.

Have you gotten your QA400 running?
My question was one to get you to suggest the answere... which i think you have done.

Most of us would be warry of damaging the front end of the FFt but warnings alone do not always prevent mistakes. I like what Keithley Instruments did on their 823 Nano-Volt amplifier... they put a 'protected' on- off switch on the front panel. can you do same?

Thx-RNMarsh
  Reply With Quote
Old 28th March 2013, 07:06 PM   #50
1audio is online now 1audio  United States
diyAudio Member
 
Join Date: Mar 2004
Location: SF Bay Area
Default QA400 measuring Jitter

Here is a jitter measurement using the QA400 Its not scaled the same as the plots on Stereophile, I need to figure that out. The essence is here anyway. The JTest generator is attached. I have not used it in a long time so I don't remember the details.

The jitter is a function of the amplitude of the sidebands of the 11.025 KHz signal. They are very obvious in this plot.
Attached Images
File Type: png Apogee Mini DAC jitter.png (43.8 KB, 414 views)
Attached Files
File Type: zip jitter3.zip (6.9 KB, 65 views)
__________________
Demian Martin
Product Design Services
  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 08:18 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki