I'm sure there are better ones.
This thread:
http://www.diyaudio.com/forums/solid-state/137843-issues-emu-tracker-thd-measurments-3.html
good if you want to get an idea about the tracker pre and 0404 interfaces, which are almost the same device. Look for posts by member Fotios, who seems to have had extensive experience with it.
Some Progress
Shielding, grounding and part swapping has actually improved things.
I shielded the both the top and the bottom of the plastic enclosure, grounded the switch, removed the "Zero Adjust" parts, converted to THAT balanced receivers and drivers, and finally used a LME 49720 in place of the OPA2134.
Life is good now. Have a look.
It is the same setup that I used before: the blue
Shielding, grounding and part swapping has actually improved things.
I shielded the both the top and the bottom of the plastic enclosure, grounded the switch, removed the "Zero Adjust" parts, converted to THAT balanced receivers and drivers, and finally used a LME 49720 in place of the OPA2134.
Life is good now. Have a look.
It is the same setup that I used before: the blue
channel is a Lynx Aurora 16 analog output connected directly to its input - the red
channel takes the signal through the Pete's Sound Card Interface.
There is just a trace of some power supply harmonics left, and the third harmonic of the input signal at close to -112dB.
There is just a trace of some power supply harmonics left, and the third harmonic of the input signal at close to -112dB.
I was pointing to both of those: there is still a bit of minor power supply related hash at ~120 Htz and ~240 Hz ... not enough that it would bother me at this point. The most significant limitation with regard to using this setup to measure is the third harmonic of the test signal at roughly -112dB. Pete's Sound Card Interface might actually have better performance than my DAC - ADC combination since both measurements are nearly identical, i.e. the path through the "sondcard" only [blue] vs. the path through the "soundcard" plus the sound card interface [red].
Regardless, 0.003% THD is good enough for me. I am extremely happy with Pete's design.
Still waiting on parts...I ought to sit down and build some cables for it...
Electronic Goldmine has their Ultraperm 80 sheets on sale at half price.
SALE! Rare Ultraperm 80 Shielding Sheet-The Electronic Goldmine
Electronic Goldmine has their Ultraperm 80 sheets on sale at half price.
SALE! Rare Ultraperm 80 Shielding Sheet-The Electronic Goldmine
Looks good, mine performs quite similarly. (The M-Audio 24192 is definitely the limiting factor in my system. Oddly enough my recollection is that the older 2496 in my other server is slightly better in terms of noise floor and thd.. Have not checked it yet.) Pretty amazing what you can do with a good sound card and a front end like Pete's. This level of performance was available only in a few high end FFT audio analyzers not too many years ago..
Sorry, I did not mean to insult Pete's interface. It should have said: " Regardless, 0.0003% THD is good enough for me." Three zeroes after the decimal point, not just 2.
An externally hosted image should be here but it was not working when we last tested it.
And for a mere $13,500*, you could get 0.002%!
*AP SYS-2702, not including options
An externally hosted image should be here but it was not working when we last tested it.
And for a mere $13,500*, you could get 0.002%!
*AP SYS-2702, not including options
This might be inspiration enough to try and get there for less ... much less.
Then again there is Rohde&Schwarz in Germany who have this monster among others: http://www2.rohde-schwarz.com/file_11899/UPV_bro_en.pdf. You can find a summary of the specs under the "Details" tab. The bleeding edge is always out there in the distance. Not that the bleeding edge matters much in audio.
I'll try for 0.0002% to be sure just to entice anyone who thinks that I'm fooling myself.
Thank you once again Pete.
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I can corroborate, in my case more like 20dB IIRC (ThatCorp line driver IC) - but haven't investigated much as I never use the balanced output mode.
In my case I just looped the I/0 both internally and externally and saw that in both approaches with the output in balanced mode and the input in floating mode the measured thd was significantly higher - switch the output to unbalanced mode or the input to non-floating mode and that distortion disappears..
I vaguely recollect having a similar problem with a design I did for a balanced driver in some ATE gear that automagically compensated output levels for externally switched balanced and unbalanced output connections. Ultimately I changed the circuit configuration for the two modes in order to compensate for the issue. It might be inherent to the chip design in both of these devices or it might not - I just don't know and haven't investigated further. I think in most balanced applications the input receiver would reject a large % of the increase in 2nd harmonic but the input of the interface box is not true differential.
I vaguely recollect having a similar problem with a design I did for a balanced driver in some ATE gear that automagically compensated output levels for externally switched balanced and unbalanced output connections. Ultimately I changed the circuit configuration for the two modes in order to compensate for the issue. It might be inherent to the chip design in both of these devices or it might not - I just don't know and haven't investigated further. I think in most balanced applications the input receiver would reject a large % of the increase in 2nd harmonic but the input of the interface box is not true differential.
Another $10,000 later
Not really $10k of course, but with careful placement and a few other changes I managed to get to 0.0002% with your interface. [Pete, you left out a zero in your message as well.] And who knows how accurately all my various pieces perform, but it's fun to get even close to this kind of performance with a diy device.
Here is the audio Tester software graph:
An externally hosted image should be here but it was not working when we last tested it.
And for a mere $13,500*, you could get 0.002%!
*AP SYS-2702, not including options
Not really $10k of course, but with careful placement and a few other changes I managed to get to 0.0002% with your interface. [Pete, you left out a zero in your message as well.] And who knows how accurately all my various pieces perform, but it's fun to get even close to this kind of performance with a diy device.
Here is the audio Tester software graph:
Grufti,
I'm in the process of ordering parts to build it in the next week or so, which THAT products did you use? and what did they replace?
Thanks for the help.
Ken