I had this project saved for later publication, but the first delivery seems to have succeeded quite well. Analog guru Duke Aguiar, who sells the LPT interface cable to the Audio Precision APIB bus (with a USB solution in the works!), has received and favourably tested my recreation of the AES17 compatible 20 kHz brick-wall measurement filter for Audio Precison System One/Two.
Before I knew what hit me there was already a review post up at DIYaudio!
The performance is stellar, like the original AP and much less costly
Brick-wall 20 kHz lowpass filter compatible with Audio Precision System One/Two
Now available for order – webshop here!
There is one thing the older Audio Precision System One and Twos don’t have which can be quite annoying: they don’t have USB host functionality. And given that all the processing and clocking happens inside the unit, the control software can’t reroute the digital signal generator to a USB output.
Tenor T7022, an often-encountered USB receiver. Does it do bit correct feed-through?
Of course you can use a PC to feed the USB sound card and measure the output with the AP, but then you don’t have the generator signal to do e.g. sweeps or automation. The best of course would be to somehow get to a full loop starting at the AP signal generator back to the analyzer. After quite a lot of tinkering, I managed to do just that.
All we are is dust in the win… eh, on the eval board.
Another post, another D/A converter. Yes, this is one of my soap boxes and hopefully I’ll be able to post something else soon. Sorry folks, we have to get through this… 🙂 Continue reading
The following measurements were taken with an M-audio Delta 1010 sound card, using channels 7 and 8. These cards have an AKM AK4393 D/A converter. The M-audio has an otherwise fault-free design and is a great converter for the price.
Input was S/PDIF, output balanced -4 dBV.
I’m dropping the raw measurements here with little comments as long as the results are in line with what you’d expect from a device like this, since I’m mostly interested in the IMD measurements, after the last post… Continue reading
I’ve been looking at designing a D/A converter for a while now. In my experience these are some of the hardest audio components to do right. It started with building output stages over a decade ago and at some point I even found myself in a company designing a D/A converter transistor by transistor.
However, as recent experiments have shown, I still have a lot to learn.
As I mentioned in the ultranalyzer post I have been searching for ages for an AP System One, but hesitant to shell out big money for such an old, unsupported machine.
So what was I to do when a System Two came along…?