Headless Amplifier Measurement Workstation

[phofman]

I have finished my headless amplifier measurement workstation, perhaps it will be of use to someone.

My key specifications:

* no ground loop (incl. monitor)
* balanced inputs for measuring at speaker terminals of digital amps
* decent performance
* inexpensive (total 120-150 EUR)

Thin-client PC Futro S900N is modified to fit the PCI soundcard ESI Juli@. Headless operation via network is provided with a python script reporting current IP address via speech synthesis into the PC built-in speaker. Pushing the power button once - IP addresses announced, pushing the power button twice within two seconds - shutting down + announcement

Operation remotely via VNC session at the reported IP address, default resolution 1024x768.

OS Linux Mint or any other low-overhead linux.

For operation the workstation needs only its Class II power adapter and an ethernet cable (wifi possible). It can serve as a measuring device, balanced/single-ended signal generator, SPDIF in/out analyser.

The project description + source code + CAD designs (GPL) at GitHub - pavhofman/measurement-station: Audio measurement workstation

Just a few pics:

Balanced-balanced closed-loop performance:

 

[1audio]

Nice project. You have ARTA running on Linux? I did not realize the balanced and unbalanced i/o's on the Juli@ card were both live at the same time.
Is the code for the voice announcements? Is there other special code to make this work?

 

[cegadede]

That's an impressive build!

 

[phofman]

You have ARTA running on Linux?

I installed wineHQ (but would run in regular wine too). Runs bitperfect at up to 192/24 directly to Juli. Juli is disabled in pavucontrol to avoid being taken by pulseaudio.

I did not realize the balanced and unbalanced i/o's on the Juli@ card were both live at the same time.

Yeah, I was pleased to learn this by testing. It is actually its fundamental feature why I used it here - I need single-ended outputs to feed the amps (most have only SE inputs) and balanced inputs to measure the speaker output properly.

I think it offers a great way to control headless devices, thanks to all involved in this technology.

Is the code for the voice announcements? Is there other special code to make this work?

Yes, all you need to pip3 install pyttsx3 (as described in measurement-station/INSTALL at master * pavhofman/measurement-station * GitHub ). The control script measurement-station/headless_controller.py at master * pavhofman/measurement-station * GitHub just selects language, speed and calls the library method engine.say("Whatever you want to say"). It uses any offline voice synthesis installed on your OS, no cloud connection required. It sounds ugly but is perfectly comprehensible. pyttsx3 2.6 : Python Package Index

 

[1audio]

That's a really cool implementation. The Juli@ card is a real workhorse. Unfortunately the opamps are in a real oddball package so no real opportunity to upgrade. And the ADC is good but not the best. Still its at the core of my headphone test systems.

I'm sure you looked at the native Linux audio test software. Still went to ARTA. I'm sure there is a story here.

 

[phofman]

Yeah, Juli's codecs are not on par with the latest development, the card is already over 10 yrs old. But for this particular use I appreciate the single-ended and balanced inputs/outputs working simultaneously. Typically DUT would be fed with the SE output and measured with the balanced input.

I analysed maximum measurement range and was surprised to learn the total usable range at balanced input without any external voltage dividers is 40Vpp. That is great for measuring apms since no dividers are needed up to 20W/8ohm.

Here is 18W/8ohm (34.6Vpp) measured with no attenuation, still -1.6dBFS headroom. It is a dirt-cheap TPA3116 amp inside a thin client PC, fed by internal soundcard of the PC and powered directly by power adapter of the PC, I will post results in the digital amps section.

I'm sure you looked at the native Linux audio test software. Still went to ARTA. I'm sure there is a story here.

Honestly, I found only the great special-purpose tools by Fons Adriaensen (jaaa etc.) but nothing comparable with Arta + perpetual demo license I would love to learn other options.

 

[Kravchenko_Audio]

Nice work!