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Setting up for electronics and amp testing, ASUS Xonar U7 USB audio
So as I setup to do some testing of electronics, line-level and amplifier (via dummy load). I plan on using this simple, older device for the DAC and ADC work. Obviously this isn't a commercial grade, maximum performance solution, it is a consumer enthusiast sound interface via USB. I looked at some online testing, and seeing good tests, did more research on the hardware. It uses Cirrus Logic CS4398-CZZ for DAC, an older but solid chip and Cirrus Logic CS5361-KZZ for ADC, similar performance to the DAC. Looking fine.
I hooked mine up in loopback (line out to line in) and fired up ARTA.
Here is a 1khz test tone and the ARTA analysis of the input:
Lives up to the tests I've seen online. While I've seen better, it has only been from commerical grade expensive stuff. I think this will work fine for what I want. It gives me a testing floor of 0.0049% THD and -130db noise. For the test above I set the hardware to 24-bit/96k, which I think is the sweet spot for this device. I did find it interesting that to get ARTA to report RMS input of -3db (the setting used for the sine wave) I had to change the line level input to 95/100 in the Windows control panel. If I set to 100, I got a report of -2.2db so there would have been some internal gain in the line level side of things.
Continued here: https://diy.midwestaudio.club/discussion/1474/setting-up-for-electronics-and-amp-testing-amp-with-dummy-load
Comments
That'll do, it always good to know the limits of your equipment. Keep in mind that -130dB is not the SNR of the device, as it's a result of averaging of the noise floor. SNR would be determined by a peak noise value (114dB in the spec sheet, still very good if it's true).
Jason, I'm not real familiar with ARTA to reproduce your loopback test, but I am familiar with Rightmark Audio Analyzer for this purpose. Just something to compare your results to, I use a Steinberg UR22mkii USB interface for all of my measurements, with RMAA I got a result of 0.00948% THD, and the spectrum looks like this. Tested at 24/96 with a 12ft mono patch cord, level set approx -3dBFS.
Given that the noise level in my test is about the same -130dB, the RMAA noise test came back at -99dBA for a result.
To get the above result, I had the output knob at max, and decreased the input gain to get -3dB at the input. It's interesting, that if I drop the output gain knob to about half way, and then increase the input gain, that I get a lower distortion result of 0.00416%, although the noise result has decreased to 92.4dBA as a result of the lower output level.
My UR22mkii uses a CS4270 audio codec FWIW. Op-amp on the input side is a JRC2068D, and on the output is the classic N5532
I've been looking into this for a while, too. I have a older Focusrite Scarlett 2i2 for an audio interface that could get me started (currently using it as a work from home headphone amp). Considering REW or ARTA for software.
What are you guys using for a dummy load? I have a few pro audio amps that it would be interesting to test (like the Samson I have been bringing to DIY Iowa for a number of years) along with some more normal amps, so I will need quite a bit of power handling capability.
Sehlin Sound Solutions
Scott, you are getting ahead of me. That is the next post in the: Setting up for electronics and amp testing, series. The parts are almost all here. HIgh-power resisters, heatsink and thermal paste to mount them, all the electronics to make a microcontroller true RMS voltmeter, etc.
Scott, if you decide to use REW there's a good thread about using it for distortion measurements at diyaudio:
//https://diyaudio.com/forums/software-tools/338511-howto-distortion-measurements-rew.html. For electronics testing I bought the Focusrite Solo and the Akita precision 1 KHz generator mentioned in the thread.
For dummy loads MPJA has 120w resistors for $6.95.
Watching with interest as I bought a Behringer USB sound card for the same purpose
I don't have any proper sound cards, other than micro DACs... what features are we looking at? or good brands/models to consider?
Not trying to high jack the tread, my brother has a Gen 2 scarlet 2x4 for sale $100. Should work good for these test.
I've often thought about seting up a test rig for amplifiers. Just dont have the time. I'll be watching the thread. ☺
Finding a good DAC these days, even in cheap USB solutions is pretty easy. Finding a good ADC in hardware, that is a lot harder. I don't have a short-list or anything. I chose the Xonar U7 because of it's ADC long ago. ASUS makes a new MK2 of that device, but I haven't heard if it is quality or crap. Three years or so ago the Xonar was a mere 80$ solution, but the new MK2 looks to be 120$ or more. Prices keep going up it seems. I wonder how hard it would be to do a quality device myself... opens up mouser and looks at ADC chip costs
That is a good deal. I did find something on ebay that I think will work for me a little better.
The problem I wound up having with the 120W resistors is I have 3 amps rated over 500 WPC into 8 ohms that i would like to compare. 4 of the MPJA resistors could get me to 480W. Other workable series/parallel arrays would require 8 or 9 and my plan would be to make two of those arrays so I could use both in parallel for 4 ohm testing. I found some 4 ohm 420W resistors on ebay. 4 of those will allow me to run over 800W into 8 ohms and double into 4. An ebay seller has sets of 2 for 19.99 plus a little shipping.
Sehlin Sound Solutions
You are looking at good signal to noise ratio for both the DAC and the ADC. RME seems to measure very well, but isn't cheap. Motu and Focusrite have more reasonably priced options, but aren't going to be clean enough on the ADC side to measure good dacs or things like the Benchmark or Hypex amps. Another interesting thing to consider is the Quantasylum QA401 if you're spending a few hundred on a decent audio interface/sound card anyway.
I think I'm going to start by trying what I have and freeware in order to learn where I want more capability.
Sehlin Sound Solutions
Ok, finally located the 12" extruded aluminum heatsinks I had stored away for an amp, and plan on re-purposing for this project. Seems I left them in a garage cupboard at my Dad's, doh! So next post in the series coming tomorrow.
The ham radio guys build their dummy loads by placing the resistor in an oil bath.
https://nonstopsystems.com/radio/frank_radio_antenna_dummy.htm#intro
Ron
Absolute wattage ratings should not be a big problem - you could mount the load resistors on a cheap heatsink and use a low noise computer fan to make sure you don't "cook" em.
I have two Dale 8 ohm, 100 Watt, 1% resistors mounted on a large aluminum finned heat sink I grabbed out of a blown up 10 HP VFD. I have them wired in parallel for a 4 ohm load. I have measured the output of my ClassDaudio amp at +50 Vrms. That's over 600 Wrms! It gets pretty warm to the touch but I can grab waveform shots in a dozen seconds. I wouldn't run it at that level continuously. I mainly used it for finding F3's (bandwidth) and clipping levels on my MUCH lower power tube amp projects.
Be sure and use a good heatsink compound (thermal grease) and properly torque the fasteners.
Maybe overkill is just my style...
Sehlin Sound Solutions
What are those? Looks like some sort of medieval torture device!!!
Sex toys?
Light sabers!
If I didn't know better (and I do) I would say they bear a striking resemblance to arbor press inserts... Or bastard files.
Ah the old Ohmite power resistors. Haven't seen any of those in a longggg time. 500 Watts each?
These are rated at 420W.
Sehlin Sound Solutions
Those are also made for variable resistance with a tap, no? I used to see a bunch like that at the old surplus shop called Pembleton's and then Misener's, and then poof, gone. I bought a good many caps and resistors from that place. I still have some big 150W(?) 75 ohm resistors I think, bought when I didn't know anything about power usage in speakers, about a foot long and brown Ohmite.
InDIYana Event Website
The do make these in fixed and variable configurations. The variable ones have an added metal strap that can be repositioned along the length of the resistor.
Sehlin Sound Solutions
It looks like you need to go a lot more expensive to get better ADC than that Asus.
Anything new happening?