Master thread on building an affordable and high performing audio analyzer utilizing the E1DA Cosmos ADCiso (crowd sourced)

[Mulder]

I have two questions that would be great if they where covered here.
1. What is the consequences and limitations of the impedance/voltage settings.
2. How to measure power-amplifiers? Do this require a dummy load and in that case, how to build and connect it?

 

[sseppala]

1. What is the consequences and limitations of the impedance/voltage settings.
2. How to measure power-amplifiers? Do this require a dummy load and in that case, how to build and connect it?

2.
Here is an excelent web page detailing of how to make amplifier measurements with E1DA Cosmos ADC
https://www.openaudiolab.com/measuring-amps/

It is really informative that at first the author was taking measurements just one channel loaded and got much better results than Amir. Then he swiched to measuring both channels loaded at the same time and basically got the same results as Amir.

Edit: Thing that I am a little buzzled about the openaudiolab guide is the usage of of the lowpass filter. To me it sound like cheating or unnecessary to get better measurements. Would it not be possible/better to solve this by averaging multiple measurements. I would love if someone more knowledgeable could comment on this.

Here is also the ASR dummy load configuration -thread.

 

[somebodyelse]

As an adjunct to this great thread; should some kind of a shared-depository be created?
For a compendium of various audio test signals/tracks/tones/sweeps, in different analog/digital audio formats, w/such files being royalty and license-free.

@restorer-john' post "SOS Magazine Test Files" is a good start.

https://www.audiosciencereview.com/...to-sox-audio-tool-as-a-signal-generator.4242/

 

[Mulder]

2.
Here is an excelent web page detailing of how to make amplifier measurements with E1DA Cosmos ADC
https://www.openaudiolab.com/measuring-amps/

It is really informative that at first the author was taking measurements just one channel loaded and got much better results than Amir. Then he swiched to measuring both channels loaded at the same time and basically got the same results as Amir.

Edit: Thing that I am a little buzzled about the openaudiolab guide is the usage of of the lowpass filter. To me it sound like cheating or unnecessary to get better measurements. Would it not be possible/better to solve this by averaging multiple measurements. I would love if someone more knowledgeable could comment on this.

Here is also the ASR dummy load configuration -thread.

Yes, I know about this site. My point is that if the goal of the first post in this thread is to summarize how to utilize the E1DA Cosmos, like a HOWTO, then I think it has to contain information about how to measure power-amps. OP have to consider if it also ought to have a collection of links.

​

 

[restorer-john]

Here is an excelent web page detailing of how to make amplifier measurements with E1DA Cosmos ADC
https://www.openaudiolab.com/measuring-amps/

It is good except for the following which is plain incorrect:

BTL amplifiers DO NOT share grounds, nor does the "-" (negative) speaker terminal connect to GND.

 

[Sokel]

It is good except for the following which is plain incorrect:

View attachment 363891

BTL amplifiers DO NOT share grounds, nor does the "-" (negative) speaker terminal connect to GND.

Some make it clear about it:

 

[Roland68]

It is good except for the following which is plain incorrect:

View attachment 363891

BTL amplifiers DO NOT share grounds, nor does the "-" (negative) speaker terminal connect to GND.

Oh yes, @restorer-john is absolutely right.
You should be very careful what you connect. This applies to a purchased or self-made dummy load as well as, for example, additional protection circuits (relay or SSR) for speakers. There could be a connection from speaker minus to device ground or network ground.

 

[johny_2000]

If I understand correctly, the APU preamplifier can be used when measuring Dynamic Range of the DUT according to the AES17 (-60dbFS) method.

A specific use case with measurements was described in the Archimago's blog about the E1DA Cosmos APU.

Measuring Dynamic Range (DR) with the Cosmos APU (C) - Archimago, 2022.

A detailed description of THD+N / SINAD measurement using Cosmos APU notch was also given.

Measuring THD+N / SINAD with the Cosmos APU (C) - Archimago, 2022.

As for the ADC, the E1DA Cosmos ADC and RME ADI-2 Pro FS were used alternately with similar results.

I think this scenario is great for DAC measurements. However, there will be some nuances when measuring headphone / speaker amps, as this will require connecting a dummy load, level matching, and taking into account the output / input impedance of the devices.

 

[NathanR]

Audio Precision whitepaper/application note for testing power amplifiers.

https://info.axiometrixsolutions.com/ap-testingpoweramplifier-appnote

Quant Asylum also has a blog/whitepaper on the topic.
Basics: Power Amps

Basics: Power Amps

This post covers some of the more important points to consider when measuring power amps. From the setup to the measurements, if you are looking to make measurements of amplifiers with your QA401, this is a good starting point. The Load We'll start with the load. Amps need to drive into a load...

quantasylum.com

Common Amplifier Format.

The CAF Reference | CAF

caf.prosoundtraining.com

 

[NathanR]

2) Is using 1% tolerance, non-inductive dummy load mandatory for amp measurements? If so, why and can you link me to US websites where I can buy the required 8 ohm and 4 ohm loads?
__________________________________________
Topics for future iterations to this post:
2) Accessories, probes, wires, dummy loads, etc. needed to build out your audio analyzer

I used the water heater heating element Lowes DIY special to make my load bank.
Not exact 2/4/8/16ohm loads, but it is close-ish.

[DIY image coming soon]

https://www.prosoundtraining.com/2011/08/09/dummy-load-testing-large-amplifiers/

Need more precision? (Ohmite has some, eBay has some)

Dynamic Braking Resistors - High Current Power Resistors | Ohmite Mfg Co

Ohmite supplies high current and dynamic braking resistors for high current applications in the transportation market and others. Click to learn more!

www.ohmite.com

 

[audio_tony]

Edit: Thing that I am a little buzzled about the openaudiolab guide is the usage of of the lowpass filter. To me it sound like cheating or unnecessary to get better measurements.

A low pass filter has to be used when measuring class d amplifiers, to filter out the switching frequency, which can cause issues with the equipment used to carry out the testing.

There is no requirement to use a low pass filter when measuring class a/b amplifiers.