Test disclosure
First I would like to thank everyone who participated in the test, sent the vote into the poll and posted comments here in the thread.
The same test was also posted in our local audio forum so I have prepared a summarized result from both.
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So we have 7 people who voted that they could hear a difference (either with or without an ABX result) and 23 people who voted they could not. This is quite a significant number of participants and quite a significant result, IMO.
Now the technical disclosure. The
“witch1” sample was recorded through my A250W4R amplifier that was also described in its thread here in the ASR:
https://www.audiosciencereview.com/...on-blameless-topology-and-measurements.21542/
and on my web
http://pmacura.cz/DIY_250W_4ohm_amplifier.html
This amplifier is capable to give 2x250W into 4ohm load at reasonably low distortion and it is a dual-mono design with two separate power supplies and minimized crosstalk between the 2 channels.
The
“witch2” sample was recorded through the modified, now 52 years old topology of the Sinclair Z-30 kit. I posted a thread about this kit and my circuit modifications at
https://www.audiosciencereview.com/...-amplifier-and-40-years-of-my-diy-mods.20198/
It is the non-bridged version and is able to give relatively clean power up to 2x40W/4ohm, however with higher distortion than the A250W, worse PSR (power supply rejection ration) and more interactions with speaker complex impedance between 50Hz and 500Hz.
Because of the big difference of the amplifiers power the files were recorded at peaks up to some 13Vp to keep the smaller amplifier well inside a linear zone. It was not the aim to test audibility of clipping.
As we can see from the poll results, “witch2” was preferred for those who posted a subjective comparison vote, which is in fact a preference for the amplifier with higher distortion. I wanted to comment on this based on many results of my previous tests but then I decided not to do so.
Last, I have prepared a new set where one of the files is the original that was used in the test and the other one is one of the test files (witch1 or witch2) used. The files were a bit shorted and renamed with the aim not to tell easily which file is which. So if you are interested, try this new challenge, but no poll is available now.
https://drive.google.com/file/d/13UpCCZT9glrFH8YNfUTb9oXxADY2hoWd/view?usp=sharing
Test setup
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THD at 1kHz / 4ohm for both amplifiers
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Deviation of frequency responses of the amplifiers used in the test measured into speaker complex dummy load