Listening test of 2 power amplifiers - files recorded for download - disclosed

[pma]

There are requests to record outputs of two different power amplifiers and prepare a listening test with such recorded files. I have decided to answer the challenge again and recorded files from 2 different class AB amplifiers, loaded with real speakers. One of the amplifiers has about 6 times more power than the other one. The files were recorded at output power up to 20W/4ohm. The level was matched by analog path (blue Alps pot) and the files were time aligned by SW.

The files are in 96/24 format and can be downloaded as a zip file from the link below. Please download and unzip the files before listening to them

https://drive.google.com/file/d/1LUMM5EmNyQt8YBHSp4eujuxArA9e_15p/view?usp=sharing

Please let me know if you can hear the difference between the files and if yes, which one do you prefer. Of course and ABX test result would be greatly appreciated.

Please feel free to use DeltaWave software by Paul @pkane to analyze the files. I will have no problems if you post the results here, for discussion purposes.
https://www.audiosciencereview.com/...test-deltawave-null-comparison-software.6633/

Have fun!
================================================================
Test disclosure on August 16, 2021

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.

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.

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 scheme

THD at 1kHz/4ohm of both amplifiers under test

Deviation of frequency responses of the amplifiers under test measured into complex speaker dummy load

 

[HorizonsEdge]

Please let me know if you can here

small correction . . . hear

 

[pma]

small correction . . . hear

Thank you and sorry for the typo, corrected.

BTW I also made a test against the original file, we may try it as a second round.

 

[cany89]

Hi @pma I was a bit rushed to judge that those are somewhat identical. I heard no difference. I'm not an expert and I don't know if I can hear subtle things in a record that I listen to for the first time. So I vote. Then curiosity hit and I opened my EQ and tried to listen to sections like what's happening between 50-120hz, or at 450hz, etc. Again, heard no difference.
(Disclaimer: I used headphones, maybe on speakers there are differences in image, soundstage, etc. I might try with speakers when I got time later)

I have some questions though!
- Do you think listening to a recording and sitting in front of the speakers are the same? Did the mic capture everything?
- I highly doubt x vs 6x power would make a huge difference when it's only 20 watts. (Maybe when an amp is 50wpc, the other is 300wpc, and you got speakers that need more power, and you are at 50w so the low powered amp clips or couldn't drive the mid/bass, then it would make a difference, no?)

(lol, the image is bigger than expected!)

 

[pkane]

There are requests to record outputs of two different power amplifiers and prepare a listening test with such recorded files. I have decided to answer the challenge again and recorded files from 2 different class AB amplifiers, loaded with real speakers. One of the amplifiers has about 6 times more power than the other one. The files were recorded at output power up to 20W/4ohm. The level was matched by analog path (blue Alps pot) and the files were time aligned by SW.

The files are in 96/24 format and can be downloaded as a zip file from the link below. Please download and unzip the files before listening to them

https://drive.google.com/file/d/1LUMM5EmNyQt8YBHSp4eujuxArA9e_15p/view?usp=sharing

Please let me know if you can hear the difference between the files and if yes, which one do you prefer. Of course and ABX test result would be greatly appreciated.

Please feel free to use DeltaWave software by Paul @pkane to analyze the files. I will have no problems if you post the results here, for discussion purposes.
https://www.audiosciencereview.com/...test-deltawave-null-comparison-software.6633/

Have fun!

Since you asked

 

[pjug]

Since you asked

View attachment 146522

Thank you Paul. Do you mind sharing what settings you use. I am not getting as good a match. I did notice that I am using an older version. Maybe I need to update?

 

[pkane]

Thank you Paul. Do you mind sharing what settings you use. I am not getting as good a match. I did notice that I am using an older version. Maybe I need to update?
View attachment 146525

From what I can see you're averaging L+R channels. Try comparing L to L or R to R. I posted left channel only.

I used just the basic settings, no non-linear corrections:

 

[pma]

- Do you think listening to a recording and sitting in front of the speakers are the same? Did the mic capture everything?

Hi @cany89 , thank you for trying the test. You seem to be confused, there was no microphone used. It would be impossible to get such files from a microphone placed in the room. Ambient noise and room reflections make all the tests with amps captured by microphones absolutely pointless and only a source of many errors.

The test is completely based on electronic scheme and it looks like this

The schematics shows one channel, the second one is identical.

 

[pma]

Since you asked

Thank you Paul, we have absolutely same result.

I posted left channel only.

Yes, the left channel was matched in amplitude by the pot. I know that DeltaWave takes one channel by default.

 

[b4nt]

recorded files from 2 different class AB amplifiers, loaded with real speakers.
...

Have fun!

Downloading the files to listen... If PKM shows 81dB I may enjoy both

- Do you think listening to a recording and sitting in front of the speakers are the same? Did the mic capture everything?

@pma could you please describe how you made the records (mics used, and mics positionning)?

 

[pma]

@pma could you please describe how you made the records (mics used, and mics positionning)?

Please kindly read the post #8 here above, it is explained there

https://www.audiosciencereview.com/...files-recorded-for-download.25646/post-874503

 

[b4nt]

Hi @cany89 , thank you for trying the test. You seem to be confused, there was no microphone used. It would be impossible to get such files from a microphone placed in the room. Ambient noise and room reflections make all the tests with amps captured by microphones absolutely pointless and only a source of many errors.

Ok, I see. Way to record using mics should be that one. But mics models and sizes plus positionning (close to speakers) would then potentially impact the record. I recently tried so, but I suspect my mic for med/bass was too big, changing the way my med was breathing.

Then I had troubles to mix the mics records (one for treble, one for med, needing level adjustment).

But it seems to be common practice to record guitar amps sound:

 

[pjug]

From what I can see you're averaging L+R channels. Try comparing L to L or R to R. I posted left channel only.

I used just the basic settings, no non-linear corrections:
View attachment 146528

I thought I was using just L; that is what my image shows anyway. But I updated the software and now I am getting the same result that you show. Probably I had some setting wrong before; I doubt it was because of the version.

 

[pjug]

Hi @cany89 , thank you for trying the test. You seem to be confused, there was no microphone used. It would be impossible to get such files from a microphone placed in the room. Ambient noise and room reflections make all the tests with amps captured by microphones absolutely pointless and only a source of many errors.

The test is completely based on electronic scheme and it looks like this

View attachment 146531

The schematics shows one channel, the second one is identical.

This is really great and thanks very much for doing this. Do you mind saying what equipment you are using: DAC/ADC, amps, speaker? Did you use a voltage divider or were you just playing at a low voltage level?

Now my question is whether any differences that you measured are due to the amplifier, or if this amplifier test is limited by the capabilities of the equipment. It would be interesting to see loopback measurements through the DAC straight back through the ADC. And also the original track. If we compare both amplifier measurements to the original track, we can see if one matches much better than the other.

 

[digitalfrost]

16:40:17 : Test started.
16:41:21 : 01/01
16:41:36 : 01/02
16:41:58 : 02/03
16:42:16 : 03/04
16:42:35 : 03/05
16:42:45 : 03/06
16:42:56 : 03/07
16:43:10 : 04/08
16:43:10 : Test finished.

----------
Total: 4/8
p-value: 0.6367 (63.67%)

I think there is a slight difference in the stereo image between the files, but I was getting tired towards the end. I might be able to ABX this if I try some other time. Or I'm just imaginging things

Btw which song is this? I like it.

 

[cany89]

@pma oh alright. I’ll wait for the poll to close for other questions

 

[pjug]

I did my own amplifier recording, but used high voltage (>40V peaks) and 220-ohm/3.3-ohm voltage divider. Comparing my results to the original track I don't get as good a match as you have been able to get (my peak mismatches look worse and I had to use the DeltaWave EQ to make these match this well). Probably because my ADC/DAC is a lowly Behringer UCA202. I am getting about the same results playing through a speaker and 8 ohm resistor. Waiting for n input adapter part so that I can compare with a different amplifier (first go is Outlaw M2200 into Usher V601). Just to be clear image below is a different recording than OP's.

 

[b4nt]

I cannot answer to the pool, there is no option for "have no preference"

According to what I saw here using Audacity and DW v1.0.70, there are differences in the files. They may be audible for some who enjoy guitar?

 

[pjug]

@pkane
It was suggested to me by @Blumlein 88 that the checking the EQ setting in DeltaWave might help improve the matching. I don't really understand what this does. Do you think it is appropriate to use this for such a comparison?

 

[b4nt]

ping @Pdxwayne have you a preference between witch1 and 2?

@pma I would later be interested in some specs of those amps.