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My Blind Test Results

Joined
Jun 5, 2024
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Hi all,

Long time lurker and finally made an account! I recently acquired a SPL Phonitor 2 for more than half off. I loved the sound of it but wanted to run tests between that and a more affordable amp as I’ve read a lot here about how one will get the same performance. After reading reviews from Amir, it appeared that the Topping L30 measured much better than the Phonitor (granted this was for a different model but I believe the circuitry is the same).

For my blind test, I acquired the Douk Audio Little Bear as Amir gave it a great review. I used identical generic cables for both inputs and outputs. I used a multimeter to measure the output of both as well as a SPL meter to confirm volumes were sufficiently matched with a sine wave. The headphones were the Audeze MM-500. had a friend switch between the two while I listened to various tracks. I wanted to make the test as fair and blind as possible.

My results were that 10 out of 12 times, I picked the SPL Phonitor. While it sounded like there was slightly less bass, it sounded more controlled or perhaps the transients were less smeared. There was slightly more top end and the SPL sounded more dynamic. I’d say overall the general impression I had was that the L30 sounded great but almost like everything was a tiny bit squashed.

Now my question for everyone here is - on paper I was expecting both amps to sound the same or the L30 to be slightly better given its measurements. What do you think caused me to prefer the SPL that measured significantly worse? Could it be certain flaws I found appealing? Perhaps the impedance was a better match (although my MM-500s are low impedance and from what I understand the Phonitor won’t be best suited)? I’m an audio engineer and am not in the business of defending my insanely expensive gear - I would be thrilled to sell the unit and pocket that cash.

Is there anything else I should be checking to confirm my results? I did try toggling the different gain modes on the L30 but didn’t seem to be that drastic of a difference.

Thanks in advance! I am not looking to turn this into a more expensive = better thread. I truly want to learn and understand why things are the way they are.
 
Looking at the SPL amp it seems to have a lot of psychoacoustic enhancement controls. Can they all be "switched off"? If yes did you have them off for your testing? Since level matching is very important what exactly was your procedure for that?
 
Looking at the SPL amp it seems to have a lot of psychoacoustic enhancement controls. Can they all be "switched off"? If yes did you have them off for your testing? Since level matching is very important what exactly was your procedure for that?
Hey there!

Thanks so much for replying and willing to help out. So I primarily used a multimeter and measured the voltage to ensure they were the same. In regard to the pyschoacoustics stuff, I did disable everything including the crossfeed, angle, center control, phase switch, and laterility.

Let me know if I can answer anything else! It has been a crazy learning journey.
 
Checking the output impedance, amir measured the L30 at < 0.5 Ohm (spec: <0.1 Ohm) and the Phonitor 2 is specced at 0.18 Ohm. The Audeze MM-500 are listed with 18 Ohm input impedance. Therefore, based on conventional wisdom, both amps should be fine to drive them. The frequency response of both amps is also ruler flat up to at least 30 kHz. Nothing to see there. THD+N of the Phonitor seems to be around -100 dB, which is worse than the topping (-121 dB), but still better than CD quality and nothing to be concerned about. It might fare worse in a 50 mV noise test, but I couldn't find any measurements to check this.

Considering these aspects, my first suspicion would be a small error in volume matching. A typical threshold would be a difference of 0.2 dB or less, which translates to a voltage ratio of V_1/V_2 = 10^(0.2 / 20) = 1.023 or a difference of 2.3% or less. That's quite small. Do you remember how close your voltages were?
 
Hey there!

Thanks so much for replying and willing to help out. So I primarily used a multimeter and measured the voltage to ensure they were the same. In regard to the pyschoacoustics stuff, I did disable everything including the crossfeed, angle, center control, phase switch, and laterility.

Let me know if I can answer anything else! It has been a crazy learning journey.
When you measured voltage were you playing a "sine wave test tone" or "music"? Test tone is fine, a music signal is an unreliable way to measure voltage. The only reason I ask is that the one thing people can hear is differences in level, even if they don't perceive it that way.
 
While it sounded like there was slightly less bass, it sounded more controlled or perhaps the transients were less smeared. There was slightly more top end and the SPL sounded more dynamic.
A difference in the bass or high frequencies is certainly possible if the RIAA equalization is "imperfect".

Something could be affecting your perception of transients or smearing but that wouldn't be an actual characteristics of a preamp (or any electronics). The only real sound quality characteristics of electronics are noise, distortion, and frequency response (or you could have some gross error like one dead channel or channel level mis-match). See Audiophoolery.

Noise is another likely difference with a phono preamp but you'd probably only hear the preamp noise when the stylus is not in the groove. Noise from the record usually masks preamp noise while the record is spinning. And you would have mentioned it.

Distortion (form the preamp) is unlikely to be audible unless something is badly broken. And again distortion is far-more likely to come from the record (or the mis-tracking of the stylus on certain records/passages).

(Amir combines noise and distortion into a SINAD graph.)

I used a multimeter to measure the output of both as well as a SPL meter to confirm volumes were sufficiently matched with a sine wave.
A sine wave form where? Do you have a test record or a low-voltage (millivolt) source to feed-into the preamp?
 
Do you remember how close your voltages were?
He used an SPL meter… guaranteed this will not be okay.

Also, if the ASR review of the X is anything to go by, it should do really badly with the 18R headphones.
 
A difference in the bass or high frequencies is certainly possible if the RIAA equalization is "imperfect".

Something could be affecting your perception of transients or smearing but that wouldn't be an actual characteristics of a preamp (or any electronics). The only real sound quality characteristics of electronics are noise, distortion, and frequency response (or you could have some gross error like one dead channel or channel level mis-match). See Audiophoolery.

Noise is another likely difference with a phono preamp but you'd probably only hear the preamp noise when the stylus is not in the groove. Noise from the record usually masks preamp noise while the record is spinning. And you would have mentioned it.

Distortion (form the preamp) is unlikely to be audible unless something is badly broken. And again distortion is far-more likely to come from the record (or the mis-tracking of the stylus on certain records/passages).

(Amir combines noise and distortion into a SINAD graph.)


A sine wave form where? Do you have a test record or a low-voltage (millivolt) source to feed-into the preamp?
Nah, this is not about "vinyl" , MM-500 is the headphone, so no stylus in whatsoever ...
 
He used an SPL meter… guaranteed this will not be okay.

Also, if the ASR review of the X is anything to go by, it should do really badly with the 18R headphones.
Explanation please :)
 
Explanation please :)
Of what?

SPL meters are way too imprecise for level matching. We’ve seen it again and again that it doesn’t work. Use a voltage meter, nothing else.

As for X review:

1717620008816.png
 
He used an SPL meter… guaranteed this will not be okay.

Also, if the ASR review of the X is anything to go by, it should do really badly with the 18R headphones.
Hi,

Sorry for any confusion - I did use a multimeter and double checked with a SPL separately. The voltages were very close - I’ll do another test tonight and share the exact numbers.

To everyone else, thanks so much for replying - I will respond to the remaining items shortly when I’m back with the amps.

*Edit*
I am using a very cheap one from Harbor Freight - could that be an issue?
 
I am using a very cheap one from Harbor Freight - could that be an issue?
Could be, yes, depending on what frequency your test tone was. Cheap multimeters are only accurate for AC (tones) up to low frequencies.

The SPL meter is probably good enough for e.g. setting up a home theater or something, but not accurate enough for determining whether there is a tiny difference between two amps.

That said you're doing all the right stuff, and I appreciate the effort involved. Matching outputs exactly is very tricky and doing really good AB tests is work.
 
A difference in the bass or high frequencies is certainly possible if the RIAA equalization is "imperfect".

Something could be affecting your perception of transients or smearing but that wouldn't be an actual characteristics of a preamp (or any electronics). The only real sound quality characteristics of electronics are noise, distortion, and frequency response (or you could have some gross error like one dead channel or channel level mis-match). See Audiophoolery.

Noise is another likely difference with a phono preamp but you'd probably only hear the preamp noise when the stylus is not in the groove. Noise from the record usually masks preamp noise while the record is spinning. And you would have mentioned it.

Distortion (form the preamp) is unlikely to be audible unless something is badly broken. And again distortion is far-more likely to come from the record (or the mis-tracking of the stylus on certain records/passages).

(Amir combines noise and distortion into a SINAD graph.)


A sine wave form where? Do you have a test record or a low-voltage (millivolt) source to feed-into the preamp?
Hello! Thanks for the thoughtful reply. It’s so amazing to learn from all you with your explanations. I used the REW tone generator. I did 200hz for my matching. I vaguely remember Amir saying this is a good frequency for this use case.
 
Good to know! Do you happen to have any suggested ones you’d use? I can go pick one up today.
I don't even own a multimeter myself so I'm not the guy to recommend one, but I do know that Fluke is considered a good brand. Unfortunately the last time I looked they were really expensive. Someone around here can point you to a suitable multimeter, I am sure.

(edit: told ya! Thanks @solderdude)
 
Aneng AN8008 is cheap and more than good enough.
Avoid the meters that have a 200VAC as the lowest setting.
 
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Aneng AN8008 is cheap and more than good enough.
Would a 'not so good' meter give different measurements? Not in absolute numbers, but for comparison?
What I mean: even if 4 V are detected as 3 V by the Multimeter, this would be reproducible using this item and so not inflict to OP's attempt to objectivity?
 
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