Yaqin MC-84L Tube Stereo Amplifier Review

[transformer-coupled]

This is a review and detailed measurements of the Yaqin MC-84L Stereo Tube amplifier. It is on kind loan from a member and costs US $600 on Amazon.
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The picture doesn't do justice to the nice design of this amplifier. The transformer case in the back nicely contrasts with the chrome parts. The latter does make the labels hard to read though when looking from above:
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One set of binding posts is available for 4 ohm and the other, 8 ohm. Seeing how speakers don't have constant impedance, nor are advertised correctly as such, I feel bad for people trying to figure out which posts to use (common criticism for all such amplifiers). Let's see how it performs.

There is a headphone jack in the back which I did not test.

Yaqin MC-84L Stereo Tube Amplifier Measurements
For all but 8 ohm power test, I used the 4 ohm tap. Let's start with our dashboard:
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We have the high harmonic distortion which we kind of expect. But a lot of mains noise comes along for the ride, causing intermodulation with our main 1 kHz, making for a mess. SINAD which is the sum of all unwanted "stuff," lands the amplifier at the bottom of our rankings:
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Noise is a step above but still nothing remotely to be proud of:
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Frequency response is flat enough if we ignore varying performance between channels:
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Crosstalk is one step above mediocre:
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You get a better feel for distortion when we use 32 tones to simulate "music:"
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Not pretty. Same story for 19+20 kHz tones:
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The amplifier is fairly rated at 12 watts, assuming you don't care about distortion:
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One channel is having trouble above 2 watts which we also saw in the dashboard. So maybe it is a bad tube or something. Best of luck to a customer figuring that out without this type of measurement.

If we "only" allow 1% distortion and noise, available power shrinks to a trickle:
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Yes, that is only 2 watts!

Using 8 ohm tap, we get similar results:

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Sweeping frequencies we see the typical rise in distortion with frequency. But also increase in distortion at low frequencies (transformer saturation?):
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I am showing both channels. Dashed line is the "good" channel.

Our power on/off test shows instability on top of noise at these events:

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Fortunately if you wait a minute or so, everything stabilizes:
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Conclusions
The Yaqin MC-84L made a very positive impression on me with its modest size and super nice industrial design. And reasonable price for such tube products. Performance though, set a new record with respect to how bad it is, taking over the slot for the worst measured amplifier to date. The amp has 42 reviews on Amazon with average of 4.5 stars. Folks must be very tolerant of noise and distortion out there!

I do like the company honesty when it comes to power rating and even SNR.

Needless to say, I can't recommend the Yaqin MC-84L valve amplifier.

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As always, questions, comments, recommendations, etc. are welcome.

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Great review thank Armir but why you removed Pass ACA amp from ranking?

 

[amirm]

Great review thank Armir but why you removed Pass ACA amp from ranking?

I forgot to extend the range to include it. Caught it in the next amp review.

 

[EL_PW]

Aww yiis. My Luxman SQ-N150 is clawing it's way to the top of the tube heap!

 

[Ein]

We need an option below "Poor".

Yep. Jesus Christ, no, No simply NO. Thats thing is broken. Someone produced simply broken amp. Intentionally

 

[Count Dacula]

Bob Carver breathes a sigh of relief.

 

[Count Dacula]

Great! And what do we learn from this?
People are very subjective in their perceptions, many love this type of sound amplification even if it is as incredibly poor as in this case.

And that's a good thing!

Not only can one assume that the main focus is actually on the music being heard and its emotional magic, but also that it is an important basic requirement to go through life unscathed.
Imagine if people were ranked by their most disgusting smell, appearance and behavior... over time no one would be left standing.
Maybe those with perfection fetishes should enjoy their music through such tube constructs every now and then, purely for therapeutic purposes

Products like this, and a few others, give audio x a bad name. It creates an aversion for regular Joe to participate in the sport. You know how we all mostly fret over audio purchases? Well regular people fret over bathroom mats and paper towel holders, so when it's time to purchase a thing to listen to, they become gripped by indecision, with not much to rely upon other than Amazon reviews......specs and schematics mean nothing without a frame of reference. Do I want the 2 watt amp or the 2000 watt amp??? They're both the same price?!?!?!

 

[Count Dacula]

Maybe North Korea can start a production line of SOTA tube amplifiers.

Don't laugh, after seeing this I'm serious.

 

[Count Dacula]

This amp is a good match for vinyl - has similar SINAD to vinyl playback. I wonder how many bits of multi-tone "clarity" a vinyl playback chain has. 5? 6?

Vinyl has between 9 and 11.5 bit depth, last number I saw

 

[Chr1]

Probably more with all the crackle and pop.

 

[Old_School_Brad]

Vinyl has between 9 and 11.5 bit depth, last number I saw

Really? That is higher than I would expect.

Probably more with all the crackle and pop.

*Turning off subsonic filter to boost DR...

 

[Count Dacula]

I could be wrong.

This source has some interesting discussion. If someone wants to digest it, I'm still interested in the answer.

Vinyl is equivalent to which digital bit-depth and sampling rate?

Vinyl is equivalent to which digital bit-depth and sampling rate?

hydrogenaud.io

Shannon–Hartley theorem - Wikipedia

en.wikipedia.org

Also. https://hydrogenaud.io/index.php/topic,35530.0.html

65-70dB on a good day with a following wind, which equates to slightly less than 12 bits

An interesting question would be, vinyl verses MP3 (ducks for cover)

 

[AnalogSteph]

An interesting question would be, vinyl verses MP3 (ducks for cover)

MP3 (alongside a number of other lossy codecs) should be good for about float24 equivalent if there were such a thing... you'll be hard-pressed to ever get an instantaneous dynamic range of more than about 16 bits out of it, but globally that chunk can be just about anywhere as amplitudes can be scaled almost arbitrarily. So if your MP3 encoder supports being fed with 24-bit or 32-bit int or even 32-bit float, there is no reason not to use that. This is how formats like Minidisc and DCC are technically capable of post-16-bit performance at macro level as well.