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Review and Measurements of Monoprice Hybrid Tube Amp

maty

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The amp is a white brand that has been sold for years with many different names.

[Polish] https://audio.com.pl/testy/stereo/wzmacniacze-stereo/2387-taga-harmony-hta-25

to English: https://translate.google.com/translate?hl=&sl=pl&tl=en&u=https://audio.com.pl/testy/stereo/wzmacniacze-stereo/2387-taga-harmony-hta-25

35725-max_taga_harmony_hta25_fot2.jpg


  • Rated power (1% THD + N, 1 kHz) [W] 8 Ω, 2x 16
  • Rated power (1% THD + N, 1 kHz) [W] 4 Ω, 2x 17
  • Sensitivity (for maximum power) [V] 1x 0.57
  • Signal-to-noise ratio (A-weighted filter, with reference to 1W) [dB] 72
  • Dynamics [dB] 84
  • Damping factor (relative to 4 Ω) 30
 

garbulky

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Clearly this is not a tube amp even. It’s a solid-state amp, and one with a horrible snr even worse than typical tubes! I’m not even sure what the tubes are doing in this design! Are they even connected to the audio path in anyway? What a terrible design. Mono price should be ashamed
 

Frank Dernie

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Clearly this is not a tube amp even. It’s a solid-state amp, and one with a horrible snr even worse than typical tubes! I’m not even sure what the tubes are doing in this design! Are they even connected to the audio path in anyway? What a terrible design. Mono price should be ashamed
It is called a hybrid in the title. Valves in the preamp, probably, and a poor chip power amp on the heat sink.
 

maty

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It is an unusual hybrid. if memory does not fail me:

* Preamp: SS

* Power: tubes
 

RayDunzl

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I'll just settle for my herd of glowing blue LED's.

The lava lamp will have to do as a "glowing tube" alternative.
 

maty

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The electronic circuit of the Taga Harmony HTA-25 amplifier is a mixture of transistor and tube techniques. The entire power amplifier was built from semiconductors, installing a pair of transistors on a small heat sink near the center of the box. The push-pull circuit uses (for each channel) a set of popular TIP41C / TIP42C elements.

However, the signal path starts from the tiny PCB next to the RCA sockets, from where the voltage is sent forward. The preamplifier is a "mix" of integrated operational amplifiers, which were used, among others, for the construction of color regulation systems and lamps. 6N1 tubes (probably Chinese production) and 6P15 Russian ones were used - pentodes with a design very similar to the popular EL84.

Any case, unusual hybrid.
 

mickeyd123

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This is a review and detailed measurements of the Monoprice Hybrid Tube Power and Headphone Amplifier. It is on kind loan from a member who sent it to Monoprice to be fixed twice. It costs US $199 from Monoprice direct. I can't find it on Amazon but there is a "Rockville" amp that looks identical and it goes for even less at US $149.

When I first reached for this amplifier, I thought it was a high-end, $1000 headphone tube amp or something. Imagine by shock that it turned out to only cost $199 or even lower per above. They have nailed all the signature bling of a much more expensive amplifier:


In person it looks even better than it does in above picture (available light late at night). We have a rather heavy unit, with fine feeling volume control, VU meter and those signature rings around the tubes. Heck, it even came with plastic covering the plastic/wood looking sides! I don't understand the economics of these things at all. Do they grow them in dirt and dig them and ship them? Can't imagine anyone building these from scratch yet selling them thousands of miles away for so little money.

The one usability I didn't like is lack of detent for the tone controls at 0 dB. I sort of eyeballed it in the middle.

The power button has a nice sold feel, belying the cost of this unit.

I won't cover the rest of the unit (including its Bluetooth functionality) here and will post a review from Z that explains it all.

Here is the back panel in case you are interested:


Let's get into the measurements and see how it performs.

Audio Measurements
I didn't test the bluetooth functionality leaving me with standard RCA input which is labeled as CD. This is our dashboard with 2 volt input and power adjusted to be 5 watts using 4 ohm load:

View attachment 25966

Where to start.... First there is all that hum and power supply noise. I tried grounding the input to it and while that reduced the 60 Hz hum, it made the rest of the spectrum worse so I left it alone. Still, that is not the worst of our problems. That lies in very high levels of harmonic distortion. And no, it is not a "tube distortion of 2nd harmonic." It is distortion at all harmonics! THD+N and hence SINAD puts it in dismal category and at the bottom of the list:

View attachment 25967

After creating these two slides I went back to my measurement software, only to notice things had gotten worse:

View attachment 25968

One channel was clipping on and off, bringing the THD+N to whopping 10%. It is asynchronously clipping. I captured and created the above slides and went back to the measurement software only to see this now:

View attachment 25969

Now both channels are busted! Can you spell garbage? I knew you could....

Humoring ourselves, and bringing every bit of motivation, I continued the testing with frequency response:

View attachment 25970

Good thing I am not the type to bang his head against the wall or I would have a concussion about now. I get that there is tone control but the channels don't match either.

The owner wanted to know about noise. Z review says the hum is there on power on. This is what I measured it half-way through testing:
View attachment 25971

And SNR:
View attachment 25972

The amplifier is advertised as having 50 watts of power. But the owner told me it is 25 watts which is much closer to the truth:

View attachment 25973

We are getting 1% distortion at 20 watts.

Intermodulation distortion picture is not pretty:
View attachment 25974

Conclusions
The monoprice hybrid tube amplifier nails the looks and aesthetics. The mechanical engineer and material procurement people deserve an A. The electronics designer know, gets a failing grade if he though this is a hi-fi product. Poor guy though was likely told to build this for nothing.

Congratulations are in order then for Monoprice to have produced probably the most faulty, and poorly measuring audio product I have tested to date. This would be good as a conversation piece on your desk and that is about it.

NOT recommended.

------------
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One last comment, the same sound quality issues were apparent for me via bluetooth, with the sad addition of drop outs from time to time.
 

folzag

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+1 on a gentlemen's agreement for whoever gets this to repair and resubmit. ;)
 

617

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I can provide a subjective review. Patricia Barber was not in the room with me. I believe she was in the foyer.
 

GGroch

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There you objectivists go again.... knocking that natural musical tube sound with all your fancy pants numbers & high falutin graphs;)

The terrible numbers do not surprise me, but I cannot understand how Monoprice can turn a profit on these hybrids. The heavy weight (and externally impressive build quality) plus their high failure/return rate (there are nearly always lots of "Open Box" units available). They must have cut quite a deal with Fedex.

Miked123 is of course right, the tested unit is advertised as 25WPC not 50. The 25W has the headphone jack and retails for about $120 unless on sale. Zeos tested the 50 watt that sells for $200 with no headphone jack.
 
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SIY

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I'm struggling to figure out what the purpose of the tubes is in that amp. Why not just use the Hypex?

Oh, yeah, "tube sound," whatever the hell that is.
 

RayDunzl

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Tks

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I'd literally want to buy this just to hear how bad something like this is >_>

Can this sort of horrid ordeal be EQ'd or DSP'd in some way to emulate this thing?

EDIT: This is one of those things that are so bad, it's so good!
 
OP
amirm

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How does it work as a headphone amp?
I don't know. Too afraid to listen to it. :) I have it boxed up to ship to SIY. All questions should be put to him from here on. :D
 

Zog

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It has all become clear. Amir has used the wrong cables with machine. No wonder it has measured poorly. A work of art like this deserves 5 nines annealed silver interconnects.
 
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