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Review and Measurements of Dayton Audio APA 150 Amp

amirm

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#1
This is a review and detailed measurements of the Dayton Audio APA 150 power (speaker) amplifier. It is on kind loan from a member. It costs USD $168 from Parts Express including free shipping. If the specs of 75 watts/channel are true, you are getting a stereo amplifier for about $1 per watt! Amazing how cheap these amplifiers have gotten.

The APA 150 is a chunky unit, departing from the typical wide cabinet format:
Dayton Audio APA 150 Power Amplifier Review.psd.jpg

As you see, there is a volume control so you can skip a preamplifier if all you have is one input. In the back, there are switches for bridging to mono, filtering and auto on.

The unit is fan cooled but it is temperature controlled and quiet.

The design is the classic class AB with a linear power supply which makes the unit heavy and inefficient. So good to see the fan there to keep things cool.

There are serious looking ETL/CE safety and regulatory markings on the unit which I take to be genuine and provide peace of mind.

Let's get into measurements and see how the APA 150 performs.

Measurements
Let's start with our dashboard view while the input is adjusted to produce 5 watts into both channels:

Dayton Audio APA 150 Power Amplifier Measurements.png


We get typical performance of budget amplifiers. SINAD (signal over distortion and noise) is in the 70s with lots of harmonic distortion and power supply noise apparent. No awards will be won at this rate.

Channel mismatch as far as distortion is fairly large which shows up in warm-up sequence just the same:
Dayton Audio APA 150 Power Amplifier Warm Up Measurements.png


Stability is really good though so you don't need to leave the unit on. It is as good or bad as when it first turns on.

As noted the fan was on during this test and blew a lot of air that was barely warm.

Frequency response is very good and typical of class AB amplifiers (which don't need filtering as switching amplifiers do):
Dayton Audio APA 150 Power Amplifier Frequency Response Measurements.png


Response is down just half a dB at 40 kHz limit of the test.

Likewise output impedance is negligible:

Dayton Audio APA 150 Power Amplifier output impedance Measurements.png


Impedance is 1 ohm or less at 20 Hz and averages 0.4 ohm above that. In other words, there will be no trouble running any impedance speaker with respect to impacting its frequency response.

Let's look at all important power versus distortion measurement:
Dayton Audio APA 150 Power Amplifier Power vs Distortion Measurements.png


Compared to our previous budget amplifiers, the Dayton Audio APA 150 beats them slightly on power, producing nearly 90 watts into 4 ohms. And it does that with lower distortion to boot.

Distortion+noise versus frequency at a few power levels is ugly though:
Dayton Audio APA 150 Power Amplifier distortion vs frequency vs power Measurements.png


At 50 millivolts of input, the graph is dominated by noise especially in high frequencies (red). As we increase the input levels, we get two clusters of lines, one for good channel and not so good channel. All show much increased distortion with frequency, rising to as much as 0.1%. Between 2 and 5 Khz where our hearing is most sensitive, we are looking at 0.02 to 0.03% or about 50 times worse than most DACs.

Conclusions
The Dayton Audio APA 150 performs along the lines that we have sunk into in budget amplifiers. Lot of cheap power with cringe-worthy distortions and noise. Fortunately when it comes to non-linear distortions, our hearing is fairly poor so likely people are satisfied with the great value they are getting.

I like the fact that the APA 150 is safety rated given the high voltages and currents running around in power amplifiers. The fan with its high air flow gives me comfort that it will run cool and likely reliable even under max load.

No doubt with good speakers and content, the APA 150 will provide an enjoyable experience. But if you are after the best as I am, this is not it. Our hunt for reasonably priced amplifier but with high performance continues....

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

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Blumlein 88

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#3
I might quibble with you on the output impedance. I'd like to see it somewhat lower. I'd call it good not excellent.

I suppose this is a fair deal all considered for the asking price. Still a little short of the old Adcom amps or similar in performance. Not by a tremendous amount plus even those amps cost twice as much 20 years ago.

Be nice to see IMD results on power amps.
 

amirm

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#4
There is good bit of wiring involved in the impedance measurements so actual value is likely lower. The measurement is also not very repeatable due to small impedance.
 

March Audio

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#6
There is good bit of wiring involved in the impedance measurements so actual value is likely lower. The measurement is also not very repeatable due to small impedance.
The Hypex modules are typically a couple of milli ohms which is extraordinarily low BUT that is at the module output. By the time you get through the connectors, internal cable and banana posts it will be a fair bit higher.
 

amirm

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The Hypex modules are typically a couple of milli ohms which is extraordinarily low BUT that is at the module output. By the time you get through the connectors and banana posts it will be a fair bit higher.
Indeed. In my case it is actually worse in that the 300 ohm load inside the analyzer is turned on and off to determine the impedance which means that all the interconnect wires from the speaker terminal to the analyzer counts too.
 

NTomokawa

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#9
...Now repackage it with a whole bunch of audiophile buzzwords and sell it for ten times the current price!
 
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#10
Hi Amir, thanks for the review really appreciated. Sigh, the search for a reasonable amp continues. I bet if one can find one even at 10-20w with low distortions it would be the best thing to happened in the mini d-amps world. Considering most of us use these amps for nearfield listening which is sufficiently enough.

Don't quite understand why the SINAD is 7x but the distortion is low at 0.01%. I thought that the SINAD could be higher?
I also wonder if the former is good the SINAD should be higher too.

Thanks for a wonderful review. Cheers.

p/s : How does SINAD and distortion translate to real world performance actually?
 

garbulky

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#12
Also if I'm not wrong this bad boy is the basis of what eventually became the Emotiva bas-x A-100 which also came in previous configutrations known as the mini-x and also a Sherbourn flex amplifier. I own the A-100 and love it for headphone listening.
 

confucius_zero

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#13
so, at that level, is the crown or the onkyo better?
 

JohnBooty

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#15
Also if I'm not wrong this bad boy is the basis of what eventually became the Emotiva bas-x A-100 which also came in previous configutrations known as the mini-x and also a Sherbourn flex amplifier. I own the A-100 and love it for headphone listening.
Emotiva once sold a version of the Dayton APA-150, but it's not clear to me that they share a lineage otherwise.

I'd love to see measurements of the A-100. However, it's my daily driver and I can't bear to part with it... selfish, I know!

(Also, I have the older revision without the headphone jack, and the world would probably prefer a measurement of the newer version... I'm sure there's a lot of interest in seeing measurements of that headphone amp)

Subjectively, the A-100 beats the pants off of my embarassingly large collection of class D amps like the Topping TP60 and even cheaper models from SMSL and Topping.
 

Blumlein 88

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#16
Hi Amir, thanks for the review really appreciated. Sigh, the search for a reasonable amp continues. I bet if one can find one even at 10-20w with low distortions it would be the best thing to happened in the mini d-amps world. Considering most of us use these amps for nearfield listening which is sufficiently enough.

Don't quite understand why the SINAD is 7x but the distortion is low at 0.01%. I thought that the SINAD could be higher?
I also wonder if the former is good the SINAD should be higher too.

Thanks for a wonderful review. Cheers.

p/s : How does SINAD and distortion translate to real world performance actually?
.01% distortion if it were the only harmonic there would translate to a SINAD of 80 db. When you add additional harmonics and some noise it obviously will get a SINAD of less than 80 db which it did.

Now yes lower distortion will get lower SINAD. SInAD is the inverse of THD+N.

Real world performance and SINAD are related, but not directly. SINAD could mislead. Imagine an amp with some awful 60 hz hum at -50 db. Yet everywhere else a great low noise level and distortion all below - 100db. You'll get a SINAD of 49 or 50 db. An amp also could have some noise, maybe 80 db down which is rather poor. Have some pretty nifty distortion levels of only .0001%, but you'll get a SINAD of something less than 80 db.

As usually is the case, one single criteria rarely conveys everything about the quality of something. But it is a place to hang your hat and look further. Usually low noise and low distortion and a good overall design and performance go together for good SINAD numbers. And usually the reverse also is true.

BTW, I'm not so sure if noise is at least -90 db and distortion -80 db or less, that you'll have a fully transparent bit of gear. Or one that will only get caught out by extreme circumstances and only rarely.
 

miero

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#17
I doubt it is possible to find new decent class AB amplifier under $500 (price of transformer + chasis + components + work will be higher).
 

restorer-john

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#18
I might quibble with you on the output impedance. I'd like to see it somewhat lower. I'd call it good not excellent.
I'm not convinced the measurement presented is correct.

...the 300 ohm load inside the analyzer is turned on and off to determine the impedance which means that all the interconnect wires from the speaker terminal to the analyzer counts too...
Based on the frequency response plot it doesn't add up. With a 1 ohm source impedance (Amir's measurement) at 20Hz, 20% of the voltage would be dropped (4R+1R) resulting in nearly 1dB being shaved off at that 20Hz. Amir's FR plot is only 0.3dB down at 20Hz and that is likely to be input filter rolloff, not rising output impedance.

Using the 300ohm internal load in the analyzer to measure output impedance where the amplifier is in milli-ohms will give the oscillating graph depicted above, due to tiny FR fluctuations and cable/connector resistance will swamp the output impedance variations. The 'standard' would be 8 ohms or if specified, 4 ohms at 1W and unloaded. Consequently, the actual amplifier output impedance would represent a greater proportion of the connected load impedance. I cannot see how a 300ohm load on a power amplifier will provide sufficient load to determine a useful damping factor and/or output impedance. Perhaps I am missing something, please correct me if I am mistaken- it has happened before. :)

The amplifier will also likely have 100% NFB at DC, so its output impedance will likely be extremely low. Look at the direction of the AP's plot of output impedance at 20Hz, it's going straight up. If it was a transformer coupled tube amp I could understand maybe, but SS? Based on that trajectory, we'd be looking at a completely un-damped system near DC and we know that's not the case.

Why not, just for fun, run a FR plot with voltage on the Y axis for both loaded ([email protected] or 4R) and also unloaded and lay them on top of each other? The difference in voltage vs frequency can easily show damping factor and output impedance via a simple equation.
 

miero

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