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Review and Measurements of Topping TP60 and FX Audio FX502SPro Amps

amirm

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#1
This is a review, measurement and comparison of two speaker amplifiers: Topping TP60 and FX Audio FX502SPro. I purchased both personally. The TP60 retails for USD $199 with free prime shipping but goes on sale frequently on Massdrop where I purchased it for just $135. I bought the FX502SPro for $68 from ebay but I see it listed at $89 right now.

From build quality to size and weight, the Topping TP60 blows away the FX Audio FX502SPro as you see in this picture on my bench:
Topping TP60 and FX Audio FX502SPro Audio Amplifier Review.jpg

The TP60 is probably four times larger. Part of that is due to the fact that it has dual linear power supplies built into it. The FX502SPro on the other hand, comes with a large laptop sized external switching supply that is nearly its own size!

The TP60 has dual inputs whereas the FX502SPro only has one. Rear speaker terminals on the FX502SPro are toy sized whereas the TP60's are much more substantial.

FX Audio rates the FX502SPro at 70 watts per channel. Topping states 80 watts/channel for TP60. Let's get into the measurements and see how real those numbers are.

Before getting into that, let me introduce you to another measurement gear, the AES-17 filter. Both of these amplifiers are switching types and hence produce a lot of ultrasonic energy. This should be inaudible but my analyzer will see them and attempt to set its internal gain using it. Or else, causes what is called "slew rate limiting." In a nutshell, the analyzer input stage is designed to be "slow" but extremely accurate. It expects to see audio frequencies and not spectrum in Megahertz whaling away. For this reason, a filter is necessary to keep this extra noise at bay.

Audio Engineering society has specified such a filter with 20 kHz response with extremely flat response. I am not happy with chopping the spectrum so early so I purchased a 40 kHz variation from Audio Precision called the AUX-0040:

1540871109977.png


Here is its frequency response:
1540871159709.png


It is a passive device (much like filters in your speaker crossover) designed for extremely low distortion (read, air core inductors). Frequency response variation is +- 0.08 dB up to 40 kHz. In other words, it is dead flat for our purposes.

Like everything else from Audio Precision, this thing does not come cheap. It retails for nearly $1,600 plus tax and shipping. I was going to build one but good suggestion was made that it is better to use a known product from AP. This made sense to my head but my pocketbook has even a larger hole in it now! :) We are having hot dogs for dinner for the next few nights instead of shrimp to make up for it.

Anyway, both amplifiers were tested using the AUX-0040 filter as without it, the high frequency noise was clearly visible even to naked eye on sine waves.

For dummy load, my only high-power one is 4 ohms. In the future I will build and test with others but for now, all the data you will see are with 4 ohm load.

Measurements
i started the testing with FX502S and almost went crazy. I could not get a proper waveform out of it to save my life. A simple sine wave was coming out way distorted and power output was all over the place. I kept thinking it was a measurement error. So I hooked it up to speakers and played music and boy, did it sound distorted and strange. Power cycled it a few times and the problem went away! I think the design is unstable and goes into oscillation on power up.

Anyway, here is the dashboard when the unit is feeling like producing good signal:
FX Audio FX502SPRO Audio Amplifier Dashboard.png


Note that I picked an arbitrary output of 5 watts for output. There is no standard for this so I will go with 5 watts from now on for consistency.

We see distortion and noise that is extremely high by standards of our sources such as DACs. SINAD is just 77 dB or a whopping 40 dB worse than the best DAC we have tested!

Let's compare that to Topping TP60:
Topping TP60 Audio Amplifier Dashboard.png


Good grief. This is even worse!

Let's sweep the input level and plot power versus distortion and see what pops out:

Topping TP60 Audio Amplifier and FX Audio FX502SPRO Power versus Distortion Measurement.png


The FX502SPro falls way short of its 70 watt spec and produces just 37 watts before clipping. The Topping TP60 does much better, producing 60 watts prior to clipping at 0.03%. If I allow higher distortion figures, it can inch up to its spec.

I needed a sanity check to know that these numbers are accurate. So I looked up the specs for the amplifier IC in Topping TP60 which is TA2022 from Tripath. There, we see a similar graph to mine:

1540872091124.png


The FX502SPro uses TI's TPA3250 and here is their measurement:

1540872224401.png


At 4 ohm, they show clearly clipping at just 20 watts so not sure why they rate it at 70 watts just the same.

Anyway, manufacturer graphs show the same thing as my graph with lower noise floor for the FX Audio but much less power.

I usually don't bother with frequency response graphs because they tend to mostly be ruler flat. Such was not the case here. Here is FX502SPro:
FX Audio FX502SPRO Audio Amplifier Frequency Response.png


We are down 2.5 dB at 40 kHz. Even at 20 kHz response is down between 1 and 1.5 dB.

The TP60 was even more strange:
Topping TP60 Audio Amplifier Frequency response.png


Something strange is going on with their output filters.

Here is intermodulation distortion:

Topping TP60 Audio Amplifier and FX Audio FX502SPRO IMD Distortion Measurement.png


We see what I mentioned before: the TI chip used in FX502SPro has lower noise and its input doesn't saturate as fast as Topping TP60.

I tried to run signal to noise ratio on FX Audio FX502SPro but the unit would go into production from sudden turning on of its input! I could not keep the volume above 1/4 or it would either blink error or shut down completely!

At this point I was sufficiently depressed that I stopped running more tests. I think we know what is going on here.

Listening Tests
Unlike headphone testing, I ran into a logistical issue of playing loud music on speakers with the rest of the family (wife and two dogs) home! :) So I only had enough time to test the FX Audio FX502SPro. I connected it to my Sonus Faber Concertino bookshelf speakers and let it play. It sounded "OK" but there simply was not enough power. It is good for background music but that is about it.

Conclusions
I try to not get emotional when it comes to testing products but sometimes the test results either get me excited or depressed. And boy, was I depressed after seeing these results. The measurements here indicate that neither one of these amplifiers fit any definition of high-fidelity we strive for in this forum. The FX Audio FX502SPro is extremely cheap but in my book, is not a proper product. It has design issues and lacks power.

The Topping TP60 should do better in power department but don't assume by any stretch that you are hearing the fidelity of any good source driving it. It might be a lot more useful as dual linear power supplies and case than an amplifier!

What we are seeing is that unlike products like DACs where the underlying silicon is superb, here garden variety amplifier ICs are used which are more likely designed for soundbars, boomboxes, bluetooth speakers, and alike.

So no recommendation here. Search will go on for reasonably priced amplifier that does justice to our source. I have a few amps to test so we will throw more darts at the board. The prognoses is not very good though based on preliminary tests.....

-----
As always, any questions, concerns, comments, corrections, etc. are welcome.

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RayDunzl

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#2
Time to measure the Levinson(s) to establish (maybe) a 5 Watt baseline...

What is it/are they? The 53?
 
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amirm

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#3
Time to measure the Levinson(s) to establish (maybe) a 5 Watt baseline...

What is it? a 53?
Yes, a No 53 although I also have the 532 Reference. Stereophile tested the 53: https://www.stereophile.com/content...erence-monoblock-power-amplifier-measurements



At similar power levels, its distortion spec is around 0.004% or 10X better.

The ncore modules have much better distortion specs so hopefully I will get my hands on units based on those as reference. Or the THX based power amplifiers form Benchmark.
 

Sythrix

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#5
Interesting review and a great way to switch things up!

I’m really interested in what components are in that $1600 filter, to make it worth that much. Regardless, I’m glad you got it if it expands your capabilities.
 

amirm

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#6
I’m really interested in what components are in that $1600 filter, to make it worth that much.
Someone has reverse engineered its schematic:

 

Sythrix

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#7
Someone has reverse engineered its schematic:

I understand the reasoning of using a known product... but I also understand your inclination to just build one.

Thanks for sharing :) .
 

Arnandsway

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#8
Thanks Amir, for choosing to measure amplifiers :)
Oh wow, this is dissapointing though. These products render good DAC's as useless.
 
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restorer-john

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#9
Welcome to amplifier testing. :)

You really should test a slew of decent 20-30 year old high quality class AB amplifiers to establish some reference points.

I still think it's pathetic that Class D is so inherently poorly designed that you need a US$1600 filter to get rid of the unwanted HF crap. This is going to be an entertaining voyage of discovery for you Amir. :)
 

JJB70

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#10
When it comes to modestly priced amplifiers, you can move up to the lower tier full size amplifiers from companies like Marantz, Onkyo, Yamaha etc and get a well made product which will last years, sound transparent (sorry restorer john:facepalm:) and have adequate power for not that much more. Or I have seen some pretty positive views of some of the lower cost professional power amps from companies like Behringer if you have a separate DAC which can act as a pre-amp.
 

FrantzM

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#11
Hi

Topping should stick to DAC this is a BS product. now I am all interested in Class D because of AC power issues I have in my location. Class efficiency is attractive be welcome but the level of ultrasonics in their output is not reassuring ... Time to test a DeVialet ;) Frank?
 

JJB70

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#12
On external power supplies and the lap top style bricks which are as big as the product itself I always feel that is a sleigh of hand as it allows designers to make things look a lot more compact than they are. This seems to be done quite a bit with headphone amps, recently I had the chance to use a Rupert Neve headphone amp which was a very nicely made compact unit with a huge brick attached.
 

March Audio

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#14

amirm

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#15
Any chance to measure also the Behringer A300 just to have some reference?
I have an A500 that I will be reviewing.
 

restorer-john

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#17
One thing to make the playing field level, is levels...

Amplifiers have always* had their FR specified and tested at 1 W @ 8ohms (~2.83V).
Power bandwidth is -3dB points (half power).
THD is specified from 250mW to rated power, 20-20KHz both channels driven.

There is no standard for this so I will go with 5 watts from now on for consistency.
Amir, if you are considering an arbitrary power figure, 5W at 4 ohms is not the number to pick. 1 watt @8ohms and rated specified power are the de-facto standards.

*since Adam was a boy.
 

rajapruk

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#18
Search will go on for reasonably priced amplifier that does justice to our source.
This is very much appreciated. Thanks!
I fear this will be a hard quest though. I think AHB2 and nCore will come out on top, and they are not reasonable priced for Average Joe, I think (maybe I am wrong here).

I wonder how we can influence THX to make a Massdrop AAA speakeramp at the 500USD pricelevel? (I already talked to Andrew Mason about this, and he knows I want one haha. But what if they would know thousands want it?).
Can I make a Massdrop poll about things like this? I never did a poll there.
 
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