Douk Audio H7 Amplifier Review

[amirm]

It matter to me, 1 dB is audible. It shows load dependency. Combine this with the fact that the amp didn't play nice with the reactive load Power cube test, not a good look.

I don't think the problem is the amp with respect to loadbox. I have to work with the designer to get to the bottom of it but I would not put blame on the amplifier.

As to 1 dB, yes, it can be audible to people with good hearing way up in treble region. You can fix that with EQ which every good sounding system needs. To the extent you don't deploy EQ, then you have bigger problems than this 1 dB.

 

[amirm]

Added power vs frequency graph to the review:

 

[PeteL]

I don't think the problem is the amp with respect to loadbox. I have to work with the designer to get to the bottom of it but I would not put blame on the amplifier.

As to 1 dB, yes, it can be audible to people with good hearing way up in treble region. You can fix that with EQ which every good sounding system needs. To the extent you don't deploy EQ, then you have bigger problems than this 1 dB.

An amp designer cannot assume that the purchaser will owh a measuring rig, especially not a 150$ amp!! Sure EQ correction are beneficial to most systems, but you should correct your room and the flaws of the speakers themselves! What if someone decide to use one of the EQ you publish in your speaker reviews but the relation with the amp and the dynamic load of the speaker, throws that response out of the window? Plus this device don’t have EQ, electronics are not made to be EQed it’s a terrible Idea.

 

[ctrl]

The only thing these two resistive measurements tell is that the amp is load dependent. -That's it. Nothing about how it behaves with real load.

That's a pity, for me personally it would have been enough to know that even with suddenly appearing 60 Ohm LS impedance (in the bass range and around the crossover frequency), the frequency response of the amplifier never shows more than 0.5dB ripple in the range 50-15000 Hz.

A cheap amplifier does not have to be perfect, if the 4 and 8 ohm impedance measurements only provide the information that load dependency is present and that there can be FR differences above 10kHz, that is very little information.

 

[AdamG]

Wow, just Wow

 

[amirm]

I checked out the VU meter. I think it is showing the input level, not output. Accuracy is not great. It needs to be zeroed as you can't get to -20 dB (there is a screw for this but not sure how to get to it). When adjusting the level down by -10 dB, it reads -7 dB (set to 0 dB reference). Ditto for going above 0 dB.

It is also slow responding.

Still, it was quite useful as I was testing it today.

 

[amirm]

A cheap amplifier does not have to be perfect, if the 4 and 8 ohm impedance measurements only provide the information that load dependency is present and there can be differences above 10kHz, that is very little information.

??? You can compute the amplifier output impedance using those two values and then apply it to any complex load.

 

[amirm]

FYI I am listening to the amplifier using Infinity R253 speakers and this thing is powerful and super clean! By accident I played it at full volume and it nearly brought the roof down! I can get it to start to distort but then it is playing very loud.

 

[ctrl]

??? You can compute the amplifier output impedance using those two values and then apply it to any complex load.

This is exactly what I was looking for.
Can you calculate once for me how big the frequency response deviation is, for example at 3kHz, if the 4 Ohm and 8 Ohm measurement shows 0.2dBr difference and the speaker has 60 Ohm impedance at 3kHz?
Step by step, so that in the future I can estimate this myself.

 

[thecheapseats]

...In general I do disregard the cost....

please keep the cost data in reviews... regarding this specific device, but any device review - cost is an important attribute... a device's hard cost (of its bill of materials) translates not only to a retail price - but what one might expect for the retail price... what any device does and how it tests and functions at a given price point is context (for me anyway)...

this little amp (even with its goofy idiosyncrasies) tests pretty well and is fit for 'some' purpose... possibly at its price point it has more value per dollar than a several thousand dollar dac...

 

[pseudoid]

please keep the cost data in reviews...

The main bar-graph ratings of different hardware (Blue/Gren/Orange/Red) shows the numerical SINAD for each hw tested. The 2-digit value (in dB) is shown above each representative bar.
A "price-range" letter can be easily inserted inside/bottom of each bar, to provide that "cost data" that can become quite relevant, valuable and worthy part of such an indices. [imo]

 

[amirm]

This is exactly what I was looking for.
Can you calculate once for me how big the frequency response deviation is, for example at 3kHz, if the 4 Ohm and 8 Ohm measurement shows 0.2dBr difference and the speaker has 60 Ohm impedance at 3kHz?

The output impedance is essentially zero at 3 kHz. That means the voltage loss relative to 60 ohm with be just the same. So no impact at all.

 

[mcdn]

I had 3 TPA3255´s dead after using a 48V power supply for months.

Sorry to hear that, but as @tonycollinet said, that's likely a problem with the specific modules, power supply or control circuitry you were using, not anything inherent to the TP3255.

There are many poor implementations around, some even designed with caps and inductors that assume a lower voltage power supply, or without sufficient heatsinking. Even at 90% efficiency, 100wpc is 20w of heat to dissipate. The 3e Audio ones were good but no longer available (https://www.aliexpress.com/item/10000090083368.html)

Once those basics are taken care of a good amp design with the 3255 should have a strongly regulated power supply, ideally with soft start as most modules don't have that built in. The bricks are always a bit suspect to me, as 48V/10A stuffed in a small plastic box like that can't be great. Something like https://connexelectronic.com/product/smps600rs/ would be ideal, but it costs almost as much as this whole amp!

And then there should also be circuitry to hold the chip disabled until the power supply settles, and disable it again before the power is removed, to deal with on/off pops.

I learned these lessons the hard way: https://audiosciencereview.com/foru...-power-amp-with-microprocessor-control.25851/

 

[Bruce Morgen]

All else being equal, probably so. The idle power consumption will go up so the amp runs at more elevated temperatures resulting in reduce lifetime. The better the cooling though, the less the concern is here. At these prices though, I would just push it to run where I want it and if it dies, it dies.

I've been running two TPA3255-based "chip amps" with thermal management that's marginal at best (Aiyima A07s with the original undersized heat sinks) at about 46 volts for nearly three years. My strategy aligns with Amir's -- I simply bought another pair of A07s as spares just in case those potential thermal chickens come home to roost.

 

[Bruce Morgen]

Just anecdotally: I ordered two 48 VDC power supplies directly from Aiyima for two recently purchased (directly from Aiyima) A07 amplifiers. Both amps squeal like pigs on those supplies and work fine on 32 volt units. I have no idea what's going on.

My guess is that those "two 48 VDC power supplies" are at fault. I have an otherwise-functional 24VDC 10A power brick that makes any amp to which it's connected squeak rather annoyingly.

 

[thecheapseats]

I've been running two TPA3255-based "chip amps" with thermal management that's marginal at best (Aiyima A07s with the original undersized heat sinks) at about 46 volts for nearly three years. My strategy aligns with Amir's -- I simply bought another pair of A07s as spares just in case those potential thermal chickens come home to roost.

how can I put this politely?... ok - here goes...

if and when I have found an inexpensive china-mfgd device for home use and if it works well and lasts a week or so - I buy a second one as a spare for 2 reasons...

(1) in the back of my mind I figure the thing is going to die because it was silly-inexpensive, and any warranty hassles which involve my time and expense would far exceed its value...

and

(2) in modern retailing at low end prices - you can never buy the same thing twice..., of anything... ever...

this purchasing strategy has paid off more than a half dozen times so far...

 

[Deleted member 48726]

??? You can compute the amplifier output impedance using those two values and then apply it to any complex load.

It's not exactly readily available info from the tests though. Maybe for an EE with sim SW.

Cheap amp without load dependency.

Ive toyed with vcad in an attempt to flatten the impedance but living up to my name, passive filters are a mystery to me. lacking impedance measurement rig doesn't help.

www.audiosciencereview.com

 

[Deleted member 48726]

Wow, just Wow

Wow. -Like "the reader don't know how to calculate Z0 from graphs and simulate complex load wow"?

Or a different wow?

Your comment isn't clear on that.

 

[thewas]

The output impedance is essentially zero at 3 kHz. That means the voltage loss relative to 60 ohm with be just the same. So no impact at all.

If the output impedance is essentially zero at 3 kHz how can the 0.2dBr difference between the 4 Ohm and 8 Ohm measurement be explained?

 

[pma]

??? You can compute the amplifier output impedance using those two values and then apply it to any complex load.

Output impedance of the amplifier is the complex impedance. It has Rout and Lout at least. In case of these class D tpa3255 amplifiers there is also output LC filter. You would need to measure output impedance as a function of frequency. From your plots of frequency response into 4 and 8 ohm resistors it is impossible to get output complex impedance of the DUT amplifier. The information about phase or imaginary part of the impedance is missing.
The output complex impedance of the amp interacts with speaker complex impedance to make a divider constituted of two complex impedances. The resulting transfer function is not trivially predictable.