Douk Audio H7 Amplifier Review

[respice finem]

Price is (or should be) irrelevant in technical reviews.
Only the performance and hints of good engineering,maybe durability,safety,etc matters.

Honestly, I don't know... If the forum would be all about "engineers talking to engineers", yes, but it's not really the case. I always tend to think (right or wrong), who is the likely buyer of the item tested and how "fit for purpose" it will be in this context. Regardless if it's cars, houses or audio gear.

BTW: Durability is actually hard to tell sometimes. I've had expensive audio gear that failed relatively fast and some cheap stuff that works long years. It seems to be: the less mechanical parts it has and the cooler it runs, the longer it can be expected to work.

 

[mcdn]

Thank you @amirm,
Some years ago, I had purchased a ClassD amp which arrived with a 32Vdc adapter, but the webpage had stated that it was a 48Vdc adapter.
When inquired about the discrepancy I was told that the TI's TPA3255 life-expectancy significantly reduces with DC@48V.
Is this true?
I also don't know whether the use of a higher input voltage results in any significant changes to your measurement results (re: @32Vdc).

No that is totally untrue. The TPA3255 has a recommended typical power voltage of 51V, with a maximum of 53.5V. 48V is commonly used in practice to allow a very safe margin. See the datasheet at https://www.ti.com/lit/ds/symlink/tpa3255.pdf

 

[Sokel]

BTW: Durability is actually hard to tell sometimes. I've had expensive audio gear that failed relatively fast and some cheap stuff that works long years. It seems to be: the less mechanical parts it has and the cooler it runs, the longer it can be expected to work.

That's why I used the word "hints",as is admittedly difficult to tell by the looks and only time can tell.

Edit:Guaranty that is offered is usually a good hint and discriminates devices,eg,5 y guaranty is a good hint against 1y one but that is also not a subject for a technical review.
Doesn't hurt of course,info is info.

 

[fordiebianco]

Chaps,

the tone on this thread is at times rather aggressive. Please tone it down, doesn't make for a pleasant read.
The wee thing hasn't done anything to hurt you.

 

[PeteL]

It's just a cheap Chinese moving coil meter strapped on the front panel just for fun. Don't take it seriously. After all, the 'amplifier' is just a teenage kid's toy in the first place.

Those actual meters (I have some here- they are made by the millions in China) are incapable of any accuracy or repeatability regardless of how you drive them. Their DCR coil resistance varies from 600R to 650R. They require between 250uA to 290uA to indicate 0dB and are not remotely linear or even return with reliability to the last position you mechanically zeroed them to. Compared to even the battery level meter on a Japanese 1960s cassette player, they are total and absolute junk. They are too small for anything useful.

Definitely very cute looking, with the internal warm white LED lighting and visually reminiscent of the proper (VU ballistics) meters on Sony/Marantz etc 'pressman' cassette recorders used in the 1980s:

On my desk:
View attachment 278277

Backlight LEDs powered at around 5mA:
View attachment 278280

OK, I personally dislike gimmicks like that when it serve no purposes. Bottom line tough, even if they were accurate, I still don't fully see the usefulness in the context of an amp. There really is no rationale at all beside looking cool? Even on very expensive equipment? I get that these don't work but what about those that DO work. What do these indicate is this context, what are they suppose to tell us? The VU meters on my teenage years Sony TC-K15 where certainly not only useful, they were essential when capturing songs from the radio. Are the meters used by McIntosh, Classe, etc also just a glorified eye candy?

 

[respice finem]

OK, I personally dislike gimmicks like that when it serve no purposes. Bottom line tough, even if they were accurate, I still don't fully see the usefulness in the context of an amp. There really is no rationale at all beside looking cool? Even on very expensive equipment? I get that these don't work but what about those that DO work. What do these indicate is this context, what are they suppose to tell us? The VU meters on my teenage years Sony TC-K15 where certainly not only useful, they were essential when capturing songs from the radio. Are the meters used by McIntosh, Classe, etc also just a glorified eye candy?

View attachment 278306

Looking cool is very important for many, especially senior,"home Hi-Fi" customers. That's why we have all these "retro waves" IMHO. Take this Sony deck - today you can get better recordings by clicking a button in software, but the "coolness factor" isn't there.

 

[PeteL]

Looking cool is very important for many, especially senior,"home Hi-Fi" customers. That's why we have all these "retro waves" IMHO. Take this Sony deck - today you can get better recordings by clicking a button in software, but the "coolness factor" isn't there.

Oh don't get me wrong, I am one of those. I value coolness more than everybody I know and am a big fan of Industrial design and would be the first to pass on something I find ugly. But form follow function, always. If not it's just tacky. To me this is very uncool if you ask me.

 

[respice finem]

Oh don't get me wrong, I am one of those. I value coolness more than everybody I know and am a big fan of Industrial design and would be the first to pass on something I find ugly. But form follow function, always. If not it's just tacky. To me this is very uncool if you ask me.

I meant more generally, I wouldn't buy that one either, using just 2 pairs of active monitors and headphones.

 

[PeteL]

I meant more generally, I wouldn't buy that one either, using just 2 pairs of active monitors and headphones.

Don't worry though, this tape deck is long gone. Just a pic from the web.

 

[respice finem]

Don't worry though, this tape deck is long gone. Just a pic from the web.

Mine too, I'm "anticyclic" somehow, the older I'm getting, the more minimalistic.

 

[sarumbear]

What does the VU meter measure?

Input or Output?

If it is adjustable, how to calibrate it?

Or is it eye candy?

Of course it’s eye candy! It’s a “meter” with an undefined level adjustment.

 

[Robbo99999]

Honestly, I am also not understood how this amplifier could get a recommendation. Know about LS, but can not assess the impact of the amplifier.

When looking at the impedance response of randomly selected inexpensive bookshelf speakers on spinorama.org (measured by Amir or Erin), each of these speakers will probably cause ripples in the frequency response.

View attachment 278254 View attachment 278255
View attachment 278256 View attachment 278257
View attachment 278258 View attachment 278259

Up to 65 ohms impedance due to the BR Helmholtz resonance and 30 ohms at the crossover frequency. But there are also LS that reach up to 80 ohms at the crossover frequency.

Amplifiers are not my specialty, is the correlation linear? So if at 4 ohm load difference at 2kHz the FR is changed by 0.2dB, will it be changed by 2dB at 40 ohm difference (or must the phase also be considered)?
Or asked another way, based on the 4 and 8 ohm load impedance measurements of the amplifier, can one simulate the effects of an arbitrary speaker impedance on the frequency response?

If the impact on the frequency response from 20-20000 Hz would remain below 0.5 dB (actually, one would have to consider the Q of the deviation as well, but it makes the consideration even more complicated), the amplifier is almost transparent, otherwise it additionally acts as an EQ and should not be recommended.

For me as an amplifier layman, these analyses by Amir were much easier to understand:
View attachment 278266 View attachment 278267

Good points, I can't answer them though. @amirm or someone else would have to address the influence of these differing speaker impedances and how they would react to this specific amp, or indeed what would be the best characteristics to look for in an amp to minimise any differences caused by these speaker's differing impedances through the frequency range. Good points you bring up I think. It's not my area of expertise as my area of concern re amps is headphone amps where you just want a super low output impedance on the headphone amp then you have nothing to worry about re frequency response issues, and my speakers are active, so again nothing to worry about there.

 

[JayGilb]

It's a $144 amplifier with fairly good measurements and people are trying to pick it apart ?

Thanks for the review Amir.

 

[sarumbear]

Honestly, I am also not understood how this amplifier could get a recommendation. Know about LS, but can not assess the impact of the amplifier.

When looking at the impedance response of randomly selected inexpensive bookshelf speakers on spinorama.org (measured by Amir or Erin), each of these speakers will probably cause ripples in the frequency response.

View attachment 278254 View attachment 278255
View attachment 278256 View attachment 278257
View attachment 278258 View attachment 278259

Up to 65 ohms impedance due to the BR Helmholtz resonance and 30 ohms at the crossover frequency. But there are also LS that reach up to 80 ohms at the crossover frequency.

Amplifiers are not my specialty, is the correlation linear? So if at 4 ohm load difference at 2kHz the FR is changed by 0.2dB, will it be changed by 2dB at 40 ohm difference (or must the phase also be considered)?
Or asked another way, based on the 4 and 8 ohm load impedance measurements of the amplifier, can one simulate the effects of an arbitrary speaker impedance on the frequency response?

If the impact on the frequency response from 20-20000 Hz would remain below 0.5 dB (actually, one would have to consider the Q of the deviation as well, but it makes the consideration even more complicated), the amplifier is almost transparent, otherwise it additionally acts as an EQ and should not be recommended.

For me as an amplifier layman, these analyses by Amir were much easier to understand:
View attachment 278266 View attachment 278267

Here is the FR vs load impedance.

It shows that you may have less that 1dB boost if you have a 2Ohm 8Ohm load at around 15kHz. How many speakers you have seen that has such a low resistance at that frequency, which is usually caused by crossover, which doesn’t exist at such high frequency and even it did will you hear 1dB boost at 15kHz?

 

[PeteL]

Here is the FR vs load impedance.

View attachment 278326

It shows that you may have less that 1dB boost if you have a 2Ohm load at around 15kHz. How many speakers you have seen that has such a low resistance at that frequency, which is usually caused by crossover, which doesn’t exist at such high frequency and even it did will you hear 1dB boost at 15kHz?

Those curves are 4 ohm and 8 ohm. resistive loads

 

[ctrl]

It shows that you may have less that 1dB boost if you have a 2Ohm load at around 15kHz. How many speakers you have seen that has such a low resistance at that frequency, which is usually caused by crossover, which doesn’t exist at such high frequency and even it did will you hear 1dB boost at 15kHz?

Can you explain to me how a layman can roughly estimate from the 4 and 8 ohm measurements of the amplifier, how the frequency response of the amplifier will be affected if, for example, in the 100 Hz range and around 2-3kHz the speaker has 60 ohm impedance?

Is there a way to calculate the frequency response deviation of the amplifier using the speaker impedance, phase and using the 4 to 8 ohm impedance difference of the amplifier?

 

[AdamG247]

For the Budget concerned. This with a VU meter and balanced connections all for under a Buck Fifty! Lots of value here for those who don’t want to spend stacks of cash on a small desktop amp. Golfing Panther territory all things considered.

Great Review @amirm appreciate the work you so tirelessly do for your community!

 

[sarumbear]

Those curves are 4 ohm and 8 ohm. resistive loads

i apologise I was confused with the figure 2 next to it. Still what would a 1dB difference at 15kHz matter?

 

[antcollinet]

Can you explain to me how a layman can roughly estimate from the 4 and 8 ohm measurements of the amplifier, how the frequency response of the amplifier will be affected if, for example, in the 100 Hz range and around 2-3kHz the speaker has 60 ohm impedance?

Is there a way to calculate the frequency response deviation of the amplifier using the speaker impedance, phase and using the 4 to 8 ohm impedance difference of the amplifier?

Note - there is no significant load dependence until you get past 5kHz. But no, I don't think it is calulateable from the measurements taken.

 

[mhardy6647]

I don't know what it is measuring. I set it to 0 dB but forgot to check to see if it accurately displays other levels.

Pretty sure it doesn't measure actual Volume Units -- and I'll bet it doesn't have the ballistics of a VU meter, either.

VU And PPM Audio Metering

ESP Project Pages - VU and PPM metering. Visit my other pages for more audio projects and articles

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https://mikeriversaudio.files.wordpress.com/2010/12/meter-madness_1-2_revised.pdf