AIYIMA A70 Stereo Amplifier Review

[john61ct]

Yes the fan issue is easily modded, but the one thing I'd want (if compromising on SQ) is moar power, these days that aspect doesn't break the bank.

A800 which performs a bit better

But you're right in that built-in bass management / xovers really DO add a lot of value

Since I'm a DC guy, Fosi CA30 is my current value benchmark, hopefully that will test well once it clears Amir's queue.


> Due to the ear's lack of sensitivity to low frequencies you probably won't hear the noise from a 'noisy' amp

I see plenty of members stating that is not necessarily true? My bookshelves only cover from midbass ~200+ Hz


> we probably wouldn't hear the difference in a properly controlled test.

Bottom line, I really would prefer that all my amps can be used for full range for future flexibility. And since they are relatively cheap these days, I see no need risking their becoming the weakest link in the chain.

...

> Subs often have relatively high distortion

I will strive for as "clean & tight" SQ as possible with mine, but yes maybe not spending much more on that aspect below, say 50-60Hz

Is fast transients performance related to low distortion?

 

[somebodyelse]

> Due to the ear's lack of sensitivity to low frequencies you probably won't hear the noise from a 'noisy' amp
I see plenty of members stating that is not necessarily true? My bookshelves only cover from midbass ~200+ Hz

Just take a look at how the threshold level shoots up below 100Hz. The contribution you're more likely to hear is mains hum (or not if you're off the grid and not running an inverter)

Is fast transients performance related to low distortion?

I'm going to pass on that one. I assume 'fast transients performance' is a subjective description, not a reference to impulse response, and it's hard to find consensus on what the subjective descriptions mean in terms of measured performance. @solderdude's chart is one of the best references I've seen as a guide to subjective terms vs. frequency response:

 

[john61ct]

Just take a look at how the threshold level shoots up below 100Hz

Sure but I am always going to be using a variable / automatic LC tied to the user-volume control.

And multiple subs tuned to get flat perceived SPL matching the ~200+ Hz main pair

across the audible spectrum as deeply as possible

(relative to the size of my current living space anyway)

...

> The contribution you're more likely to hear is mains hum (or not if you're off the grid and not running an inverter)

I do try to avoid those AMAP, but select clean sine-wave units for when necessary.

What do you mean by "contribution" there?

 

[john61ct]

>> Is fast transients performance related to low distortion?

I'm going to pass on that one. I assume 'fast transients performance' is a subjective description, not a reference to impulse response, and it's hard to find consensus on what the subjective descriptions mean in terms of measured performance

Isn't REW's waterfall graphing an objective measurement? T30 vs EDT

I understand group delays aren't so critical, but I thought (aside from multiple LP smoothing) the central point of multiple freely placed subs, physical room treatments and DRC below-Schoeder was speeding up decay drop-offs, preventing the "smearing" caused by room resonance effects.

On the attack / onset side, say for the initial impulse response of a kick drum at 120-180Hz, I thought rise time slope is important in speaker selection and an important tuning focus for phase alignment.

I would think allowing distortion down there would also contribute to "muddy" bass.

This discussion is way above my pay grade,

Understanding subwoofers

I believe it is settled science that a wave front from a point source has higher impact than a wave front from distributed sources. I also know the room messes up point source wave fronts but it also messes up distributed source wave fronts so it still makes sense that a point source wave front...

www.audiosciencereview.com

but I think it's an important part of what I'm after, and I do want to learn how to get there as objectively as possible.

Maybe best to continue discussion there, apologies for diverting.

 

[dcolak]

Eww

Behringer NX1000D Review (Stereo Amplifier)

This is a review and detailed measurements of the Behringer NX1000D power amplifier with DSP. It is on kind loan from a member. Can't tell if it is discontinued or not but see it on sale at one place for $299. Retail cost is $549. I am a fan of orange displays and NX1000D delivers on that...

www.audiosciencereview.com

Can someone tell me why people think it's OK to use gear with crappy measurements when it comes to subs?

It isn't even powerful!

I got a couple of Yamaha P5000S and P3500S as my main amps

Inside Yamaha amps

That sounds to me like plenty. I have a pair of ATC SCM19v2, not the most sensitive ones, and they go loud with the A-S1000 and 1200. Not saying that there aren't speakers that need more for loud listening, but they should be rare. How much power do you think one needs? @SacreDro since you are...

www.audiosciencereview.com

Measure very well, but still not as refined as my now dead NAD M3.

 

[antcollinet]

On the attack / onset side, say for the initial impulse response of a kick drum at 120-180Hz, I thought rise time slope is important in speaker selection and an important tuning focus for phase alignment.

If you look at the actual waveform of a kick drum (or any other drum) you'll find the attack phase is not fast at all compared to the audio frequency range up to 20kHz. Quite pedestrian in fact.

For a similar illustration (A cymbal strike - probably "faster" than a kick drum), look at my post here:

Speaker "Speed"

I know on ASR, they are so big on measurements and basically saying if you can’t measure it it’s not real, but this seems like a pretty fundamental example for how not everything can be measured. Not agreeing on what to measure != not able to measure it.

www.audiosciencereview.com

I would think allowing distortion down there would also contribute to "muddy" bass.

I think "muddy bass" is more a function of speaker room interaction (room modes, reflections, etc), than anything to do with how fast a speaker cone can pressurise air. Certainly getting good room equalisation in place (combined with proper sub integration) does wonders for perceived bass "impact" or "speed" (if I have any understanding of what people mean by bass speed), that I've never achieved by messing about with different speakers.

 

[somebodyelse]

Sure but I am always going to be using a variable / automatic LC tied to the user-volume control.
And multiple subs tuned to get flat perceived SPL matching the ~200+ Hz main pair across the audible spectrum as deeply as possible (relative to the size of my current living space anyway)

That's got nothing to do with the amp's noise though. Your loudness compensation may be boosting the bass signal, but that's happening before it reaches the subwoofer power amp. It might make LF noise in your signal more audible, but it does nothing to the amp's self noise.

> The contribution you're more likely to hear is mains hum (or not if you're off the grid and not running an inverter)
I do try to avoid those AMAP, but select clean sine-wave units for when necessary. What do you mean by "contribution" there?

Just that many amps show peaks above the broadband noise floor from ground loops and/or PSU at mains frequency and its multiples. That's more of an issue with linear supplies than with switching ones. Not only are they often at a higher level than the broadband noise, but being at a specific frequency makes them more audible. The combination means that they make more contribution to audible noise than the broadband noise does. You do need to be a bit careful regarding FFT gain making the noise appear lower when looking at the plots though - REW's set of separate numbers for noise, distortion and levels of specific harmonics can give a better indication of noise level.

 

[john61ct]

OK thanks to both of you for taking the time, bookmarked for further study as my capacity for understanding grows.

 

[ICIETDIYEUR]

People hi

Here is a small table that is easy to understand (the powers are indicated in watts RMS per channel) ->

If your objective is to operate this amplifier properly (without heating up, even and especially when it does not receive a signal at its inputs), with maximum power but also minimum distortion then the ideal is to use an 8 Ohm load and in absolute terms a 42V/8.3A PSU.

You will thus obtain 2 x 70W RMS per channel ('only'? -> try listening at this power level out of curiosity).

And if your ultimate goal is to obtain maximum SPL then you will have to look for high efficiency speakers with this 8 Ohm load and not persist in using excessive power supplies with low load speakers (worse low efficiency) which will be nonsense with the basic objective which seems to me to be what corresponds to so-called 'high fidelity' listening.

It's simple to understand, it's purely technical and confirmable by calculation or by measurements during tests.

Have a nice day everyone

NB: regarding the opamps, I confirm that the use of the original ones or the OPA1612 or OPA1656 are 'ideal', all the other models sold (too expensive) with lots of snake oil are absolutely useless, except to spend your money...

 

[john61ct]

Note that an amplifier only PULLS current Amperes (thus power) from the PSU to the extent you crank the volume.

You could have 1000W on tap no problem

so long as the voltage is below spec, that's different

 

[ICIETDIYEUR]

Hi nohn61ct

Basic electrical concept ->


The electrical power exchanged by a dipole, the intensity passing through it and the voltage at its terminals are linked by the relationship: P = U × I. P = power in watt (W). U = voltage in volts (V).

According to what you say, this notion is therefore false: please correct yourself

 

[john61ct]

The electrical power exchanged by a dipole, the intensity passing through it and the voltage at its terminals are linked by the relationship: P = U × I. P = power in watt (W). U = voltage in volts (V).

According to what you say, this notion is therefore false: please correct yourself

Sorry I cannot understand why you think that contradicts what I wrote.

Possibly my fault, so feel free to ignore this.

Otherwise I stand by what I wrote, the main point being, the power/current source only "offers" a maximum capacity.

It is up to the load device how much is actually provided, so a PSU with "too high a current" is not a thing, except for wasting money.

However, the maximum VOLTAGE is critical, going over spec on that can reduce longevity / reliability.

 

[dcolak]

Sorry I cannot understand why you think that contradicts what I wrote.

Possibly my fault, so feel free to ignore this.

Otherwise I stand by what I wrote, the main point being, the power/current source only "offers" a maximum capacity.

It is up to the load device how much is actually provided, so a PSU with "too high a current" is not a thing, except for wasting money.

However, the maximum VOLTAGE is critical, going over spec on that can reduce longevity / reliability.

As in, Amps are pulled, Volts are pushed?

 

[john61ct]

As in, Amps are pulled, Volts are pushed?

Yes amps are pulled

volts are just the given, pressure of the pipe?

Until the load device is asking for more amps relative to the "available capacity" then volts can start to drop.

Which is a problem with my LS50s impedance variability

when approaching max safe SPL with a chip amp, as opposed to the GFA-555.

Will be testing at some point if PFFB really makes a difference.

 

[dcolak]

Yes amps are pulled

volts are just the given, pressure of the pipe?

Until the load device is asking for more amps relative to the "available capacity" then volts can start to drop.

Which is a problem with my LS50s impedance variability

when approaching max safe SPL with a chip amp, as opposed to the GFA-555.

Will be testing at some point if PFFB really makes a difference.

That's why prefer class AB, the capacity is much higher even with lower W amps.

 

[john61ct]

I need DC-powered externally and small, efficient.

3e A7 series delivers 34A if needed for ultra-low impedance dips,

both Stereo (two chips vs A70 only one, so capped at 17A) and Mono models, both capped at 48V.

Mono version A7 is spec'd to accept 51Vdc, so 9-10A PSU gives a bit more headroom.

Apparently the A7 Stereo version may handle peak heat outputs better.

It would be rare for these difference to be audible IRL

 

[magreen]

That's why prefer class AB, the capacity is much higher even with lower W amps.

I don't see why that would be true. Care to explain?

 

[dcolak]

I don't see why that would be true. Care to explain?

Just compare the specs, it is easy to see. Bass is first to go.

My Pioneer SA9800 100w amp is brutally better power and otherwise than fosi v3 mono "100w" amp.

 

[magreen]

Nobody who knows what they’re doing pays attention to specs. It’s the measured power at a reasonably low distortion that matters.

 

[john61ct]

Yes, those are specs, just from trusted third parties like Amir and Erin.

Maybe more accurate if the mfg ones are "optimistic" or imprecise