AIYIMA A70 Stereo Amplifier Review

[Panelhead]

The graph is really expanded scale. The comments about corner frequency are spot on.
The 150 - 600hz range is about 3 times higher frequency range than of most sub outputs. Something around 40 - 200Hz is common and gives usable results.
I do not like double sub filtering. If using a a subwoofer built in frequency range adjustment, feed it with a full range input.
But even set to 150Hz, this sub out does not cut off soon enough. Almost every speaker will have full output below 150hz The overlap frequency range will yield very poor results.

 

[john61ct]

I do not plan to use this sub output at all.

However, just for my learning, feedback on the below is welcome

I have a pretty big space and want max SPL from OG KEF LS50s, within the bounds of SQ and safety.

So, just because they "can" output below mid-bass frequencies, does not mean I want them to.

So, I will be HP filtering them at 200Hz maybe higher with testing

Choosing a woofer/subwoofer solution that has good SQ with high power right up to 300-500Hz

The overlap frequency range will yield very poor results.

Using real room correction / subwoofer integration (to address elsewhere), not part of any speaker amp.

 

[antcollinet]

I have never heard of any manufacturer putting a 3db per octave filter for subwoofer crossover so very much doubt this is the case that @AIYIMA did that here?
The 150/600hz indication were endpoint ones, where those frequencies were starting to near the relative noise floor and not onset of filtering frequencies!?

At no point did I mention 3db per octave.

See section starting with “ Frequency Response of a 1st-order Low Pass Filter”

https://www.electronics-tutorials.ws/filter/filter_2.html

Particularly the discussion on cut off point.

 

[antcollinet]

I did not mean 0dB, I meant the 150/600Hz are not the points where the filters start, but where they have finished

No, they are not finished. They have reached -3dB. SInce this is the cutoff freqeuncy, Erin doesn’t show the rest of the curve where it drops doen below -3dB at 12db/decade - right up to high frequencies.

50Hz and 250Hz might be better labels, where the filters' impact has begun?

“Where it has begun” is not how the cutoff frequency of a filter is defined: -3dB is. This is basic electronics. If you don’t understand this, and you don’t understand dB, you should really stop guessing.

 

[Panelhead]

Two other items, the blue curve above is 150 Hz, the yellow curve is 600 Hz. Another reason not to use this sub out into a sub with frequency controls is there appears to be a subsonic filter on the sub out. If the sub also filters subsonic the bottom end may get attenuated.
Most subs have a subsonic filter built in. When people get carried away with output levels it can blow amp or damage the voice coils. The filter protects your sub and reduces warranty claims.

 

[john61ct]

Anyone who did want to use this sub out, would only do so to amp + passive.

With an active sub you'd want a plain fullrange main input signal.

There's never been anything but a 100% consensus on that fact from anyone in the thread.

 

[MadMan]

If you were to use this amplifier from a single-ended (RCA) source, but have a passive/switch conversion to XLR connector first, would you get the superior balanced input performance out of the amplifier? In other words, is the balanced performance of this amplifier an inherent part of the balanced inputs? The definite problem with this would be the gain structure of the setup with a typical 2V RCA signal.

 

[antcollinet]

If you were to use this amplifier from a single-ended (RCA) source, but have a passive/switch conversion to XLR connector first, would you get the superior balanced input performance out of the amplifier? In other words, is the balanced performance of this amplifier an inherent part of the balanced inputs? The definite problem with this would be the gain structure of the setup with a typical 2V RCA signal.

The benefit of balanced connections has nothing to do with the input to the amp.

They are about the connection between the source and the amp. The idea is that if noise is picked up between source and amp, it is picked up equally on both the positive and negative inputs. On the input of the amp, when the negative input is subtracted from the positive input, the noise picked up on the cable cancels out;

See section "Making a difference" in this article.

https://www.hypex.nl/media/fa/d8/a3/1682342122/The%20G%20word.pdf

You can get most (but not all) of the benefit using a passive conversion cable IF it is wired to provide a pseudo balanced connection as shown in this diagram. (most RCA to XLR connectors are not wired this way and it is difficult to work out which are - you may need to make your own)

But see this thread also:

RCA to XLR Cable ("pseudo-balanced") to buy ?

just a short question here: I want to buy (not DIY) RCA to XLR (male) cables in the ("pseudo-balanced") fashion that Hypex and others recommend (see picture below). I want to buy ready made / 'off the shelf' cables (of several different lenght) that are of very good* "mechanical" quality, *by...

audiosciencereview.com

with this connector you send the ground twice - both for the shield, and the negative input of the XLR.

The reason you don't get the full benefit of a full balanced connection is the impedances are not matched. On a balanced output - you will get both negative and positive outputs with the same impedance - eg 100ohm

With an RCA output the pin will have an impedance, but the ring is ground - essentially 0 impedance. On a rough back of the envelope calculation I did this results in a reduction in noise rejection from around 40dB to 30dB.

 

[somebodyelse]

They are about the connection between the source and the amp. The idea is that if noise is picked up between source and amp, it is picked up equally on both the positive and negative inputs. On the input of the amp, when the negative input is subtracted from the positive input, the noise picked up on the cable cancels out;

They are also about separating the audio signal from ground so that ground noise (leakage currents, loops etc.) doesn't get mixed in with the audio. In a domestic setting this is the main benefit as there usually isn't that much interference, and cable runs are relatively short.

You can get most (but not all) of the benefit using a passive conversion cable IF it is wired to provide a pseudo balanced connection as shown in this diagram. (most RCA to XLR connectors are not wired this way and it is difficult to work out which are - you may need to make your own)

This is true for proper balanced inputs - taking signal as the difference between the hot and cold, then splitting phase to drive the halves of the bridge. Unfortunately with some amps we've seen the halves of the bridged amp effectively treated as separate single ended inputs, one having hot/ground as input and the other having cold/ground. If you drive that with the RCA-XLR cable you can't get the full power output of the amp, but you should at least get the ground noise rejection. I don't know how they implemented it in this amp.

 

[antcollinet]

They are also about separating the audio signal from ground so that ground noise (leakage currents, loops etc.) doesn't get mixed in with the audio. In a domestic setting this is the main benefit as there usually isn't that much interference, and cable runs are relatively short.

This is true for proper balanced inputs - taking signal as the difference between the hot and cold, then splitting phase to drive the halves of the bridge. Unfortunately with some amps we've seen the halves of the bridged amp effectively treated as separate single ended inputs, one having hot/ground as input and the other having cold/ground. If you drive that with the RCA-XLR cable you can't get the full power output of the amp, but you should at least get the ground noise rejection. I don't know how they implemented it in this amp.

Ground noise and common mode noise are the same thing.

 

[MadMan]

Ground noise and common mode noise are the same thing.

Thanks, I know how a proper balanced connection works and the reason for it. The purpose of my question is whether, with this amplifier, one could use a single-ended source into the balanced input (via pseudo-balanced cables) to avoid the poor performance of the single-ended input without issue...whether that may depend on a specific amplifier's implementation or not. Some amplifiers do have issue connecting this way, perhaps the only way to know is test but without the proper equipment getting a definitive answer is hard.

I did not have the time to read a 35 page thread and thought maybe someone had tried this obvious solution to the worse single-ended input performance.

 

[antcollinet]

What is worse about the single ended input?

 

[MadMan]

What is worse about the single ended input?

It's in the review...10 dB worse SINAD: 95dB for balanced so roughly 16-bit, versus 85 dB for single-ended. Possibly due to the higher gain needed for the single-ended input which matches the typical 6dB, but the performance difference is more than 6dB especially if you look at the noise versus frequency graphs in detail. It would really need to be tested to know I suppose...

 

[antcollinet]

It's in the review...10 dB worse SINAD: 95dB for balanced so roughly 16-bit, versus 85 dB for single-ended. Possibly due to the higher gain needed for the single-ended input which matches the typical 6dB, but the performance difference is more than 6dB especially if you look at the noise versus frequency graphs in detail. It would really need to be tested to know I suppose...

Exactly - the 6dB is from the needed gain difference. So you can't gain that back since the supplied voltage from an RCA output will still only be 2V - you'll still need higher gain (or the volume up higher which has the same effect) to get to the same volume.

However the further 4dB lost - which is unusual may well be differences in the specific input circuit. You may get some of that improvement.


However, in reality - the difference will most likely be inaudible.