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AIYIMA A07 TPA3255 Tear Down

Bruce Morgen

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Does anybody know how the 3.5mm/RCA inputs work (i.e. are they just wired together)? Should you avoid connecting different sources at the same time?

They're just wired in parallel -- unfortunately the 3.5mm jack has the channels reversed compared to the de facto standard of tip=left/ring=right. Connecting to both inputs at same time shouldn't cause any damage, but I'd certainly avoid it. I use the the 3.5mm jack as a stereo output to my active sub, where the channels are summed and the channel reversal doesn't matter. :cool:
 
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amirm

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so long as you are using this for a desk system, you are very unlikely to average that output.
I have easily maxed out desktop amps that put out that kind of power in desktop use. Desktop doesn't mean you use them for background music. When the right rack comes in my playlist, I turn up the volume to enjoy good bass and such.
 

daniboun

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JohnYang1997

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LM4562 would be my first choice based on op-amp rolling a CMoy back in the day.

In the CMoy thread, @JohnYang1997 recommended OPA2156 and OPA2189.
According to the peripheral circuit, I would choose opa827. But I would rather changing the the peripheral circuit and make opa1612 or lm4562 work best.
 

pma

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According to the peripheral circuit, I would choose opa827. But I would rather changing the the peripheral circuit and make opa1612 or lm4562 work best.

But OPA827 is a single opamp, not dual. There is also no DIP version. So it would need a new PCB design. Talking about this part, which I also testem years ago, as of today I would try OPA828.
 

JohnYang1997

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But OPA827 is a single opamp, not dual. So it would need a new PCB design. Talking about this part, which I also testem years ago, as of today I would try OPA828.
You need soic to dip adapter board anyway. So single to dual is not much to add. Opa828 doesn't improve much over 827 (especially noise) and removed some characteristics I like, eg diamond buffer output. Both of these are expensive. I would also prefer just modding peripheral circuit for lower noise.
 

pma

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OPA828 will have lower THD20kHz - my guess. Re noise, 4nV/rtHz is good enough for me. Lower current noise will accept higher source and FB impedances.

When I tested OPA827 vs. OPA627, I liked OPA627 better. Even more expensive, but cost is not important to me. I make it for myself or in a very small lot. At higher gain, I use OPA637.
 

DuncanTodd

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no, I mean a set of security bits. The one in question might be odd, but I'd be surprised if a comprehensive set of security bits wouldn't take care of things.
Had an epiphany this morning and recalled I have a small set of hex bits. Two of them were fitting to open the A04 :)
 

ace_xp2

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I have easily maxed out desktop amps that put out that kind of power in desktop use. Desktop doesn't mean you use them for background music. When the right rack comes in my playlist, I turn up the volume to enjoy good bass and such.

Hmm, when there's racks on my desktop I usually turn the volume down a bit.
 

daniboun

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Regarding OP Amps, I tested the following with the A04 and A07 and Drmodor TPA3255 modules :

OPA1656 / OPA1612 / Burson V5i / OPA627 / Genuine NE5532 / Genuine Muse 02 / 0PA1622 / OPA1642 / OPA1602

The question of Op amps has already been debated on DIY audio, and I had used the OPA1656 and I think the opinions are unanimous, these Op amps are very good and seem to work the best with those amps.

BUT : I just rolled back my Genuine Muse 02 and after a week : I can say that I am really really impressed. : in particular with regard to the restitution of mediums and voices. I listened to David Munyon's HD album on repeat and it really feels like he's singing next to you! At least with my setup.

OPA1656 > will provide the best Soundstage and a clean balance between treble / bass and mids
Genuine Muse 02 > bring vocals to the front of the stage while maintaining a great soundstage and very clean bass
 

trl

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@JohnYang1997 has posted the link to the excellent test. The TI board is much better than the AIYIMA.
Regarding the statement from Quantasylum link: "Class D amps require the output filter be designed for a specific load. If you change the load, the output response will change", I've seen this trebles roll-off behaviour to more expensive Class-D amps too, loosing at least 0.5 dB @ 20 kHz. I wonder why manufacturers are not designing the output filter for 4 Ohms loads instead of 8 Ohms; this way the roll-off will be almost non-existent for 4 Ohms loads, while for 8 Ohms loads will start to roll-off a bit higher (at 24-26 kHz perhaps). I don't think amps will start to oscillate if they'll do that.
 

wwenze

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Actually it will probably ring a bit before rolling off at higher ohms. Random example:

vQ0Xpjd.png

https://www.stereophile.com/content/sonic-impact-model-ta2024-super-t-power-amplifier-measurements

Anyway, as long as we have a filter, we can't avoid having that curve downwards, we can only choose the shape / Q factor. And as far as I understand Q, there is no way to make it a very clean drop with just a second order filter so I give up on it. (Yay 0.707 always works.) And we hate ringing and we hate amplitude >1.0 since it has a chance of causing oscillation as mentioned, so we choose a lower Q. Which means a Q of <1.0 at 8 ohms, and the Q at 4 ohm will be even lower.

A better question will be, who decided the LPF frequency cannot be higher? I'm genuinely curious. We can easily avoid any problem by shifting the frequency way out of hearing range.
Ok, wait, actually, an even better question would be why do some class-AB amps limit their frequency response like this too.

https://www.stereophile.com/content/gryphon-essence-mono-power-amplifier-measurements
1120Gryphfig01.jpg
 
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trl

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Actually it will probably ring a bit before rolling off at higher ohms. Random example:
I do like J.A.'s approach: "Even at the level of a few millivolts, unless this energy is filtered, you can never be sure that you're not actually measuring the interaction between the RF content and the test gear instead of the absolute performance of the amplifier under test (again, see the PS Audio review). Therefore, to ensure that I was measuring what I thought I was measuring, I repeated the THD-related measurements using an active sixth-order low-pass filter set to 30kHz".

Ok, wait, actually, an even better question would be why do some class-AB amps limit their frequency response like this too.
Less than 0.5 dB @ 20 kHz is probably not an issue. An amplifier that measures perfectly flat till 100 kHz or more might have stability issues with high impedance loads. Of course, there are several amps that measure flat from 10 Hz till 100 kHz or more, but in the end it's all about the design I guess.
 

pma

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Regarding the statement from Quantasylum link: "Class D amps require the output filter be designed for a specific load. If you change the load, the output response will change", I've seen this trebles roll-off behaviour to more expensive Class-D amps too, loosing at least 0.5 dB @ 20 kHz. I wonder why manufacturers are not designing the output filter for 4 Ohms loads instead of 8 Ohms; this way the roll-off will be almost non-existent for 4 Ohms loads, while for 8 Ohms loads will start to roll-off a bit higher (at 24-26 kHz perhaps). I don't think amps will start to oscillate if they'll do that.

They are probably trying to find some trade-off? The engineering maths behind the used LC filters is trivial. I am posting a simulation of the frequency response of the LC filter as shown in the TPA3255 TI datasheet. It is valid just for the BTL circuit.

Edit: I removed the plot as I made a mistake reading the datasheet values. The plot would be same as the one in the next post.

output LC filter response into 4 and 8 ohm load.
 
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pma

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I am posting a simulation of the frequency response of the LC filter as shown in the TPA3255 TI datasheet. It is valid just for the BTL circuit.
output LC filter response into 4 and 8 ohm load.

Tried to make a "reverse engineering" from the posted photos of AIYIMA A07. The filter (itself) seems to be better balanced, with less Q when damped by 4 and 8 ohm. We shall see after the real unit arrives.

AIYIMA_filter.png
 

PeteL

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Tried to make a "reverse engineering" from the posted photos of AIYIMA A07. The filter (itself) seems to be better balanced, with less Q when damped by 4 and 8 ohm. We shall see after the real unit arrives.

View attachment 103376
Did you enter the ESR of the parts in those Bode sims?
 
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pma

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Did you enter the ESR of the parts in those Bode sims?

Yes 0.1 ohm, the difference with respect to the plots shown is small or negligible. I think the last plot posted will be close to real thing.

Edit> ESR 0.1 ohm (caps) influence, plus Gen Zout = 0.1 ohm, at 4ohm load. Practically same as above
AIYIMA_filter_ESR.png
 
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