AIYIMA A70 Stereo Amplifier Review

[Schlippwhip68]

Differences like night and day? Really? When swapping op amps?

Technical basics aside, have you ever wondered why people keep popping up on forums, YouTube, etc., who hear such significant differences but can't provide any measurements or other evidence?
When you then ask them to do a blind test, these people either back out or have to admit that they can't hear any difference in a blind test.
As I said, the excuses for this could fill books, and the list of users who promised proof and blind tests and couldn't deliver is endless.

In the same way, you could easily record and compare the signal, as several people have already done here in the forum, but there are no such recordings with audible differences.

How much money could someone, or even the manufacturers, make if there were even one consistent proof of such differences?

I always recommend conducting your own blind tests; afterward, the issue is always resolved, even if some people quickly fall for the next snake oil trick.

Does Op-amp Rolling Work?
Op-amp Rolling Using Sparkos on Fosi V3 Mono
Does Op-amp Rolling Work? [Video]
Amplifier Op-amp Rolling Part 2 [Video]

Goodness me yes! Big differences to my ears, are you being sarcastic?

Regardless to say I am remaining firmly in the camp of op amp preference. For me personally I find components synergy is very, very real.
For my own listening tastes for example and with the A70 in particular I find the Muses 8920 works together very well with my Fiio K7bt (AKM chip based) and to me that makes a lot of sense. Both have a more natural sound together, they don’t sound as synthetic as some other combinations.

 

[DavidM1]

For me personally I find components synergy is very, very real.

That’s nice.

The thing that makes ASR worth visiting is the shared commitment to objective reality. Arrange for someone else to switch level-matched samples and find out for yourself how well you can differentiate between them.

 

[oyasai]

My Conclusion:In the end, it's always the power supply.
Thank you all for the incredibly insightful discussion. It has helped me to consolidate my thoughts into a coherent logical framework. Here is the final thought process that is guiding my modification project, based on the evidence and expertise shared here.

1. The Problem Definition:

• Observation A (Measurement Data): As seen in the A80 vs. Devialet comparison video, affordable Class D amps can exhibit significant low-frequency phase distortion under load, which correlates to subjective reports of "bloated" or "uncontrolled" bass.
• Observation B (Physics): As detailed in Analog Devices' app note on Power-Supply Pumping, an amplifier's power supply can be subjected to significant voltage stress from the woofer's back-EMF, especially at low frequencies.

2. The Bottleneck Hypothesis:
Based on the above, my primary hypothesis is that the root cause of this poor low-frequency control is not the TPA3255 chip itself, but the power delivery system's inability to act as an ideal voltage source.

• The bottleneck is fundamentally the Power Supply Architecture. This includes the external power supply's output impedance, its ability to sink current (counteract pumping), and its transient current delivery.
• The secondary bottleneck is the quality and ESR of the onboard electrolytic capacitors, which act as the final, critical "last-mile" reservoir for the amplifier chip.

3. The Countermeasures (My Modification Plan):
My upgrade path is a direct, systematic attempt to address these specific bottlenecks.

• Priority 1: External Power Supply Upgrade. This is the most critical step. Moving from the stock adapter to a high-current, low-ripple, stabilized power supply is the single most effective way to improve the amplifier's foundation.
• Priority 2: Onboard Capacitor Upgrade. This is a necessary follow-up. Even with a perfect external supply, the performance can be throttled by subpar onboard capacitors. Swapping them for high-reliability, low-ESR components like the Rubycon ZLJ is not about "tuning the sound," but about ensuring the integrity and transient capability of that final power reservoir. (I have reasons to believe the stock caps may not be genuine, which further justifies this step).

4. The Inference (The Business Case):

• My inference is that Aiyima offering an optional, more powerful ($80) 48V/10A power supply is a tacit admission of this reality. To hit the $200 price point for the A70, the compromise had to be made on the included power brick. The amplifier's true performance is only unlocked with a more capable supply.

And finally, the op-amp swap...

• Priority 3: Op-Amp Swap to OPA1612. I did this one first while waiting for my capacitors. Why? Because it looks cool, doesn't it? (Haha)

This entire process has been a fascinating journey from subjective listening, to measurement data, to electrical engineering principles.
Thank you all for being a part of it.
(And yet, I still swapped the op-amps. Go figure.)

 

[Dave TR3A]

My Conclusion:In the end, it's always the power supply.
Thank you all for the incredibly insightful discussion. It has helped me to consolidate my thoughts into a coherent logical framework. Here is the final thought process that is guiding my modification project, based on the evidence and expertise shared here.

1. The Problem Definition:

• Observation A (Measurement Data): As seen in the A80 vs. Devialet comparison video, affordable Class D amps can exhibit significant low-frequency phase distortion under load, which correlates to subjective reports of "bloated" or "uncontrolled" bass.
• Observation B (Physics): As detailed in Analog Devices' app note on Power-Supply Pumping, an amplifier's power supply can be subjected to significant voltage stress from the woofer's back-EMF, especially at low frequencies.

2. The Bottleneck Hypothesis:
Based on the above, my primary hypothesis is that the root cause of this poor low-frequency control is not the TPA3255 chip itself, but the power delivery system's inability to act as an ideal voltage source.

• The bottleneck is fundamentally the Power Supply Architecture. This includes the external power supply's output impedance, its ability to sink current (counteract pumping), and its transient current delivery.
• The secondary bottleneck is the quality and ESR of the onboard electrolytic capacitors, which act as the final, critical "last-mile" reservoir for the amplifier chip.

3. The Countermeasures (My Modification Plan):
My upgrade path is a direct, systematic attempt to address these specific bottlenecks.

• Priority 1: External Power Supply Upgrade. This is the most critical step. Moving from the stock adapter to a high-current, low-ripple, stabilized power supply is the single most effective way to improve the amplifier's foundation.
• Priority 2: Onboard Capacitor Upgrade. This is a necessary follow-up. Even with a perfect external supply, the performance can be throttled by subpar onboard capacitors. Swapping them for high-reliability, low-ESR components like the Rubycon ZLJ is not about "tuning the sound," but about ensuring the integrity and transient capability of that final power reservoir. (I have reasons to believe the stock caps may not be genuine, which further justifies this step).

4. The Inference (The Business Case):

• My inference is that Aiyima offering an optional, more powerful ($80) 48V/10A power supply is a tacit admission of this reality. To hit the $200 price point for the A70, the compromise had to be made on the included power brick. The amplifier's true performance is only unlocked with a more capable supply.

And finally, the op-amp swap...

• Priority 3: Op-Amp Swap to OPA1612. I did this one first while waiting for my capacitors. Why? Because it looks cool, doesn't it? (Haha)

View attachment 477605
This entire process has been a fascinating journey from subjective listening, to measurement data, to electrical engineering principles.
Thank you all for being a part of it.
(And yet, I still swapped the op-amps. Go figure.)

 

[Roland68]

Goodness me yes! Big differences to my ears, are you being sarcastic?

Regardless to say I am remaining firmly in the camp of op amp preference. For me personally I find components synergy is very, very real.
For my own listening tastes for example and with the A70 in particular I find the Muses 8920 works together very well with my Fiio K7bt (AKM chip based) and to me that makes a lot of sense. Both have a more natural sound together, they don’t sound as synthetic as some other combinations.

I'm completely serious. Differences like night and day when it comes to good components, especially operational amplifiers, are snake oil and fairyland.

You have an expectation based solely on the price, the MUSES name, and the marketing reputation. This influence is so powerful that it's fooling you.
Read the article, especially the last paragraph. These are truly experienced people who were fooled by a pair of LEDs.
Audio Listening Test That Fooled the Hollywood Sapphire Group
There are reasons why we've been arranging our blind tests for 25 years so that no one knows what's being tested or whether a switch has been made. This then informs whether we conduct further tests and complex measurements, or whether that would be nonsense.
This is also the reason why our tests are extremely unpopular with "audiophiles," and most people shy away from testing, especially with their own devices.
Because excuses for why they can't hear a difference or absolutely don't know which device is running are no longer valid.

But everyone should have their own hobby. If that's yours, that's fine. It's your time and money that you're wasting. And it will stay that way as long as you don't conduct an honest test where you don't know what's going on.
The manufacturer NISD is happy to sell such a cheap op amp for x times the price, as are the dealers. Most of these op amps from unofficial sources are counterfeit and fake anyway.
But what isn't okay is that inexperienced users in this forum are led astray with such nonsense.

 

[Schlippwhip68]

Has anybody tried parallel op amps in the A70? Lets say sitting one op amp on top of the other starting with a pair of NE5532?

 

[somebodyelse]

Has anybody tried parallel op amps in the A70? Lets say sitting one op amp on top of the other starting with a pair of NE5532?

Why do you think that would help? It's usually used to lower distortion driving low impedances. IIRC from Self's measurements that used to be up in his site the distortion starts rising below ~1.2k. I wouldn't expect it to be anywhere near that low in the A70.

 

[Schlippwhip68]

Why do you think that would help? It's usually used to lower distortion driving low impedances. IIRC from Self's measurements that used to be up in his site the distortion starts rising below ~1.2k. I wouldn't expect it to be anywhere near that low in the A70.

Our Polish friend there used a stacked NE5532 (maybe Muses) in this test and wowed more than a few with the results. I read elsewhere that a 'ballast' capacitor to balance the voltage should be considered, which I am not sure if one was in this test.

 

[antcollinet]

@somebodyelse, thank you once again. Your last post was exceptionally insightful and genuinely helpful. You were absolutely correct to point out the fundamental misunderstanding in my initial hypothesis.


This was the critical piece of information I was missing. Your explanation sent me back to the TI application notes (specifically, SLAA788A for the TPA3255), and now I see it clearly. The PFFB loop is, as you said, entirely contained within the TPA3255's own ecosystem, feeding back to the chip's input, not the preceding op-amp stage. My premise was indeed faulty, and I appreciate the correction.

However, this correction does not invalidate my modification plan; paradoxically, it reinforces it from a different logical standpoint.

Here is my revised and now more accurate understanding of the signal chain in my system:

1. miniDSP SHD (DAC Stage): Creates the initial analog signal.
2. Op-Amp Stage (A70 Input): Functions as an independent buffer/pre-gain stage. It operates under its own local feedback. Crucially, any noise or distortion introduced at this stage is outside the TPA3255's PFFB loop.
3. TPA3255 Stage (Modulator + Power Stage + PFFB): Receives the signal from the op-amp. The PFFB loop works brilliantly to correct for non-linearities in the power stage and, most importantly, the output LC filter. But it can only correct the signal it receives. It cannot correct for flaws already present in that signal.

Therefore, my conclusion remains the same, but with a more robust foundation:

To achieve the highest possible fidelity, the signal fed into the TPA3255 must be as pure as possible. Since the op-amp stage is not "cleaned up" by the PFFB loop, its own self-noise and distortion directly impact the final sound quality.

This confirms that my planned upgrades are correctly targeted:

• Op-Amp Swap (OPA1612): This is a direct measure to improve the quality of the signal before it enters the TPA3255, minimizing the noise and distortion that the PFFB loop cannot address.
• Power Capacitor Swap (Rubycon ZLJ): This is to optimize the "power reservoir" directly serving the TPA3255 power stage, ensuring its ability to deliver instantaneous current without compromise, thus maximizing the effectiveness of the PFFB's control over the speaker load.

Thank you for helping me to refine my understanding. The discussion has solidified my confidence that this modification path, focusing on these two specific areas while leaving the core PFFB architecture untouched, is indeed the correct one for my goals.

---

In short, the correction clarified the limits of PFFB — and precisely because of those limits, op-amp and power supply upgrades remain the most effective path.

---

Documentation
TPA324x and TPA325x Post-Filter Feedback
Op Amp Measurements

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[ampguy]

I ordered one of these. I was actually waiting hoping a PA5ii would go on sale by BF for < $150, but the A70 went on sale today, so I ordered one. I don't see the need for the sub LPF as I do use a sub, but would prefer using the filter on the sub. I also don't need a HPF as the KEF LS50s, to my ears, don't have audible distortion with full freq amplification, though on an A300 amp, which does have a fixed HPF, I do enable it but can't discern if it is on or off, I believe it has been measured at around 100Hz. I like the specs of the a70, but not really expecting to hear much difference between PA5 (og), and A300, Fosi v3, and ClassAB made in Japan Marantz PM7005 int amp.

 

[john61ct]

KEF LS50s

Yes HPF would only be of benefit, if trying to safely squeeze every last dB of SPL out of them with a suitable high-current high damping factor power amp.

 

[Schlippwhip68]

I ordered one of these. I was actually waiting hoping a PA5ii would go on sale by BF for < $150, but the A70 went on sale today, so I ordered one. I don't see the need for the sub LPF as I do use a sub, but would prefer using the filter on the sub. I also don't need a HPF as the KEF LS50s, to my ears, don't have audible distortion with full freq amplification, though on an A300 amp, which does have a fixed HPF, I do enable it but can't discern if it is on or off, I believe it has been measured at around 100Hz. I like the specs of the a70, but not really expecting to hear much difference between PA5 (og), and A300, Fosi v3, and ClassAB made in Japan Marantz PM7005 int amp.

It’s a great little amp and I say little but this has a huge amount of power! Much more power than my Douk Audio A5 using the same op amps, SX52B, and the same power brick, 36v 6a. It is 1.00 o'clock on the A5 and 9 -10 o’clock on the A70!

I also use an Fosi Audio DC Power filter with it and a custom 20cm cable which also makes enough of a difference to keep it in the chain. The custom 20cm cable makes a big difference over the stock cable that came with the Power filter. Better tighter and cleaner bass, the stock cable let the bass run wild in comparison. These are just minor tweaks but the A70 sounds great straight out of the box. I also changed the main knob as I found the stock knob a little over weighted for smooth gain. It’s a solid lump of aluminium and it’s not on the most robust of potentiometers either. I bought (Ali Express) a 30mm x 13mm aluminium knob but it’s not solid. It has a thin aluminium shell with a plastic internal frame and no where near as heavy so it turns a lot more accurately.

I am going to put an Ampapa A1 pre amp with Mullard EF95 (M8100) tubes on the top shelf next week and pass the K7 dac through it. I have two of these, the A70, one with the SX52B op amps which work very well and are loud. I am waiting for a pair of Muses 02 to arrive next week which I will pop into the other. The opa2134 and Muses 8920 also work well with this amp. Just depends on your taste as to which op amp you may prefer imo but the SX52B covers all genres very well and so does the Muses 8920 op amp. I found the opa2134 great for bass driven music like EDM, Reggae, Ska, HipHop, Drum and Bass etc. That said the stock sound of the A70 with the NE5532 is very good but the SX52B will take it up a notch or two for clarity and refinement.
Sorry about the photo angle.

 

[ampguy]

It’s a great little amp and I say little but this has a huge amount of power! Much more power than my Douk Audio A5 using the same op amps, SX52B, and the same power brick, 36v 6a. It is 1.00 o'clock on the A5 and 9 -10 o’clock on the A70!

I also use an Fosi Audio DC Power filter with it and a custom 20cm cable which also makes enough of a difference to keep it in the chain. The custom 20cm cable makes a big difference over the stock cable that came with the Power filter. Better tighter and cleaner bass, the stock cable let the bass run wild in comparison. These are just minor tweaks but the A70 sounds great straight out of the box. I also changed the main knob as I found the stock knob a little over weighted for smooth gain. It’s a solid lump of aluminium and it’s not on the most robust of potentiometers either. I bought (Ali Express) a 30mm x 13mm aluminium knob but it’s not solid. It has a thin aluminium shell with a plastic internal frame and no where near as heavy so it turns a lot more accurately.

I am going to put an Ampapa A1 pre amp with Mullard EF95 (M8100) tubes on the top shelf next week and pass the K7 dac through it. I have two of these, the A70, one with the SX52B op amps which work very well and are loud. I am waiting for a pair of Muses 02 to arrive next week which I will pop into the other. The opa2134 and Muses 8920 also work well with this amp. Just depends on your taste as to which op amp you may prefer imo but the SX52B covers all genres very well and so does the Muses 8920 op amp. I found the opa2134 great for bass driven music like EDM, Reggae, Ska, HipHop, Drum and Bass etc. That said the stock sound of the A70 with the NE5532 is very good but the SX52B will take it up a notch or two for clarity and refinement.
Sorry about the photo angle.View attachment 481417View attachment 481420

Interesting, I’m planning to keep mine stock. I assume the A70 has linear vol pot, unlike the Fosi v3 audio taper?

 

[Schlippwhip68]

Interesting, I’m planning to keep mine stock. I assume the A70 has linear vol pot, unlike the Fosi v3 audio taper?

I think so, it feels and sounds like one. Jumpy start with little increase at higher volume.

 

[Jon L]

Interesting, I’m planning to keep mine stock. I assume the A70 has linear vol pot, unlike the Fosi v3 audio taper?

Douk A5 volume pot seems to build volume quite slowly and evenly, so I don't think A70 actually has significantly more power, more likely difference in volume pot and/or gain..

 

[ampguy]

Only listened for an hour, but balanced SMSL D6 DAC with Roon source, and vinyl (RCA) are sounding better than the SMSL A300. I'm using my REL filter, and have the sub dial (on amp) all the way up, and at about 100Hz on the HT/1205. I’m not a bass head, and only 25 to 33 of my music has much below what the ls50s can reproduce. Don't want to get into subjective audiophile terms, but the clarity is better with the A70. A70 has no remote, but I can control volume with DAC. Great bargain!

 

[martin11]

It’s a great little amp and I say little but this has a huge amount of power! Much more power than my Douk Audio A5 using the same op amps, SX52B, and the same power brick, 36v 6a. It is 1.00 o'clock on the A5 and 9 -10 o’clock on the A70!

I also use an Fosi Audio DC Power filter with it and a custom 20cm cable which also makes enough of a difference to keep it in the chain. The custom 20cm cable makes a big difference over the stock cable that came with the Power filter. Better tighter and cleaner bass, the stock cable let the bass run wild in comparison. These are just minor tweaks but the A70 sounds great straight out of the box. I also changed the main knob as I found the stock knob a little over weighted for smooth gain. It’s a solid lump of aluminium and it’s not on the most robust of potentiometers either. I bought (Ali Express) a 30mm x 13mm aluminium knob but it’s not solid. It has a thin aluminium shell with a plastic internal frame and no where near as heavy so it turns a lot more accurately.

I am going to put an Ampapa A1 pre amp with Mullard EF95 (M8100) tubes on the top shelf next week and pass the K7 dac through it. I have two of these, the A70, one with the SX52B op amps which work very well and are loud. I am waiting for a pair of Muses 02 to arrive next week which I will pop into the other. The opa2134 and Muses 8920 also work well with this amp. Just depends on your taste as to which op amp you may prefer imo but the SX52B covers all genres very well and so does the Muses 8920 op amp. I found the opa2134 great for bass driven music like EDM, Reggae, Ska, HipHop, Drum and Bass etc. That said the stock sound of the A70 with the NE5532 is very good but the SX52B will take it up a notch or two for clarity and refinement.
Sorry about the photo angle.View attachment 481417View attachment 481420

schlippwhip68: Could you write a little more about the 20cm cable you are using, or what connector you are using? I would be interested. A photo would be nice. Thank you.

 

[Roland68]

Only listened for an hour, but balanced SMSL D6 DAC with Roon source, and vinyl (RCA) are sounding better than the SMSL A300. I'm using my REL filter, and have the sub dial (on amp) all the way up, and at about 100Hz on the HT/1205. I’m not a bass head, and only 25 to 33 of my music has much below what the ls50s can reproduce. Don't want to get into subjective audiophile terms, but the clarity is better with the A70. A70 has no remote, but I can control volume with DAC. Great bargain!

If you think it sounds better than the A300's internal DAC with USB or Bluetooth, you're absolutely right.
SMSL has installed a $1 Chinese chip for the USB/BT/DAC function in the A300, which is noticeably worse than the usual DACs tested by ASR.

The A70 also performs better in other measured values. Even if it's not immediately audible, it adds up.
But the A300 is a fantastic subwoofer amplifier when bridged to 4 ohms, delivering 400 watts.

 

[ampguy]

If you think it sounds better than the A300's internal DAC with USB or Bluetooth, you're absolutely right.
SMSL has installed a $1 Chinese chip for the USB/BT/DAC function in the A300, which is noticeably worse than the usual DACs tested by ASR.

The A70 also performs better in other measured values. Even if it's not immediately audible, it adds up.
But the A300 is a fantastic subwoofer amplifier when bridged to 4 ohms, delivering 400 watts.

I never tried the built-in DAC of the A300.

 

[magreen]

I just bought an Aiyima A70 stereo for $71 shipped at AE after coupons (without the power supply, but I have extras around the house anyway). That is simply an unbelievable value for money.