You should be able to effectively balance the two channels from a mono source while listening/adjusting for the "phantom center."
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Aiyima A07 Max Amplifier Review
- Thread starter amirm
- Start date
I still think the most likely culprit for the channel imbalance (and potentially the R channel distortion) is a faulty volume pot on the sample that was sent to Amir. But, I'm not loving the 1.0 volt description from Aiyima (compared to the 2v for the Fosi V3). Does their rationale make sense?
solderdude
Grand Contributor
It does... it allows people to use phones/tablets etc. as a music source and still get to the max. output power.
are people really using 3.5mm on a phone out to this? i cant imagine its that many people that it matters in the age of bluetooth and iphones? but then we dont know that if every 1 unit is sold in the west 10 are sold in china...
I think he was asking if their logic makes sense to explain channel imbalance, not in general as a design choice.
solderdude
Grand Contributor
Channel imbalance is highly device dependent.
So agree with @Joe Smith about the volpot being the most likely culprit (but not for the distortion, nor 1V sensitivity decision)
Of course a 1V input voltage means it will be 6dB lower in setting which might mean closer to the 'off position' of the amp and thus having more channel imbalance.
The fix is easy (if the above is the case)... dial back the output voltage of the source or use an attenuator in front of the amp.
It is unknown if its the pot or not as the usual 'volume control position vs output level' measurement is not shown or done so we will never know for this particular copy that was sent to Amir.
So agree with @Joe Smith about the volpot being the most likely culprit (but not for the distortion, nor 1V sensitivity decision)
Of course a 1V input voltage means it will be 6dB lower in setting which might mean closer to the 'off position' of the amp and thus having more channel imbalance.
The fix is easy (if the above is the case)... dial back the output voltage of the source or use an attenuator in front of the amp.
It is unknown if its the pot or not as the usual 'volume control position vs output level' measurement is not shown or done so we will never know for this particular copy that was sent to Amir.
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Speaking of pure design choice, I also don't think this justification makes much sense, 3.5mm audio jacks are a species in danger of extinction, I believe that anyone who uses the phone as a source for casual listening at least uses Bluetooth or a streamer, but I really see very limited use of the smartphone/tablet analog output directly at the amplifier input. However I have no data on this and I could be wrong
solderdude
Grand Contributor
It's just a $ 80 amp.... it can be used in just about any situation and not all sources have 2V out.
OP
- Thread Starter
- #170
This is the position of volume control for all of my tests:
What AIYIMA says is that the pot has that channel imbalance at that position but not at max. For Fosi tests, I did have to crank it up to max due to lower gain so what they say kind of makes sense. What I am surprised is that the volume control at that position would have so much mismatch. As you know, that usually happens close to minimum, not close to max where I have it.
solderdude
Grand Contributor
Ah... in that position there should not be a channel imbalance unless the pot is really crappy.
It could be just a matter of using very poor tolerance resistor range that happens to have the misfortune of having a combination of resistors that happens to give that difference in the gain determining circuit.
Could still be the pot which may not have been put together well (one wiper being in another physical position for instance).
Perhaps the 'volume control' test could give the answers (or having the pot fully clockwise)
I have a Quad 33 + 303 (rescued and repaired) which has a similar 'volume/on-off' construction. It also has a slight channel imbalance but did not bother to look into the reason and just used it with the volume control moved slightly to the left. No such luck with this amp though.
Quad now gathering dust it was just fun to get it operational again instead of it ending up in the trash.
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Not the one provided by @AIYIMA with the imbalance, but i think it may make sense to have a higher gain for this device.
Consider that we are just a small part of their customers.
I suspect most people don't use this amp with "legacy" hifi devices. Maybe they have a phone with headphone or dongle out. Maybe they use the headphone out of their PC, laptop or TV, maybe they use a small DAP, something like a Sansa Clip.
They probably thought these customers and tried to avoid people not getting the full output power. The Fosi V3 thread had some people that complained about it, i suspect they studied the thread in detail.
I think it's fair to put out full power at 1V input. I wouldn't expect this from regular hifi 19" devices, but for this class of devices i can understand their reasoning.
Higher gain can amplify the effect potentiometer deviations have, maybe this was what they where talking about?
I don't think it explains this much of a difference, but we are trying to think about a situation where @AIYIMAs prose makes sense, right? Goodwilled as we are? Right?
BTW, have we talked about the pre-out for the subwoofer yet? Is it attenuated?
Because that was, to my knowledge, the only real problem of the Fosi V3.
isaac507
Member
Got my set today. I tested the psu and it really has a problem. The voltage drops
Of course it's voltage drops if you pull 6 amps, how is this a problem?
Under what condition would you be able to hear the difference an additional 1.2V at 6A make?
isaac507
Member
The issue is that the psu isn't stable and keeps tripping into protection mode after around 20 minutes. I've just uploaded a video to show this.
6A for 20 minutes is no joke for these kinds of power supplies. It certainly is more than what i would have expected.
Again i ask for a real life scenario where this will be relevant.
I probably sound like an apologist for Aiyima, but i really don't think this PSU is a problem.
Well, except that it's below what the chip can take, it should be 48V obviously.
frabor
Active Member
The power supply might be an issue. Seems that Aiyima choose SE amp mode so they could undercooled the unit below it's max stereo power to save money on aluminium extrusions. The amp will go into themal shutdown before you can get the best out of it. The TPA3255 has four amplification modules that can be run in SE ( up to 4 channel), BTL ( bridged stereo) and PBTL (mono). The unit , according to the advertised output, is on SE. On BTL, 51V it is over 200Wpc at 1% distortion.
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Do you have the 32v or 48v power adapter came with V3? I think you could try a comparison test.
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