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Topping A90 Headphone Amplifier Review

JustAnandaDourEyedDude

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Ok just confirmed!

A90 on Balance input Hi Gain Balanced output 6.0x gain..
No distortion!

Tested with 0dB 1KHz Sine Wave
Distortion happens no matter the volume at highest Gain 3 , 6.6x of THX 887 amplifier

Wonder is it because of the A90 whooping 49Vpp swings?

I love it! Now I can use my headphone on Highest Gain Balance input!

Start saving for the courses in sign language your family will need.
 

saadi703

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Ok just confirmed!

A90 on Balance input Hi Gain Balanced output 6.0x gain..
No distortion!

Tested with 0dB 1KHz Sine Wave
Distortion happens no matter the volume at highest Gain 3 , 6.6x of THX 887 amplifier

Wonder is it because of the A90 whooping 49Vpp swings?

I love it! Now I can use my headphone on Highest Gain Balance input!

This is useful piece of info as I am having this problem with D90 + THX 887. I just came here to ask this specific question. D90 + 887 connected using short XLR cables will result into distortion / clipping at high gain settings no matter the volume level. My guess is that it is because of the voltage supplied to THX887 (4v in case of XLR connection) and THX887 is probably not design for that voltage. Can anyone confirm this? I can work around this problem by using either RCA cable or by using D90 in preamp mode and lower the volume a bit on D90. Both are not ideal solution as in both cases I am loosing headroom in terms of loudness / volume. The volume is important to me as I am using Hifiman Susvara which requires high gain on 887 to reach good level of listening.

Yes I need high gain for my Hifiman Susvara headphones to reach good listening levels on THX887 and A90 will be no different and if I buy A90 then I have to use high gain on A90 as well. Am I reading it correctly that A90 is free from this problem? Is there any distortion / clipping at high gain mode when A90 is connected with D90 using XLR?
 

JohnYang1997

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This is useful piece of info as I am having this problem with D90 + THX 887. I just came here to ask this specific question. D90 + 887 connected using short XLR cables will result into distortion / clipping at high gain settings no matter the volume level. My guess is that it is because of the voltage supplied to THX887 (4v in case of XLR connection) and THX887 is probably not design for that voltage. Can anyone confirm this? I can work around this problem by using either RCA cable or by using D90 in preamp mode and lower the volume a bit on D90. Both are not ideal solution as in both cases I am loosing headroom in terms of loudness / volume. The volume is important to me as I am using Hifiman Susvara which requires high gain on 887 to reach good level of listening.

Yes I need high gain for my Hifiman Susvara headphones to reach good listening levels on THX887 and A90 will be no different and if I buy A90 then I have to use high gain on A90 as well. Am I reading it correctly that A90 is free from this problem? Is there any distortion / clipping at high gain mode when A90 is connected with D90 using XLR?
Gain stage of 789 887 etc is a intermediate stage. The gain is before the volume. Hence the the gain stage will always output the full scale with gain. Hence if you surpass that level it will clip regardless of volume position.
A90 and following amps have the gain after the volume. At 9db gain setting the output stage will have 9db gain. But since the volume comes before the output stage the level is already attenuated. So no clipping unless you turn the volume up.
The former solution was to reduce noise before the volume control. However that doesn't really make sense because when you need high gain you don't need very low noise, that case you use lower gain setting. HOWEVER, even when a90 runs at high gain with gain after the volume control the noise is still much lower than 789 887 about half of the noise. The noise is even a few times lower than that at unity gain. So the noise performance is miles ahead while no issue about internal clipping.
 

Ddd

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This is useful piece of info as I am having this problem with D90 + THX 887. I just came here to ask this specific question. D90 + 887 connected using short XLR cables will result into distortion / clipping at high gain settings no matter the volume level. My guess is that it is because of the voltage supplied to THX887 (4v in case of XLR connection) and THX887 is probably not design for that voltage. Can anyone confirm this? I can work around this problem by using either RCA cable or by using D90 in preamp mode and lower the volume a bit on D90. Both are not ideal solution as in both cases I am loosing headroom in terms of loudness / volume. The volume is important to me as I am using Hifiman Susvara which requires high gain on 887 to reach good level of listening.

Yes I need high gain for my Hifiman Susvara headphones to reach good listening levels on THX887 and A90 will be no different and if I buy A90 then I have to use high gain on A90 as well. Am I reading it correctly that A90 is free from this problem? Is there any distortion / clipping at high gain mode when A90 is connected with D90 using XLR?
I can only let you know I owned the 887 as well and experience the clipping too.. Which is one of the reason I'm happy with this A90 which doesn't have this problem! Can confirm for you as I tested two unit of A90 and used D90 DAC mode 4V XLR ..

Summary. A90 doesn't have this distortion problem at highest Gain of 887.
 

Racheski

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Gain stage of 789 887 etc is a intermediate stage. The gain is before the volume. Hence the the gain stage will always output the full scale with gain. Hence if you surpass that level it will clip regardless of volume position.
A90 and following amps have the gain after the volume. At 9db gain setting the output stage will have 9db gain. But since the volume comes before the output stage the level is already attenuated. So no clipping unless you turn the volume up.
The former solution was to reduce noise before the volume control. However that doesn't really make sense because when you need high gain you don't need very low noise, that case you use lower gain setting. HOWEVER, even when a90 runs at high gain with gain after the volume control the noise is still much lower than 789 887 about half of the noise. The noise is even a few times lower than that at unity gain. So the noise performance is miles ahead while no issue about internal clipping.
Is one or the other more difficult to manufacture and develop? Which one does the HPA4 do?
 

saadi703

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I can only let you know I owned the 887 as well and experience the clipping too.. Which is one of the reason I'm happy with this A90 which doesn't have this problem! Can confirm for you as I tested two unit of A90 and used D90 DAC mode 4V XLR ..

Summary. A90 doesn't have this distortion problem at highest Gain of 887.
This is great news. Thanks so much. It seems that I have to buy A90 to replace my THX887 just for this very reason but I am happy that I don't have to use work around and do not lose the output volume headroom. On top of that A90 matches with D90 in terms of appearance so it would look better as combo. I doubt that I will hear any difference in sound though.
 

saadi703

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Gain stage of 789 887 etc is a intermediate stage. The gain is before the volume. Hence the the gain stage will always output the full scale with gain. Hence if you surpass that level it will clip regardless of volume position.
A90 and following amps have the gain after the volume. At 9db gain setting the output stage will have 9db gain. But since the volume comes before the output stage the level is already attenuated. So no clipping unless you turn the volume up.
The former solution was to reduce noise before the volume control. However that doesn't really make sense because when you need high gain you don't need very low noise, that case you use lower gain setting. HOWEVER, even when a90 runs at high gain with gain after the volume control the noise is still much lower than 789 887 about half of the noise. The noise is even a few times lower than that at unity gain. So the noise performance is miles ahead while no issue about internal clipping.
Thanks so much for the detailed explanation. Now, I know why. Seems like A90 is the way to go for me in order to avoid the clipping.
 

JohnYang1997

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Is one or the other more difficult to manufacture and develop? Which one does the HPA4 do?
I think it has to do with using THX AAA circuitry. With that there are ratios of capacitors and resistors with a wide range for the circuit to work. That limits the resistor values to higher values.
Geshelli also achieved very low noise. And to my knowledge no issue with internal clipping (correct me if I'm wrong).
I'm not sure which way hpa4 went. I know something about the thx 888 being used in sp200 which has inherent 6db gain in the output stage which cannot be changed(that's why the low gain setting is 6db hence the dreaded volume control issue). However hpa4 does seem to have unity gain setting. So not sure about that.
edit:I think the gain structure is inherent in their volume control design. It's more sophisticated and should have the clipping issue.
 

saadi703

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Gain stage of 789 887 etc is a intermediate stage. The gain is before the volume. Hence the the gain stage will always output the full scale with gain. Hence if you surpass that level it will clip regardless of volume position.
A90 and following amps have the gain after the volume. At 9db gain setting the output stage will have 9db gain. But since the volume comes before the output stage the level is already attenuated. So no clipping unless you turn the volume up.
The former solution was to reduce noise before the volume control. However that doesn't really make sense because when you need high gain you don't need very low noise, that case you use lower gain setting. HOWEVER, even when a90 runs at high gain with gain after the volume control the noise is still much lower than 789 887 about half of the noise. The noise is even a few times lower than that at unity gain. So the noise performance is miles ahead while no issue about internal clipping.

@JohnYang1997 Thanks once again for explaining this. One last question, what do you think that how well A90 can drive Hifiman Susvara in terms of volume as well as dynamic range. I will appreciate if you can explain this to me. Thanks
 

JohnYang1997

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@JohnYang1997 Thanks once again for explaining this. One last question, what do you think that how well A90 can drive Hifiman Susvara in terms of volume as well as dynamic range. I will appreciate if you can explain this to me. Thanks
Susvara is a very good match. If Susvara is more inefficient I may say it's not as good as it is. Susvara takes low distortion very well. It doesn't like energetic sounding amps, it needs powerful yet calm amps imho. You don't want the highs out of control.
 

Ddd

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This is great news. Thanks so much. It seems that I have to buy A90 to replace my THX887 just for this very reason but I am happy that I don't have to use work around and do not lose the output volume headroom. On top of that A90 matches with D90 in terms of appearance so it would look better as combo. I doubt that I will hear any difference in sound though.
Sadly, came from D90 and 887 previously,

The A90 just transformed the D90

Haha, get one yourself and experience it! You won't regret it! Hope you like it! Enjoy! Haha!
 

Dealux

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^ It's a softer knob lol but it does feel kinda nice.

Mine also arrived today. Will have to save up a bit more to get the slightly better looking and better measuring SMSL M400 to complete my "end-game" source set-up (currently using a cheap Roland interface as a DAC).

EanzCwnXYAEI__6.jpg
 

DavidH

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Is it normal for the volume knob to be this loose before gripping the pot?QUOTE]

Well, from what I've read, only a small number of owners report that behaviour. One owner requested a replacement due to that issue and the replacement was 'better'. However, the designer has said that it is normal, indicating it is not a problem.

My A90 does not behave like that, and I am glad. There is no slack on the volume control on my A90.
 

frogmeat69

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Susvara is a very good match. If Susvara is more inefficient I may say it's not as good as it is. Susvara takes low distortion very well. It doesn't like energetic sounding amps, it needs powerful yet calm amps imho. You don't want the highs out of control.
Guess that goes for the HE-6se also?
 
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