Topping A90 Headphone Amplifier Review

[Daredev1l7]

Is signal ground of A90 and D90 connected to mains PE ( protective earth), in other words are they class I instruments?

All three devices (A90, SU-9, and DA-8S), are connected to the same UPS (APC Back-UPS Pro 1500 S) which shows a good ground.

 

[Daredev1l7]

Are you connecting an RCA unbalanced cable and an XLR balanced cable to the DA-8s at the same time?
Connecting DA-8s RCA and XLR to the other device at the same time may cause problems in some cases.
Try connecting and testing only one of them.

Initially, just the RCA on the DA-8S were connected to anything (since the XLR cables for the DA-8S arrived a day later) and I just moved the RCA cables from a direct connection on the SU-9 to the preamp out on the A90. With just the RCA cables connected, I had the same issues as described in my original post.

I know once the XLR cables arrived, I tried them with both the XLR and RCA cables connecting the A90 to the DA-8S. I switched back and forth between the RCA and XLR inputs on the DA-8S to listen to the difference between the two connections and experienced the issues described originally. I then moved the RCA cables from the A90 to the SU-9, while leaving the XLR cables connected to the A90, so that I could again switch between the inputs on the DA-8S to compare the difference between the preamp XLR out from the A90 and the direct RCA out from the SU-9. Again, I had the exact same issues as described in my original post and this was how I more easily identified that that A90 preamp out was outputting mono.

I also tested with both the XLR and RCA inputs on the DA-8S connected to the SU-9 and had zero issues when switching between those two inputs on the DA-8S, which should rule out problems with either the XLR or RCA cables I'm using.

I did not try the configuration with just the XLR cables connecting the A90 to the DA-8S and nothing connected to the RCA input on the DA-8S. I also didn't test any configuration that utilized the RCA input on the A90 as I never intended to use the RCA input on the A90. I can test those configs after work this evening.

A buzzing sound or higher noise floor I could see being a potential grounding issue, but having the RCA connected to another device causing the XLR premp out on the A90 to output mono on both channels?

And thank you to both of you for the responses!

 

[pma]

All three devices (A90, SU-9, and DA-8S), are connected to the same UPS (APC Back-UPS Pro 1500 S) which shows a good ground.

... and also a good groundloop, if they all are class I instruments.

 

[Toku]

Initially, just the RCA on the DA-8S were connected to anything (since the XLR cables for the DA-8S arrived a day later) and I just moved the RCA cables from a direct connection on the SU-9 to the preamp out on the A90. With just the RCA cables connected, I had the same issues as described in my original post.

I know once the XLR cables arrived, I tried them with both the XLR and RCA cables connecting the A90 to the DA-8S. I switched back and forth between the RCA and XLR inputs on the DA-8S to listen to the difference between the two connections and experienced the issues described originally. I then moved the RCA cables from the A90 to the SU-9, while leaving the XLR cables connected to the A90, so that I could again switch between the inputs on the DA-8S to compare the difference between the preamp XLR out from the A90 and the direct RCA out from the SU-9. Again, I had the exact same issues as described in my original post and this was how I more easily identified that that A90 preamp out was outputting mono.

I also tested with both the XLR and RCA inputs on the DA-8S connected to the SU-9 and had zero issues when switching between those two inputs on the DA-8S, which should rule out problems with either the XLR or RCA cables I'm using.

I did not try the configuration with just the XLR cables connecting the A90 to the DA-8S and nothing connected to the RCA input on the DA-8S. I also didn't test any configuration that utilized the RCA input on the A90 as I never intended to use the RCA input on the A90. I can test those configs after work this evening.

A buzzing sound or higher noise floor I could see being a potential grounding issue, but having the RCA connected to another device causing the XLR premp out on the A90 to output mono on both channels?

And thank you to both of you for the responses!

I'm not good at English. I'm worried that the meaning of my text will be conveyed to you correctly. I read your text over and over again and managed to understand it.

I researched the UPS you are using.
The output waveform is displayed as "Stepped approximation to a sinewave" in the specifications table of this UPS. This UPS is a simple UPS that outputs a stepped pseudo sine wave. The output has many harmonic noise components. I find this UPS a good choice for use in digital devices such as computer equipment, but not very suitable for use in audio equipment applications. Maybe if you power your audio equipment from a wall outlet, the noise problem will go away.

I want to check the symptoms.
Does the "A buzzing sound or higher noise floor" you say come out only from the DA-8s speaker output?

Does the noise come out even when the DA-8s input cable (RCA & XLR) is disconnected?

About the phenomenon that the sound goes into monaural mode Please try how it changes when you make the next connection.
(I'm wondering about the DA-8s' XLR and RCA input circuits.)

When A90 and DA-8s are connected only with RCA cable.
SU-9 ------- XLR or RCA -----> A90 ------ RCA -----> DA-8s

When A90 and DA-8s are connected only with XLR cable.
SU-9 ------- XLR or RCA -----> A90 ------ XLR -----> DA-8s

When A90 and DA-8s are connected with both XLR and RCA cables.
SU-9 ------- XLR or RCA -----> A90 ----- RCA &XLR ----> DA-8s

 

[Daredev1l7]

... and also a good groundloop, if they all are class I instruments.

My background is biomedical engineering, so I'm more typically focused on grounding from a safety perspective and then trying to balance that out with signal quality, lol. I'll try taking the UPS out of the loop or borrow an extra isolation transformer from work to see if that helps. I deal with intracardiac electrograms at work, so deal with many of the same signal quality problems that affect audio.

 

[Daredev1l7]

I'm not good at English. I'm worried that the meaning of my text will be conveyed to you correctly. I read your text over and over again and managed to understand it.

No worries at all! Your English is far better than my mediocre German or Spanish and I appreciate the help.

 

[Daredev1l7]

I researched the UPS you are using.
The output waveform is displayed as "Stepped approximation to a sinewave" in the specifications table of this UPS. This UPS is a simple UPS that outputs a stepped pseudo sine wave. The output has many harmonic noise components. I find this UPS a good choice for use in digital devices such as computer equipment, but not very suitable for use in audio equipment applications. Maybe if you power your audio equipment from a wall outlet, the noise problem will go away.

I want to check the symptoms.
Does the "A buzzing sound or higher noise floor" you say come out only from the DA-8s speaker output?

Does the noise come out even when the DA-8s input cable (RCA & XLR) is disconnected?

About the phenomenon that the sound goes into monaural mode Please try how it changes when you make the next connection.
(I'm wondering about the DA-8s' XLR and RCA input circuits.)

When A90 and DA-8s are connected only with RCA cable.
SU-9 ------- XLR or RCA -----> A90 ------ RCA -----> DA-8s

When A90 and DA-8s are connected only with XLR cable.
SU-9 ------- XLR or RCA -----> A90 ------ XLR -----> DA-8s

When A90 and DA-8s are connected with both XLR and RCA cables.
SU-9 ------- XLR or RCA -----> A90 ----- RCA &XLR ----> DA-8s

As I mentioned above, I'll try taking the UPS out of the equation as well as try utilizing an isolation transformer to see if that helps.

Does the "A buzzing sound or higher noise floor" you say come out only from the DA-8s speaker output?
Yes, the loud buzzing and high noise floor only comes out from the DA-8S speaker output.

Does the noise come out even when the DA-8s input cable (RCA & XLR) is disconnected?
No, the loud buzzing only occurs when I connect the right RCA connector to the A90 when the A90 is either off or in HPA mode. The loud buzzing does not occur with the XLR connection is involved.

About the phenomenon that the sound goes into monaural mode Please try how it changes when you make the next connection.
(I'm wondering about the DA-8s' XLR and RCA input circuits.)

When A90 and DA-8s are connected only with RCA cable.
SU-9 ------- XLR or RCA -----> A90 ------ RCA -----> DA-8s
Only get the actual audio from the right speaker, though there is audible noise like a high noise floor from both speakers

When A90 and DA-8s are connected only with XLR cable.
SU-9 ------- XLR or RCA -----> A90 ------ XLR -----> DA-8s
I get the actual audio from both speakers, but its the same audio coming out of both and I suspect it is the right audio channel playing on both speakers.

When A90 and DA-8s are connected with both XLR and RCA cables.
SU-9 ------- XLR or RCA -----> A90 ----- RCA &XLR ----> DA-8s
RCA and XLR connections behave the same as described above.

Additional scenarios
When the A90 is removed entirely
SU-9-------> RCA-----> DA-8S
No issues at all, audio sounds normal

SU-9-------> XLR-----> DA-8S
No issues at all, audio sounds normal

When SU-9 and DA-8S are connected with both XLR and RCA cables
SU-9-------> RCA &XLR-----> DA-8S
No issues at all, audio sounds normal utilizing either input on the DA-8S.

Using the Bluetooth input on the DA-8S
BT----->DA-8S
No issues at all, audio sounds normal

My old setup prior to the A90
SU-9-------> RCA-----> DA-8S
SU-9-------> XLR-----> Monolith THX 887 headphone amp (not the DAC/amp combo unit)
No issues at all, audio sounds normal from either the DA-8S and the Monolith THX 887

 

[Toku]

My old setup prior to the A90
SU-9-------> RCA-----> DA-8S
SU-9-------> XLR-----> Monolith THX 887 headphone amp (not the DAC/amp combo unit)
No issues at all, audio sounds normal from either the DA-8S and the Monolith THX 887

Let me ask you another question.
Is the RCA and XLR cable when the above A90 is removed the same cable as when it was connected to the A90?

 

[Mikechw]

Does the noise come out even when the DA-8s input cable (RCA & XLR) is disconnected?
No, the loud buzzing only occurs when I connect the right RCA connector to the A90 when the A90 is either off or in HPA mode. The loud buzzing does not occur with the XLR connection is involved.

There may be a ground loop (RCA) acting as an antenna..
I think you may try discconnect DA-8S and test it with headphones first..

 

[Daredev1l7]

Let me ask you another question.
Is the RCA and XLR cable when the above A90 is removed the same cable as when it was connected to the A90?

Yes, it's the same cables as I wanted to to eliminate one variable at a time.

 

[Daredev1l7]

There may be a ground loop (RCA) acting as an antenna..
I think you may try discconnect DA-8S and test it with headphones first..

That was the first thing I did when I got the A90 the other day. I have zero issues on the headphone output of the A90 no matter what and zero issues with the DA-8S connected directly to the SU-9 DAC. I also had zero issues previously with with my Monolith THX 887 in place of the A90.

The only issues occur when I try connect the DA-8S to the either the RCA or XLR preamp output on the A90 and listen to the speakers connected to the DA-8S. Any other configuration I have attempted works without issue.

Appreciate the suggestion.

 

[Toku]

That was the first thing I did when I got the A90 the other day. I have zero issues on the headphone output of the A90 no matter what and zero issues with the DA-8S connected directly to the SU-9 DAC. I also had zero issues previously with with my Monolith THX 887 in place of the A90.

The only issues occur when I try connect the DA-8S to the either the RCA or XLR preamp output on the A90 and listen to the speakers connected to the DA-8S. Any other configuration I have attempted works without issue.

Appreciate the suggestion.

From my many years of trouble shooting experience, I tried to select and eliminate each of the possible causes in my head.

The noise generated by UPS is not the cause because it is normal when connected to equipment other than A90.

The symptom only occurs when the A90 pre-output is connected to the DA-8s input. Symptoms are the same for both RCA and XLR connections.

If you connect the DA-8s input directly to SU-8 with the RCA / XLR cable used at that time, you can play normally. Therefore, there is no defect in the cable.

Those symptoms are on the speaker output of DA-8s
1, There is noise.
2. There are two types of noise, such as power frequency hum noise and white noise.
3. The music to be played will be monaural.

The above symptoms are mixed and output to the speaker.

From these facts, if the causes are considered one by one by elimination, some abnormality in the pre-output circuit of A90 is most likely.
Possible causes include defective relays, defective soldering of PC boards, adhesion of dust such as solder bridges and metal pieces, and contact with other wiring.

This is a very primitive method, but it may be fixed by hitting the A90 with your hand and giving it vibration.

 

[Daredev1l7]

From my many years of trouble shooting experience, I tried to select and eliminate each of the possible causes in my head.

The noise generated by UPS is not the cause because it is normal when connected to equipment other than A90.

The symptom only occurs when the A90 pre-output is connected to the DA-8s input. Symptoms are the same for both RCA and XLR connections.

If you connect the DA-8s input directly to SU-8 with the RCA / XLR cable used at that time, you can play normally. Therefore, there is no defect in the cable.

Those symptoms are on the speaker output of DA-8s
1, There is noise.
2. There are two types of noise, such as power frequency hum noise and white noise.
3. The music to be played will be monaural.

The above symptoms are mixed and output to the speaker.

From these facts, if the causes are considered one by one by elimination, some abnormality in the pre-output circuit of A90 is most likely.
Possible causes include defective relays, defective soldering of PC boards, adhesion of dust such as solder bridges and metal pieces, and contact with other wiring.

This is a very primitive method, but it may be fixed by hitting the A90 with your hand and giving it vibration.

Yep, the folks at Apos Audio suggested many of the same things the folks on here helpfully suggested and came to the same conclusion that it's likely an internal fault in the A90. They are starting the RMA process to send me a new A90 and returning this one.

Thank you again for all the help!

 

[Toku]

Yep, the folks at Apos Audio suggested many of the same things the folks on here helpfully suggested and came to the same conclusion that it's likely an internal fault in the A90. They are starting the RMA process to send me a new A90 and returning this one.

Thank you again for all the help!

Please let us know the result when you receive a new A90.

 

[Daredev1l7]

Please let us know the result when you receive a new A90.

Will do!

As one last check, I hooked up a set of Adam T5V's to the preamp out on the A90 and had the exact same issues as with the DA-8s amp and Jamo s803 speakers. The T5V's also work perfectly fine connected directly to the SU-9. So just one last little confirmation before packing up and shipping back the A90.

 

[Tachyon88]

@Daredev1l7 That sucks. I'm using a90 as a preamp for my speaker too and everything has been great. Optical, SU-8, A90, all XLR cables running to the speaker amp.

Are you replacing or returning ?

 

[Daredev1l7]

@Daredev1l7 That sucks. I'm using a90 as a preamp for my speaker too and everything has been great. Optical, SU-8, A90, all XLR cables running to the speaker amp.

Are you replacing or returning ?

Replacing with a new A90.

Boxed the current one up tonight and will ship it back tomorrow as Apos sent me the return label this morning. Hopefully won't take too long to get the replacement, but Apos has been very responsive so far.

 

[trl]

Also if anyone knows a replacement for the pot that is better all round, please let me know. I was not able to find a existing model that suited our need. Bourns's 4 gang and 8 gang pots were candidate but the tracking was just bad. I really liked the feel of that pot but no luck. There will be some trade-offs in designing these things.

Trying myself to buy 4-gang 10K pot, but without succes. ALPHA used to build these, but seems that nobody is willing to manufacture such small 4-gang pots these days. I need them as backup for my ASUS Essence One combo, too bad I can't find any.

 

[Toku]

I don't know if it will be helpful,
https://www.vishay.com/potentiometers/

 

[KTN46]

Hello, I was wondering if there were SE measurements for this amp as well.