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Topping A90 Headphone Amplifier Review

mt196

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Strange that the D50 exhibited this because it does not have the 3-pin ground power plug. Perhaps you plugged it directly into the PC for the power source. This means that it would then have 2 USB connections to the PC - data and power. Perhaps that created an additional ground loop.
Nope, I used a separated switching power supply, 5V 2A. My PC with an overclocked 5820K and a Vega64 is very noisy, I know that and I am very sensitive to this kind of noise, but the strange part was that 2 DACs based on AKM chips didn't have the hiss, 3 with ESS did instead. Anyway the electrical tape resolved 95% of the noise coming from the DAC, and the XLRs solved the other 5%, through headphones I cannot hear anything, now I only have a bit of noise coming from my speakers' woofers connected to an Anaview module (this wasn't there with a JDS Atom, it is there with the A90 connected through RCAs). I will use XLRs also on it and, hopefully, problem solved even there
 

Audimon

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USB. The D50 is USB powered. So you'll have noise regardless of the input or not if you have a especially clean USB port.

Not sure as I can only judge from the photos I see on the internet but on all of them there is a separate 5V input so I would presume usb power is not needed.

I would try what @mt196 mentions above. I did the same and just covering the usb ground did the trick for me even with RCA. Dead quiet.

I mentioned it here
 

Tks

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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.
On the defense of the price....bruh, fully balanced headamp, with preamp as well as internal power supply. Man. People just can't get enough....

What does "tracking" mean in the sense of it being "bad"? And when you say you liked the "feel", in what way?
 

jhm

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Apologies if these are ignorant questions but if I use XLR cables between my D90 (connected via USB to my computer) and A90, does that prevent the ground loop problems mentioned above ?

Or should I think about getting a USB isolator mentioned above or should I only do so if I can hear hiss, hum or other noises which are linked to my computer's activity if I turn the volume up ? If the latter, I'm inclined not to rely on my hearing and just do it if it would help (albeit may be inaudible).
 

Audimon

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Apologies if these are ignorant questions but if I use XLR cables between my D90 (connected via USB to my computer) and A90, does that prevent the ground loop problems mentioned above ?

Or should I think about getting a USB isolator mentioned above or should I only do so if I can hear hiss, hum or other noises which are linked to my computer's activity if I turn the volume up ? If the latter, I'm inclined not to rely on my hearing and just do it if it would help (albeit may be inaudible).

With any noise I would start with the easiest steps first. Take a look at the photo in this post.
This was free, took me a couple of minutes and solved my noise problems. If it doesn't help you can always undo it and try the xlr and isolators.
 

Dealux

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Yeah, my cheap DAC has fake balanced outputs that I used with an RCA cable. There was background noise leaking from the outputs (ground loop noise) but then I switched to a balanced cable (TRS to XLR) and the noise disappeared.
 

Rigel

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With any noise I would start with the easiest steps first. Take a look at the photo in this post.
This was free, took me a couple of minutes and solved my noise problems. If it doesn't help you can always undo it and try the xlr and isolators.

Indeed, it is a method that I know works in at least certain cases. Better that it be fine as cellophane, one turn would be enough.

I have USB cables that, from the factory, lack this connection between the shield of the two metal connectors

If, in the absence of that ground connection, the DAC does not work, another option is to use an idefender for example. It is "cheap" and does not harm the sound by maintaining the ground connection.
Otherwise, without any noise problems, the D90 does not require USB signal conditioners or USB power filters. Although USB power is required for a first boot, the rest of the time it is taken internally.
 

hmscott

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That volume knob issue would drive me nuts. I don't remember ever having a loose one like that even on some really crappy gear. For all the precision preached about here at ASR and then see that sloppiness is a head scratcher especially at half a grand.
The A90 volume dial is precise in control of the volume.

The A90 volume control isn't what I am used to, but it didn't take long to get confidence in the precise volume control - there's no vagueness in setting, even with sensitive IEM's on L Gain at the bottom of the volume dial - I get the instant volume advance and decrease I expect from the turning of the knob.

There is no "move with no change" feeling to the volume at all. If I move the volume dial the volume changes with no delay or hysteresis effect whatsoever.

It is a powerful amplifier, almost 7.6w watts in H Gain, and with an XLR connection there is no noise even at the top of the volume control in H Gain with sensitive IEM's - Denu DK2001 / KZ AS16.

The A90 / D90 MQA is a really enjoyable stack to use and listen to. :)
 

hmscott

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I'm not 100% sure on that.
A more traditional alternative solution is to lift the earth on the a90 power supply and use very short RCA cable to connect between the two devices and use the earth connection from the first device for earth.
If the dac is usb powered, then the usb cable can play a role too, shorter the better.
In the end, XLR connection is just hassle free for these devices.
I've not spent a lot of time tracing the source of the "noise", but enough to isolate the noise to the RCA connection - if an RCA cable is plugged in while XLR cable is also plugged in XLR only mode the noise starts as soon as I switch to H Gain even with the volume all the way down.

If I remove the RCA cable the A90 / D90 is dead silent even with the volume all the way up in H Gain.

Further, with the RCA and XLR connected if I remove the USB cable the H Gain crackling noise is gone, but with the volume all the way down as soon as I switch from M Gain to H gain there is a high pitched background sound that increases at the 50% and above volume setting. This is with both the RCA and XLR cable connected between the A90 / D90 and no USB cable connected in XLR only mode. My PC is powered off as are the lights and any other electronics shared with the PC power.

The A90 / D90 are plugged into the same EMI / RFI filtering power strip, which is plugged directly into the wall - with no other devices plugged in to the wall or the strip.

Given time I'll try an optical connection, other USB cables, another DAC (M15), and perhaps a dedicated USB PCIE card for audio like the element H USB 3.0 interface:
https://www.matrix-digi.com/en/products/333.html

But, really it doesn't matter - it's only academic at this point, the XLR connection is dead silent and I'll look for a powered speaker that takes an XLR input. :)
 
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hmscott

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The only semi-safe way I know of doing this would be to use the Hum-X from EB Tech. Schiit actually recommends this device in their user manuals. The absolute safest way to break the ground loop without affecting the integrity of the signal would be to buy an USB isolator.
It should be safe to use the EB Tech Hum X as it maintains ground - there's a ground connection in and out, unlike a traditional "ground breaker" which is usually just an adapter that doesn't have a ground pin on the power connection.

At least in my set up the crackling noise comes from the USB connection to my PC - passed through the USB cable from my PC. Without that USB connection the A90 seems to have some internal generation of a signal that is audible in H Gain with the volume all the way down that increases starting around 50% volume.

With an XLR only cable connection - RCA cable removed - there is no noise at all in H Gain even at 100% volume. :)

@JohnYang1997 - there seems to be some signal interaction between the XLR / RCA connections when both cable sets are connected...
 
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Matias

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I lift (disconnect) the ground of my amplifiers and keep them connected on the source. Avoids ground loops and the equipment is still grounded by the cables. Works fine and I consider it to be just as safe.

AVRs rarely have ground plug on their IEC inputs, have you noticed?
 

GXAlan

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Out of curiosity, why wouldn’t US readers just go for a Geshelli headphone amp for essentially the same performance but with much quicker shipping and local manufacturing? They can even do custom colors.
 

ReaderZ

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Out of curiosity, why wouldn’t US readers just go for a Geshelli headphone amp for essentially the same performance but with much quicker shipping and local manufacturing? They can even do custom colors.

The number of connections and power output difference is really big. A90 has 6.3 SE, 4.4 Bal, 4ping XLR Bal, for headphone, as well as RCA and XLR in and out. Also has 25% more to 250% more power out of single ended output depends on load. For balanced we need wait for review but spec also shows A90 having more than double the power.
 
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Racheski

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Out of curiosity, why wouldn’t US readers just go for a Geshelli headphone amp for essentially the same performance but with much quicker shipping and local manufacturing? They can even do custom colors.
I think you are talking about the new Erish?
I think its ugly, no pre-amp/pass thru, only XLR headphone jack, not nearly as powerful. But if checks all the boxes for you, its a great value.
 

GXAlan

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I think you are talking about the new Erish?
I think its ugly, no pre-amp/pass thru, only XLR headphone jack, not nearly as powerful. But if checks all the boxes for you, its a great value.

Even the Archel2 (and likely the Archel2 Pro) measure well. But that’s a good point about the preamp pass through mode.
 

mt196

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Out of curiosity, why wouldn’t US readers just go for a Geshelli headphone amp for essentially the same performance but with much quicker shipping and local manufacturing? They can even do custom colors.
I'm not in the US, but even if I were the Topping products are 100 times more beautiful than geshellis. They look like DIY products, with strange transparent fumé look.

Ah and of course no preamp, very important for me (but the ugly look was for me the major shortcoming)
 

imrul

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Out of curiosity, why wouldn’t US readers just go for a Geshelli headphone amp for essentially the same performance but with much quicker shipping and local manufacturing? They can even do custom colors.

The aesthetics -- I prefer the clean flow design as opposed to a box that only exists to house the electronics. The only striking part of the Geshelli is the transparent front and back -- and even then it looks as if that was done out of convenience rather than a conscious attempt to maximize aesthetic design flow.

The features -- The Topping amps have more output choices for different headphones whereas with Geshelli, I'd need to purchase adapters. The gain settings are more granular to allow for a more optimal pairing for a larger number of headphones. The input choices on Topping allow for better flexibility -- I can input RCA or XLR and output to the common 6.3mm or 4-pin XLR or 4.4mm. This simply isn't possible with Geshelli -- if I get something with flexible inputs, I can only output 6.3mm; if I get balanced input, I can only output 4-pin XLR. And another point others have pointed out is the ability to use the amps as a pre-amp.
 

Tigi

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-Why RCA input measures better?
A: According to Douglas Self's small signal book, balanced connection is inherently more noisy than unbalanced. The benefits of balanced connection is to avoid interference and ground related issue. In ideal condition, RCA input outperforms XLR in.

-Atom didn't have the noise with RCA but A90 has
A: This is very common with a device that has ground connection. This is classic ground related issue. It's not severe enough to be a ground loop but it's there. Also SMPS needs ground return path to work the best because of leakage current. So RCA connection + separated two grounding route is the cause of the issue. XLR is recommended.

-Will L30 have the issue?
A: Similar to Atom, external transformer based AC power supply is used. This eliminates SMPS's leakage current, traditional transformer magnetic interference, also the earth connection. Hence its unbalanced connection be more robust to interfacing to other devices. Less than 100nV(70nV typical) of mains noise is what you will get.

Hello John,
I very appreciate your work and willingness to discuss various issues in detail. I think of buying Topping A90 to the Chord Mojo. This little DAC/amp has own battery and only unbalanced outputs (2 x jack 3.5). I use its optical input. Do you think the above mentioned noise/interference is likely in this configuration?
 

Wazzupi

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-Why RCA input measures better?
A: According to Douglas Self's small signal book, balanced connection is inherently more noisy than unbalanced. The benefits of balanced connection is to avoid interference and ground related issue. In ideal condition, RCA input outperforms XLR in.

-Atom didn't have the noise with RCA but A90 has
A: This is very common with a device that has ground connection. This is classic ground related issue. It's not severe enough to be a ground loop but it's there. Also SMPS needs ground return path to work the best because of leakage current. So RCA connection + separated two grounding route is the cause of the issue. XLR is recommended.

-Will L30 have the issue?
A: Similar to Atom, external transformer based AC power supply is used. This eliminates SMPS's leakage current, traditional transformer magnetic interference, also the earth connection. Hence its unbalanced connection be more robust to interfacing to other devices. Less than 100nV(70nV typical) of mains noise is what you will get.
How can I avoid grounding issues with my a90 amp so I can use rca?
 
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