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Topping A90 Discrete Review (Headphone Amp & Preamp)
- Thread starter amirm
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shrimp_dude
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I use the A90D's ground lift switch to solve a coil whine/ground loop sound that comes through USB on my computer. The only other solution is to use a usb isolating device like the ifi idefender or Topping HS01.
Between those two choices (ground lift switch vs usb isolator), which is the optimal choice?
Between those two choices (ground lift switch vs usb isolator), which is the optimal choice?
If the ground switch solves the problem, then you're fine
There is new Topping isolator HS02
Here I want to share some experience with headphones and A90D.
It seems like there is not enough power for some use cases.
I have Beyerdynamic DT 770 Pro 250 Ohm and Dan Clark Audio Stealth (23 Ohm).
When I watch a movie I mix, for example, 7.1 to Stereo.
Left = 0 dB, Right = 0 dB, Center = -3 dB, surrond channels = -3 dB, LFE = +7 dB (+10 dB to Left and Right).
Before this I attenuate each channel to -15 dB FS to avoid clipping.
In this case I can have full dynamic range.
This means I need to crank the volume up a lot.
In this case A90D can power DCA Stealth without any problem (surprise).
But in the case of DT 770 Pro A90D has not enough power (surprise again).
I can tell this for sure because the distortion is the same on both channels.
If the headphones itself are distorting it usually has some kind of imbalance/difference.
So I think there is still a room to make the headphone amp better by providing more power for high impedance headphones.
It seems like there is not enough power for some use cases.
I have Beyerdynamic DT 770 Pro 250 Ohm and Dan Clark Audio Stealth (23 Ohm).
When I watch a movie I mix, for example, 7.1 to Stereo.
Left = 0 dB, Right = 0 dB, Center = -3 dB, surrond channels = -3 dB, LFE = +7 dB (+10 dB to Left and Right).
Before this I attenuate each channel to -15 dB FS to avoid clipping.
In this case I can have full dynamic range.
This means I need to crank the volume up a lot.
In this case A90D can power DCA Stealth without any problem (surprise).
But in the case of DT 770 Pro A90D has not enough power (surprise again).
I can tell this for sure because the distortion is the same on both channels.
If the headphones itself are distorting it usually has some kind of imbalance/difference.
So I think there is still a room to make the headphone amp better by providing more power for high impedance headphones.
ivanfraser
Member
Hi. I have ground loop hum when I use my coax from preamp to dac. This only affects the phono stage output from my dac to the headphone amp. The balanced circuit is fine from player to A90D.
I want the higher end coax in situ and the ground lift solves the hum. Topping indicates to leave the lift off - if I'm interpreting correctly - for normal use.
Does this imply any deleterious effects in the measured signal if simply left on all the time?
When in balanced mode especially - which suffers no issues. Or is it best to switch to lift as required only in rca mode? (something which would be a real pain as my kit is on a shelf and the switch not easy to access).
Currently, I'm using a relatively cheap optical cable instead to solve the issue. Would much prefer the better coax.
Thanks
I had that problem with my headphone amp (China production too). I have disconnected the grounds (they had them soldered together in factory) and added a 680nF capacitor between them.
That's how is done in my Denon, HK, and basically every serious equipment sold in US. Probably is because the way we have the grounded receptacles here as opposed to not grounded in other countries... IDK.
In your case, I would keep it lifted. Not sure if your device has the capacitor between the two grounds or not.
That's how is done in my Denon, HK, and basically every serious equipment sold in US. Probably is because the way we have the grounded receptacles here as opposed to not grounded in other countries... IDK.
In your case, I would keep it lifted. Not sure if your device has the capacitor between the two grounds or not.
Topping recommends to leave it off if you have no issues.
If you have hum and lift solves your issue, that's exactly why they included this switch - that's 100% it's designed function
Just to be clear, your headphone amp is not the Topping A90 Discrete right ?
ivanfraser
Member
It's the Discrete. That's what the D stands for in the name.
I wasn't quoting and asking you... Sonic is talking about grounding issue about another headamp...
ivanfraser
Member
I know that this is the intended purpose, but I'm not sure if there's a measurable deleterious effect in keeping it lifted.
This would be a factor in choosing to go with the coax and lifted or perhaps consider a higher end optical cable to negate the ground loop altogether without the lift.
I like to squeeze every last ounce of performance from my kit, within the limits of my budget, and would prefer to keep the cabling of my entire system entirely Shawlined from preamp to dac to headphone amp
So the question remains, if anyone has any knowledge of the potential deleterious effects of permanent lifted - including the balanced circuit with no hum; would that signal suffer from the lift?
ivanfraser
Member
Gotcha, sorry. I jumped in from the email and replied to yours instead of Sonic
I thought it was an odd question
No, in your case the measurement would improve with ground lifted.
The hum you eliminate would show an improvement in measurement
Worry less !
These measurements are so symptom dependent too
There is no way anyone can talk about your system measurements
You'd need to buy a Cosmos ADC if it bothers you
ivanfraser
Member
Yes. But I don't have to have hum at all. I don't at present. I never had it on the balanced circuit. I've eliminated it on the unbalanced side by using optical.
The improvement is relative to the use of the coax. Of course the signal improves in that case, by eliminating the hum.
It would only be a factor if I put the coax back.
I can't be reaching to the back of the amp every time I switch from balanced to unbalanced circuits - it's not practical. I use both and balanced and unbalanced inputs and outputs. I have one set of balanced phones and one unbalanced. I bought the amp partially for the remote, so I'm not up and down switching my amp manually.
I'll restate my question - please forget the other issues and my particular setup. And it's fine if you don't have the answer
Within the amp - regardless of the rest of the system - does having ground lift 'on' have any measurable deleterious effect on the signal, compared to 'off'? Either in balanced mode or rca mode? I.e. does the lift only eliminate hum, if present, and leave the audio signal entirely unaffected?
Furthermore, would I be altering my balanced signal, by leaving lift engaged, on the balanced circuit, which does not suffer hum at all?
Let me deal with the 'worry' side of things. I've ADHD and will worry anyway. I accept psychoacoustics as an issue too. Just want to be sure there's no measurable issue that might affect the best possible quality of the signal chain. Then I don't need worry about anything anyway
Thanks for your efforts in trying to help, but you're missing the essence of my gist here
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ivanfraser
Member
Thank you for your input. I know these kinds of posts are frustrating to address - I've had plenty experienceYes. But I don't have to have hum at all. I don't at present. I never had it on the balanced circuit. I've eliminated it on the unbalanced side by using optical.
The improvement is relative to the use of the coax. Of course the signal improves in that case, by eliminating the hum.
It would only be a factor if I put the coax back.
I can't be reaching to the back of the amp every time I switch from balanced to unbalanced circuits - it's not practical. I use both and balanced and unbalanced inputs and outputs. I have one set of balanced phones and one unbalanced. I bought the amp partially for the remote, so I'm not up and down switching my amp manually.
I'll restate my question - please forget the other issues and my particular setup. And it's fine if you don't have the answer
Within the amp - regardless of the rest of the system - does having ground lift 'on' have any measurable deleterious effect on the signal, compared to 'off'? Either in balanced mode or rca mode? I.e. does the lift only eliminate hum, if present, and leave the audio signal entirely unaffected?
Furthermore, would I be altering my balanced signal, by leaving lift engaged, on the balanced circuit, which does not suffer hum at all?
Let me deal with the 'worry' side of things. I've ADHD and will worry anyway. I accept psychoacoustics as an issue too. Just want to be sure there's no measurable issue that might affect the best possible quality of the signal chain. Then I don't need worry about anything anyway
Thanks for your efforts in trying to help, but you're missing the essence of my gist here
I had a good look at all connections. Turns out the main buzz was from the pc usb out to preamp, and only evident when the coax was used. With a secondary issue of loop hum when a usb was sent to dac. It was the latter that was solved using the lift.
The buzz continued from pc to preamp to DAC.
Complicated I know, it took me a while to fathom it.
The upshot is, it's sorted (to a liveable with point). Coax is back in, hum is barely audible at high volume and no buzz. No need for the lift now I've routed the pc from a port on my Surface Dock, instead of the laptop's usb port. Lift on or off, I'll just assume it's not affecting sound quality and not worry.
Thanks again.
No. But the ground lift / separation is a similar issue.
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Lifting ground with small value capacitors between them is the general solution done by manufacturers in US. Other countries don't have grounded power receptacles, so the problem is not that "visible".
I use this on my coax SPDIF:
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Refresh your SPDIF audio signal. The SPDIF iPurifier2 goes into your SPDIF port and solves audio caused by poor quality signal transmission. TV, games and movies sound transformed.
ifi-audio.com
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