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Topping A90 Discrete Review (Headphone Amp & Preamp)

Rate this Headphone Amp/Pre-amp

  • 1. Poor (headless panther)

    Votes: 16 4.0%
  • 2. Not terrible (postman panther)

    Votes: 13 3.2%
  • 3. Fine (happy panther)

    Votes: 69 17.1%
  • 4. Great (golfing panther)

    Votes: 306 75.7%

  • Total voters
    404

staticV3

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1.
Could someone please explain this measurement to me?
How does it work? And what kind of signal is used for it?
The Amp's volume knob is set to max.
It is connected like so: APx555 DAC->A90->Dummy load->APx555 ADC (last two in parallel)
Then, the APx555's DAC plays a 1kHz sine wave at very low level and measures what comes out of the Amp.
Increase the level and measure again, rinse and repeat.
At some point, the Amp reaches its maximum output level and clipping occurs.

2.
What volume would I get with the A90D and a 60 ohm headphone, 83 dB sensitivity
(and what frequency are you referring to on this)?
The A90D can drive the Susvara to about 116dB SPL peak. Both at 1kHz and as an average value between 300Hz and 3kHz.
It is not 83dB/mW btw. HiFiMAN likes to overestimate their headphones' sensitivity. 3rd party, independent measurements have shown closer to 80dB/mW.
 
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Bow_Wazoo

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if the volume knob is at 0db (Display 99), then the measurement signal is less than 0 dB TPL before clipping starts, right?
What does it actually sound like when the a90d is clipping?

According to my brain, with my HE-1000 Stealth, I can't get the amp to clip. I can turn to a maximum of 80 (Harman target, preamp -7db), and there the bass is already so loud, that I fear for my life!
 

solderdude

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What does it actually sound like when the a90d is clipping?

Use a player like VLC for instance. Go to the equalizer, set it to 'flat' and turn up the pre-amp. Set windows volume to max. Set the DAC volume to max and adjust volume with the A90 to a pleasantly loud level.
At some point the sound will become a bit grittier, less nice sound. The higher you go the more clipping
 

staticV3

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True peak level
0dB(FS I presume) TPL is a unit of digital signal amplitude.
The measurement signal is not digital. It's analog (Because the A90D is an Amp, not a DAC).
But yes, the measurement signal that comes out of the APx555 is never clipping. All distortion comes from the DUT.
 

Atanasi

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0dB TPL (dBFS I presume) is a unit of digital signal amplitude.
The measurement signal is not digital. It's analog (Because the A90D is an Amp, not a DAC).
But yes, the measurement signal that comes out of the APx555 is never clipping. All distortion comes from the DUT.
I suppose True Peak Level is the Peak Level (as opposed to RMS) and takes into account inter-sample overs, so the True Peak Level of a digital sound wave can be more than 0 dbFS.
 

Bow_Wazoo

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I see. TPL is an indication of the digital signal. But the measuring signal of the AP must not exceed a certain value (I don't know if you talk about dB or vrms), otherwise the input signal will be distorted at some point.
0dB(FS I presume) TPL is a unit of digital signal amplitude.
The measurement signal is not digital. It's analog (Because the A90D is an Amp, not a DAC).
But yes, the measurement signal that comes out of the APx555 is never clipping. All distortion comes from the DUT.
I see. TPL is an indication of the digital signal. But the measuring signal of the AP must not exceed a certain value (I don't know if you talk about dB or vrms), otherwise the input signal will be distorted at some point?!
 

staticV3

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But the measuring signal of the AP must not exceed a certain value (I don't know if you talk about dB or vrms), otherwise the input signal will be distorted at some point?!
I don't follow, sorry. The APx555 can output an analog measurement signal with up to 26Vrms amplitude. It will not output a clipped sine wave unless you explicitly ask it for that.
The APx555's input can accept signals up to 300Vrms amplitude.

At 60Ω, the A90D's output will clip at about 15.75Vrms. At that point, the signal at the A90D's input has 8Vrms amplitude when in Low gain, or 2.7Vrms when in High gain.
 

Bow_Wazoo

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Use a player like VLC for instance. Go to the equalizer, set it to 'flat' and turn up the pre-amp. Set windows volume to max. Set the DAC volume to max and adjust volume with the A90 to a pleasantly loud level.
At some point the sound will become a bit grittier, less nice sound. The higher you go the more clipping
But wouldn't it just be an overload of the input signal? And no clipping of the amplifier?

That would be in principle the same as if I bring a test signal, as here 1000hz, with the preamp to say +3dB to overdrive?
(thats Neutron player on my smartphone).

Preamp 0dB
Screenshot_20230101_130100_Neutron Player.jpg
Screenshot_20230101_130109_Neutron Player.jpg

Preamp +3.2db
Screenshot_20230101_130132_Neutron Player.jpg
Screenshot_20230101_130126_Neutron Player.jpg
 
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Bow_Wazoo

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I don't follow, sorry. The APx555 can output an analog measurement signal with up to 26Vrms amplitude. It will not output a clipped sine wave unless you explicitly ask it for that.
The APx555's input can accept signals up to 300Vrms amplitude.

At 60Ω, the A90D's output will clip at about 15.75Vrms. At that point, the signal at the A90D's input has 8Vrms amplitude when in Low gain, or 2.7Vrms when in High gain.
Yes the problem is, that my English sucks, and I am only conditionally able to explain what I want to say.

Anyway, the measurement signal / input signal must not exceed a certain Vrms value, the input signal is distorted before the amplifier clip, right?! In other words, the A90D accepts input signal, right?
Or is this always related to the position of the volume knob?
 

staticV3

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@Bow_Wazoo please don't post a bunch of smartphone screenshots in full res, one below the other. Makes it a chore to scroll through, see here.
Better to do it like this:
Screenshot_20230101_130132_Neutron Player.jpeg Screenshot_20230101_130132_Neutron Player.jpeg Screenshot_20230101_130132_Neutron Player.jpeg Screenshot_20230101_130132_Neutron Player.jpeg
 

staticV3

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Anyway, the measurement signal / input signal must not exceed a certain Vrms value, the input signal is distorted before the amplifier clip, right?! In other words, the A90D accepts input signal, right?
Or is this always related to the position of the volume knob?
The test tone that comes out of the APx555 will never clip.
The A90D's input may clip at some point. We don't know though, no one tests this.
What we do know is that the A90D's input definitely won't clip with any signal amplitude that you and I can create with consumer gear.
And we know the signal amplitude at which the A90D's output clips.
 

solderdude

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But wouldn't it just be an overload of the input signal? And no clipping of the amplifier?

In this case the audible effect will be exactly the same. So this would answer your question as to how a clipping amplifier sounds like.
 

Snoopy

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This error seems to be common enough not to buy an A90D without a warranty. I really hope Topping will find a proper fix whatever that might be.
Still glad I dodged a bullet and got the SMSL SP400 instead a few weeks before the topping was released.

Seems like nothing but bugs since it's release till now.
 

zhgutov

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I was initially skeptical about my observations, but finally made the comparison with the matched volume.
I used Topping D90SE and A90 Discrete with XLR connection and LCD-3 connected via 4-pin XLR.
First setup: D90SE at -1.0 dB and A90D (low gain) at volume 81 (-9 dB).
Second setup: D90SE at -10.0 dB and A90D (low gain) at volume 99.
The music was attenuated before the DAC by 15 dB in both cases.

I have more harsh high frequencies with the first setup (and high-mids too).
Another confirmation of this is that I can make the volume higher (at least by 6 dB with the second setup) until it starts feel too loud.

That's why I measured the pre-outs of the A90D (D90SE -> XLR -> A90D -> XLR -> Lake People ADC RS04).
The crosstalk looks like this for the different volume levels (H for high gain):

ct.png


V99 H is almost the same as V99 (around -115 dB, flat).

The corresponding noise floor (self-noise of ADC), which doesn't allow me to go below -120 dB:

dr.png


This actually corresponds to the measurements of the headphone outputs here:
https://www.l7audiolab.com/f/random-inspection-of-topping-a90d/

Just wanted to notice, that this is possible to hear (probably because of the specific crosstalk phase, need to check this).
Since D90SE has it's own good digital preamp I think this is the case when the digital volume is actually better :)
 
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pouni

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Hello all,

being new to HiFi, I have a question that is probably a bit silly: could I use a suitable adapter to connect my headphones (Meze 109 Pro) to the XLR outputs on the back of the A90d? Are the rear connectors not suitable for headphones for some reason?

Best regards

Bojan
 
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