Topping A90 Headphone Amplifier Review

[thefsb]

Does the volume go to 11?

What? Do you want distortion?

My Headrush board goes to eleven but it's not an ultrafi device like this phones amp.

 

[ferongr]

must be quite sensitive cans, yet I am sure those would sing better with an external amp.

I mostly drive them with an RME ADI-2 DAC.

 

[MalinYamato]

isnt the point in differential amplification not to refer to a fixed ground when arriving at the final output voltage level?

Differential math is quite easy to grasp : Vout = (|hotV| + |coldV|) / 2, thus cold may me regarded as a variable ground.

 

[Tks]

Great work Topping and great work Johnny boy!

But it is not big enough....lol, just joking. Size is not everything. Plus, the shaft looks gold plated. Ok, enough Freudian symbolism. All joking aside, what is that 1/4 inch headphone jack? I have never seen a completely sealed jack with no exposed contacts. Not on amplifiers or guitars. Looks very sleek.

Meh, I couldn't care less about pot size. My biggest qualm is since getting into headphone audio, all the amps I've used, every one of them develop scratchiness in less than a few months. Meanwhile a hand-me-down $100 pair of of Bose desktop speakers (those bad meme-level ones) have a pot that is smooth and flawless even after nearly 6 years. I don't understand this scratchy pot nonesense, and why it always develops on the amps I have that aren't digitally or resistor handled...

I understand it has to do with corrosion or something, but I really wish someone would take care of this scratch nonsense with more care. The only fixes seem to be take Deoxit and spray and create a grime/corrosion soup in the pot, or replace the pot (which I am inept to do, and nor do I feel like I should seeing as how this throwaway pair of powered bose desktop speakers can go without scratch for all this time, and the knob be mega smooth operation-wise).

 

[JustAnandaDourEyedDude]

isnt the point in differential amplification not to refer to a fixed ground when arriving at the final output voltage level?

I think you are right about the term differential! I should have checked into it before posting a vague recollection about something that confused me when I read it. In the post, I was trying to say that the phase inversion was relative to something (ground? neutral?) but that only L+ and L- are output with double the voltage swing between them. Which is probably gibberish, and reflects my poor understanding of it. Lots of posts about "balanced" amplification on ASR and on the internet. Something for me to study in the future , though I have already bought a lot of balanced earphone cables to use the balanced outputs of DAPs and headphone amps

 

[JohnYang1997]

Differential math is very easy : Vout = (|hotV| + |coldV|) / 2, thus cold may me regarded as a variable ground.

Where's the /2 coming from? Also why absolute values?

 

[JustAnandaDourEyedDude]

Differential math is very easy : Vout = (|hotV| + |coldV|) / 2, thus cold may me regarded as a variable ground.

Do you mean Vout = Gain * [(Vin+) - (Vin-)]? (with a very high CMRR)

 

[Francis Vaughan]

It's simple in the name. It's nothing vague like AAA which is completely confusing.
NFCA(nested feedback composite amplifier) is as direct as it can get. Ultra high gain feedback is also straightforward, the total loop gain is very high. Current voltage hybrid feedback is also just as described, tpa6120 is CFA, 1612 is VFA. I can't just make a good performing module and not name it right?

Sure. I agree about the names. They give a hint. What I was curious about was the nesting and composite current/voltage. There are a range of ways of doing this. Nesting is always interesting as there are a range of topologies and interesting issues managing stability. When you mention very high feedback this makes it all the more so. Getting it right isn't trivial, and you have got it right. So one asks.

 

[JohnYang1997]

Sure. I agree about the names. They give a hint. What I was curious about was the nesting and composite current/voltage. There are a range of ways of doing this. Nesting is always interesting as there are a range of topologies and interesting issues managing stability. When you mention very high feedback this makes it all the more so. Getting it right isn't trivial, and you have got it right. So one asks.

Gotta make it work man.

 

[gvl]

The M400 output omits buffer after passive LPF. Hence large and reactive output impedance. It's not a poor design per se but not compatible in this case.

Is it not compatible because A90 has low input impedance?

Also, are the line level outputs just headphone output taps or are they taken from an earlier stage?

 

[JohnYang1997]

Is it not compatible because A90 has low input impedance?

Also, are the line level outputs just headphone output taps or are they taken from an earlier stage?

You can think it that way. But it is not an issue with D90 tho. Many other models from them has output buffer as well as other implementations of 4499. I guess it's a issue where both of us want to give the best measuring performance. It's not completely unusable just the level will be lower. In some way that tames the high voltage output of 5.2V from M400 to a more normal level.
The preamp is taken from the headphone out with a resistor.

 

[Steven Hill]

Will the planned preamp have a remote control for the volume?

 

[JohnYang1997]

Will the planned preamp have a remote control for the volume?

Yes

 

[auronthas]

Thanks for the measurements @amirm

Any chance of having A50 measured?

Good question.

I am happy with A50 except with the multipurpose button (power and lower/high gain). Want to compare A50 vs. A90 measurement for D90 pairing. I am HD650 user too

I am placing my order now

 

[raif71]

Sorry, I'm confused ....what is all the talk about preamp version? I thought that the A90 back output whether via rca or xlr act like a preamp...ie volume out is controlled by the volume knob as opposed like a fixed line-out, right?

 

[auronthas]

Sorry, I'm confused ....what is all the talk about preamp version? I thought that the A90 back output whether via rca or xlr act like a preamp...ie volume out is controlled by the volume knob as opposed like a fixed line-out, right?

It means you can connect this A90 to another power amplifier/integrated amplifier (via XLR output) while receiving from DAC eg. D90 via XLR input. There is selector switch for pre-amp and HPA.

I believe volume control is locked under Pre-amp mode. Volume control only for headphone.

 

[777]

Why isn't the input impedance in the user manual?

 

[JohnYang1997]

Why isn't the input impedance in the user manual?

There's also no output impedance in M400 manual

 

[raif71]

It means you can connect this A90 to another power amplifier/integrated amplifier (via XLR output) while receiving from DAC eg. D90 via XLR input. There is selector switch for pre-amp and HPA.

I believe volume control is locked under Pre-amp mode. Volume control only for headphone.

So , if I connect A90 to active monitors, volume to the monitors can still be controlled by this A90, right?

 

[auronthas]

So , if I connect A90 to active monitors, volume to the monitors can still be controlled by this A90, right?

I believe you are still able to control active monitors as what you usually control but not from A90, it is fixed volume at A90.