# Topping A90 Discrete Review (Headphone Amp & Preamp)

• ### 4. Great (golfing panther)

• Total voters
408

#### RosalieTheDog

##### Active Member
Thanks I did find that yesterday.
And thanks to the guy that measured.

That is abnormally low input impedance but not an issue if DAC output impedance is (actually) < 200 ohms (XLR)
Could you guys explain briefly or refer to an explanation of what ratio we should be looking add between these variables?
Output impedance DAC: Input impedance PRE-AMP (A90D). Am I correct this should be 1:8 or 1:10 at least?
Does the same hold for output impedance PRE-AMP (A90D): Input impedance POWERAMP ? Where can I find the XLR output impedance of the A90D? If I'm not mistaken, the cited post only shows the XLR output impedance for the headphone connector?

#### staticV3

##### Master Contributor
Where can I find the XLR output impedance of the A90D? If I'm not mistaken, the cited post only shows the XLR output impedance for the headphone connector?
XLR4 is the 4pin XLR Headphone out:

They did not have the right connectors for it, so could not measure its Zo.

XLR3 is the 3pin XLR Line out:

Zo is 40.6Ω at 1kHz.

#### RosalieTheDog

##### Active Member
XLR4 is the 4pin XLR Headphone out:
View attachment 274072
They did not have the right connectors for it, so could not measure its Zo.

XLR3 is the 3pin XLR Line out:
View attachment 274071
Zo is 40.6Ω at 1kHz.
Thank you. And how should this number (40.6Ω) relate to the input impedance of a power amplifier?

#### staticV3

##### Master Contributor
Thank you. And how should this number (40.6Ω) relate to the input impedance of a power amplifier?
The higher the result of input impedance divided by output impedance is, the better. 10 is usually enough.
To get to 10 with the A90D, your Amp has to have an input impedance of 406Ω or more.

Some of the lowest power amp input impedance you can encounter in the wild is a Purifi Eigentakt with the pre-gain bypassed. In this state, the input impedance is 4400Ω.

In other words, no matter the Amp, the A90D's output impedance is low enough to never be an issue.

#### RosalieTheDog

##### Active Member
Fantastic, thanks so much.

#### rula3000

##### New Member
Just bought the a90 discrete and in my system it sounds better than connecting my dac directly to the amp.

#### WeBuild4Life

##### Member
Just stopping in - my A90D bought in January, updated firmware, has static in ALL right outputs whether a source input is connected, and is present in different electrical outlets. Just started an hour ago.

Muting removes, but setting volume to 0 does not and the static does not get louder or quitter.

Wonder if there is any other troubleshooting I can do, or if I need to RMA.

Damn, I use this has a balanced in and out and also balance out to my Stereo.

#### aphysically

##### Member
Does anybody else have issues with IR remote? i.e. having to point very directly at it? I'm not sure if i'm covering up the IR receiver somewhere - does anyone know where it is? I ordered some new AAA batteries so I'll find out if my remote is just weak.

#### aphysically

##### Member
Just stopping in - my A90D bought in January, updated firmware, has static in ALL right outputs whether a source input is connected, and is present in different electrical outlets. Just started an hour ago.

Muting removes, but setting volume to 0 does not and the static does not get louder or quitter.

Wonder if there is any other troubleshooting I can do, or if I need to RMA.

Damn, I use this has a balanced in and out and also balance out to my Stereo.
This seems to be the reported failure mode in the Topping PA5 a lot. Is there any consensus on *what* is failing here and has anybody else reported the same problem with the A90D?

#### staticV3

##### Master Contributor
Does anybody else have issues with IR remote? i.e. having to point very directly at it? I'm not sure if i'm covering up the IR receiver somewhere - does anyone know where it is? I ordered some new AAA batteries so I'll find out if my remote is just weak.
Common issue with Topping gear. I doubt new batteries will make a difference.
The IR receiver diode is probably just placed poorly inside the chassis.

#### aphysically

##### Member
Common issue with Topping gear. I doubt new batteries will make a difference.
The IR receiver diode is probably just placed poorly inside the chassis.
Okay then, thanks! I use it on my desk so I won't actually be a heavy remote user, but I wanted to make sure my experience was typical.

#### WeBuild4Life

##### Member
This seems to be the reported failure mode in the Topping PA5 a lot. Is there any consensus on *what* is failing here and has anybody else reported the same problem with the A90D?
Well they wanted me to RMA it to China. I am not doing that. I was able to have Amazon do a restocking fee return and I'll get the difference covered by my CC. An amazon reviewer reported the exact same issue after 3 months (I too have had this for 3 months.) So my guess is this is going to start popping up more and more.

Just getting the Schiit Jotunheim 2 which amir reviewed as favorable for balanced connections. Just not going to bother with expensive Chifi anymore. Not worth the hassle. Shame because I loved the A90D.
Does anybody else have issues with IR remote? i.e. having to point very directly at it? I'm not sure if i'm covering up the IR receiver somewhere - does anyone know where it is? I ordered some new AAA batteries so I'll find out if my remote is just weak.
Yes, I have to do that too. There is an art to it haha.

#### Bleib

##### Major Contributor
Well they wanted me to RMA it to China. I am not doing that. I was able to have Amazon do a restocking fee return and I'll get the difference covered by my CC. An amazon reviewer reported the exact same issue after 3 months (I too have had this for 3 months.) So my guess is this is going to start popping up more and more.

Just getting the Schiit Jotunheim 2 which amir reviewed as favorable for balanced connections. Just not going to bother with expensive Chifi anymore. Not worth the hassle. Shame because I loved the A90D.

Yes, I have to do that too. There is an art to it haha.
SMSL has more sensitive remotes. Something I've complained about Topping before.

#### RosalieTheDog

##### Active Member
SMSL has more sensitive remotes. Something I've complained about Topping before.
It's ironic considering the possibility of remote control is actually a stand out feature of this amp, differentiating it from so many other 'desktop' size products (that Schiit, the Singxer etc), and a prerequisite for its use as preamp in my opinion.

#### Bleib

##### Major Contributor
It's ironic considering the possibility of remote control is actually a stand out feature of this amp, differentiating it from so many other 'desktop' size products (that Schiit, the Singxer etc), and a prerequisite for its use as preamp in my opinion.
Yes, but I should say that I do not have personal experience with A90D. I've had about 3 of both Topping and SMSL each and the SMSL stay just because the remote works better.

#### RosalieTheDog

##### Active Member
I have to admit my Topping remote (the RC-15A) did gain about 2 meters in range after swapping the batteries, haha (wish I tried that sooner...). Not sure if it's the same as the A90D one.

#### BossBunos

##### Active Member
Maybe someone can help me out here. Using the a90D as a pre amp and using a dac as input feeding it a 4v RMS sinewave via balanced connection. What can de a90D output as voltage rms? The spec shows 49vpp max. That would result in 17v RMS balanced out?
Does the gain selection on the a90D have influence on the pre amp out?
Hope someone knowledgeable can lift some veils for me

#### staticV3

##### Master Contributor
Maybe someone can help me out here. Using the a90D as a pre amp and using a dac as input feeding it a 4v RMS sinewave via balanced connection. What can de a90D output as voltage rms? The spec shows 49vpp max. That would result in 17v RMS balanced out?
Does the gain selection on the a90D have influence on the pre amp out?
Hope someone knowledgeable can lift some veils for me
The A90D's preamp has +15.3dB gain at most, with Bal in->Bal out:

That means that with 4Vrma in, you can fully max out the output at 49Vpp = 17.3Vrms.

Be careful though as feeding 4Vrms to the A90D in High gain, full volume will clip the output.
You have to keep the A90D's volume at -3dB or below to avoid clipping.

#### BossBunos

##### Active Member
The A90D's preamp has +15.3dB gain at most, with Bal in->Bal out:
View attachment 280794

That means that with 4Vrma in, you can fully max out the output at 49Vpp = 17.3Vrms.

Be careful though as feeding 4Vrms to the A90D in High gain, full volume will clip the output.
You have to keep the A90D's volume at -3dB or below to avoid clipping.
It will clip because the input sensitivity is 3v? Does that mean if I provide 3v in i will get the 17.3v out when the volume is maxed at high gain?
There is no such thing possible as input clipping?
Is it a simple formula to calculate Vrms-out for a given Vrms-in with a given gain factor in db?

#### Music1969

##### Major Contributor
I returned my A90D - much happier with my SMSL SP400 (47k ohm input impedance, also with stepped resistor relay volume control, and the best THX amp modulates AAA-888)

No firmware issues.

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