Topping A30Pro Review (Balanced Headphone Amp)

[daftcombo]

Basic explanation of "ground lift".

"Removal of the safety ground connection on equipment can expose users to an increased danger of electric shock and may contradict wiring regulations."

No free lunch.

 

[JohnYang1997]

"Removal of the safety ground connection on equipment can expose users to an increased danger of electric shock and may contradict wiring regulations."

No free lunch.

I knew someone was going to ask that.
https://www.audiosciencereview.com/...view-balanced-headphone-amp.20366/post-672317

 

[respice finem]

"Removal of the safety ground connection on equipment can expose users to an increased danger of electric shock and may contradict wiring regulations."

No free lunch.

There's never a free lunch, but 5V via USB ground lift is hardly a "safety ground" (that's why it's legal), unless you have a completely knackered home electricity circuit, but then you have much more serious problems. One remedy (sometimes) without "ground lift" is having all gear connected to the same socket. There are even chip-based "USB isolators", but your mileage may vary with those...

 

[sam_adams]

"Removal of the safety ground connection on equipment can expose users to an increased danger of electric shock and may contradict wiring regulations."

No free lunch.

If the "ground lift" is implemented correctly, it breaks the shield connection on pin 1 of the XLR connection on the receiving device so the loop current does not flow in the signal cable shield. Current flowing in the shield conductor induces a voltage in the signal conductors which results in noise or SCIN (Shield-Current-Induced Noise)—see Bill whitlock, et al; "Common-Mode to Differential-Mode Conversion in Shielded Twisted-Pair Cables". It does not/should not break the earth ground of the AC power cord.

If the safety earth ground on a device is defeated with a ground lifting "cheater plug" and there is a ground fault, lethal voltages can flow in the shield of signal cables. That would be very bad thing. See Bill Whitlock, "An Overview of Audio System Grounding and Interfacing".

 

[JohnYang1997]

If the "ground lift" is implemented correctly, it breaks the shield connection on pin 1 of the XLR connection on the receiving device so the loop current does not flow in the signal cable shield. Current flowing in the shield conductor induces a voltage in the signal conductors which results in noise or SCIN (Shield-Current-Induced Noise)—see Bill whitlock, et al; "Common-Mode to Differential-Mode Conversion in Shielded Twisted-Pair Cables". It does not/should not break the earth ground of the AC power cord.

If the safety earth ground on a device is defeated with a ground lifting "cheater plug" and there is a ground fault, lethal voltages can flow in the shield of signal cables. That would be very bad thing. See Bill Whitlock, "An Overview of Audio System Grounding and Interfacing".

Actually not the way I implemented it. And basically it's implemented for RCA input induced ground loop. There shouldn't be ground loop with XLR connections in the first place.

 

[sarumbear]

Oh no! Man I have a lot to do to get this video thing right....

If you only had some experience in media players... [couldn’t resist, sorry ]

 

[MWeston]

A30pro actually outputs 16Vrms to 300Ohm before clipping. 840mW
The max power is at around 20Ohm, so 33Ohm is still somewhat voltage limited.
At 16Ohm it outputs 6W before clipping.

Hi John.

That sounds like the rails are about +/- 24V. Did you implement a fully discrete output stage or did you find a powerful opamp capable of such high voltage? It's a great accomplishment either way!

 

[DualTriode]

Hello All,



Just thinking out loud here.



5.5 Watts times 2 into 33Ohms and A JBL D2 compression driver. The D2 driver has two 16Ohm coils, in series that makes 32Ohms.



That could be 5.5Watts into my D2 / M2 Compression Driver M2 horns.



Sounds like a matching for a test drive in my listening room.



Thanks DT

 

[JohnYang1997]

Hello All,



Just thinking out loud here.



5.5 Watts times 2 into 33Ohms and A JBL D2 compression driver. The D2 driver has two 16Ohm coils, in series that makes 32Ohms.



That could be 5.5Watts into my D2 / M2 Compression Driver M2 horns.



Sounds like a matching for a test drive in my listening room.



Thanks DT

I wouldn't recommend it but use with caution.

 

[DualTriode]

I wouldn't recommend it but use with caution.

Okay with an abundance of caution.

What risks are we trying to avoid?

Thanks DT

 

[JohnYang1997]

Hi John.

That sounds like the rails are about +/- 24V. Did you implement a fully discrete output stage or did you find a powerful opamp capable of such high voltage? It's a great accomplishment either way!

Massive paralleled RRO opa1656*10 + discrete flying supplies. All under a large heatsink. Opa564 was a good candidate but it's too similar to thx888 and running at the edge of the voltage can be some what non ideal.

 

[JohnYang1997]

Okay with an abundance of caution.

What risks are we trying to avoid?

Thanks DT

Heat dissipation. Running too hot for too long is not good.

 

[amirm]

Was going to ask the same. @amirm, think you need to clarify your review. Neither of the rear outputs are preamp. Both rca and bal are simple pass thru of the matching input. It's not a preamp.

Good idea. Just put this note in:

NOTE: there is no pre-amp functionality here. The rear connectors are pass through for convenience. Also, the output is only unbalanced and connectors are there for convenience, not more power.

 

[amirm]

What is the ground lift knob for?
@amirm , did you try its two positions?

I did. I had that tiny peak in the measurement so I flipped it but it made no difference. I was using XLR anyway so didn't apply to that so I need to re-test with RCA.

 

[amirm]

On the implication of a golden sample send to me, Topping in the past has offered that I go and buy all of their gear again and they would reimburse me to show they never hand pick a unit. So I for one, have high confidence that we are not being gamed here. I consider them some of the most ethical companies that I have worked with.

 

[Veri]

Massive paralleled RRO opa1656*10 + discrete flying supplies. All under a large heatsink.

That sounds very nifty. Great work, John. Seriously gotta resist buying this one.. haha.

 

[ShiZo]

Is snr in full gain anywhere?

 

[JohnYang1997]

That sounds very nifty. Great work, John. Seriously gotta resist buying this one.. haha.

It literally cost more than A90. And in many ways it's certainly a better achievement than A90.

 

[JohnYang1997]

Is snr in full gain anywhere?

And

 

[deafenears]

Did you read the thread a bit? haha...

Anyway, no. Balanced input, all amplification is single ended from there.

haha, first post after a review should probably be the FAQ.