Ideas? Topping A30 Pro--Mains Hum

[Ssend]

Hi,
I am getting 60hz hum on one channel from the pass-through interconnects on my A30 Pro. The hum is only there when the A30 is on and engaged, and it happens only in the output directly adjacent to the mains input. If I switch the output lines, the hum appears on the other channel, the one that is now adjacent to the mains. The hum is not influenced by the volume control (which would be disconnected from the pass-through when the amp is on).
How to remove the hum? Should I be thinking about isolating outside the amp, so maybe wrapping the mains connect in copper foil? Or inside the amp? doing?

Any ideas?

Thanks!

Stef

 

[Helicopter]

Hi,
I am getting 60hz hum on one channel from the pass-through interconnects on my A30 Pro. The hum is only there when the A30 is on and engaged, and it happens only in the output directly adjacent to the mains input. If I switch the output lines, the hum appears on the other channel, the one that is now adjacent to the mains. The hum is not influenced by the volume control (which would be disconnected from the pass-through when the amp is on).
How to remove the hum? Should I be thinking about isolating outside the amp, so maybe wrapping the mains connect in copper foil? Or inside the amp? doing?

Any ideas?

Thanks!

Stef

When A30 is off, does the signal pass through it passively without hum, or if you skip the pre and go straight.to the amp, hum is gone?

 

[Doodski]

How old is this unit? I suspect you may have a issue with it more than something you can solve. Is it in warranty?

 

[JohnYang1997]

What input output are you using? Are you plugging TS into TRS jack?

 

[Ssend]

Good questions.

Inputs/output: XLR in, TRS out.
Hum occurs only in one speaker-- whichever speaker is fed from the TRS out adjacent to the mains in.
Hum occurs only when A30 is powered on.
Hum occurs in all input switch settings, but is slightly louder when switch is set to RCA.
Hum is unaffected by gain setting.
Hum in unaffected by ground lift.

Of course, I can effectively bypass the problem by turning off the power amp, but it would be better for it to work properly.

Purchased recently from another ASR member, but I believe unit is still covered.

I had not heard of this as a known bug.


Thanks!
S

 

[JohnYang1997]

Good questions.

Inputs/output: XLR in, TRS out.
Hum occurs only in one speaker-- whichever speaker is fed from the TRS out adjacent to the mains in.
Hum occurs only when A30 is powered on.
Hum occurs in all input switch settings, but is slightly louder when switch is set to RCA.
Hum is unaffected by gain setting.
Hum in unaffected by ground lift.

Of course, I can effectively bypass the problem by turning off the power amp, but it would be better for it to work properly.

Purchased recently from another ASR member, but I believe unit is still covered.

I had not heard of this as a known bug.


Thanks!
S

Try swap left right cable.

 

[Ssend]

swapping l/r cables shows that the hum occurs only in the channel fed by output adjacent to mains in.

 

[aandres_gm]

May I ask why you're keeping the A30 Pro on while using speakers? Since the unit doesn't work as a pre amp, I believe it makes no sense keeping it on. Topping even mentions the pass-through works when the A30 Pro is off.

 

[JohnYang1997]

swapping l/r cables shows that the hum occurs only in the channel fed by output adjacent to mains in.

We have test in setup like this but no mains hum showed up. Maybe try different cables?
Or it may be a contact issue of the socket.

 

[Ssend]

May I ask why you're keeping the A30 Pro on while using speakers? Since the unit doesn't work as a pre amp, I believe it makes no sense keeping it on. Topping even mentions the pass-through works when the A30 Pro is off.

good question! The issue is that when I'm using phones, the hum is there for others to enjoy!

 

[Ssend]

We have test in setup like this but no mains hum showed up. Maybe try different cables?
Or it may be a contact issue of the socket.

I have tried reseating the connector, but I've not yet tried a different power cable, nor have I tried new interconnects (I only have one pair). I will get after it.
Have to be out of town for a few days, but I will test when I return.

 

[JohnYang1997]

I have tried reseating the connector, but I've not yet tried a different power cable, nor have I tried new interconnects (I only have one pair). I will get after it.
Have to be out of town for a few days, but I will test when I return.

I meant the TRS cable.

 

[Ssend]

Right. I only have that one pair. But the problem is evident in both cables (the hum is only in one channel, the one adjacent to the mains in). But I will get my hands on a different pair!

 

[JohnYang1997]

Right. I only have that one pair. But the problem is evident in both cables (the hum is only in one channel, the one adjacent to the mains in). But I will get my hands on a different pair!

The construction and shielding may have an effect. I'd recommend starquad cables.

 

[aandres_gm]

good question! The issue is that when I'm using phones, the hum is there for others to enjoy!

Well that makes a lot of sense. I was thinking the hum was there when listening through the speakers.