HiFi Subjectivist ¦ Audio Forum ¦ NVA User Group

I'm hoping someone will be able to help..

I've noticed hum on all inputs (including those not in use) on my p80 with the exception of cd input which is connected to my dac...

If the volume is at minimum or maximum the hum disappears and its dead silent (tdk pot)

It doesn't matter if all inputs are disconnected (including the built in phono rca's and power supply) from the preamp.

I'm wondering now if the phono board is somehow causing the issue or if its the amp or possibly noise from the mains..

Can someone advise if its safe to power up the amp while connected to the speakers but not to the pre amp please?

Yes, it is safe

Do you have a switching power supply somewhere plugged into the mains connection to your amp. A noisy wallwart can ruin your noise floor.

I have my power amplifier and DAC running from one run from the mains, and everything else running from a different run from the mains. That keeps the noise down. When I had everything running on one, was noisy as hell.

Other alternative is maybe get an NVA BMU. That’ll provide a clean electrical signal and reduce noise.

Thanks. I use a Topping D30 which I think has a switching power supply. I will have to check tomorrow to see if its on the same block as the amp. Its funny, when the dac is selected the hum disappears at min and max volume. I will have to disconnect it completely from the mains to see if it helps, so far I've only disconnected the rca's. I also tried to run an earth from the volume pot but it made no difference.

Could the cables running from P80 to power amps be picking up some interference? Are there any mains cables close to them?

Fretless wrote: ↑Thu Aug 31, 2023 10:38 pm Could the cables running from P80 to power amps be picking up some interference? Are there any mains cables close to them?

Yeah unfortunately there is a lot of cables lurking behind the gear and I'm really limited for space

Try to get mains cables away from interconnects and speaker leads. See if that helps.

My lenco ptp MK1 and home made naim clone phono amp introduced a lot of noise when playing phono. The power supply for the phono is two 500va transformers but it is located in the corner of room.

Nevertheless when not playing a record it was very noisy , there were lots of EMF and noise it was picking up .

When I built MK11 , I connected the earth wire from the mains lead at the turntable end to the motor .

It worked a treat , it's so silent now , I've abandoned plans to copper line the acrylic phono box .

Thanks all for the replies.

I tried the amp this morning with just the speakers connected and no pre and I Unplugged both the TT and DAC power supply it was quieter, the main buzzy sort of hum has gone but I am left with a very quiet hum if I put my ear right next to the speaker.

I am wondering about making a BMU since I can't afford to buy one. I'm also wondering about DC Blockers such as that offered by Audiolab or more likely make my own with some research.

I can see myself doing more tests plugging and unplugging equipment to figure out causes... And if its definitely the switching power supplies I'll have to look at linear alternatives... Again, something I could make I suppose

Slight hum with your ear right next to the speaker doesn't sound all that unusual.

If it is audible from your normal listening position - then I would be worried.