Hum with aleph P

[Babowana]

We dont have cappusino here only Americano.
You already do have full of Americano, dont you?

 

[rchua77]

All right, I need another hint, I tried Babowana's suggestion (except the thermistor, will buy one this weekend if i can find time). Does anyone spot another ground loop?

If all else fails, I'll rewire as AndrewT's suggestion.

 

[AndrewT]

Hi,
if you KNOW that your mains side is not faulty (=unsafe) then you can temporarily substitute a resistor for the Power Thermistor to check if it improves the hum situation.
But, you MUST reconnect the Safety Earth to the Audio Ground to allow fault current to flow if you want to use your mains operated equipment.

 

[rchua77]

Hi guys,

Tried out a resistor in the gnd, there's still a slight humming noise. And I've also rewired the grounds channel seperately before joining them at the AC Ground IEC connector. The grounding diagram is the same as Babawano's earlier.

Do you think having two resistors, one at each channel before connecting to the IEC ground would help?
Any other suggestions I could try out?

 

[spzzzzkt]

I also have a problem with hum from the dantimax kit. I have connected the input card directly to the attenuator. I am quite sure that we're talking about some sort of ground loop on the relvol3 card (no sure).

Are there any means to find out if there is a ground loop?

From the input card to the attenuator card there are at least 3 connections to ground. Through the serial connection (5 ground pins), from the output of one channel on the input card (confusing) and from the PSU ground (the attenuator draws power from the input card).

This is before the preamp card is connected.

The humm in my cases has the 50Hz hum, and something more similar to white noise - or higher order noise.

thanks for any help

F

Apologies for reviving a long dead thread....

Not sure how I missed this post when I first built my Veteran P1.7 // Dantimax preamp. I shelved the preamp about 5 years ago because I couldn't solve the hum issues, but recently decided to box the preamp and rediscovered the hum. Lifting the five ground pins on the connection between the Input 2 and RelVol3 has finally brought silence!

folkeb if you are still around, I can't thank you enough for posting this information!

cheers
Paul

 

[tze-hao yen]

yes try to put the vr in the output and the input directly to what ever come in

 

[koja]

i never saw this thread before. but, like folkeb, I noticed that Mikkel (dantimax) had common ground for all chanels on his RelVol3 attenuator board. so if one is using star ground from the PS caps, the attenuator board is going to close the loop. so i routinely cut the ground trace in the middle to separate the two channel grounds, and solder one wire where necessary to complete it for the bastardized half. no hum whatsoever.

 

[AudioSan]

it's a easy fix. do NOT solder the beed on both input board and attenuator board. that creates a ground loop. only use ONE of the beeds.

 

[spzzzzkt]

it's a easy fix. do NOT solder the beed on both input board and attenuator board. that creates a ground loop. only use ONE of the beeds.

I'm running with both beads removed and wiring back to the star ground from the input board. Probably not necessary but it is working for me.

I had to reinstate the ground wires in the ribbon cable as I was getting the volume switching to 0dB attenuation without warning every couple of days. I haven't had a recurrence in the week since I did this, and there is no additional hum.