Background high pitched noise/RF Interference ?

[lachlanralph]

Hi All,

I have built my Crack and was working fine for the first month or so and then i took it into my office and then the noise stated.

I am having some background noise issues with my Crack and have a feeling that it might be RF related. the noise is a high pitched whine in the left channel almost like a high speed dremel with some pops/crackles in an almost rhythmic fashion, it seems to reduce when i tilt the Crack to about 45 degrees, The only impact that the volume control has is that if i turn the knob to 0 then it becomes louder.

The reason that i suspect RF is that i have it at work with a high number of fluorescent tubes and Wifi access points as well as a lot of switch mode power supplies. and i do not remember having this issues at home when it was built. I have not taken it home to check in a quiet environment now that it has burnt in.

Can anyone provide any insight as to what the issue might be and how to resolve it ?

Thanks,

Lachlan

 

[adamct]

Sounds like you may have already identified the source of the problem. But just to check, what are you using as your source? Are you using a USB DAC attached to your work computer?

And have you ruled out tube issues?

Best regards,
Adam

 

[lachlanralph]

Thanks Adam,

Yes i use a Schiit Modi DAC but the noise is present with it disconnected and also across several pairs of headphones

I have not been able to rule out a tube issue as i live in Australia and unfortunately they are a bit thin on the ground out here.

I think the next step is to take it home and see if i have the same issues. If i don't and it points to some sort of environmental issues can anyone provide some feed back on how best to  minimise local interference ? extra grounding or some sort of RF choke

Thanks

Lachlan

 

[Paul Birkeland]

Try turning off your cell phone.

-PB

 

[lachlanralph]

Hi Paul,

Thanks for the tip but unfortunately I have tried that i got into the office before anyone else today so no other Cell phones and still had the noise

Thanks

Lachlan

 

[Paul Birkeland]

Next, I would try an outlet tester in the outlet at your office to be sure there is an appropriate ground reference.

-PB

 

[Doc B]

If it's not from a cell phone my hunch is that it might be coming from a computer. That fact that it is reducing when you tilt the amp suggests that it is coming through the air rather than thru the AC mains. If you have the space it might be worth experimenting by putting the amp in different locations to see if the noise changes.

 

[lachlanralph]

Hi All,

Thanks for the replies i think the next step will be to take it home and test it there. If this does prove the cause any advice on how to resolve the issue ?

Thanks

Lachlan

 

[lachlanralph]

Update!

I was looking out my windows this afternoon at work and noticed a Cell tower pointing directly at my desk from the building opposite(I work in a high-rise build in a CBD)  :-[ So i rearranged my desk to put my amp behind a metal partition and it is now dead silent not sure if that was the total cause but from what it looks like its a good bet...

I will keep an eye on it and see how we go once i get my Speedball in as well.

Thanks,

Lachlan

 

[Doc B]

excellent!

 

[howzz1854]

sorry to reply to an old post. but i've run into the same problem with my newly built crack, and after extensive testing i've found it to be my computer CPU and GPU. particularly, if there's a 3d program running, where the GPU kicks into full throttle, the RF interference is the worst. sometimes when CPU is doing something, there's also small amount of RF interference. funny thing is, if i down-clock the GPU core frequency from 1100mhz to 815mhz, the RF interference sound is reduced.

i tried taking a side panel (steel) from another computer and tried placing it directly underneath the amp and it didn't help at all.

what type of "metal" material did you use to block the interference?

i also noticed that if i turn the Crack knob to below 70% the RF interference sound is un-noticeable when CPU/GPU is busy. but it would be great if i can completely block it with a shield somehow, so i can crank the crack all the way up. 

 

[murray]

These are just general comments, not specific to this particular amplifier...
Make sure that the amplifier is on a separate electrical circuit to the computer.  RF can travel via all conductors, including ground/earth.
Also, consider that a sheet of metal can also make a good reflector instead of blocking RFI - it may make things worse.
RFI is not just a beam that can be blocked.  It will be bouncing around all over the place. Try moving the amplifier around.

 

[Doc B]

You have a big clue in that you say the interference goes away with the volume turned down. This means the amp itself is probaby not picking it up, and your cables probably are. Start with better shielded cables.