Strange sound coming from my AKSA

KlausF · « **on:** 22 Jan 2006, 06:23 pm »

Hi AKSA fans,

I hope you can help me with a problem I have. I have put my AKSA 55N in a new case and now I have a strange sound that sounds like a radio that is not set to any channel. I thought I used a good arrangement by having the torroids at the front and the bords facing to the back using the heatsinks as a shield against magnetic stray. I have used satelite cable from the back to the switch in the front as a shieldet cable, could this be the problem?
I am thankful for any help.

Klaus

ShinOBIWAN · « **Reply #1 on:** 22 Jan 2006, 06:29 pm »

Do the cables carrying AC pass over the amps? I assume they do if the toroids are at the front.

That could be a problem.

I'm sure Hugh will offer advice as he knows the amps very well.

PSP · « **Reply #2 on:** 22 Jan 2006, 07:22 pm »

Hi Klaus,
Can you short the inputs to the amp? Take two of the cheapest male RCA plugs you have, and solder a wire from the center pin (hot) directly to the ground on each RCA and then plug them into the amp inputs. Do you still have noise? After you have made them, keep these shorting RCAs around... they are very handy for troubleshooting noise issues.

If you can do this and report back, it will help diagnose your problem.

I have built three 55s and am working on my third 100; all have been extremely quiet. We will figure out how to get yours quiet too.

Good luck,
Peter

Jens · « **Reply #3 on:** 22 Jan 2006, 09:22 pm »

Hi Klaus,

I have a similar arrangement to yours in my 55 N+. You should be aware that the heatsinks do not act as a shield against magnetic fields, because they are made of a non-ferrous material (some kind of aluminum). For proper shielding you will need an iron or steel shield.

I had some hum/noise before I installed an iron shield between the trannies and the amp boards. After installing that there are no problems

AKSA · « **Reply #4 on:** 22 Jan 2006, 09:33 pm »

Hi Klaus,

Thanks for your post.

This is RFI entering the amp from some inductive pickup point.

As Peter (PSP) has said, short the input terminals, sig Hot and sig GNG, on the pcb. If the radio goes, the pickup is likely from the input wiring. Use coax to the RCA and it should be fine.

If it's still there, and this is very unlikely, use shielded wire for the speaker output lead and make very sure that the power leads into the amp are far from the input and speaker leads.

HF response of this amp tails off very rapidly after 40KHz, so this problem is occuring after something is detecting and rectifying an RF carrier. Simple steps above should fix it. If it persists, talk to me privately; a picture would be helpful as well.

Cheers,

Hugh