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-   -   Arcam Alpha 8 with RF interference (http://www.diyaudio.com/forums/solid-state/228030-arcam-alpha-8-rf-interference.html)

Uncertain 17th January 2013 04:12 PM

Arcam Alpha 8 with RF interference
 
I'd be most grateful for some advice.....

I recently bought a s/h Alpha 8 to replace my Alpha 5, mainly to get the remote volume control.

I tested it in my workroom and it seemed fine. I then installed it my living room in place of the Alpha 5. It sounded horrible and I noticed RF interference on both speakers totally unaffected by any controls. Close to the speakers I could clearly hear a single radio station to the point I could just about make out what was being said.

I then disconnected everything apart from the speakers and turned off all nearby electrical items - no difference!

I spoke to Arcam. A pleasant chap said he thought he had heard of this problem before and he was sure it was being picked up on the speaker cables. Unfortunately the person "best able to advise" was not available today.

Currently it is bi-wired to a pair of Castle Kendal speakers using two lengths of reasonable quality speaker cables. There was no trace of any problem when the same speakers / cables were plugged into the Alpha 5 in the same way.

Whilst I will try to get to speak to the guy at Arcam when I can, perhaps this rings a bell with somebody here. Any suggestions would be most welcome.

Thanks

DF96 17th January 2013 04:16 PM

Ferrite chokes on the speaker cables near the amp are worth trying. You can get them in two halves which clamp together, or thread the cable through holes in solid ferrites.

You could ask Arcam why this amp has poor RF immunity, too.

Uncertain 17th January 2013 04:35 PM

Quote:

Originally Posted by DF96 (Post 3330116)
Ferrite chokes on the speaker cables near the amp are worth trying. You can get them in two halves which clamp together, or thread the cable through holes in solid ferrites.

You could ask Arcam why this amp has poor RF immunity, too.

Thanks.

Is it known for this problem? Seems odd when the 5 worked so well in the same installation!

Bare 17th January 2013 05:23 PM

erm.. it's broken?
No amp should exhibit that problem if Healthy. Certainly not an Arcam
Send it back to Arcam for a repair?

jaycee 17th January 2013 06:30 PM

That is odd, as looking at the schematic there is plenty to stop this happening.

DF96 17th January 2013 06:33 PM

So are there faulty components, or (as it may have been made in China?) missing components? They have 'form' for omitting EMC suppression components, as they save a few pence and in many cases nobody will notice.

Uncertain 17th January 2013 07:33 PM

Quote:

Originally Posted by DF96 (Post 3330302)
So are there faulty components, or (as it may have been made in China?) missing components? They have 'form' for omitting EMC suppression components, as they save a few pence and in many cases nobody will notice.


Any suggestions as to what maybe missing (or faulty)?

I have the service manual, some very basic electronic knowledge, a multimeter and a very old scope!

jaycee 17th January 2013 08:31 PM

DF96, i was thinking that:

* The chassis is earthed - that alone helps
* There is an RL network on the speaker output
* There is sensible bandwidth limiting via lowpass filters all around the amp, and at the power amp inputs (1K with 100pF to ground on the power amp).

jaycee 17th January 2013 08:31 PM

Uncertain, try making a phono plug that shorts to ground. Install this on an input, select that input, and see if the RF goes away

JonSnell Electronic 17th January 2013 08:52 PM

I would check that R207 a 100R MF 1/2 Watt resistor is OK. That is the only link to ground this silly amplifier has!
It is unlikely that there is enough RF power to activate the loudspeakers and therefore the interference must be getting in through a poor earth/ground connection and the loudspeaker cables are a good aerial.
Ferrite inductors are good but the amplifier should reject the interference.


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