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Arcam Alpha 8R problem
Arcam Alpha 8R problem
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Old 6th July 2006, 02:24 PM   #1
goodlife is offline goodlife  United Kingdom
diyAudio Member
Join Date: Oct 2004
Default Arcam Alpha 8R problem

Arcam Alpha 8R amplifier

when i turn the amplifier on the amber standby (mute) light does not go off. The volume knob turns when the remote is used but does not go off mute. No sound comes out of the speakers. Obviously the protect circuit has kicked in.

I have removed the link which connects both amplifier channels to the protection circuit (VI_PROTECT link LK1085), to see if I could find out which channel is causing the protection circiut to kick in. However now the amplifier works; sound from both speakers, tone controls, volume, remote, mute all work.

Just for reference one channel has a speaker output dc voltage of 23mV and the other 15mV.

I thought protection would only start if the amplifier had generated a fault which would stop it working, whereas mine appears to work fine. Am I completely wrong on this?

Does anyone have any ideas why the protection has started even though the amplifier appears to work with protection disabled?

Is it safe to run the amplifier with this protection disabled?

Kind Regards
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Old 6th July 2006, 08:36 PM   #2
jaycee is offline jaycee  United Kingdom
diyAudio Member
Join Date: Apr 2004
Location: Norwich, UK
The VI protect circuit kicks in if it detects too much current flowing through the MOSFETS. Does any channel get very hot at idle?

If you contact Arcam they will send you the service manual for this amp as a PDF, which is nice

I would check any resistor in the VI protect circuit marked as "FU" (fusible) first. It's possible one of them decided to open.

Your amp will be fine without the VI protect provided you don't abuse it by playing it excessively loud for long periods.
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Old 7th July 2006, 08:16 PM   #3
goodlife is offline goodlife  United Kingdom
diyAudio Member
Join Date: Oct 2004
thanks for the reply.

Both channels are cold at idle. I think I'll follow your advice regarding fusible resistors. I'm begining to think that it is probably a fault in the current detection circuit on one of the channels as nothing gets hot during full operation at a reasonable volume. Thanks to the good people at Arcam I have a copy of the service maunal to assist in my fault finding.

I'll post anything new I find

Kind Regards
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