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Old 31st August 2010, 09:40 AM   #101
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OK, i changed the ground wiring slightly. Now i have made the signal ground star on the black Spk out of each channel by connecting the RCA ground here. a Wire connects this star to the channel's pcb, where the 0v rail is connected. This has lowered the hum slighly, but it is still loud enough to be unlistenable...
im all out of ideas so any further suggestions would be very much appreciated

cheers,
mymindinside
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Old 31st August 2010, 09:43 AM   #102
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Hi Andrew,
i think you posted as i was typing. the cables are secured together. i will try removing one of the shields at one end..

thanks,
mymindinside
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Old 31st August 2010, 09:59 AM   #103
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Andrew,
It didnt help , i just got a really loud buzz from the channel that i had removed one shield from.
any other suggestions, did my wiring diagram look ok to you?
what do you think of the fact that the amp is silent with the rca - minplug cable plugged in but starts humming when i plug the ipod in.

thanks to all for the patient help and advice
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Old 31st August 2010, 10:07 AM   #104
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by mymindinside View Post
what do you think of the fact that the amp is silent with the rca - minplug cable plugged in but starts humming when i plug the ipod in.
the RCA miniplug has an outer shield, with two signal cores.
If you plug it in and leave the other end open, I would expect some noise on the output of the amplifier.
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Old 31st August 2010, 10:15 AM   #105
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Hi Andrew,
The amp was silent with the miniplug end open, it started humming as soon as i plugged in the ipod.
the hum i have is quite loud, not the put your ear against the speaker kind.
it fills up the room...

EDIT: with the miniplug cable,these are the possibilities and the resultant hum
1. Both RCAs plugged into the amp but miniplug open - no hum
2. One RCA plugged into the amp and miniplug plugged into ipod headphone out - no hum (both speakers are connected to the amplifier in this case)
3. Both RCAs plugged into the amp and the miniplug plugged into the ipod - loud hum

cheers,
mymindinside

Last edited by mymindinside; 31st August 2010 at 10:18 AM. Reason: clarity
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Old 31st August 2010, 08:41 PM   #106
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It seems like somewhere in your case the two channels are unintentionally electrically connected.

To be honest I think it might be quicker, to pull everything out of that case and build it again one channel at a time and triple checking everything.

Are you sure there is not another connection to the chassis check all your binding posts, rca's.
Also check ALL of your pcb standoffs.

Build it again.
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Old 31st August 2010, 08:56 PM   #107
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Quote:
Originally Posted by mymindinside View Post
OK, i changed the ground wiring slightly. Now i have made the signal ground star on the black Spk out of each channel by connecting the RCA ground here.
The speaker-return should be attached to star, not speaker-out.
Is black, speaker-out, or is red, speaker-out?
The conventional wiring is red (for speaker-out) but I think Nelson recommended black to account for phase reversal of amp.
Be careful not to short the amp, it is very easy to make silly mistakes when your patience is wearing thin.
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Old 1st September 2010, 07:50 AM   #108
cviller is offline cviller  Denmark
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What are those input caps for? I would remove them before trying more fancy solutions. Also the speaker wires could benefit from being twisted. Just make sure you don't have power conducting wires in the loop - right now you have one of the supplies in the speaker loop on the left channel.
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Old 1st September 2010, 08:17 AM   #109
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Originally Posted by cviller View Post
What are those input caps for? I would remove them before trying more fancy solutions. Also the speaker wires could benefit from being twisted. Just make sure you don't have power conducting wires in the loop - right now you have one of the supplies in the speaker loop on the left channel.
Hi Christian

If you are referring to my picture, the input caps were added whilst trying to solve the hum problem. I'll remove them for now.

I'm not sure I follow this comment...

'- right now you have one of the supplies in the speaker loop on the left channel'

I've just checked and it appears the right channel is wired the same as the left

Regards
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Old 1st September 2010, 08:24 AM   #110
cviller is offline cviller  Denmark
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If you look at the left side of the picture, the V- supply is running through the loop of gnd and out.

Could you take some pictures of the rca plugs? Sometimes I have used tape to make sure that they are not touching the chassis.
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