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Thread: NAD 7100 (7400/7600) weak in one channel |
    
New member Username: Mashley_nad
Post Number: 1
Registered: Jun-09
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| Posted on Saturday, June 27, 2009 - 06:38 am: |
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I have a NAD 7100 receiver that is weak in the right channel. It is a definitely a pre-amp issue, and I have replaced all the electro caps in the signal path, but the problem still remains. I have adjusted the channel balance trimpot as per the service manual, but while that makes the channels equal at full volume, the difference remains at normal levels. Help!!!  |
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Platinum Member Username: Nuck
Post Number: 12765
Registered: Dec-04
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| Posted on Saturday, June 27, 2009 - 07:57 am: |
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You would have to go to the next devices in the circuit after the trim pot, MA.
Unfortunately, I bet thats a discrete device on a pcb. As the problem is not linear, it cannot be attenuated in one channel alone. |
Platinum Member Username: Nuck
Post Number: 12766
Registered: Dec-04
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| Posted on Saturday, June 27, 2009 - 07:58 am: |
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Pardon me, also welcome to the forum! |
Gold Member Username: Mike3
Wylie,
Tx
USA
Post Number: 2021
Registered: May-06
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| Posted on Saturday, June 27, 2009 - 04:03 pm: |
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Michael, how did you determine it was a pre-amp issue?
Should we assume that you did not change anything else in the system, even interconnects of speaker wire?
You did not change anything about the room like furniture or flooring?
Please do not think I am questioning your ability to diagnose your issue, I am simple gaining confirmation and exploring some other options.
The more info we have the more we can assist. |
New member Username: Mashley_nad
Post Number: 2
Registered: Jun-09
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| Posted on Saturday, June 27, 2009 - 08:26 pm: |
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In reply to Michael Wodek: I determined it was a pre-amp issue by 1 putting Left pre-amp out into BOTH power amp Left and Right and seeing output was equal, and 2 putting preamp L out into power R and preamp R out into power L and noting the mis-balance had swapped channels. I set the preamp channel balance as per the service manual by setting volume to max and putting 100 mV 1kHz into L and R CD input and adjusting trimpot for equal preamp out (using oscilloscope). However even after that adjustment, the channels are still unbalanced. At normal listening levels the balance control has to be at 3 o'clock for equal output. Observing the preamp outputs with the scope, they gradually become equal as the volume increases. |
New member Username: Mashley_nad
Post Number: 3
Registered: Jun-09
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| Posted on Saturday, June 27, 2009 - 08:39 pm: |
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Here are the relevant sections of the circuit diagram. Note that I replaced all the signal path electros on the pre-amp board, but NOT in the tone control section which is on the main amp board. Sorry about image quality, but the 600x600 <100k rule is pretty limiting.
---- relevant section frompre amp board ----
---- tone control on main board ---------------
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