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Old 25th June 2012, 05:46 PM   #1
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Default Leak Delta 30 amp HELP!!

Hi All.
I have this amp. Works great, but one channel motorboats when 4ohm 15"speaker is connected.
So this morning I decided to replace all the high ESR Caps on poweramp and pre amp boards. The problem is still there. Swapping out preamp and/or poweramp boards visa-versa yields the same result. The problem stays on the right channel.
Any ideas?
Here is the schematic
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Old 27th June 2012, 04:59 AM   #2
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Motorboating is caused usually by AC coupling of the amplifier output stage back to the input stage. This can be as simple an issue as dangling the output wires near the input lead. Since it is independent of which amp. or preamp. channel is in the RH position, the fault is going to be in the remaining fixed wiring so I would be checking that for signs of deterioration or wiring that is just too close to the sensitive input area.

I'm not familiar with these, only repaired one that I recall and have long forgotten the construction but I would look for physical clues. Take a close look at SW1 for poor contact and perhaps check over any ancient carbon comp. resistors that may have drifted over the decades. Whilst you are under the bonnet, why not put in a decent ~4,700 uF output cap. to allow a little bass. 1,000 uF might compare with typical valve amplifiers of the day but now would be considered very weak in the bass.

This might make interesting reading too.
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Last edited by Ian Finch; 27th June 2012 at 05:26 AM.
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Old 28th June 2012, 10:24 AM   #3
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Thanx IAN!!
Thought as much. Got to be the wiring layout. No screened wires inside these amps. Will fiddle a bit on it later.
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