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Old 16th July 2007, 05:40 PM   #1
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Default P88 Preamp problem

OK, so my third project is almost complete. I have built a P88 preamp with boards supplied by Mr. Elliot. I have had the preamp in services with the recently completed Leach amp and the sound is awesome. Of course I wouldn’t be posting if there wasn’t one small problem. I built the amp with the balance and volume control as per the P88 instructions. (see attached)

The problem is the balance control only affects the left channel. Turning the pot full right results in signal to only the right channel. However, there is no effect on the right channel so turning the pot anywhere left of centre results in a balanced signal between the two channels. I have rewired the volume and balance pot three times making sure all connections are done as outlined above.

Does anyone have an idea of what could be causing this problem. The pots are a single 10K for balance and a dual 100K for volume linear pots as outlined in the diagram.

Any ideas or comments would be appreciated.

Thanks,

Curioprop
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Old 16th July 2007, 06:20 PM   #2
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Unfortunately I am at work and cannot investigate this right now but I cannot think of anything beyond a faulty pot, which would cause this. The wiper (2) is working in correlation to the left channel (3) but not the right (1) Does this make sense??

Any other thought are appreciated.
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Old 16th July 2007, 06:46 PM   #3
Nordic is offline Nordic  South Africa
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yep, P88 works, I have built 2 allready for less important projects...
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Old 16th July 2007, 07:13 PM   #4
anatech is offline anatech  Canada
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Hi Curioprop,
It appears that your 10K pot is open on the right channel side. Can you measure the resistance between to two outside terminals?

-Chris
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Old 16th July 2007, 10:02 PM   #5
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Quote:
Originally posted by anatech
Hi Curioprop,
It appears that your 10K pot is open on the right channel side. Can you measure the resistance between to two outside terminals?

-Chris
Thanks Chris,

The right channel of the pot is open. If I push the terminal forward it makes contact and I get a reading (about 11K). I have a backup I'll try and see if that does it.

Thanks Again

Steve
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Old 17th July 2007, 02:01 AM   #6
anatech is offline anatech  Canada
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Hi Steve,
Good luck on this. Your other pot should be good.

-Chris
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