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Old 27th June 2005, 11:03 AM   #1
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Default Nuuk Buffered Passive Preamp Issue

Hi all,

I have just finished a Pre-amp for my Lm3886 MonoBlock. The Passive preamp was being used before with a 100k motor Pot built using a LiteAudio Input and Motor pot control. I had an issue with this setup sounding a bit dull and so i started a thread about my dissapointment with the passive setup.

People on this forum told me that the pot value was too high and so i tried lowering this value by placing a resistor acroos the input and output of the pot to lower the value, this did seem to help however i wasnt fully satisfied so i order a replacement pot and set about builting a Nuuk Buffer and PSU. Over the weekend both of these went into the setup, I has been a lot of work since i keep insisting on building everthing into way too small enclosures. Still that my problem.

What i wanted to ask people advice about was the results.

Basiclly the issue is that at zero volume on the pot the actual volume is a loud listen level. The pot works but very rapidly so if a turn it even a few degree the neighbours start banging on the floor!!!

Nuuk brought up the isssue of grounding and that maybe the pot isnt grounded properly. I have enclosed a diagram on the current grounding layout. If anyone has any comment as to wether this is wrong please tell me. If not i will take it the pot is defective and stick back in the old 100k one and put resistors across it.

Any comment very gratefully recieved.

Phil
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Old 27th June 2005, 11:10 AM   #2
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It could be that by mistake you got a linear taper pot instead of a log (audio) taper pot. If that is the case, you can emulate a quasi-log taper by placing a resistor of 1/5 the pot value from the wiper to ground.

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Old 27th June 2005, 11:20 AM   #3
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Well i was assured it was log when i bought it and i dont see how at min volume ie 10K it would make any difference wether is was log or lin, since the value should be the same and surely it should be enough to make the amps silent. Also if i put resistors acroos the wipers i will lower the value of the pot and therefore make min volume even higher wont it?
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Old 27th June 2005, 03:24 PM   #4
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Quote:
the neighbours start banging on the floor
Fixing the neighbours may be easier then fixing the pot in this situation - how difficult can be to get 3 wires soldered correctly?
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Old 27th June 2005, 03:45 PM   #5
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Are you sure the buffer is set for a gain of 1X or are you amplifying the input signal?
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Old 27th June 2005, 03:53 PM   #6
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how difficult can be to get 3 wires soldered correctly?

well there are 10 pins on the pot plus 2 for power and i got it with no doumentation, and for some stupid reason i thought that the resistance between input and output should vary as opposed to the resistance between input and ground.

Should be 30 minutes work tonight to fixed. Head screwed back on the right way now. Actually to be honest i didnt quite understand how a a pot worked until i thought about it long and hard today. Then after 1 or 2 hours of drawing pictures on paper I worked out the way i had it and the way it should be.

It should be I- G-O and i had is G-O-I if G is ground, I is input and O is ouput.

Live and learn thanks for the help anyway guys.


Phil
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Old 27th June 2005, 10:34 PM   #7
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Ok i have messed up again, can somebody help before i shoot myself.

Which should be wire where please please please.

I have 2 as ground, 1 as in and 3 as out.


please begging help

fil

the two 1's arent join how i have it, still doesnt work
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Old 27th June 2005, 11:38 PM   #8
moamps is offline moamps  Croatia
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Old 28th June 2005, 12:39 AM   #9
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Quote:
Originally posted by filholder
well there are 10 pins on the pot plus 2 for power and i got it with no doumentation...
Well, try to get it.
It shouldn't be that hard.
With all those pins it probably has dedicated pins for loudness circuits and all that %$$&%$%&$, so you may be connecting it wrong.
Or use your multimeter.
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Old 28th June 2005, 12:49 AM   #10
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Carlos my poor multimeter is worn out as am I.

Still it works, i cannot believe how many times i have had to re wire the F@?#ing thing. BY the law of averages i should have hit it before now several times and what makes it worse was i was bloody measuring it with a multimeter everytime.

A drunk monkey with a soldering iron would have got it quicker.

Just shows you how dangerous a little knoweldge can be. Almost there now just some LED's to rewire and i can get them wrong twice can I???

Phil

Thanks to everyone especially the man of so few words moamps, your diagram showed me I had the inputs and output backwards.
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