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Old 7th November 2003, 06:26 PM   #1
Stever is offline Stever  Canada
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Default Pin 7 to ground question for IGC

Hi all,

With about 5 hours on my minimal IGC, things are sounding great. I'm impressed.

I'm getting 15mv and 22mv DC offset with a wire between Pin 7 and ground. I wanted to experiment with a resistor from Pin 7 to ground.

Should I use EXACTLY the same value as my feedback resistor (237k) or can I get by for now experimenting with whats in the drawer (220k).

I assume you would want a close match ultimately.

Thanks again,

Steve
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Old 7th November 2003, 07:27 PM   #2
GregGC is offline GregGC  Canada
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If you have input cap in ser. with the 10k res. and no res. to gnd to provide DC current to -In, then theoreticaly 220k will be good enough. Mind you be prepare to experiment with a cap in paralel to the 220k resistor.
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Old 7th November 2003, 11:25 PM   #3
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Probably using a trimpot would bring the best results. You could zero out exactly. Be prepared for different sound though.
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Old 8th November 2003, 12:39 AM   #4
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why not set it up for a trimpot, find the setting, then remove the pot and use 2 higher quality, fixed resistors, if you are worried about such.
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Old 8th November 2003, 01:05 AM   #5
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Even when you'll replace trimpot with a fixed resistor, the sound will change. It's not a matter of trimpot or resistor, but physical resistance in that place.
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Old 8th November 2003, 12:12 PM   #6
Nuuk is offline Nuuk  United Kingdom
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I agree with PD. By all means, experiment for yourself (that's what DIY is all about) but with those offsets, I would stay with the wire!
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Old 8th November 2003, 07:57 PM   #7
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yes, but the idea was to minimize the difference. it's whats at the core of engineering, compromize. in order to remove DC offset, he has to decrease snr too. kinda like choosing between the lesser of two evils.
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