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Date Posted: 20:37:42 12/14/01 Fri
Author: Lcs
Subject: Re: Washed out picture.
In reply to: Potter 's message, "Re: Can Someone Please Point Me In The Right Direction." on 20:01:43 12/14/01 Fri

The Lm733 (and replacements) is impossible
to find in this country...

I'll check if the resistor accross the output
cap improves picture quality in Canton 4.2.
But maybe not, because i had connected the board
straight to the 75ohm input of different TVs and VCRs.

I built a different transistor video amp using more stages and negative feedback resistors (which Canton doesn't
have). Then the picture was great. Canton 4.2 seems
to trade distortion for high gain.

lcs


>The LM733 is noticably better than a discrete
>(transistor) input buffer/amplifier (for me at least).
>A note about pale & washed out looking picture: I had
>this problem with all types of amps I tried and it
>appeared due to the very high input impedance of the
>unbiassed circuit I was feeding the 3chip's output
>into. What happens is there is a difference in the
>average DC level of each channel tuned so the output
>capacitor (typically 47-470uF) acquires a DC charge
>which can not dissipate due to the high impedance and
>really makes a mess of the picture on a channel with a
>lower average DC level than the last one tuned. The
>answer was very simple - put a resistor across the
>output capacitor, ~1K did it and no more problems.

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