by AncientBrit » Fri Jul 05, 2013 6:15 pm
Hi Steve,
I've done a little digging of circuits that have used the 1496 in the past.
From CQTV, my own PAL encoder, and Linsley Hood's synchrodyne AM Rx.
Certainly the 100R looks a little low.
The general consensus seems to be a 1k resistor to a reference potential (rail or mid rail) from each of pins 1 and 4
Then a mid range pot, say 4k7 or 20k across pins 1 and 4, with a 47k resistor from pot wiper to either supply rail, or 0v.
What you are trying to do is introduce a small balancing current so the wiper can go via the 47k to either rail
From what I remember in my PAL coder design the chip is well balanced and only a very modest correction was needed to achieve accurate sub-carrier nulling
Hope this is of use
Cheers,
Graham