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Old 24th Feb 2005, 4:20 pm   #10
David_Robinson
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Join Date: Feb 2004
Location: Nottingham, UK
Posts: 94
Default Re: VHF Modulator wanted

Quote:
Originally Posted by oldeurope
I must look at the data sheet for the IC maybe there is a way to use the audio section too.
Trust me, there isn't! The sound-vision spacing can only have certain values and 3.5 isn't one of them! You could put an external audio subcarrier into the MC44BS373CA in the 20-pin version. Except the 20-pin version is unobtainable.

Quote:
In the audio stage you don't need a tandem pot.
The problem with your circuit with the stereo mix to mono directly on the input, is if the source device (in my case a set top box) also feeds other places (my stereo amp). The mixer may reduce stereo separation on all destinations due to the output impedance of the source. I put the pot right on the input so that the system can't be overloaded.
Quote:
...the bias adjust via the emitter follower. It must be temperature compensatet.
Good point!
Quote:
...the IC makes not 100% video modulation.
True, but think about what the diode detector in the average vintage TV will do to the signal if it reaches 100% mod!
Quote:
Hope the audio carrier can be switched off.
Not at the moment, but I can add that to the software.
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Last edited by Dave Moll; 27th Jun 2007 at 9:21 pm. Reason: correct for username change in quote
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