[Coco] New circuit video coco2

[Zippster]

Oh yeah, that too.. :)  lol

Mostly due to generation of regulated 12v on the board I suppose,
allowing a little more flexibility in adjusting the amplitude of the final output.

Though the data sheet circuit works well too.

The only way I can see to really improve on these would be using op-amps
instead of transistors after the 1372 for a simplified layout, which I will probably
do for the MC10 and any CoCo1 adapter.

- Ed


> On Mar 11, 2015, at 12:47 PM, Joe Grubbs <jsgrubbs at hotmail.com> wrote:
> 
> And Ed, didn't you also notice that the circuit you're using (Tandy) was better than the application circuit in the 6847 datasheet?
> 
> 
>> From: zippster278 at gmail.com
>> Date: Wed, 11 Mar 2015 12:12:10 -0500
>> To: coco at maltedmedia.com
>> Subject: Re: [Coco] New circuit video coco2
>> 
>> Hi Luis,
>> 
>> Though there are some simple transistor driver circuits out there,
>> they seem to only drive some composite inputs.
>> 
>> Implementation of the MC6847/MC1372 pairing varies by CoCo model.
>> 
>> Those with the 1372 in the RF box have an oscillator frequency tuning circuit
>> connected to the RF tank inputs, where a DC offset voltage is needed to generate
>> baseband composite.  This would be all CoCo2’s.
>> 
>> CoCo1’s do generate baseband composite from the 1372 before it is sent to
>> the RF box, but there is a transistor amp circuit in-between.  The signal could be
>> tapped here and levels adjusted with a simple driver circuit.
>> 
>> The boards I put together connect directly to the MC6847 and generate proper baseband
>> composite, along with handling sound, and put it into one convenient output jack.
>> They are based on Tandy’s own composite output solution, found on educational model
>> CoCo2’s.
>> 
>> Like anything with electronics, there are several ways to a similar destination, this is one way.  :)
>> 
>> - Ed
>>