[Coco] Coco Cassette interface help

[Dave Philipsen]

Here's a circuit that works.  It does the SMPTE/EBU linear time code for 
me which is very similar to the CoCo cassette data.  You can tweak the 
50K resistor between pins 1 & 2 on the op amp for different gain 
levels.  This circuit will accept a balanced or unbalanced line level 
input and will output a nice square wave.  The op amp is a fairly 
inexpensive part chosen for it's ability to swing to the rails of the 
power supply.

http://retr09.com/images/d-o-t-decoder.jpg

Dave



On 2/28/2017 1:25 PM, RETRO Innovations wrote:
> On 2/28/2017 1:05 PM, Dave Philipsen wrote:
>> All you want to do is amplify the signal that is coming from the CoCo 
>> cassette out. Use a capacitor to de-couple it from the comparator 
>> circuit. It won't matter if there's DC bias on the output of the op 
>> amp because you will effectively remove it with the cap.
> True, and I will give it a shot, but I'll continue to search for a way 
> to make the comparator idea work alone.  Amplifying the source only to 
> get it "over the bias" of the comparator just seems wrong to me :-)
>
> Still, I already was thinking of your idea, in the context of using an 
> LM386 to amp the signal brute force to get it to work. So, I agree 
> it's a workable solution.  Thanks for the suggestion.
>
> I am also going to see if I can feed some known signals into the 
> comparator to see if I have messed up the design.
>
> Jim
>