[Coco] Coco Cassette interface help

Dave Philipsen dave at davebiz.com
Tue Feb 28 14:05:44 EST 2017

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.


----- Reply message -----
From: "RETRO Innovations" <go4retro at go4retro.com>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Subject: [Coco] Coco Cassette interface help
Date: Tue, Feb 28, 2017 12:46 PM

On 2/28/2017 11:07 AM, Dave Philipsen wrote:
> True, the cassette output is designed to be plugged into a MIC in jack 
> on the tape recorder as I remember.  So the output of the cassette 
> interface apparently does not generate a signal with enough amplitude 
> to drive the input of the cassette interface.  Sounds like a job for a 
> simple op amp circuit where you can experiment with the gain.  A good 
> book for op amp circuits is Forrest Mims' /Engineer's Mini-Notebook/ 
> here: Engineer's Mini-Notebook 
> <https://archive.org/stream/Forrest_Mims-Engineers_Mini-Notebook_Op_Amp_Ic_Circuits_Radio_Shack_Electronics/Forrest%20Mims-Engineer%27s%20Mini-Notebook%20Op%20Amp%20Ic%20Circuits%20%28Radio%20Shack%20Electronics%29%281%29#page/n9/mode/2up>.
I have the book (original, from when I was but a tyke).  I will try the 
circuit tonight, but it looks like it is biased around 2.5V, which is 
far too high for me.   I suspect I can move the bias down to .5V, but 
the more changes I make to the default circuit, the less confident of 
success I am.


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