[Color Computer] [coco] The coco cassette

[Gene Heskett]

On Friday 24 February 2006 20:28, George's Coco Address wrote:
>----- Original Message -----
>From: "Gene Heskett"Sent: Friday, February 24, 2006 6:54 PM
>
>> On Friday 24 February 2006 19:28, Diego Barizo wrote:
>>>The first tape I bought after getting my CoCo was a 90 min. one.
>>> They are supposed to be less reliable than others, but after
>>> 22...23....24 years, it only got a couple of bad spots.
>>>Most of my friends had Sinclair Spectrum. A real pain to get a game
>>> to load!
>>
>> I had nothing but bad luck with the CTR-81/82.  And being an
>> electronics type, I came to the conclusion that 99% of the trouble
>> was the DC bias used in nearly all those things sold as computer
>> tape recorders by anybody.
>
>snipity
>
>> as is.  This would have reduced the background shot noise by at
>> least 30 db.  Or to have put a motor control circuit into a better
>> one, either would have worked a treat and would have had a lip lock
>> on that data market once word spread that hey, here is one that
>> WORKS!.
>>
>>> Diego
>>>
>>>George Ramsower wrote:
>>>> I dimly recall that the coco was famous for being the fastest and
>>>> most reliable.
>>>>
>>>> Once I got a CCR-81, I had very few problems, unless I had a bad
>>>> tape.
>>>>
>>>> I tried several, cheaper tape machines and none worked properly
>>>> until I finally broke down and bought the CCR-81.
>>>>
>>>> I bet a PC sound card would be better than a cassette deck.
>>>>
>>>>George
>>
>> --
>> Cheers, Gene
>
>  At that time, I was working for Motorola C&E and we had equipment to
> study the waveform (O-Scopes).

I've had scope probe or two in hand since I was 16, George. 1951 TBE.

>  I studied the waveforms and found that the cheap machines(which I
> tested) were not acceptable due to the "Push-Pull" circuit in the
> record amplifier. It  would make a HORRIBLE transition on the peaks.
> The CCR-81 did not have this error. The peaks were smooth and easy.

That 'horrible transition' was in fact the tapes magnetic hysteresis in 
most cases.  The CTR-81 did have, IIRC a dc bias applied to the 
recorded signal to offset the magnetic curve to one side or the other 
of that characteristic, something the ac bias if at the right level, 
totally compensates for.  So it was some better, but still, using 
permanent magnets to erase the tape left a builtin bias that very 
faithfully reproduced the coating anomalies as shot noise in the output 
when the tape was played back on any machine.  And in restricting the 
record level so as not to hit either tape saturation or that hysteresis 
point, resulted in a tape that was recorded at about 15 to 20% of the 
level the tape itself was capable of.  Couple that low record level 
with the extra 20-30 db of noise, and making it work often required a 
virgin to be sacrificed per load attempt, rather like poorly designed 
scsi circuits of the day.

>GEORGE

-- 
Cheers, Gene
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