[Coco] Speech/Sound cartridge

[Gene Heskett]

On Saturday 07 February 2009, jdaggett at gate.net wrote:
>There is two issues with 1.78 MHz bus clock.
>
>1) Q1 and its associated circuitry acts as voltage inverter to generate a
>negative voltage to the opamps. The problem can be corrected with a
>change in Q1. This will work if the right Q1 is used. The real issue is the
> RC network of R16 and C26. The intention of this filter is to round off the
> edge of E clock square wave so to minimize rigning in the coil. The problem
> is that the RC network rounds off the negative transistion of the E clock
> sufficiently when increased to 1.78 MHz. This does not allow Q1 to stay on
> long enough to build up charge in L1. Thus not enough negative voltage for
> the opamps. Changing Q1 to a 2N3906 will help. Changing the time
>constant of R16 and C26 will also improve teh invertor performance. .
>
>2) Second issue is that IC3 XORs the E and Q clock. Due to the quadrature
>nature of the E and Q clock this will result in a frequency that is twice
> that of either the E or Q alone. When generatign sound the sound will now
> be one octave higher because of the increase in frequency. This can be
> corrected simply by not XOR ing the two clocks when in high speed mode.
> There is a file on RSTI that describes how this can be done. One method
> locks you into high speed mode another method uses a switch to allow the
> pack to be used in fast or slow mode.
>
>james
>
Thanks for bailing me out there, James.

>On 8 Feb 2009 at 12:27, Bob Devries wrote:
>> George,
>>
>> The stock SSC did have an issue with running at 2MHz. There were a
>> couple of suggested fixes, including replacing a transistor with
>> another type. This is the road I took, and it was successful.
>>
>> There's only one transistor in the SSC, a 2SA984K (Q1), a PNP. From
>> memory (and someone correct me if I'm wrong), I replaced it with a
>> 2N3906. Be careful to match the pins correctly. I seem to remember
>> that the 2N3906 had it's pins different from the existing transistor.
>>
>> Other fixes were also suggested, which may or may not be easier or
>> more effective.
>>
>> The problem (as I understood it) was that no (or low) -5 volt was
>> generated to drive the op-amps.
>>
>> --
>> Regards, Bob Devries, Dalby, Queensland, Australia
>>
>> Isaiah 50:4 The sovereign Lord has given me
>> the capacity to be his spokesman,
>> so that I know how to help the weary.
>>
>> website: http://www.home.gil.com.au/~bdevasl
>> my blog: http://bdevries.invigorated.org/
>>
>> ----- Original Message -----
>> From: "George Ramsower" <georgeramsower at gmail.com>
>> To: <coco at maltedmedia.com>
>> Sent: Sunday, February 08, 2009 12:09 PM
>> Subject: [Coco] Speech/Sound cartridge
>>
>> > Was there an issue with the SSC running a CC3 at 2mhz? I'm about to
>> > add this cart to one of my OS9 systems on a CC3.
>> >
>> > George
>> >
>> > --
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>> > Coco at maltedmedia.com
>> > http://five.pairlist.net/mailman/listinfo/coco
>>
>> --
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>> http://five.pairlist.net/mailman/listinfo/coco
>
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-- 
Cheers, Gene
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