[Coco] Speech/Sound cartridge

[jdaggett at gate.net]

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

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
> >
> > --
> > Coco mailing list
> > Coco at maltedmedia.com
> > http://five.pairlist.net/mailman/listinfo/coco 
> 
> 
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