Speech & Sound Pack Modification for High Speed

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Home / Hardware - Speech & Sound Pack Modification for High Speed

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From: Robert Emery (archived web page)

Automatic switch by Robert Emery (email link)

March 1, 2003

A little background info:

This modification is based on two existing articles detailing the modification of the Tandy Speech and Sound Cartridge so that it works with the high speed poke. I will not cover the details of these articles, the links are included.

The first article is located on CoCo3.com (archived), or CoCopedia, and suggests replacing a transistor to fix the negative voltage circuit, which fails at high speed on a stock SSC. This article also provides instructions for adding a mechanical switch so the user can manually set the cartridge to work at the desired speed.

The second article I found is on Robert Gault's homepage (archived) or new site or CoCopedia and also features a manual switch, but instead of replacing the transistor, Mr. Gault points out that the same effect can be achieved by simply adding a capacitor across R16 (or C26 as in my photo). Beautifully simple, and it works.

The switches are located differently in the two articles, but provide the same function... they provide the sound effects chip with a 2MHz clock, which is normally provided by doubling the CoCo's Q clock. If the CoCo is running at high speed, we no longer need to double this clock.

Someone asked if the switch could be automated...

Looking at the CoCo3 article, I figured out that I could replace the mechanical switch with a 74LS08 AND gate. This gate could then act as an automatic switch if it is fed a signal which is controlled by the CoCo's clock. That signal is provided by the Turbo Light circuit. Any Turbo Light circuit for the CoCo could be used to control the switching. If you don't have the Turbo Light circuit, you can simply install a jumper on the plug for high speed or remove it for low speed operation.

The Hack...

Since the AND gate switch uses the same connections as the CoCo3.com article, it requires cutting the same trace on the circuit board. The trace goes from card-edge pin 7 (Q Clock) to pin 9 of IC3 (74LS86). I lifted C8 and cut the component-side trace as indicated in the image. The eyelet here also makes a good place to get the Q clock to feed pin 9 of the AND gate.

The AND gate (74LS08) is piggybacked on top of IC3. Make sure to align pin 1 of both chips. Only pins 7 (Vcc) and 14 (Gnd) should be soldered to IC3... all other pins of the 74LS08 should be bent out, preferably removed with the exception of pins 8,9 and 10, a single AND gate. I actually cut my 74LS08 from an old 8088 motherboard with some small diagonal cutters, desoldering only pins 7 and 14.

Connect pin 8 of the 74LS08 to pin 9 of IC3. Connect pin 9 of the 74LS08 to the Q clock at the eyelet under C8 (the blue wire in the photo). Connect pin 10 of the 74LS08 to one pin of a 2 pin jumper plug, the other pin goes to ground.

Finally, take a twisted pair of wires with a 2 pin socket (such as an LED or Reset switch connector from a PC) and connect the wires to pins 6(/Q) and 7(Gnd) of the 74LS74 of the Turbo Light circuit. Make sure you don't plug the connector into the SSC plug backwards or you'll be shorting you're CoCo's Q clock to ground... probably not a good thing.

Speech and Sound for OS-9 Level II, Part 1

by Robert Gault, world of 68' micros, September 1994

The Tandy Speech/Sound Cartridge (SSC) model # 26-3144A is an interesting device made for the Color Computer 2 in 1984. The SSC's functions are: 1) convert text into speech, 2) play 3-part musical harmony, 3) create complex sound effects, 4) create speech via an allophone table. The SSC has 8 speech and 8 sound storage buffers. The hardware is based on General Instrument Corporation's GI PIC 7040-510 chip set: PIC 7040, AY3-8913, SP0256-AL2.

I don't intend to review the device as it is no longer in production. The thrust of this article is how to make the device work with OS-9 Level II. Let's start with some history. The Coco2 had available OS-9 Level I v.2. This software ran at 0.89MHz and expected at most 64K RAM.

The design of the SSC incorporates the above parameters. It expects a clock signal (Q) of 0.89MHz which is doubled internally to 1.79MHz and used by the sound effects chip. If the Coco clock is set to 1.79MHz (fast mode), all sounds and tones go up one octave although speech is not affected. The SSC also requires a -6v DC source for it's operational amplifiers. This is created by feeding the Coco E-clock line to a coil and rectifying the output. The circuit used fails at 2MHz because insufficient negative voltage is produced to run the amplifiers.

Hardware Modification

Connect a 470pF ceramic capacitor across the leads of R16. This capacitor value works on my unit. Check the output of the negative supply at both 1MHz and 2MHz. Look for minimal change from -6v at both 1 and 2MHz. Use a value that gets +-1v of the target value. This modifies the negative power supply for 2MHz operation. (This feed forward capacitor corrects the frequency response of the transitor used in the circuit. It is the simplest possible fix. RG 1999)

Connect a single throw double pole switch with the common lead going to the circuit board feed-through as indicated in the diagram. Pole A can go to IC3 pin 8 and pole B to pin 9. Mark the switch "normal" when pin 8 is in circuit and "fast mode" when pin 9 is in circuit.

You must now cut the trace line leaving IC3 at pin 8 on the bottom side of the printed circuit board. BE CAREFUL! This modifies the clock line for 2MHz operation.

          ********************************************************* 
          *                                                       * 
              ------------------------------------------------    * 
             |         ----------  ----------  -----------    |   * 
             |         |        |  |        |  |         |    |   * 
             |         ----------  ----------  -----------    |   * 
             |                      o---------------common------------switch 
             |                  ------------------ ------     |   *     | | 
             |                  |                | |    |     |   *     | | 
             |                  ------------------ ------     |   *     | | 
             |         --------           ---------           |   *     | | 
             |         |      |     X     |       |           |   *     | | 
             |         --------    R16    ---------           |   *     | | 
             |                                                |   *     | | 
             |         ------- ------- ------      ----       |   *     | | 
             |         |     | |     | |    |      |  |       |   *    A| |B 
             |         ------- ------- ------      ----       |   *     | | 
             |                 !!=======================================|-| 
          *   ------------------------------------------------    * 
          *                    pins 8&9                           * 
          *********************************************************

                               SSC pack

Upgrading the Sound / Speech Pack for 2Mhz www.coco3.com by Roger

This document describes how to use the Speech/Sound Pak with OS-9 Level II’s higher clock speed operation.

ftp://os9archive.rtsi.com/OS9/OS9_6X09/SYSMODS/SS_Pak_Driver.lzh

Speech-Sound Pak 1.78 MHz. Modifications

This text attempts to explain how to modify the Radio Shack/Tandy Speech-Sound Pak (catalog numbers 26-3144 and 26-3144A) to work with the COCO3 at 1.78 MHz. The hardware modifications are fairly straightforward, but vary slightly between the two models (26-3144 & 26-3144A). Make sure that your Speech-Sound Pak is one of the Paks described, and that you make the correct modifications. Externally, the 26-3144′s that we have seen have a Radio Shack label, while the 26-3144A’s have a Tandy label. Internally, the 26-3144 uses a 2907 transistor and the inductor (marked L1) is in a resistor-style (axial) package. The 26-3144A uses a different transistor, and the inductor (also marked L1) is in a small plastic box. In both Paks the transistor & inductor (coil) are close to the post hole in the circuit board. It is necessary to change the transistor in order for the Speech-Sound Pak to work properly in most cases. We have seen only one unmodified Pak which worked when the COCO3 was running at 1.78 MHz. The voltage inverter circuit used must supply at least -5VDC in order for the output OP-AMPs to function. Unfortunately, the transistor used is sensitive to the frequency input to the circuit. The input signal used is derived from the bus E clock. When the COCO3 runs at 1.78 MHz, the circuit typically produces only -2.5VDC, which is not sufficient for the OP-AMPs. The 2N3906 is a PNP transistor. Looking at the flat face, with the pins pointing down, the pin out should be Emitter, Base, Collector from left to right. The 2N2907 transistor should have the same pin out as the 2N3906. The transistor in the 26-3144A Pak should have a pin out of Emitter, Collector, Base when viewed in the same manner as the 2N3906. When installing the 2N3906 transistor into a 26-3144A circuit board you must swap the Base and Collector pins so that they match the original transistor’s pin out.26-3144 Voltage Inverter Transistor Change:

Make note of the 2N2907′s pin out & orientation. Most manufacturers should use the same pin out, but its worth checking. De-solder the 2N2907 transistor & remove it from the Speech-Sound Pak circuit board. Solder a new 2N3906 transistor into the Pak’s circuit board. The 2N3906 should be oriented the same as the 2N2907 that was removed, but again its worth checking the pin out! 26-3144A Voltage Inverter Transistor Change:

Make note of the transistor’s pin out & orientation. Most manufacturers should use the same pin out, but its worth checking. De-solder the transistor & remove it from the Speech-Sound Pak circuit board.

Carefully bend a new 2N3906 transistor’s base and collector pins so as to swap the holes they fit into. Make sure that they do not touch each other or anything else that could cause a short circuit.

Solder the new 2N3906 transistor into the Pak’s circuit board. The 2N3906 should be oriented the same as the transistor that was removed (except 2 pins swapped), but again its worth checking the pin out!

The other hardware change required alters the clock frequency of the Pak’s micro-controller and sound effects chips. The Speech-Sound Pak uses a frequency doubling circuit to provide the clock signal for these ICs. These chips use a typical clock of 2 MHz, and the old COCO’s clock of .89 MHz was doubled to provide the Pak’s ICs with a 1.78 MHz clock. This is close enough to 2 MHz that the Pak runs properly. However, when the COCO3 runs at 1.78 MHz, this frequency is doubled to 3.56 MHz, which is well above the ideal 2 MHz clock. We’ve found that most Paks will work at this speed as long as the voltage inverter has been modified. If the clock doubler isn’t modified, the speech synthesizer will sound normal, but the sound effects will be one octave higher than they should be. That is, sound effects will not sound as they should, with the result that software which uses the Pak for sound effects will probably disappoint you.

Here’s a diagram of the 74LS86 (viewed from above), where the ‘D’ represents the notch at the “pin one” end of the chip. Some chips do not have a notch to indicate pin 1. In that case, look for a small indentation (represented here by the lower case ‘o’) close to pin 1 to find the orientation of the chip’s pin numbers. The upper case ‘O’s represent pins.

pin 14              pin 9
  !                   !
 +O---O---O---O---O---O---O+
 !                         !
 D         74LS86          !
 !o                        !
 +O---O---O---O---O---O---O+
  !

Here’s a diagram of the 74LS86 (viewed from above), where the ‘D’ represents the notch at the “pin one” end of the chip. Some chips do not have a notch to indicate pin 1. In that case, look for a small indentation (represented here by the lower case ‘o’) close to pin 1 to find the orientation of the chip’s pin numbers. The upper case ‘O’s represent pins.

pin 14              pin 9
  !                   !
 +O---O---O---O---O---O---O+
 !                         !
 D         74LS86          !
 !o                        !
 +O---O---O---O---O---O---O+
  !
pin 1                   pin 7

Here are two alternatives to fixing the Speech-Sound Pak’s clock rate. The first will limit your Pak to use at 1.78 MHz, unless you restore the Pak to its original state before using it at .89 MHz. The second will allow you to switch the Pak to operate at either .89 MHz or 1.78 MHz. Both fixes will work on either the 26-3144 or 26-3144A Speech-Sound Pak. 1.78 Mhz COCO3 Clock Frequency:

Cut the trace leading from the Pak’s bus Q signal (card-edge pin 7) to pin 9 on the 74LS86. Connect pin 9 of the 74LS86 to the Pak’s ground.

.89/1.78 MHz COCO Switchable Clock Frequency:

Cut the trace leading from the Pak’s bus Q signal (card-edge pin 7) to pin 9 on the 74LS86.

Connect pin 9 of the 74LS86 to the centre (common) pole of a small SPDT (Single Pole Double Throw) switch.

Connect one outside pole of the SPDT switch to the Pak’s ground.

Connect the remaining pole of the SPDT switch to the Pak’s bus Q signal.

Mount the SPDT switch on or in the Pak, wherever its convenient, and will not accidentally short to anything.

We hope that your Speech-Sound Pak modification goes as smoothly and successfully as ours did (once we figured out the voltage inverter problem it was all downhill!). Thanks to Kevin Darling and others who believed that there was no good reason why it wouldn’t work!

Speech-Sound Pak modification by Bill Boogaart (CIS 72075,615), Mario Dilallo, and Bruce Isted (CIS 76625,2273). Radio Shack TM Tandy Corporation, OS-9 TM Microware & Motorola, Inc.