Finished Pieces


    casperelectronics Speak and Spell: ST505

    To make this piece I started with the standard “T4” design. Then I added two more switches for introducing different types of distortion into the sound. Then I built an LFO circuit into the body of the Speak&Spell. You can achieve lots of different effects with this. It can be used to turn the Speak&Spell into a sort of rhythm/drum machine. View a large scale diagram of the ST505.

    casperelectronics Speak and Spell: ST505

    The LFO has two functions. It can act as a pitch modulator and it provides rhythmic trigger pulses. These functions can be used individually or in conjunction. The LFO rate can be adjusted with the LFO rate knob and is indicated by a blinking light to the left of the knob. Pitch modulation has two settings, “depth” and “slope.”

    “Depth” controls how much the LFO will effect the overall pitch. “Slope” is used to transform the shape of the LFO waveform. The wave can be changed from straight square wave shaped modulation to a smooth triangle modulation. The trigger pulses can be used to regularly trigger the “ON” or “hold” functions of the Speak&Spell. This means that every time the LFO indicator lights, it’s the same as pressing the “ON” button or pressing the “hold” switch. Using the “hold” trigger and pitch modulation at the same time can make some really amazing drumbeat like sequences.


    4 Responses to “ST505”

    • 1

      POE said:
      September 23rd, 2010 at 5:07am #

      I really love how this mod sounds and I am at work building the LFO now. As per the schematic you posted. But I am confused to how you accomplish this:

      “The trigger pulses can be used to regularly trigger the “ON” or “hold” functions of the Speak&Spell.”

      I really want to incorporate these features but after looking at the schematic of the circuit and the large diagram I am still not sure about it. I am assuming it has to do with the switches in the cloud and D1/D2 and E1/E2???

      I was also curious about the power switch?

      Thank you very much for your time.

    • 2

      Chris said:
      June 16th, 2011 at 10:48pm #

      Can you explain how to hook the LFO up to the hold feature?

    • 3

      Mr James said:
      July 20th, 2011 at 11:34am #

      Hello, really wondering how to hook the hold feature on the LFO. I managed to protoboard the LFO to your schematics,the pitch modulation works brilliantly. I think confusion is coming from there being two points for the hold and tone features and only one for the pitch.
      Also,there is a control pin on the 555 timer, could this be used for CV sync? That dam bug!
      Thank you, all the best

    • 4

      casper said:
      September 2nd, 2011 at 5:44pm #

      @Mr. James.
      The two points for hold are just “hold base” and “+”. when those are connected you get the hold effect. therefore you can just connect the output of the 555 (which is simply pulsating current) pin 3 directly to the “hold base” point. That’s the one all the way on the left. I think the same goes for the tone effect.

    Leave a Reply

    If you're not already logged in, there might be a question you need to answer before you post to prove you're human. It's there to help stop comment spam.