MATRIXSYNTH: Tauntek Rhodes Chroma Dual Channel Board Tester

Friday, August 07, 2020

Tauntek Rhodes Chroma Dual Channel Board Tester


via Tauntek

"I have been thinking for several years that I would like to design a test fixture for Chroma voice boards, to allow stand-alone testing with easy access to the circuitry. Initially I was planning to have the tester automatically run through a number of tests and give an overall pass/fail result. But I decided it would be better to offer tests that would be helpful in evaluating a board, and let the user make the decisions. In addition to the tests, I implemented a full manual mode, with control over all parameters. The tester requires +/- 12.0 volts DC, well regulated as these voltages power the voice board. Current limiting would be nice, if possible. The tester and voice board together draw less than 150 mA from either supply.

While listening to the output during some of these tests may be useful, most were designed with oscilloscope testing in mind. A trigger signal is provided to allow synchronizing an oscilloscope to the test sweep. Best results will be obtained with a digital sampling oscilloscope. The audio output signal is available for probing on the tester pcb, and an 1/8" jack is provided for it as well. The S&H tests require probing op amp outputs on the voice board.

The following tests are currently implemented:
1) Oscillator and filter A/B tunability test
2) Oscillator A/B volts/octave measurement
3) LP Filter A/B volts/octave measurement
4) Osc A/B saw frequency sweep with control of filter cutoff
5) Filter A/B LP filter frequency sweep with control of resonance
6) Filter A/B HP filter frequency sweep with control of resonance
7) Oscillator A/B PW sweep, pulse or saw waveform
8) VCA A/B sweep with saw oscillator running
9) Oscillator sync mode with control of oscillator B frequency
10) Oscillator ring mod with control of oscillator B frequency
11) FM mod with control of oscillator B frequency
12) S & H two second drift test - stop refreshing and monitor control voltages
13) S & H update speed test - pulse all 8 control voltages in slow and fast modes

This is not a test, but is in the test menu:
14) Switch to Manual mode, default initial settings

Manual Mode offers individual control of these parameters: (via a menu and an encoder)
1) Osc A/B waveform selection (white and pink noise inputs fed with constant tones)
2) Osc A/B Pitch
3) Osc A/B Pulse Width
4) Filter A/B Cutoff frequency
5) Filter A/B Resonance
6) Channel A/B Volume
7) Filter A/B Mode
8) Cross Mod
9) Patch
10) Oscillator Enable
11) Output channel

These are not parameters, but are in the Manual mode menu:
12) Load Preset A
13) Load Preset B
14) Save as Preset A
15) Save as Preset B
16) Switch to Test mode"

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