Model D Saw Ramp Up on Oscilloscope Weirdness
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Model D Saw Ramp Up on Oscilloscope Weirdness
Hello, I hooked up a Korg NTS-2 audio oscilloscope to a Minimoog D (1975) and was surprised to see that the Sawtooth (ramp up) actually seems to ramp down (on all 3 oscillators). And the reverse sawtooth on oscillator 3 actually ramps up instead of down. Yet, if I use the sawtooth or reverse sawtooth as an LFO, it clearly Is modulating In the right direction. Is this the intended behavior, I'm just wondering. I have tested w/ other synths and the saw is correct., so I don't think it's the scope? Thank you.
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Re: Model D Saw Ramp Up on Oscilloscope Weirdness
Hi there!
Might seem a stupid question, but have you double-checked you haven't inverted the scope inputs?
Might seem a stupid question, but have you double-checked you haven't inverted the scope inputs?
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Re: Model D Saw Ramp Up on Oscilloscope Weirdness
I have checked that, yeah. Pretty strange?
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Re: Model D Saw Ramp Up on Oscilloscope Weirdness
Your observations are correct. The signal path from the OSC to the output is non-inverting and the path through the modulation mixer is inverting.
The sawtooth/ramp graphics on the panel correspond correctly to the direction expected in the modulation path. However, the pulse graphics are inconsistent. For the narrow pulses as modulation it is the “low phase” that is actually shortened. Conversely, the saw/ramp graphics are inverted with respect to the audio output, yet the pulse graphics match the audio output (IIRC).
The sawtooth/ramp graphics on the panel correspond correctly to the direction expected in the modulation path. However, the pulse graphics are inconsistent. For the narrow pulses as modulation it is the “low phase” that is actually shortened. Conversely, the saw/ramp graphics are inverted with respect to the audio output, yet the pulse graphics match the audio output (IIRC).
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Re: Model D Saw Ramp Up on Oscilloscope Weirdness
Now, that's accurate!
Thanks
Thanks
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Re: Model D Saw Ramp Up on Oscilloscope Weirdness
Thank you! Very helpful information
sdwillingham wrote: ↑Thu Jan 04, 2024 6:01 pm Your observations are correct. The signal path from the OSC to the output is non-inverting and the path through the modulation mixer is inverting.
The sawtooth/ramp graphics on the panel correspond correctly to the direction expected in the modulation path. However, the pulse graphics are inconsistent. For the narrow pulses as modulation it is the “low phase” that is actually shortened. Conversely, the saw/ramp graphics are inverted with respect to the audio output, yet the pulse graphics match the audio output (IIRC).
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Re: Model D Saw Ramp Up on Oscilloscope Weirdness
The behavior you're describing with the Mini Moog D's sawtooth waveforms is not the intended behavior, and it's good that you noticed it. Here's what's likely happening:
Possible Issues:
Faulty Oscillator Circuit: There could be a problem with the circuitry generating the sawtooth waveform in one or more oscillators. This could be due to aged components or other issues.
Incorrect Calibration: The Mini Moog D can be calibrated, and your sawtooth waveforms might be out of calibration, causing them to appear inverted.
Scope Settings: While unlikely, double-check your oscilloscope settings to ensure it's displaying the waveform correctly and not inverting it accidentally.
Additional Notes:
It's good that the LFO sawtooth behaves correctly, as it indicates the issue is likely isolated to the oscillator section.
Comparing the Mini Moog D's sawtooth waveform to other synths is a good troubleshooting step.
Remember, tampering with vintage electronics can be risky. If unsure, professional help is the safest and most reliable option.
Possible Issues:
Faulty Oscillator Circuit: There could be a problem with the circuitry generating the sawtooth waveform in one or more oscillators. This could be due to aged components or other issues.
Incorrect Calibration: The Mini Moog D can be calibrated, and your sawtooth waveforms might be out of calibration, causing them to appear inverted.
Scope Settings: While unlikely, double-check your oscilloscope settings to ensure it's displaying the waveform correctly and not inverting it accidentally.
Additional Notes:
It's good that the LFO sawtooth behaves correctly, as it indicates the issue is likely isolated to the oscillator section.
Comparing the Mini Moog D's sawtooth waveform to other synths is a good troubleshooting step.
Remember, tampering with vintage electronics can be risky. If unsure, professional help is the safest and most reliable option.
Re: Model D Saw Ramp Up on Oscilloscope Weirdness
Not true.KushnomGhatak wrote: ↑Tue Feb 13, 2024 7:54 am...
Faulty Oscillator Circuit: There could be a problem with the circuitry generating the sawtooth waveform in one or more oscillators. This could be due to aged components or other issues.
Incorrect Calibration: The Mini Moog D can be calibrated, and your sawtooth waveforms might be out of calibration, causing them to appear inverted.
...
keep on turning these Moog knobs
Sequence:
Prodigy * minimoog '79 * Voyager * MF102 * MF103 * MF104z * MP201 * Taurus 3 * Minitaur * Sub Phatty * MF105 * Minimoog 2017+ MUSE * One 16
Sequence:
Prodigy * minimoog '79 * Voyager * MF102 * MF103 * MF104z * MP201 * Taurus 3 * Minitaur * Sub Phatty * MF105 * Minimoog 2017+ MUSE * One 16
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Re: Model D Saw Ramp Up on Oscilloscope Weirdness
Neither this. Inverter circuits can be involved in there.KushnomGhatak wrote:the LFO sawtooth behaves correctly, as it indicates the issue is likely isolated to the oscillator section
Now this is true. Do you have a short list in our region please?KushnomGhatak wrote: ↑Tue Feb 13, 2024 7:54 am If unsure, professional help is the safest and most reliable option
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