Ramp wave ugliness

[Thomas_Henry]

Hi Gang,

If any of you have VCOs using the CEM3340, would you do me the great favor of looking at the ramp wave carefully and tell me if you see any undershoot, or other asymmetric behavior? I don't really care what the design is, homebrew or commercial. I'm just curious if your ramp is "perfect."

Many thanks, and in return I promise a new design in the offing.

Thomas Henry

[varice]

I have a Prophet-5 rev3.3 that uses the CEM3340 chip. I recall that the saw waveform was very free of distortion when viewed on an oscilloscope.

If you are interested, I recorded and uploaded a wavefile sample of the Prophet-5 saw wave. It is a recording of the output of the synth (with the VCO going through the mixer, the low pass filter set wide open with no resonance, and the VCA circuits). The digital recording was done with a sample rate of 44.1kHz. The sample is here (along with other waveform samples):

http://electro-music.com/forum/topic-12389-25.html

Using a wavefile editor, the saw waveform appears to me to be very clean, without any significant under or overshoot, or any other ugliness.

I hope this helps, and good luck with the new VCO design!

[varice]

[blue hell]

When the wave editor is using sinc filtering on displaying wave forms (like cooledit did) you will always see 'ringing' - between quotes as it is not actually ringing but an artifact of the limited bandwidth of the recorded signal, i.e. an approximation of the signal as a sum of sines.

[varice]

[Thomas_Henry]

Thank you, lads! I'm not sure the older CEMs do this, but on 7 different new ones (Revision G) we (three different experimenters) were seeing an undershoot to -0.7V on the ramp. Not necessarily ringing, but a short glitch/fall below zero.

However, I'm happy to report that one of our team nailed a solution tonight, after several days of real sweat. This is going to be a cool design!

Thanks again,

Thomas Henry