Synth-DIY Yahoo! Groups Archives

Correct or Incorrect - EML 100 OSC 3 waves?

2014-11-12 by zaum@...

Was scoping my EML100's waves and I noticed the front panel for OSC 3 draws a Triangle, then what looks like a half rectified sine and then a square as the wave shapes. When scoped I see a Triangle with the bottom clipped instead of a triangle - sort of like a half rectified triangle but not on zero volts, then a Triangle/Square hybrid that is nothing like a half rectified sine in the center, then a square as expected on the right.

So… was just wondering if that's "normal" for the 100 and the panel is wrong, or am I having a problem with my wave shaping?

Nick

RE: [emlsynth] Correct or Incorrect - EML 100 OSC 3 waves?

2014-11-12 by Pete

Hi. Where in the synth are you actually scoping for your waveforms? You should have triangle, sawtooth and square waves. I’m not so sure that graphic on the front panel for sawtooth is correct. Doesn’t sound like your triangle is healthy. Can you read schematics? I linked to it if you don’t have it. You can see the test points to look with your scope and check waveforms. If any are clipped, I would start confirming my voltages, first at the power supply, then at the actual VCO 3 circuit. Offset or clipped waves usually indicate voltage problems, for whatever reason causing it. Are the electrolytic and tantalum caps original? If so, you need to change the caps and give it a good cleaning and calibration first.

You can see at the 10K Color pot the 3 incoming waveshapes before the color pot mixes them.

Schematic: http://manuals.fdiskc.com/flat/EML%20101%20Schematic%20Re-Draw%20%28%20Draft%201%20%29.pdf

Peter

From: emlsynth@yahoogroups.com [mailto:emlsynth@yahoogroups.com]
Sent: November 12, 2014 10:41 AM
To: emlsynth@yahoogroups.com
Subject: [emlsynth] Correct or Incorrect - EML 100 OSC 3 waves?

Was scoping my EML100's waves and I noticed the front panel for OSC 3 draws a Triangle, then what looks like a half rectified sine and then a square as the wave shapes. When scoped I see a Triangle with the bottom clipped instead of a triangle - sort of like a half rectified triangle but not on zero volts, then a Triangle/Square hybrid that is nothing like a half rectified sine in the center, then a square as expected on the right.

So… was just wondering if that's "normal" for the 100 and the panel is wrong, or am I having a problem with my wave shaping?

Nick

RE: [emlsynth] Correct or Incorrect - EML 100 OSC 3 waves?

2014-11-13 by zaum@...

Thanks Peter for responding.

I'm talking about the (blue faceplate) EML 100, not the 101, it has different waves from the 101. I've yet to see a full set of schematics. OSC 2 and OSC 3 on the 100 are definitely not identical as they are on the 101 schematics. Though I've not attempted yet to compare their differences from the 101.

I was scoping the waveforms via the OSC 3 out jack up top and the filter mixer out jack up top.

> I’m not so sure that graphic on the front panel for sawtooth is correct.

That's what I'm trying to find out before I go back inside. The factory graphic (looks like a half rectified sine) has nothing resembling a saw at 12 o'clock (what Peter mentions) but then again neither does it look like my wave at 12 o'clock.

Then again contemplating further. OSC2 which is working shows a cosine to a half rectified (co)sine going to a square on the front panel and I'm getting that when looking at the actual wave. So OSC3 seems to be intended as having a triangle instead of the cosine looking at the front panel. So that does sort of seem like the clipped on the bottom only triangle I get in real life might be out of calibration and spoiling the 12 o'clock mix of waves.

The power supply was doing +15.5v -15.5v with original caps. Since I was replacing the electrolytics I did the power supply and the voltage remained the same.

I did not see any Tantalum caps in the 100 (or the 101). Has anyone spotted any?

Though still curious on the original question. OSC 3 on a 100 (not a 101), are the actual waveshapes (on a believed to be fully working unit) similar to what is drawn on the panel?