Calibration Oscilloscope

[LaxSlash1993]

Can anyone reccomend an oscilloscope for calibrating a Memorymoog?

[thealien666]

Can anyone reccomend an oscilloscope for calibrating a Memorymoog?

I'm thinking you would rather need an accurate (4 or better yet 5 digits) frequency meter and digital multimeter more than an oscilloscope to calibrate voltages and frequencies inside a Memorymoog.
Unless you want to actually look at the wave output. Then, any analog (or digital) oscilloscope will do, as long as it's got trigger sync, and is of reasonable quality (I'm thinking Techtronix as affordable).

I'm sorry but, if you have to ask that question in the first place, I'm not totally convinced you might be qualified to tinker with such a fragile and capricious beast... Do you know what's involved in recalibrating a Memorymoog ? Do you have any idea of what fastidious task awaits you ? Have you thought about scratchy trimpots giving poor performance not having been touch for so many years ? Wire connectors making poor contact after having been moved or unplugged ? Have you had a look at the 3 analog boards sandwiched together, on which there are more than 30 trimpots each to adjust ?! (that's over 90 in all folks)

I just wanted to make sure you knew what you're about to do...

But if only one analog board has a problem, then it might not be such a nightmare after all recalibrating only that one, provided nothing is defective on it.

[LaxSlash1993]

Yes, I do know what a ***** it can be to do this. I have tuned the synth before, almost perfectly 7F values, too; so I'm not completly inexperienced with that aspect of calibration. The biggest thing I need to calibrate is the filter on one of the voices, as well as the VCAs, which according to the Service Manual requires an oscilloscope. I'll look into Techtronix. Thanks for the suggestion and concern.

[MC]

If you buy a Tektronix scope, buy one that from a reputable shop not ebay. Most sellers on ebay do not refurbish them and they often need repair after the sale.

[LaxSlash1993]

I think I may be able to borrow one from somebody. However, I may have a bigger issue than I thought.

I went to set up a self oscillating patch, and one of the voices won't self oscillate. I did some testing, and the "whistle effect" in the filter sweep when there is an oscilator set to saw is much higher than the other ones. I'm pretty sure that just means I need to recalibrate it, but just want to make sure that the filters not bad.

[thealien666]

I think I may be able to borrow one from somebody. However, I may have a bigger issue than I thought.

I went to set up a self oscillating patch, and one of the voices won't self oscillate. I did some testing, and the "whistle effect" in the filter sweep when there is an oscilator set to saw is much higher than the other ones. I'm pretty sure that just means I need to recalibrate it, but just want to make sure that the filters not bad.

If the filter for that voice seems to operate normally, except not self-oscillating, it could simply mean that the emphasis trimpot for that voice needs to be re-adjusted. Now the trick is to be able to identify which voice, and therefore on which board that needs to be done.

Do you have a copy of the service manual (pdf or otherwise) ? If so, you could use the autotune calibration mode to disable all the voices except one at a time to isolate the one with the non self-oscillating filter.

[LaxSlash1993]

It's Voice 3. I do have the original service manual for it. Besides the self oscillation, it is operating normally. So, thankfully it just sounds like a calibration issue. I just wanted to make sure. Thanks for the reply!

[thealien666]

It's Voice 3. I do have the original service manual for it. Besides the self oscillation, it is operating normally. So, thankfully it just sounds like a calibration issue. I just wanted to make sure. Thanks for the reply!

Of course, one has to wonder why suddenly the CV coming from the software isn't high enough anymore to have that filter self-oscillate. Could it be a slowly failing OTA (U21), or possibly Q12 ?

Anyway, I hope for you that it's just a trimpot issue.

[LaxSlash1993]

That's what I was thinking, too. But the fact that there was still a "whistle effect" when there was an oscillator turned on, and the fact that it just sounded like a different pitch, is kind of making me lean towards a calibration issue.