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Calibration question (general, for analog synths)
Old 4 weeks ago
  #1
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Calibration question (general, for analog synths)

This may sound weird, but I'll ask it anyway.

I'm in the process of calibrating my Memorymoog. Now, probably not entirely specific to this synth, there are procedures in the manual that require the use of a scope, strobe tuner, and (specifically stated) an "HP 400F A.C Voltmeter".

During oscillator tuning, it specifies hooking up the voltmeter, strobe tuner, and scope to a pin on an IC (output). How in the hell do I accomplish this? Like I'm literally sitting here being stupid thinking about how I can pull an audio signal right from a pin on a chip and at the same time have two more pieces of test equipment hanging off it. Am I missing some extremely obvious step?

Also, I know I don't need a specific brand of voltmeter, much less an analog voltmeter that was manufactured close to 40 years ago, so I'll presume that any modern multimeter will be suitable in this case as it has been for the other stages of my calibration? Same with the tuner; do I need to use a strobe for accuracy or would I be fine with a standard chromatic guitar tuner?

Just getting ideas before I start investing in different/more test gear.
Old 4 weeks ago
  #2
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Not all modern voltmeters would necessarily be suitable; you'd need one that is accurate for the frequency being measured. The 400F apparently was usable from 20 Hz to 4 MHz; many (particularly less expensive/less well specified) multimeters are mainly suited for AC voltage measurements in the general vicinity of 60 Hz. If the exact voltage need not be particularly precise, a modern digital oscilloscope may well be sufficient for measuring it.

A decent standard tuner would I think be sufficient, as would a frequency counter (along with a table of note frequencies). At least some digital oscilloscopes with frequency measurement capabilities would probably be entirely sufficient. Some guitar and general instrument tuners are none too precise, only accurate to within a few cents or worse; that may or may not be sufficient for you here. GarageBand on the Mac (and I assume many other programs) has a nice accurate tuner function.

To hook more than one instrument up to the signal, you just...well, hook them up in whatever way works. It may be necessary to have a little clip on test lead and then connect the intermediate lead to the various instruments. On the other hand, with a good enough oscilloscope, you may not need the other instruments at all these days, which of course simplifies things considerably.
Old 4 weeks ago
  #3
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Quote:
Originally Posted by DrewE View Post
Not all modern voltmeters would necessarily be suitable; you'd need one that is accurate for the frequency being measured. The 400F apparently was usable from 20 Hz to 4 MHz; many (particularly less expensive/less well specified) multimeters are mainly suited for AC voltage measurements in the general vicinity of 60 Hz. If the exact voltage need not be particularly precise, a modern digital oscilloscope may well be sufficient for measuring it.

A decent standard tuner would I think be sufficient, as would a frequency counter (along with a table of note frequencies). At least some digital oscilloscopes with frequency measurement capabilities would probably be entirely sufficient. Some guitar and general instrument tuners are none too precise, only accurate to within a few cents or worse; that may or may not be sufficient for you here. GarageBand on the Mac (and I assume many other programs) has a nice accurate tuner function.

To hook more than one instrument up to the signal, you just...well, hook them up in whatever way works. It may be necessary to have a little clip on test lead and then connect the intermediate lead to the various instruments. On the other hand, with a good enough oscilloscope, you may not need the other instruments at all these days, which of course simplifies things considerably.
Thanks Drew - I'll have to check my current meters and see what they're spec'd for; I have a Southwire meter I bought at Lowe's not too long ago which seems to do the trick for most things, but I also have an old Fluke 77 (presumably an original, not series II) that works well too.

I also bought a Siglent digital scope recently; I never really even thought about not needing the other tools if the scope could get me where I need.

But let's assume I need to 'connect a tuner to pin 7 on IC***" is there some kind of probe tip with a 1/4" socket/adapter I can cobble together? I'm just curious how this is possible, unless I'd just leave it external and use the built in mic... or am I reading too much into it?
Old 2 weeks ago
  #4
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Quote:
Originally Posted by whinylittlerunt View Post
Thanks Drew - I'll have to check my current meters and see what they're spec'd for; I have a Southwire meter I bought at Lowe's not too long ago which seems to do the trick for most things, but I also have an old Fluke 77 (presumably an original, not series II) that works well too.

I also bought a Siglent digital scope recently; I never really even thought about not needing the other tools if the scope could get me where I need.

But let's assume I need to 'connect a tuner to pin 7 on IC***" is there some kind of probe tip with a 1/4" socket/adapter I can cobble together? I'm just curious how this is possible, unless I'd just leave it external and use the built in mic... or am I reading too much into it?
I have used things like this: https://www.digikey.com/products/en/...t-clips-ic/624 when I needed access to IC pins in close quarters. If you need to hook multiple devices to a pin at the same time, a quick solder of some jumper wire (or any wire lying around) to the top of the clip will do the trick. I usually end up with a mini alligator clip on the top of the clip and then everything else clips to the other end of that.

I'll often unscrew a 1/4" cable end and use alligators to go from a pin/component to an audio lead. I made a dedicate one for MIDI testing years ago but couldn't be bothered to make one for audio since it's usually only 2 (or 3) clips.
Old 1 week ago
  #5
Gear Maniac
 
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Know what’s funny? After all that (and it’s calibrated and working great, FYI) I didn’t even need to use the tuner for anything... I got all the voices in tune by measuring frequency, and then using the built-in software tune procedure. Worked like a charm!

But I got myself a rad Peterson strobe tuner in the process which is mad useful elsewhere ������
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