Oscilloscope - What to buy for synth calibration?

StepLogik · Post by **StepLogik** » Fri Aug 24, 2007 2:57 pm

Since I own a few old clunkers, I figure an oscilloscope is a worthwhile investment so I can run the calibration procedure when its needed. I don't want to spend too much money since its not going to get a lot of use.

Does anyone have any recommendations?

I see the Madell CA8016 on ebay for $150 new and it seems up to the task.

Altitude · Post by **Altitude** » Fri Aug 24, 2007 3:35 pm

I would say for analogs, I would just get a good meter that has a counter. A low end fluke is about that much and do a lot more. That scope will allow you to look at the waveforms but wont tell you anything else

portland · Post by **portland** » Fri Aug 24, 2007 3:58 pm

You're going to need some wacky cable adaptor for the input.
There are oscilloscope AUs (and probably VSTs too) that do this for free without hassle.

Post by **meatballfulton** » Fri Aug 24, 2007 4:33 pm

Buy a used one. I have an all tube Tektronix scope I got with a set of 3 probes for $20. This thing was the Rolls Royce of lab scopes in it's day (50s to 70s) and other than being big is more than up to the task.

StepLogik · Post by **StepLogik** » Fri Aug 24, 2007 6:21 pm

Altitude wrote:I would say for analogs, I would just get a good meter that has a counter. A low end fluke is about that much and do a lot more. That scope will allow you to look at the waveforms but wont tell you anything else

i think (iirc) that the jp-6 service notes require you to inspect the actual waveform in a few places. i'll double-check when i get home. i'd love to just get a nice fluke DMM.

StepLogik · Post by **StepLogik** » Fri Aug 24, 2007 6:22 pm

portland wrote:You're going to need some wacky cable adaptor for the input.

thats just a standard BNC connector... adapters for those are readily available at rat shack.

Helix · Post by **Helix** » Fri Aug 24, 2007 6:52 pm

I use a frequency counter to tune my Pro-One but the easiest way to tune it is to just play a 440hz tone and tune the synth after that.

Altitude · Post by **Altitude** » Fri Aug 24, 2007 7:37 pm

StepLogik wrote:
Altitude wrote:I would say for analogs, I would just get a good meter that has a counter. A low end fluke is about that much and do a lot more. That scope will allow you to look at the waveforms but wont tell you anything else
i think (iirc) that the jp-6 service notes require you to inspect the actual waveform in a few places. i'll double-check when i get home. i'd love to just get a nice fluke DMM.

That may be true however your still going to need something that will output the period of the waveform and counting pulses on a screen is really not that accurate of a way to do it.

Analog Freak · Post by **Analog Freak** » Sat Aug 25, 2007 7:19 am

The accuracy of a frequency (period) measurement from an oscilloscope would depend on how well calibrated your horizontal timebase is. I would recommend something like an older used solid-state oscilloscope. I wouldn't mess around with anything that is tube based because of all the reliability problems you are going to have with something of that vintage. Since you aren't really going to be looking at any high speed signals, I figure a low-bandwidth scope should do pretty well. Something like the Tektronix 5000 or perhaps 7000 series scopes (7000 series are very good for the money), just avoid any of the Sony/Tektronix models, they were absolute junk. Leader, HP (not the 1980 system), and Hitachi also made decent to wonderful Oscilloscopes back in the day. Any for those of you who think a frequency counter is an end all, just because the frequency is right doesn't mean that the waveform (and thus the harmonics) are anything like what they should be. You can only see that kind of stuff with an Oscilloscope.

xpander · Post by **xpander** » Sat Aug 25, 2007 9:19 am

tektronix are pretty standard, it's hard to go wrong with a vaguely modern one from eBay.

if you find a local ham radio club, you'll find lots of helpful people who should be happy to help you set it up, too!

if you get into more pro-level calibration, consider buying an accurate strobe-style tuner by Peterson, they're a pretty giant step up from the inexpensive Korg ones.

Post by **nathanscribe** » Sat Aug 25, 2007 6:03 pm

I picked up one of these for about £70 new. Small, handy, portable, runs on batteries (but eats them quickly) and has a nicely configurable display. And it's cheaper than a traditional scope, at least here in the UK.

A scope is definitely worth it. Being able to check things like the offset of waveforms or the width of a pulse is quite useful.

StepLogik · Post by **StepLogik** » Sun Aug 26, 2007 1:33 am

That velleman HPS10 looks like it might get the job done.

I found a bad review of it on amazon:

This instrument is like most Velleman measuring equipment attractively priced but completely useless for any serious work. The specifications are very misleading and apply only to 3 of the voltage ranges (50 mV/1V and 20V). The bandwidth of 2 MHz is also only valid within these ranges. At this frequency however the scope is not able to produce a sine wave properly. Degradation of waveform in the ranges mentioned starts very early at about 1 MHz. All the other ranges behave different some are only useful to 150 kHz. Testing the scope with a Tektronix scope calibrator shows for some ranges differences for positive and negative values of DC voltages. I didn't expect Fluke quality but this is really a very inaccurate scope although the voltage values are presented with 3 to 4 digits. Only within the audio range and up to about 50 kHz acceptable measurements can be made. I own many scopes and this one definitely is not very useful to put it mildly. Any good second hand analogue scope can be obtained for the same price and will outperform the HPS10 easily.

Even though its negative, it sounds like it might still be good enough for synth calibration work.