OT: buying an oscilloscope

[ethrbunny]

Im looking at o-scopes on ebay. Each has a 'bandwidth' listed at the bottom.  What sorts of frequencies are we dealing with in stompboxes? All I can think of are vibrational frequencies (IE 'a' = 440 hz).

Also - are there models to steer to / away from? Or a better source here in the NW US for a used 'scope? Boeing surplus?

[toneman]

almost any scope will work for audio.
Say, 1MHz bandwidth.
Make *sure* it's a --TriggeredSweep-- scope.
Most new/recent//solid-state ones are.
they will have a "trig" knob with + and -.
This means it can trigger on the positive-going transition,
or the negative-going transition.Most will have "auto trigger" also.
Lots of scopes on ebay. Lots of good deals; lots of junk.
Try to get a dual trace scope.
Much more usefull for comparing ins & outs simutaniously.
One last thing, look for probes while you're at it.
There are generic probe sets, AWA the ones that originally came with some scopes.
My 465B, that's a Tektronix, came with 2 Tek probes.
I've seen just the probes for $20 to $40 each.
I use a scope for nearly everything--voltage, waveforms, frequency, timing.......
stayscoped
tone

[niftydog]

Tektronix, Fluke/Philips and Agilent are great brands - although you're not likely to encounter them cheaply, except maybe an old tektronix.

Ensure the CRT still works, because they are nigh on impossible (or stupidly expensive) to replace.

oh, and audio range is considered to be 20hz to 20khz at absolute maximum. Just about any scope will suffice for these frequencies.

[ethrbunny]

Great stuff. TY.

20hz to 20khz at absolute maximum

Say, 1MHz bandwidth.

How would I know whether a specific model satisfied these needs?

The models on ebay are generally listed like:

foo model 28 - 100 mHz

or

quack model a1a - 35 mHz

Is the frequency # the maximum sweep rate?

[niftydog]

the frequency is the bandwidth of the scope inputs.

1M or higher would be fine for audio stuff.

[ethrbunny]

the frequency is the bandwidth of the scope inputs.

1M or higher would be fine for audio stuff.

So if I got one that said, say 100mhz it would still work for the slower stuff?

[brett]

Hi.  Yeah, the bandwidth over 20kHz in scopes isn't necessary for boxes *unless* you have some high frequency signal in a clock or oscillator or similar to monitor.  
Don't forget the hand-held scopes such as the Velleman HPS5 and HPS10.  They not only display the waveform, they calculate peak to peak and RMS voltage, estimate frequencies (though I think it's only to nearest 0.5kHz, which is annoying for audio work).  They are solid-state and fairly cheap.

Whatever you get, you'll find a scope very handy.

[niftydog]

So if I got one that said, say 100mhz it would still work for the slower stuff?

absolutely.

[ethrbunny]

Would this one work?

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=104247&item=7510298852&rd=1&ssPageName=WDVW

I might have a local offer for US50$  to get one.

Unf - I can't find any more specs on it. No clue whether it has 'auto triggering' or not. I haven't used an oscope since I was in high school.. and *that* was a while ago. Yikes!

[niftydog]

it looks good. it does auto-trigger.

The add is slightly vague, which would turn me off. And the sentance "The unit does not include the power supply but appears to be in perfect working order" is slightly scary...


power supply? Maybe he means the cable. "appears" to work... hmmm.


That seller isn't doing himself any favours by posting such vague drivel on the add.

[ExpAnonColin]

I would definitely get a scope that could go over the audio range (.1hz to maybe 10mhz) so you could measure everything from slow LFOs to clock signals.

-Colin

[niftydog]

What Colin says is right, but just to clarity - you don't have to worry about the lower end of the bandwidth. All oscilloscopes measure right down to DC (ie; 0hz).

And it's pretty rare these days to see a scope with less than 10Mhz bandwidth.

[ethrbunny]

Awesome. Thanks for all the speedy responses.

[H.Manback]

Well this is a coincidence. I actually worked with this one (I think) at school! We used the new tektronix scopes which are completely digital, but I wanted to see what the difference would be with one of those old fashioned scopes.

Of course this is no comparison since those tektronix things go for like around $1000, but I did prefer the new ones . I didn't spend much time on the thing, and I couldn't figure out how it works that fast (I do computer science, and I just followed this one electronics course at the physics department, so that was the first time I even used a scope).

The specs seem pretty good as said by the rest here, 35MHz is more than enough, and it looks like some probes are included as well.

[troubledtom]

by the way this NOT OT   , a scope is very cool to have and learn how to use.
  best wishes,
         and be careful on e[evil]bay :wink:
                    - tom

[ethrbunny]

(bump)

Im going  to look at an hitachi scope sometime this weekend. What sorts of tests should I do / things to look at before I buy?

[toneman]

Hey EB,
First U will need a probe
So U can check the input amplifiers.
Sometimes, but not always,
there is a test/calibration squarewave signal
on the front of the scope.
Hang your probe there, check the proper scale/resolution.
That way U can check triggering, amplitude accuracy, etc.
Hitachi makes good little scopes.
HOpe it's a dual-trace....
good luck.
tone

[barret77]

are those software-oscilloscope for windows any good?

[toneman]

software-based Oscopes R not DC coupled.
that is, they only read AC signals.
Might B OK 4 U if U just want 2 view stompbox waveforms.
But, if U *really*really* want 2 troubleshoot,
a good scope can measure DC, AC, frequency, period, &
heh, those waveforms look far-out man.  tone