Why should I buy an oscilloscope? or not.

[tenser75]

I build pedals but I've never used an oscilloscope but im intrigued to go to the next step in my expertise.

what exactly do you measure with an oscilloscope while building a stompbox? when is necessary, when don't?

thanks!

[GibsonGM]

Hi Tenser, welcome to the forum.  Good question you have there...

An o-scope is a great investment for anyone who is expecting to be VERY into electronics, IMO...you use it to measure voltage changes over time, generally (altho there are other uses...).   You CAN make, repair, debug stompboxes without one, so they're not absolutely required or anything, but they give you interesting info on the spot...

Example:

You can use the scope to see if a stage in an amp or effect is "alive", and what shape the signal is that is going thru it - is it distorting?  How does your LFO wave look - is it really a triangle like you wanted?

Is the stage biased correctly, working ok? 
Or is it changing the signal in a way you don't want?

What happens when I adjust some circuit parameters, like resistor values around a transistor?  You can watch as you do it...

I got a nice 1982 Tektronix scope for $99 on Ebay!   You have to be cautious in buying used stuff that way, but the prices are low enough to be worth the risk IMO.

So should someone buy a $3,000 scope for hobby use?  Not in my world, LOL...but a few hundred could be a great investment, if you plan to be doing electronics for a long while! 

[amptramp]

You may not need an oscilloscope for much of your work, but when you do need one, nothing else will do.

One good use for an oscilloscope is if you get symptoms of oscillation on part of a waveform in an amplifier.  Oscillation does not always result in a continuous squeal.  This may happen, for example, only when the signal is going from high to low voltage and only on part of the waveform.  You get sort of a fuzzy sound because you can reach the signal clipping limits in the oscillation riding on the signal even though you don't exceed the normal clipping level.  You may also get current limit oscillations because the feedback network cannot keep up with the amplifier returning from current limit to linear operation.

In general, it is good to have an oscilloscope available to diagnose problems that you have to see to understand and the partial oscillation I mentioned is one of them.  There are a large number of used and surplus oscilloscopes available, so get one with at least 10 MHz response so you can see spurious oscillations even if only audio frequencies are supposed to be there.  I have one scope I built from a kit, one that got left in the garbage one night, one I got from a guy at work, two that I bought at a garage sale and a few more that I got at the London Vintage Radio Club (in London, Ontario, Canada).

Other than that, you can get some insight into problems where signals disappear at some stage or power supply noise is getting into the signal (quite often from an LFO, the Low Frequency Oscillator used for tremolo and vibrato effects).  You can continue without one, but certain problems lend themselves to visual representation better than other diagnostic methods.

[karbomusic]

You can build pedals without one, you can learn an awful lot with one.

[bluebunny]

Do you need one?  No.  Can they be fun/useful/interesting/educational?  Sure.

[antonis]

What Marc said...!!!

I once "upgraded" one of my multimeters with another with o-scope capabilities..

Did I ever need it..?? -> No
Did I ever use it..?? -> All the time

[pdavis68]

OScopes are terrific. For me the most important feature they offer is an easy way to track a signal through a circuit to find out where the signal is getting lost. I find it far more frustrating to debug circuits without one.

I used to have old Tektronix 465 & 466. They're fantastic scopes and you can usually find them on Craigslist for $150 or less. These guys are big and heavy and they're made like tanks. They last forever. But being big and heavy is why I got rid of mine. My current workspace is too small for something of that magnitude. Also, since I mostly use my scope for a yes/no on signal at a point and have no requirements for high fidelity, I use one of these: http://www.jyetech.com/Products/LcdScope/e112.php.

You can find them on e-bay for about $50 or so. They don't work at high voltages (I mainly build tube amps, so I have to be careful what I probe with it), the touch screen isn't the best in the world, but: It works well enough for me, it's itsy bitsy and easily fits in the palm of my hand, and it easily handles audio frequencies.

The last amp I built was actually designed almost entirely with an oscilloscope. I laid out a rough approximation of the circuit I wanted on the breadboard and spent a lot of time tweaking the circuit with my scope (and ears). Don't think I did a bit of math designing that one and it's my favorite amp.

[wavley]

I'd say yes.

You can find them pretty cheap if you look hard enough, I've found a few $50 scopes in my day (a friend of mine just got a Tek dual trace used for $50 just the other day) and they will totally save you $50 worth of time.  Plus, there is a lot that you can learn about how things work by seeing it visually on a scope, sometimes I'll still put a probe on something and say "Oh, THAT's how that works!"  It's pretty cool to look at the shapes of LFOs and listen to the sound as you change them.  And the best part is that you can inject a tone into the input and trace where it disappears when your circuit doesn't work, yes you can also do this with an audio probe.

So, you can pretty much build pedals without a scope and be just fine, but a scope certainly makes life a lot easier when troubleshooting.