Oscilloscope needed

[jallenfuzz]

I am getting much more into building my own effects and I wanted to pick up an inexpensive oscilloscope.  Any suggestions?  I will mostly be using this for effects projects.

[amptramp]

Where are you?  Someone here may be nearby and have an extra.

[R O Tiree]

You might look at entry-level USB Pico-Scopes. I've used these for a while and they're bullet-proof, unless you feed them too much voltage and then it's Goodbye Mr Chips. For FX pedals up to +/-18V, though, they're extremely powerful diagnostic tools. They have saved me so much time when debugging circuits and have massively aided my understanding of exactly what happens to signals as they progress through the various stages in a circuit.

If your budget can stretch that far, I'd go with the PS2004, 2 inputs, AWG (Arbitrary Waveform Generator). Two inputs are great for the ability to instantly compare 2 signals for distortion, gain, phase shift/reversal, etc... The AWG enables you to push any signal you like out of the box into your circuit and then see what happens to it via the probes.

[jallenfuzz]

Anyone know if a Hitachi V-222 would work? There's one on eBay for cheap.  It's two channels up to 20 MHz.

[armdnrdy]

That will work fine for what we're doing.

I have an ancient Kenwood (remember the cool stereo equipt?) and I haven't come across any limitations building/testing stompbox circuits.

As Mike mentioned in his last post, put a waveform generator on your list as well. An oscilloscope can be pretty useless in certain situations unless you input a signal through the circuit.

[Seljer]

I've got the $325 50Mhz Rigol (that can be reflashed into 100Mhz) and am very happy with it's performance for the price.

[gcme93]

I've just sent an email to my engineering department asking if I could buy an old one off them cheaply. I've heard that universities tend to buy a whole new set when a few of the old ones stop working so that the whole class is working with the same tools.

Fingers crossed!

[deadastronaut]

http://www.zeitnitz.de/Christian/scope_en

i have this free pc one..

no idea what i'm doing with it, but my guitar looks cool going through it...

[gcme93]

cool software but I'd be reluctant to throw a raw circuit's voltage at my laptop 

[samhay]

cool software but I'd be reluctant to throw a raw circuit's voltage at my laptop 

Then build a simple buffer with a current limiter (series resistor) and voltage clamping (e.g a couple of Zener diodes). I have been meaning to do this for years, as I use software too (iSpectrum and WaveWindow). I have put 10V peak-to-peak into a few mac laptops. The sound card clips the signal, but there is no smoke, and this is why i haven't got round to building the buffer yet.
However - I might have got lucky and YMMV.

[Kesh]

http://www.zeitnitz.de/Christian/scope_en

i have this free pc one..

no idea what i'm doing with it, but my guitar looks cool going through it...

trouble with those is a common thing you are looking for is high frequency artefacts, oscillations, ringings, that take place above audio frequency, and the ADCs of a soundcard are typically at 44, 48 or 96 kHz if you are lucky.

[R.G.]

You're right Kesh. Audio is pretty dull stuff for oscilloscopes, but things can get out of hand pretty quickly with today's parts. A small signal MOSFET like the BS170 or 2N7000 can easily oscillate at over 100MHz. Even a 20MHz scope may not see your circuit singing in the aircraft radio bands. It's hard to say how much bandwidth is enough.

However, getting to over 100kHz is a huge improvement, and getting SOME kind of idea about the waveform is huge.

This is one of those diminishing returns things. Getting a picture of the audio waveform at all is over 80% of what you want, and it's semi-free with a sound card. But there are times when you need better. Getting to 1MHz gets you another 8% if all you're doing is audio. Not much use if you're designing logic, but for audio, very, very much better. Getting to 20MHz gets you another 0.8%. Getting over 100MHz gets you close to as good as you need. Beyond that, you're messing with GHz stuff, and may &deity. have mercy on your soul.

I have used the cheapest picoscope for years. I have tektronix and Hitachi "hard" scopes, and find that I haven't needed to fire them up in a LOOOONG time. They didn't have the picoscope with a waveform generator when I bought mine, but I've thought several times about ditching the one I have for one with a generator.

One HUGE advantage of any software scope is that it doesn't just tell you the waveform. It captures it and may well have routines to produce things like FFTs and other results that used to take several other instruments as expensive as the o'scope. Simply the fact that you can grab a single trace and keep it visible instead of trying to set up the event you're looking for is huge to someone who had only hard scopes. Storage scopes used to be about 2-3 times as expensive as their non-storage cousins. And then you can simply save the picture to a computer file. Huge, huge advantage for serious work.

[Kesh]

true, but for that 80% below 20Hz (make that maybe 15 at my age) we do have our ears

[bluebunny]

I've just sent an email to my engineering department asking if I could buy an old one off them cheaply. I've heard that universities tend to buy a whole new set when a few of the old ones stop working so that the whole class is working with the same tools.

Fingers crossed!

Could you ask for two?   

[EATyourGuitar]

I've got the $325 50Mhz Rigol (that can be reflashed into 100Mhz) and am very happy with it's performance for the price.

don't tell people they can flash it when they most likely can not. this was patched over a year ago. there have been over 10 firmware revisions to prevent hacking. the work around is burried in a 500 page thread but even that does not work anymore. people are breaking perfectly good new scopes and voiding warranties because of something they read on the internet. did you flash your scope to 100mhz?

[R.G.]

I've just sent an email to my engineering department asking if I could buy an old one off them cheaply. I've heard that universities tend to buy a whole new set when a few of the old ones stop working so that the whole class is working with the same tools.

Fingers crossed!

Could you ask for two?   

There is a hidden problem with old hard oscilloscopes. They have a lot of switches and knobs. These get dirty and intermittent over time, even if the circuits work fine, so it pays to do a massive contact and pot cleaning, as well as replacement of all the electrolytics, which have drifted, most likely. It's a lot of work, and if you don't do it, the old scope is always flakey and intermittent.

I've owned at least one oscilloscope of my own since about 1972, always an older good-brand-name device, and they all had this problem sooner or later. It becomes a pay me now or pay me later situation. You either take the time to do the maintenance once or pay a little bit of time and frustration every time it gets flakey.

Sorry - this is one of my pet peeves. 

[slacker]

I've got the $325 50Mhz Rigol (that can be reflashed into 100Mhz) and am very happy with it's performance for the price.

Same here, I've got the DS1052E and that does everything I need from a scope.

[gcme93]

I've just sent an email to my engineering department asking if I could buy an old one off them cheaply. I've heard that universities tend to buy a whole new set when a few of the old ones stop working so that the whole class is working with the same tools.

Fingers crossed!

Could you ask for two?   

I've owned at least one oscilloscope of my own since about 1972, always an older good-brand-name device, and they all had this problem sooner or later. It becomes a pay me now or pay me later situation. You either take the time to do the maintenance once or pay a little bit of time and frustration every time it gets flakey.

I understand you entirely R.G, but I am pretty sure these scopes are fairly new anyway, and the broken ones are from purely from abuse. My unnamed uni has a fair bit of resources to replace them so I doubt the old ones are even a decade old. My tutor is yet to reply though...

[Seljer]

I've got the $325 50Mhz Rigol (that can be reflashed into 100Mhz) and am very happy with it's performance for the price.

don't tell people they can flash it when they most likely can not. this was patched over a year ago. there have been over 10 firmware revisions to prevent hacking. the work around is burried in a 500 page thread but even that does not work anymore. people are breaking perfectly good new scopes and voiding warranties because of something they read on the internet. did you flash your scope to 100mhz?

ah, duley noted. I bought it a year ago :shrug:.

Still, the jump from 50mhz to 100mhz isn't even that crucial (maybe it went to 200mhz, then we'd be talking), it still works fine. I much prefer using it to the damn windows xp powered agilent/lecroy touchscreen scopes we have at university.

[R.G.]

I understand you entirely R.G, but I am pretty sure these scopes are fairly new anyway, and the broken ones are from purely from abuse. My unnamed uni has a fair bit of resources to replace them so I doubt the old ones are even a decade old. My tutor is yet to reply though...

That's great! I always wanted scopes like that, and had a very hard time finding them. You're lucky!