[NEWBIE] Question on testing equipment - Scopes etc...

[Guest]

I have noticed that on some of the projects we need oscilloscopes and signal generators to check settings and set trims

I have looked at most of the oscilloscpe for dummies websites but none seems to be audio electroincs related or stuff that I can relate to...

Anybody got a dummies guide?
Is a dual scope an absolute necessity?

For a signal generator - can I just use a tone out of a Midi tone generator?
i.e. one of my Emu XL1 or MoPhat module - or even and old sampler or QY700 that has a sine wave tone.. or is this too dirty...
The only question then is converting a sampled sine wave tone to a paticluar frequency -
i.e. for the green mic pre trim setting using a 100Hz tone...

aaahhh.. problem is that there is no musical note or midi note number that corresponds to 100hz....
We have note G (midi note number 43) which is... 97.9988589954 Hz or Ab (44) 103.8261743950

So therefore I need some sort of Frequency or Sound generator? Are there cheapish ones out there??


Kind regards
Simon

 

[jrmintz]

Simon,

Many sequencers - ProTools, Logic, etc have signal generators in them. If you're using one of those, take a look and see if you have a generator plugin. Also, I got a really great Tektronix scope off ebay for about $100.00. Be careful though, I actually bought two of them without realizing it - the other one now resides with Admin.

Good luck.

 

[owel]

I bought a Tektronix dual oscilloscope, 20Mhz for $150.

And a Tenma signal generator, max 1Mhz, sine and square wave for $49.

A digital true rms bench multitester for $30.

all on eBay.

Oscilloscope jacks for $19 at OSElectronics.

For audio testing, you just need an oscilloscope that can go up to at least 1Mhz.

 

[Underthebigtree]

I would be sure to look for an analog signal generator, not a digital one. Why? Because at a sampling rate of 44.1kHz, a 20kHz sin wave will actually look like a triangle. And forget about generating any frequencies higher than that.

And if anyone has a good link for a cheap analog signal generator, please let me know - I just handed mine back to the guy I borrowed it from.

 

[Mbira]

Dual traces are nice because then you can see the input signal of something and the output signal. As for, digital vs analog, why not just go analog out of your computer or whatever? Then no need to worry about samplerate.
Joel

 

[Ethan]

[quote author="jrmintz"]I actually bought two of them without realizing it - the other one now resides with Admin.[/quote]

Still working just fine!
I use the signal generator in Pro Tools also, although I should probably be more careful of what I feed back in through my 192 IO. I need to get a real signal generator, and a cheap speaker to test my circuits.

 

[Samuel Groner]

As for, digital vs analog, why not just go analog out of your computer or whatever? Then no need to worry about samplerate.

You don't get a clean squarewave above some kHz and below a few 100 Hz out of your computer, because the DA-converter (computers are digital inside... :wink will mess it up.

Samuel

 

[DrFrankencopter]

You don't get a clean squarewave above some kHz and below a few 100 Hz out of your computer, because the DA-converter (computers are digital inside... ) will mess it up.

and

would be sure to look for an analog signal generator, not a digital one. Why? Because at a sampling rate of 44.1kHz, a 20kHz sin wave will actually look like a triangle. And forget about generating any frequencies higher than that.

You guys need to try putting a scope on the output of your sound card's D/A. Once the signal goes through the anti-imaging (or reconstruction) filter it's nothing but clean clean sine waves. All those triangles are just higher harmonics that get filtered out. Digital sine tones are great, and very stable. I've only seen a few really decent analog function generators...most aren't very stable.

Cheers,

Kris

 

[NewYorkDave]

Get a proper analog sinewave generator if you ever want to do distortion measurements. Digitally-generated waveforms are fine for simple signal tracing, though.

 

[owel]

I debated between stand alone units and PC-software based oscilloscopes and signal generators.... I went for stand alone units. I can easily carry the signal gen and oscilloscope to my studio setup if I need to, and they can sit on my work bench, besides my soldering station, tools, wires, etc... if I'm troubleshooting.

It's easier than lugging a PC box, monitor, mouse, keyboard, etc....

 

[Category 5]

[quote author="underthebigtree"]I would be sure to look for an analog signal generator, not a digital one. Why? Because at a sampling rate of 44.1kHz, a 20kHz sin wave will actually look like a triangle. And forget about generating any frequencies higher than that.

And if anyone has a good link for a cheap analog signal generator, please let me know - I just handed mine back to the guy I borrowed it from.[/quote]

http://www.oselectronics.com/ose_p11.htm

The kit version of the FG500K is onlt $31. It takes about 30 minutes to build.'

The only issues I have with it are that you need a frequency capable voltmeter to set the frequency exactly, and the sine wave seems to have a slight negative DC offset.

All of the resistors were 5% carbon though, and I'm sure if I go through an replace them with tested 1% resistors (measured for accuracy) I'll get better results.

The sine wave looks clean all the way up, and the triangle wave doesn't have the DC offset.

Shane

 

[NewYorkDave]

Function generators are very handy--I use them--but again, the sine outputs are not clean enough for distortion measurements. They look fine on a scope, but the THD is usually pretty high. Your typical function generator doesn't generate a true sine; rather, it creates a quasi-sine out of a triangle wave.

 

[PRR]

> for the green mic pre trim setting using a 100Hz tone... aaahhh.. problem is that there is no musical note or midi note number that corresponds to 100hz.... We have note G (midi note number 43) which is... 97.9988589954 Hz or Ab (44) 103.8261743950

Use common sense. What good is a mike-amp that has radically different gain for 97.99, 100, and 103.8Hz? If the bass plays G, Ab boom,boom, or bends that G up 30 cents, do we want it to come out BOOM,boom? No, we want "flat". Maybe we want to slope an octave down (though that is a job for EQ, not preamp). But gain variation from one 12-tone note to the next should be nearly-zero. Even with a 6dB/octave slope (bass knob all the way down) it is only 6% difference of gain from one note to the next.

Really, the gain should not vary more than 10% from 50Hz to 15KHz, and if it happens to be 10% off from the marking over the whole band that is not a problem. And there is nothing in the Green, or most boxes, that will amplify 100Hz a lot more/less than 98 or 104Hz.

I don't know why 100Hz is suggested. 400 or 1KHz is traditional. Problem with 1KHz is that many new digital meters suck bad above 400Hz. 100Hz (or 98Hz or 104Hz) is pretty sure to be in the passband of even the most lame digi-meter.

Tuning narrow-band EQ, or measuring the exact "-3dB point", may call for finer resolution than music-notes. But by the nature of the material, usually not. Round everything to the nearest Bach-note and it is plenty good enough for jazz.

 

[Guest]

Many thanks for the answers...
PRR outstanding as per usual

I did buy an dual beam scope in the end (I got the buyer to put on a buy it now feature for £50 and went and collected it and paid cash last night - the guy lived in a town on the way home from work)
It came with a probe, a standard, x10 probe, a manual and two books abotu oscilloscopes (one a 1950s electronics book that contained a sh*t load of circuit diagramsabout valve oscilloscopes and valve sine wave generators, valve based PSUs etc...)
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&category=45014&item=3842995278
He demonstrated it using a home made signal generator

I am trying to get away from using my computer to do things - even to the extent of thinking about building my own Electronic drum kit and making my own drum trigger and sampler

 

[PRR]

> the guy lived in a town on the way home... books about oscilloscopes (one a 1950s electronics book that contained a sh*t load of circuit diagrams about valve oscilloscopes and valve sine wave generators, valve based PSUs etc...) He demonstrated it using a home made signal generator

You want to visit this guy more often. There is a generation-gap but a few pints should bridge it.

 

[Mark Burnley]

Yep,

I've met lots of older and wiser electronics guys at radio fairs, and had some fascinating insights into things I'd never even thought about!



Mark

 

[SonsOfThunder]

[quote author="Category 5"]http://www.oselectronics.com/ose_p11.htm
The kit version of the FG500K is only $31. It takes about 30 minutes to build.'[/quote] Haven't used the model you are referring to but have used and measured the GF-800 on the same page. Pretty cheap and not too bad, really. Lower THD is this one from Fostex, but not as adjustable obviously.

The October issue of Mix Magazine has a great primer on using a 'scope, written by my friend and G'DIY lurker Eddie Cilletti. Its not online just yet but soon available at this link.

HTH!
Charlie

 

[echomancer]

This article can be found here:
http://mixonline.com/mag/audio_oscilloscope/

 

[bradzatitagain]

Anybody got a dummies guide?
Is a dual scope an absolute necessity?

http://www.tone-lizard.com/Oscilloscopes.htm

Not bad for a start.

I have a question you guys, I'm looking at a Boonton inductance bridge (wanna buy an inductance bridge) and on the front panel it say it has a frequncy range of 5Khtz to 500Khtz. It's a model 63H, well, it's here:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=25421&item=3849465818&rd=1&ssPageName=WDVW

I've used an old Heathkit LCR bridge and the military ZM 11/U, neither gives super fine measurements, I'd be happy to replace the ZM. But it doesn't look like this Boonton is going to be useful, it looks like an RF thing. Whaddya think?

 

[NewYorkDave]

No, it won't be too useful for your purposes.