Oscilliscope

[sl-15]

Ha, I was just in Cody for a few days, and, having been following this thread and finding out that you are in Wyoming, my main advise to you will probably be of no use. There was a time when I desperately wanted an Oscilloscope and I found one with a bunch of other test equipment for way too much money. I only later found the local historical radio club here in the Bay Area in CA to learn that older analog scopes are around plentiful, for close to nothing, if you have a radio club in your area. Now, knowing that you are in Wyoming, I wonder if there is much going on in the means of radio swap meets or historical radio clubs where you would be able to find working analog oscilloscopes for a fair price. But, Doc is right. Eventually these older units need repair and it can be rather involved. So do not spend a lot of money on an older, analog oscilloscope. Tektronics has a reputation but even Leader or Phillips scopes are great. I am not sure if an oscilloscope is the right tool for what you want to measure/do. But I think an oscilloscope is a great and essential tool in audio and if its just for the learning purpose only. Seeing a sound signal is kind of fun. If you find a cheap (around$100) analog scope somewhere, go for it. But the newer digital ones are pretty good too, but you have to make the decision if you want to spend the money. I think PB is right too, you can probably do a lot with a PC and a sound card and the right software. There is decent oscilloscope software too. Good luck.

[4krow]

 Well, I probably turned left in front of you at some point, since I am only about 22 miles from Cody.

   Here is the deal about new hardware. I would Not be using my computer in my office for such measurements. Rather it would be far more practical to have the equipment in the shop. That of course, means that whatever I do, it will involve money. I suppose that I could find a good used computer for not much money and go that route. The apps can then be downloaded as needed. Just thinking out loud here.

[sl-15]

I remembered that there where a bunch of older oscilloscopes at the radio club I volunteer at. I will check and see if any are available and let you know. If we get lucky I might be able to get one for free but better to not get too excited.

[4krow]

  Thanks!  I went to one of those radio shows when I lived in Flagstaff, and was really impressed. Not just the equipment, but the people there were a rare breed, maybe like me.

[Paul Birkeland]

Are you looking to measure filters that are speaker level or line level? 

If you don't want a computer, then you will need a stand alone spectrum analyzer.  I see sketchy ones on eBay selling for $600 or so.  Nice ones look to be $2000-3000.  Some of the newer, nicer scopes have FFT's built in.  You can throw periodic noise into your line level circuit and look at the output on a spectrum analyzer to get a good picture of what a filter might or might not be doing.  To get the same picture from a scope, you would need to hook up a signal generator, then run signal in at different frequencies and measure the voltage.  If you had a T-table of enough values, you could then put that into excel to get some kind of approximation of the response.  This slow and painful, as most older scopes are stuck displaying voltage/time when you really need voltage/frequency.

If you want to measure filters that you are applying to loudspeakers, you would need an RTA with decent resolution. There are stand alone RTA's that you can buy, but the ones that are useful are several thousand dollars, and they require very specific and expensive microphones to work their best (TES-1358C is a good, compact example of what you'd want).

If you buy a ten-year-old Windows XP box for $100 on CL, buy a decent sound card for it for another $100, then buy a microphone with a .mic calibration file from PE for $50, you will be able to do both.  If you upped your budget and got an inexpensive laptop, all of this equipment could be placed inside a plastic tote and stored while you're not using it.

You will also get a very capable distortion analyzer out of this setup with the addition of a loose 8 Ohm 25W resistor.

[4krow]

   Thanks so much for the informative reply.

[JamieMcC]

If you have a Apple I device you might be able to find a app to down load. Something like the one in the below. But there are a loads of others.

 https://itunes.apple.com/en/app/audiotools/id325307477?mt=8

[mcandmar]

Arta looks interesting, not heard of that one before.

I have dabbled with RMAA using a pc soundcard and had very good results with it measuring frequency response and distortion. The software is free so all you need to do is to make up a few cables and source some dummy load resistors. Only caveat to keep in mind is most soundcards wont take more than 4volts before you frazzle them.  So for testing higher voltages like speaker outputs you need something else, the solution i used was one of Pete Millets sound card interfaces between the amp and soundcard. http://www.pmillett.com/ATEST.htm  The whole setup works very well for me, and has proved very useful.

[Paul Birkeland]

Only caveat to keep in mind is most soundcards wont take more than 4volts before you frazzle them. 

Pro audio external cards have trim pots at the inputs, so you can throw considerably more voltage into them. 

[4krow]

   Well, here is the update. First , I bought a Kiethley benchtop meter that performs all the reasonable functions, plus has a signal generator. Of course, as mentioned above the inboard signal generator will only produce one frequency at a time. Regardless, I purchased a 2215A Tektronics 60 mghz  two channel scope. Seems to me that a white noise signal could be applied to a circuit that is to be measured,and then run into the O'scope. Of course, the 2015 Kiethley doesn't have that function. There well may be other test equipment that I will be purchasing to complete this setup. So with the decisions that I made, what might be my options at this point?