Oscilloscope, for "debugging" audio signals

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john curl said:
Get 50-100MHz older analog scope. They are relatively cheap, and will give you enough bandwidth to see real oscillation in audio circuits. Trust me on this. 20MHz is too low. Sorry about that, but the parts oscillate at whatever frequency they choose.

100% agree. A decent 100MHz scope can be gotten for $100-300, and it will give decades of useful service. Circuits oscillate and troubleshooting can be damned frustrating if you can't see it.

An expensive digital scope is a nice-to-have, but only if you already have a good analog scope and know how to use it. The cheap digital scopes are a total waste of time and money, IMO.
 
I had the same goal and I chose a TiePie HS-3 two channel USB scope with signal generator few months ago after extensive search

TiePie HS-3

As it's summer and less time to work inside I'm still very happy with the after some tests and first experiments.

You'll get a
* decent scope
* FFT analysis
* arbitary waveform signal gen
* 12, 14, or 16 bit resolution depending on bandwith
* a very flexible software with averaging, summing etc features.
* fully USB powered

So for hobby use I consider it quite useful. It would of course be nice to have an analog scope with 100MHz band, a signal gen, a sweep gen etc but the cost even if buying used gets gigh very fast.

My 2 cents,
Ergo
 
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It's really interesting to hear the different opinions on this you know. My own 'scope which I use all the time is a 100Mhz model but I very rarely need that bandwidth-- and never for audio. In fact I mostly have it switched to a 20Mhz bandwidth as this gives a slightly cleaner trace ( no not because I am cutting out the HF oscillation :D ).
I am with Wakibaki on this one 30 Mhz is all you need for most things. If you have an amp that oscillates at HF or VHF you know about it anyway-- high current draw that varies as you touch various parts of circuit etc or wiping TV and radio out for half a mile.
 
I agree that much more than a 50MHz scope is probably unnecessary, even for stability testing. However, I think the ease of use of a decent analog scope may be underestimated. If things like the trigger settings are hidden away, it makes the scope a chore to use. Hitting a button or two on the front panel for every possible setting is the easiest concievable way to control the scope. You should not have to hunt for the controls.
 
sparcnut said:
You should not have to hunt for the controls.

This is a good point. I ws once required to assist a colleague with an unfamiliar 'scope of great age but high specification with about 50 buttons and ganged knobs.

It took me several minutes of study before I could turn it on.

It was a button the same size as all the rest, near the centre of the panel, but offset a bit, with the legend LINE.

My somewhat younger colleage said: - "I thought that turned the line on and off...."

w
 
50-100 MHZ scopes are almost a neccesity in the US. troubleshooting RF interference from CB radio and 49Mhz (as well as certain "business" adio services beyond 100 Mhz) devices requires at least 50Mhz bandwidth. with analog scopes, you can see signals beyond the specified bandwidth of the scope (i.e. you can see signals 100Mhz and above) but your amplitude measurements aren't accurate beyond the bandwidth spec. digital scopes cant do that because there's effectively a "brick wall" at the sampler's Nyquist limit (which is essentially the same type of limitation that sound cards suffer from).
 
i was using a speaker testing program (SpeakerWorks IIRC) and running the impedance/frequency tests with it. the first time i tried this was a disaster. the curves were all over the map and inconsistent. the program uses the sound card to send a burst of noise to the speaker, and measure the impedance across the spectrum using FFT. the problem turned out to be the long canles i was using. not only was the cable capacitance and crosstalk pretty high, but i suspect that the cabled were somewhat microphonic as well. i got much more consistent results with short cables. what i'm getting at is that you have to check for sources of error when you use any test equipment, especially sound card based (or any DSP system)
 
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