<5k O-Scope worth messing with ?

[petemoore]

  In brief, my preponderance of O-Scope is limited by no real experience.
   Here are questions that make sense so far?:
    ~5k frequency limit would be useful for setting bias on amplifiers?
     And would show clipping shapes of distortions..but 'blurry' above ~5k ?
      Is it sometimes necessary to see frequencies between say 5k and 18k [or above] when examining a DC rail for AC ripple ? [quantify: "how often?" ..if that makes sense.
   How often do you find relevant information when looking at Oscope above 5k for basic audio stuff where the HF's can be tuned by ear ?

[SISKO]

    ~5k frequency limit would be useful for setting bias on amplifiers?

Yes, most of the time you are fine with 1k when measuring bias.

     And would show clipping shapes of distortions..but 'blurry' above ~5k ?

Depends how you see and understand distortion, or what are you expecting from it.  I havent done any measurement beyond 42MHz (my o-scope limit), so i can`t tell you how it will look like, but i think it will look "less distorted" because of it inability to show a frequency beyond its limits (when an amp or a dist pedal distort the signal, it adds new frequencies to the signals that are multiples of the original frequency (those called harmonics), so when a 1k signal is distorted, you now have the sum of the frequencies of 1k, 3k, 5k, 7k, 9k, 11k,(if you have odd harmonics) and so on .

      Is it sometimes necessary to see frequencies between say 5k and 18k [or above] when examining a DC rail for AC ripple ? [quantify: "how often?" ..if that makes sense.

Again, its depends. If you are going to be working with switched supply, you will see and use freqs >5k.
But if you work with analog supplies, you are going to need just 50/60 Hz, or 100/120Hz when looking for ripple.
How often? The times you need.

   How often do you find relevant information when looking at Oscope above 5k for basic audio stuff where the HF's can be tuned by ear ?

Most of the time I use 1k when working with audio circuits. But knowing what is happening beyond 1k (say, in the region of 10k) its always handy. So, answering your question, I would say that 75% of the time, when working with audio circuit I find relevant information above 5k.

[Gurner]

   ~5k frequency limit would be useful for setting bias on amplifiers?

Alternatively...use a $10 Chinese Voltmeter to measure bias, you don't need a scope for this.

Also google for soundcard software osccilloscopes (many are free) .....that'll give you more bandwidth than the 5K you mention.

[petemoore]

  Sorry for the generalizations.
  thanks for covering the topic rather completely for me !
  Just the ability to bias and experiment makes it worth the entry
price.
       

[R.G.]

I very much recommend the "Picoscope"  devices. $200-$300 gets you a fully functional two channel digital scope with a built in programmable signal generator. Within its limits of 20MHz and sampling speed and resolution, it's a completed amp and effect tester that plugs into a computer.

The biggest limitation is that it can't withstand inputs more than +/-20V without damage. If you're doing tube amps, you'll want something else. But for effects, it's the bees' knees.

[Earthscum]

I got one of these:

http://www.sparkfun.com/products/9484

I didn't get the DIY kit, I found a deal on an assembled kit that came with the adapter. For the $70 I spent, it was worth the price to get a real working scope. Test signal is 500Hz square wave @5V, which seems to be fine. Input is 50V max. I made a little filter circuit with 500Hz cut, 4 poles, into a transformer pickup sim, and sits at about a 50mV sine. When I apply the signal, the output actually reacts and levels out (fairly quickly) like a plucked guitar signal, it's kinda neat. That's what I use for test signal, and just set it for internal triggering. Then I just tweak away on the circuit and the only adjustments I really need to make are to scaling.

Even though I got myself a nice scope finally, I still use the digi... it's hand sized, works good for my purposes.

(btw, you should see what a Bazz Fuss puts out when you hit it with a 5V square wave! Looks like the "square root" symbol)

[Gurner]

Actually, just last week I bought this.....

http://www.vellemanusa.com/us/enu/product/view/?id=522377

(previously I had a Chinese USB scope - awful!)

The reason I went for it over the competition, was cost & features (it does bode plots.....perfect for audio work)...it was only £130 delivered here in the UK.

I'm very happy with it....the developers are very reactive to user suggestions .....eg I wanted the zero degrees line on their bode plot graph emphasised, and also the waveform attributes displayed on the trace display (vs a separate window), there was a new release of software the next day with my suggestions included!

[Earthscum]

http://www.sparkfun.com/products/10244

Hmm... wish I would've spent extra... this one is nicer than the one I got.

[Ronsonic]

  Sorry for the generalizations.
  thanks for covering the topic rather completely for me !
  Just the ability to bias and experiment makes it worth the entry
price.

In general there isn't anything coming out of a guitar amp over 5K that you want to look at or hear in great detail. And a scope will show the presence of frequencies well beyond its rated response. It will show you everything you'll need to know about what is going on in the power supply. Sometimes you'll do something stupid to a 12AT7 and make it freak out somewhere in the range of 250KHz, they were born to radio and will take the opportunity if you let them. You'll see the trace turn into a blur or even disappear depending on the settings.

Some things might be hard to see, say a parasitic on an edge of the waveform. Those can be very high frequency, you should still see a blob, but maybe not enough to tell you anything.

My question is where a 5K scope comes from? Is this a sound card thing? Real scopes go for cheap nowadays. With so many GHz devices on the market, and the gradual extinction of the TV repairman used 100M scopes are very reasonable. Lesser scopes than that can be had for downright cheap.

[Earthscum]

... Real scopes go for cheap nowadays. With so many GHz devices on the market, and the gradual extinction of the TV repairman used 100M scopes are very reasonable. Lesser scopes than that can be had for downright cheap.

Aye... I picked up a 100M B&K dual channel for $60 out of random luck (that'll never happen again, lol). The little digi's I linked to are 2MHz and 1MHz, respectively.

You don't mean 5MHz, not 5kHz, do you?

[petemoore]

  Arduino based project.
   Pretty sure it was 5khz I was reading about as far as limited HF.
  I'm buying a book that lists this as one of the projects, much of the peripheral hardware required are multi task items anyway screen etc.
which led to contemplating scopes.
  Thank you for satisfying my curiosities and more, I feel 'almost like I've owned and got familiar with a few scopes.