Using online audio sweep generator with analogue oscilloscope

[Boulevardier]

Pretty basic question really. I am planning to use an online audio sweep-generator programme to get a frequency-reponse curve for an audio amplifier. How do I set up the scope to get the X-sweep to synchronise with the sweep output from my PC?

My scope is a two-channel 20 Mc/s Hitachi one with X-Y functionality. Is it simply a matter of setting the trigger level correctly? How should I set the trigger input selector? Etc, etc...

Grateful for any tips, and I hope the wording of the questions makes sense...

Mike

[wireman]

I see that nobody replied so far so hopefully this helps.

Is there some reason you want to use an oscilloscope? It would be some trouble to get a sync signal into it from the PC.

Alternatively if you can get the output back into the PC then you could use something like Rightmark Audio Analyzer (bearing in mind you are testing the PC audio circuitry or audio interface as well as your amplifier).

[Boulevardier]

Thanks for that Wireman. I had assumed that this sort of software could somehow be used to display a response curve for an audio amp. One example of such offerings says: “SweepGen turns a PC into an Audio Oscillator and Sweep Generator which can be used for testing audio or educational purposes. In conjunction with audio test instruments, you can make frequency response plots”. I had assumed that they could be used in much the same way as an RF sweep generator is used to display the response of IF circuits. I’m not sure what the point of them is if they can’t be used like that.

I must have completely misunderstood their purpose.

I do take your point though that the whole process would be completely dependent on the PC's soundcard, and that there would be a very small likeliehood that the output level would be constant over the audio range. I'm still left with the question - what on earth is the use of them - other than as toys?

Mike

[Diabolical Artificer]

AFAIK you can get your scope to display a frequency response, the time of the sweep is too long I think. I use paper and a manual sweep but REW can display a frequency response as can ARTA, I've used them but have little tolerance for PC based software,it's just not my bag.

To analyse an amp frequency wise all you need to do is display a sinewave filling the display, say at 1khz, flick to 20hz, then flick to 20khz and maybe manually sweep from 20 to 100hz, then 10-20khz, if the amplitude falls by half, then your response is 3dB down.

One nifty bit of free software I do use is Soundcard scope,it's THD meter is as good as a HP3903B and it has FFT, usefull for checking harmonics. Lastly I've tried every free bit of PC based software,most are useless, finicky or glitchy, Rightmark especially so.

Andy.

[Goldie99]

The simplest I've found was to use a (free) software package, like 'ARTA', and a decent quality pc soundcard (quality of the soundcard output limits any THD measurements). I'm using an older M-Audio Audiophile 2496 soundcard (£20 from a certain auction site...)

You'll also need some decent quality audio in/out cabling, and something to attentuate the Amplifier output that's being measured, before it's looped back to the soundcard input - I built the attenuator described on the Akitika site, that works well:

https://akitika.com/documents/Buildi...nuatorRev4.pdf

As Andy says, it's somewhat of a learning curve (and I'm certainly not there yet !), but as an example, this is what a typical FR scan looks like, with 2 (3) different attentuation levels, in a 'loop back' test, just from when I was checking the attenuator build - each scan takes only seconds once it's set up.



Alan