Audio Test Oscillator

[RaceDriver205]

Just made an audio test oscillator using the schematic from geofex.com. I changed R4 to 160 to make the sinewave near-perfect. If anyone wanted to build one from a PCB, the layout and artwork are at www.tothemax.web1000.com under Misc.

[boyersdad]

Cool thanks! I'll build one tomorrow

[Paul Perry (Frostwave)]

The sine wave is the best when the gain is just sufficient to make the circuit oscillate. I expect that the optimum value of that resistor varies depending on the gain of the transistor.

[WelshWonder]

This looks really cool. I'm new to electronics and effects building but learning quickly all the time (thanks to this site and the people who post). Help me if I'm wrong but is this a usefull tool for analysing the effects we build i.e. directing the sine wave throuugh the effect an analysing the output? If so, what would we use to analyse the output signal? Oscilliscopes cost £500+. Is there a way of getting software to run on windows to analyse input from the sound card?

[RaceDriver205]

I expect that the optimum value of that resistor varies depending on the gain of the transistor

Aye, I may make a note of that somewhere on the page.

Oscilliscopes cost £500+. Is there a way of getting software to run on windows to analyse input from the sound card?

You don't need an oscilloscope that good. I got a small one for $128 (about 55 pounds), which is very basic, but thats all you need.

[mdh]

Is there a way of getting software to run on windows to analyse input from the sound card?

There are a bunch of programs that do this. I can't recommend a specific one, but Googling "software oscilloscope" will get you a bunch of hits. Jack Orman has a couple available on his free info page (http://www.muzique.com/schem/tips.htm), and I think he also has a more extensive list elsewhere on his site.

It's also supposed to be good to build a buffer to put between the circuit under test and your sound card to protect the sound card and prevent it from loading the circuit under test too severely. I built the one here: http://xoscope.sourceforge.net/hardware/hardware.html. As far as I can tell, it's working fine. I haven't had many opportunities to play with it since I put it in my computer, though.

RaceDriver205, thanks for the tip, I've been meaning to try tweaking that circuit to get rid of the clipping. I'll try playing around with R4.

Edit: corrected the buffer hardware URL.

[brett]

Hi
I used a Velleman hand-held scope for a couple of years.
It had some cool DMM-type functions as well (e.g. RMS and dB voltage).
It was as-new and cost about US$100 or $120 on e-bay, including extra leads. 
cheers