[sdiy] Audio test generator and mesurement tool - can anyone suggest a good set?

Robyn Mayol rominbayol at gmail.com
Tue Apr 23 10:37:23 CEST 2013

Hey D.

If you just want to build a tuneable oscillator you can easily make you own.

The data sheet for the LM358 (dual op amp) has the schematics for a triangle / square VCO: http://www.ti.com/lit/ds/symlink/lm158-n.pdf (top of page 2). I was able to put it together easily even though it was only the 3rd circuit I ever breadboarded.

In case you don't have 51K and 50K resistors you can just replace them all with 47K, it worked fine for me. You can use a single power supply with the LM358 so all you'll have to do is make a voltage divider for the positive input of the right op amp (where it says V+/2). I am using two 100R resistors but any value is good as long as it is two resistors of the same value (http://en.wikipedia.org/wiki/Voltage_divider). I also replaced the 0.05uF feedback cap with a 0.047uF (also called 47nF) because I didn't have the right value.

Here is what it will sound like: https://www.facebook.com/photo.php?v=640919502590636.

And here is a simulation of the circuit: http://www.falstad.com/circuit/#%24+1+5.0E-6+54.00526672067058+68+5.0+43%0Aa+224+176+336+176+0+6.0+0.0+1000000.0%0Aa+512+192+608+192+0+6.0+0.0+1000000.0%0Ac+224+96+336+96+0+4.7000000000000004E-8+-2.3766784613120984%0Aw+336+96+336+176+0%0Aw+336+176+512+176+0%0Aw+336+176+336+304+0%0Aw+336+304+608+304+0%0AO+608+192+656+192+0%0AO+608+304+656+304+0%0Aw+608+192+608+272+0%0Aw+608+272+608+352+0%0Ar+608+352+224+352+0+10000.0%0Ar+608+272+512+272+0+100000.0%0Ar+512+208+448+208+0+47000.0%0Aw+512+208+512+272+0%0At+224+352+192+352+0+1+-0.1803259537834405+-5.230656564744769E-5+100.0%0Ar+192+336+192+160+0+47000.0%0Aw+192+160+224+160+0%0Aw+224+160+224+96+0%0Ar+192+160+112+160+0+100000.0%0Ar+224+192+112+192+0+47000.0%0Aw+112+160+112+176+0%0Aw+112+192+112+176+0%0A174+112+176+16+208+0+1000000.0+0.35150000000000003+Resistance%0Ar+224+192+224+272+0+47000.0%0Ag+224+272+224+288+0%0Ar+448+208+448+272+0+1000.0%0Ag+448+272+448+288+0%0Ar+448+208+448+80+0+1000.0%0AR+448+80+400+80+0+0+40.0+6.0+0.0+0.0+0.5%0AR+16+176+16+128+0+0+40.0+6.0+0.0+0.0+0.5%0Ag+192+368+192+400+0%0Ao+7+64+0+34+10.0+9.765625E-5+0+-1%0Ao+8+64+0+34+5.0+9.765625E-5+1+-1%0A

By the way, if anyone more experienced than me has feedback about the modifications I made to the original circuit I'm happy to take it on board!
> But no, this is mostly just so that I have a tuneable oscillator that
> goes below 20 Hz, that's all.

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