Sine wave - Square & Triangle wave generator using Transistors / OP-Amps

[lineup]

Amplifiers, solid state discrete, tubes or chip amps,
they all can need some evaluating and testing.
Small circuits, transistor- or op-amp based can be built to supply some different test signals.

I bet some of you have some good basic transistor circuits to share here.
I start by pointing to a website with a few useful op-amp circuits
for generating high quality sine, square and triangle wave.


Using Op-Amps it is not very difficult generating test signals of different shapes.
I say anyone that can buy a few op-amps can do this.
Most useful is of course sine waves as they comes closer to the nature of analog sound
than the other, triangle & square waves.

Other waveforms very useful for testing if you have oscilloscope are sawtooth waves.
There are 2 kinds of them: Rising and Falling sawtooth
http://en.wikipedia.org/wiki/Sawtooth_wave

At this site I found some basic sine, square- and triangle wave generator circuits schematics.
Shown is basic information how to create these test waves:
http://www.play-hookey.com/analog/si...generator.html


This is a schematic of a sine wave generator.
With both sine and cosine waves available,
this circuit is sometimes known as a quadrature oscillator.


lineup audio lab
>> lineup.awardspace.com <<

[keantoken]

ummm... The site must be offline or something, I'm not getting the picture or the site when I click on the link. I know of a site with some generators. Though I don't know of their quality, but I believe it would depend more on the OPamps and components used.

http://www.4qdtec.com/#indx

PS: Any ideas of the usefulness of the circuits on this site?

[CBS240]

IMO, simple oscillators are fun to build and test, but when it comes to running tests on amp circuits it is better to just fork it out for a decent function generator. So much easier and more precise.

[lineup]

Originally posted by CBS240
IMO, simple oscillators are fun to build and test, but when it comes to running tests on amp circuits it is better to just fork it out for a decent function generator. So much easier and more precise.

thanks CBS240

yeah,
I can think of at least 3 ways to create test signals

1. build a circuit - the DIY way
2. use a generator machine you buy ( this is my own way )
3. use your CD-player, with a recording of different signals

Number 3 using CD
will give VERY high quality signals!
I have one such Test-Signal record, originally designed for CarAudio testing purpose.

Nevertheless, it can be fun and you will learn something useful
by building your own sine wave circuit.
Most simple is using only 2 transistors followed by a RC-filter at the output
to make such a test-signal!


>> lineup Audio Lab <<

[bear]

dunno if they are still around, but eXar used to make a chip that did all three functions, sine, triangle and square in a single chip.

if you want low distortion sine waves, you need a "fancy" circuit.

or, as someone mentioned, a CD recording, or the output of your computers sound card...

_-_-bear

[keantoken]

I have my computer connected to my sound system, but I haven't gotten around testing it with my scope. I suppose a 10Mohm impedance on the speaker outputs won't hurt anything, right? Or do I need an impedance matching circuit to get real-life data? If so, can someone post a simple matching circuit?
I don't want this to become a full-blown threadjack, just so y'all know.

EDIT: would 4.7 ohm and 3.3 ohm resistors in series with the scope connected in their centerpoint and ground work?

[Johan Potgieter]

Keantoken,

It is certainly better to have a dummy load, and the simplest one is an 8 ohm resistor (necessary wattage of course; but it does not necessarily need to be non-inductive, as loudspeakers become inductive at high frequencies anyway).

I have a test load circuit equivalent to my loudspeakers, but is is quite involved, and speakers can differ quite substantially. I would suggest both open circuit and loaded output tests, though some commercial amplifiers do not like open circuit. Hopefully they will tolerate at least 80 ohms for an 8 ohm system. Good square wave response at both will ensure that your amplifier is probably without blame for most loudspeaker loads.

Though I have a commercial signal generator, I would agree with the fun factor of building one - have done that too! Only if one goes to spectrum (distortion) analysis a very low distortion sine wave generator is necessary, unless of course one has access to a modern complete spectrum analyser. Such a sine wave generator can also be home built for at least 2 frequencies. (Suitable state-variable circuits capable of about 0,002% distortion is shown in a rather old book by Walter Jung on op-amps. Unfortunately I am unable to give the title now as I am not at home.)

Regards.

[keantoken]

Just so everybody knows, the amp that I use is the one on top of my TV in my avatar. Either it is a good amp, I am just a bad listener, or my speakers just cancel out the distortion.

The only inductor I have is 100uH. Is there any way that I can turn this into a suitable speaker model? I all sorts of capacitors but I can't find any source of inductors that I can use. All I can think of for speaker models would be 4.3 and 3.3 ohm resistors in series.

[bigpanda]

Hi lineup,

The most important part of the story : a pc base simulated oscilloscope. Is there any place we can get information about this or download this software? I guess we have to make a small circuit before we can do this, any info. on this ?

Tks.

[keantoken]

I don't know anything if your looking for a PC scope, but there is a program called audacity that can generate sine and square waves and can be used to view the recorded waveforms. It is here:

http://audacity.sourceforge.net/

It has barely any problems and is completely free! Enjoy...