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

[AndrewT]

Hi Kean,
the 4r7 and 3r3 will not dissipate the same power when operating in series. The 4r7 will dissipate about 42% more power than the 3r3. Take that into account when designing the heatsinks for the resistors.

I think the test resistor needs to be substantially non inductive for the frequencies that are used as test signals.

The highest frequency you are likely to use is 10kHz. At this frequency even a wire wound will be substantially non inductive. Do not forget that operating an amplifier into a reactive load SERIOUSLY stresses the output and driver stage many times worse than driving a purely resistive load.

If you want an amp that is capable of driving an 8ohm reactive load (a speaker) then I recommend testing at 4r as well as at 8r.

If you plan on using either 6ohm or 4ohm speakers then your test loads need to be scaled accordingly.

[MikeB]

You can't generate squarewaves with a pc based signal generator, the bandwidth of a squarewave is way too high.
But, there is a simple way out, i use the attached circuit as squarewave generator. It's not perfect, but way good enough to test an amplifier. Frequency is ~10khz.

Another possibility would be connecting a schmitt-trigger to the soundcards output, this way you can create squarewaves with variable frequency.

Mike

[jackinnj]

Pick up Jim Williams excellent book "Analog Circuit Design" -- he sketches several low distortion oscillator ideas.

I don't know how much oomph you can get out of an IC based oscillator -- Ron Mancini (one of the design guys at TI who writes a column for EDN) states that voltage feedback opamp based oscillators run out of bandwidth.

the easiest low distortion oscillator which I have used was based upon a CMOS clock generator and a couple of switched capacitor filters -- the ideas is to knock down the 2nd and higher harmonics -- the idea was in AudioXpress (I think Charles Hansen was the author) but I had earlier implemented it with a BasicStamp micro-controller.

"Analog Circuit Design" should be on everyone's bookshelf, along with "OpAmp Applications Handbook" by Walt Jung and "Trouble Shooting Analog Circuits" by Bob Pease...and to think that my wife complains that I read this stuff while she watches "Jane Eyre" on TV.

the best oscillator I ever built -- there's a thread on this somewhere -- the current feedback design from Linear Technology -- ain't no distortion in this one but it is tricky keeping it going. -- and it operates at 10kHz -- this is a pic of the residuals:

[AndrewT]

Hi Jack,
give us a clue on what to search for.

[jackinnj]

Low Distortion Signal Generator

[d3imlay]

As I recall, the first product from HP was the 200 oscillator which used the nonlinear characteristics of a light bulb for stability. Linear Technology published an excellent article on low distortion sine wave generators based on this principle using opamps. It was in a an app notes book in the late 80's.

I use a USB oscilloscope from USB instruments for non critical work at my day job. Below is the link. The main reason I use it is to be able to display signals in real time during presentations for UPS systems. for this application I have to use isolation probes. The scope also has a function generator built in.

DS1M12 sope

I bought my scope from Saelig instruments. They have a lot of cool stuff.

Saelig Instruments

[jackinnj]

Originally posted by d3imlay
Linear Technology published an excellent article on low distortion sine wave generators based on this principle using opamps. It was in a an app notes book in the late 80's.

The oscillator shown in the pic is the Linear Tech design using current feedback amplifiers -- the ones you describe are all codified in Jim Williams excellent book "Analog Circuit Design" --

[janneman]

Originally posted by 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

XR8038 or MAX038

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1257

Jan Didden

[jackinnj]

Originally posted by janneman


XR8038 or MAX038

Jan Didden

MAX038 is "past tense"

[janneman]

Originally posted by jackinnj



MAX038 is "past tense"

Really? I have a design out there that is still being produced that used it. Paramedical stuff, generating 'curative' waveforms .

For a new design, yes, I would probably mate a PIC with a DDS chip.

Jan Didden