Test oscillator design

[peterc]

What about the MAX038? Isn't this an 8038 on steroids?

Not cheap tho', about 13-00 GB pounds..

Peter

 

[dpaton]

I had pretty good luck with a 1kHz quadrature oscillator before I got my Minirator. I built it by accident when trying to make a S-K active filter. Omit the feedback on the 3rd opamp (of 4) and whammo, instant sine oscialltor, with a nice low THD (mine measured about 0.08% on the breadboard). Higher precision parts (matched resistors and caps) would create a lower THD output. It's dead-simple to junkbox too. The only downside is that if you want to sweep the output you need a 4 section pot with extremely close tolerances.

My $0.02.

-dave

 

[clintrubber]

[quote author="Steffen"]just for the record
a low distortion thingy...not too complicated, down to 0.002% THD
I´ve this bookmarked for a while. never built it...ended with test tone compact disc and a cd player to use with my thd meter.

steff[/quote]

First of all, it's about our ears etc.
Having stated that disclaimer, I'm curious to how clean the sinewaves are that you get from a computer/CD/etc.

I made a 24-bit 1kHz FS sine with CoolEdit & sent it out from my DAW. I've tried two different types of output but didn't see much difference;
hardware distortion analyzer said THD wasn't better than -83dB / 0.007% (@80kHz LPF) for any of those outputs. The residue was (unsurprisingly) very noisy.

The hardware box itself (HP8903B) has a clean sine generator of -93 dB / below 0.0025 %. Always nice to see a hardware box being 'better' than a PC ! :wink:

But it clearly shows the limitation of a soundcard based test setup. Obviously it'll be fine for the larger distortions but that 10dB better HP-generator can't do the stuff deeper down either:

http://www.dself.dsl.pipex.com/ampins/webbop/5532.htm

But OK, if we could stuff like this with a soundcard then why would we be lusting after AP-gear any longer. :thumb:

FWIW,

Peter

 

[Viitalahde]

Funny you brought this back up, I was just damping some trafo ringing and though that I'd need to build a signal generator version 2. One with metering, better box and other good features. Also I've been thinking of building the simplest possible battery powered 400Hz sine wave (hell, dosn't even matter what wave! :shock: ) generator that'd be really tiny and be handy in squaking when you're doing tech work somewhere else. :wink:

 

[clintrubber]

[quote author="Viitalahde"]Funny you brought this back up, I was just damping some trafo ringing and though that I'd need to build a signal generator version 2. One with metering, better box and other good features. [/quote]
Yes, I just did some testing to get a feeling for PC-DAW performance vs expensive hardware boxes from 20 years ago, so was wondering about what has been said here about that topic.
Only then I'd realized that we'd quickly enter the 'beyond measuring capability' unless AP-boxes were thrown in.
But hey, an answer like 'beyond measuring capability'
(say THD below -95dB for my setup) are an answer as well,
as in: "it's OK enough, get on with life NOW". :wink:

Also I've been thinking of building the simplest possible battery powered 400Hz sine wave (hell, dosn't even matter what wave! :shock: ) generator that'd be really tiny and be handy in squaking when you're doing tech work somewhere else. :wink:

If waveform & quality & level are not important then how about a tiny get-it-free-with-your-washing-powder mp3-player with an mp3-version of own created test-wavs ? (Or from that recently downloaded test-CD of course :thumb: )

Bye,

Peter

 

[Viitalahde]

[quote author="clintrubber"]If waveform & quality & level are not important then how about a tiny get-it-free-with-your-washing-powder mp3-player with an mp3-version of own created test-wavs?[/quote]

A damned good idea! :thumb: Now what washing powder I'm using..

 

[clintrubber]

[quote author="Viitalahde"]Now what washing powder I'm using..[/quote]
Dunno, don't llama's just bathe in their own spit ? :?


I'm sorry, let's jump back to THD & %.