What is ideal Function Generator for audio?

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
You can use a soundcard, and it will likely have much better THD than a typical FG (as discussed). However, you can get an FG cheaply secondhand (as previous posts say), it'll have the convenience of sitting on your bench, without having to boot; and crucially, when testing DIY projects, if you accidentally send 200vDC up its probe, it won't be the end of the world. If you do this to a nice soundcard you won't be too happy.
 
What about those new-fangled DDS-synthesizers - e.g. http://www.banggood.com/UDB1200-Programmable-DDS-Signal-Generator-Dual-TTL-Drive-IGBT-With-ADC-p-947789.html

Jakob E.
 
when testing DIY projects, if you accidentally send 200vDC up its probe, it won't be the end of the world. If you do this to a nice sound-card you won't be too happy.

that's right ! That could be solved quite easily by adding a cap big enough to not interfere in the audio frequency response.
 
I would add a buffer, maybe with discrete output transistors like a DOA but with a good audio opamp in front, at least a NE5534 but better is better. 50Ω/150Ω/600Ω outputs are easy to add, we don't use 50Ω a lot but is easy and may be useful for measuring transformers. AC couple is easy too, but would require a big cap to maintain really low output impedance and must be taken into account, that cap may be dominant as a THD source in some cases.

Using an output transformer for it at least as an option when using it for probing around without have to be careful with grounds is a good option too, probably I wouldn't use it for LF low THD stuff, and in any case we still will have the THD floor of the converters which unless you have a really good card could be a problem, and if you have that card you probably can afford a proper signal generator.

The THD of the DDS is almost 1%, you can't measure THD with it, I don't know the frequency linearity of it, I would trust my sound card much better, and if 1% THD isn't a problem or uncalibrated freq response isn't a hard job to get there with a DIY product, still can be a useful tool, if calibrated (at least you know the unlinearity) and the time base is good enough I can see a couple of uses for it.

JS
 
Even though I have a Audio Precision at work, I have to think of what I will use when I retire in  couple years. I am looking t a good USB to audio interface and using software on my laptop. Like RMAA or the like. The days of dedicated instruments for this sort of thing are over. For a few hundred dollars for an interface and software, most AP functions can now be replicated.
 
Chuckles said:
Even though I have a Audio Precision at work, I have to think of what I will use when I retire in  couple years. I am looking t a good USB to audio interface and using software on my laptop. Like RMAA or the like. The days of dedicated instruments for this sort of thing are over. For a few hundred dollars for an interface and software, most AP functions can now be replicated.

I no longer have access to an AP.  I was spoiled with a few system 2 with DSP, burst etc. etc.. a lot more firepower than I even had knowledge to use properly. 

I'm interested in correlating tests done on a calibrated AP next to RMAA/interface or in my case a TEF25.  Mainly interested in frequency response of electronic circuits.  I haven't tried RMAA.  How does it stand next to an AP for simple things like 20-20kHz response? 
 
Back in the mid 1980's, I built a Heathkit SG-1271 function generator which has been a mainstay in my test gear "pile".  It is especially useful when aligning analog tape decks due to its ultra-flat frequency vs output level and ultrafast settling time.

The square wave output is also super useful as I quickly evaluate an "unknown" device, such as all of the channels of an analog mixing desk

I also see that Jameco still sells this kit, in spite of the fact that Exar discontinued the chip at the heart of the circuit:

http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_20685_-1

Years ago, I installed one of those cards into a mixing  desk which always had a crappy (non-flat frequency response, sloooow settling time) on-board test oscillator.

Bri

 

Latest posts

Back
Top