I use a 8111A Pulse/Function Generator for basic test and refining the feedback values. Not ultra low distortion but it has a pretty good square wave, soemthing that most computer drivers don't do very well. I picked it up on fleabay pretty cheap.
For thd analysis, response, etc I use my computer sound card with AudioTester. Some pretty good USB cards out there getting great results. Use an amp in between to test speakers.
For thd analysis, response, etc I use my computer sound card with AudioTester. Some pretty good USB cards out there getting great results. Use an amp in between to test speakers.
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You want full audio coverage and beyond up to at least 100KHz. A standard 600 ohm output (unbalanced). And at least 5 volts RMS output with step & variable attenuation and low distortion. Square waves are also nice in the same instrument.
Hewlett-Packard 209A is a good choice. HP 204D is nice but only sine waves. 204C is similar but less attenuator. Leader LAG-120B has everything mentioned. Leader LAG-125 has even more, as does an LAV 191A, but they're more expensive with meters. A Krohn Hite 5700 meets these requirements. Also a General Radio (Gen Rad) 1310A or B is nice but sine only. Then there's the Tektronix TM-500 series plug-ins that require a mainframe to use. SG-501A, SG-502 & SG505 for very low distortion.
Wavetek makes a lot of function generators but the sine waves are derived from square waves with a progressive diode array, so the distortion is not as low as an RC oscillator is.
All the above are SS. But there is always the older tube oscillators from HP like the 200 series. (201C, 200CD, 200AB, etc) These use more power and have a larger footprint. But you might find a 5AR4 in some of them
Your talking about an old HP 200AB or something like it. that would do what you want, but... I tested and caliberated test equipment for many years and just after one of those has been gone over they work great. After 500 hours you better cal. it again. THD will be off the chart, hum will be high, output my be low. They just drift a lot. If you want to use it for distortion testing never shut it off, or let it warm up for 24 hours before you use it. As you change frequency the output level will change. After 6 months you will need to spend money to get it caliberated again. Its just not worth the hassle.
Use the computer. Every time you use it you will get the same stable signal, plus you will have more than just sine waves to test with.
Use the computer. Every time you use it you will get the same stable signal, plus you will have more than just sine waves to test with.
BZed:
I too have been in the test equipment business for many years. And I've bough, repaired, calibrated and sold many of the old 200CDs and 201Cs. They're just not "that bad" as you claim. Perhaps you just had some really funky ones that didn't hold up well. Me experience is nothing so drastic. But I would recommend the SS units above these old timers.
I too have been in the test equipment business for many years. And I've bough, repaired, calibrated and sold many of the old 200CDs and 201Cs. They're just not "that bad" as you claim. Perhaps you just had some really funky ones that didn't hold up well. Me experience is nothing so drastic. But I would recommend the SS units above these old timers.
For basic workbench use, a knobs-and-dials gen can be easier to use than a computer. For anything more sophisticated, like THD, spectral analysis etc., it's hard to beat a decent sound card and some software.
Hint: if the model name includes "signal generator", it's usually a multi-purpose piece with fairly high distortion. If it includes the word "oscillator", it's very likely low(er) distortion.
Hint: if the model name includes "signal generator", it's usually a multi-purpose piece with fairly high distortion. If it includes the word "oscillator", it's very likely low(er) distortion.
For what it is worth I have been using a Tenma signal generator since 1994 and I have had not one problem with it.
It has never had to be recalibrated and the dial is still dead on,
http://www.mcmelectronics.com/product/TENMA-72-455A-/72-455A
Although you could probably pick up a nicer older model HP or something for around the same price,But it has been good to me so it was worth mentioning.
It is tuned by a variable air capacitor and came with a schematic should I ever have an issue with it and need to repair it.
jer
P.S. And it goes to 1Mhz sine or square wave output, And I leave it on for months at times.
It has never had to be recalibrated and the dial is still dead on,
http://www.mcmelectronics.com/product/TENMA-72-455A-/72-455A
Although you could probably pick up a nicer older model HP or something for around the same price,But it has been good to me so it was worth mentioning.
It is tuned by a variable air capacitor and came with a schematic should I ever have an issue with it and need to repair it.
jer
P.S. And it goes to 1Mhz sine or square wave output, And I leave it on for months at times.
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Function generator kits start at about $30 US. The main ic is the XR-2206 which sells for about $6.50 US. That will get you about 1% distortion at best. The better oscillators (sine only) use Wein Bridge oscillators. Those range from .05% down to .001 or better. The cleaner you buy the deeper your wallet needs to be. For driving speakers directly you are probably going to need a buffer amp. Lowest output impedance for sig gens is a rare 50 Ohms, most common is 600. Tube style sig gens will drive up to 30VAC out, but into a 600 Ohm load. Most won't be happy driving an 8 ohm load.
There is lots of information on the web about Wien Bridge oscillators including how to build state of the art models or retrofit existing models to current spec needs.
For your needs I'd either pick up an old used one off ebay or build a kit / from scratch and slap a buffer amp behind it. In old HP oscillators look for a 204C/D or 651-654 In the big knob tube models don't buy the 200AB as it only goes to 20Hz - 40KHz. 200CD will get you from 5Hz to 600KHz. (All sine only.)
Doc
There is lots of information on the web about Wien Bridge oscillators including how to build state of the art models or retrofit existing models to current spec needs.
For your needs I'd either pick up an old used one off ebay or build a kit / from scratch and slap a buffer amp behind it. In old HP oscillators look for a 204C/D or 651-654 In the big knob tube models don't buy the 200AB as it only goes to 20Hz - 40KHz. 200CD will get you from 5Hz to 600KHz. (All sine only.)
Doc
I use an old Belco,
http://www.diyaudio.com/forums/parts/126467-belco-sig-gen-age-info-etc.html
and a Tenma similar to this,
Tenma 72-5016 | Used Function Generator | Used Test Equipment | Refurbished Test Equipment
For speaker testing you need an amp. The computer option and burned CDR is a very usable option. Use a cheapo portable CD player as a source. The distortion from that set up will beat any function generator on THD over the audio band. At LF it's unbeatable.
http://www.diyaudio.com/forums/parts/126467-belco-sig-gen-age-info-etc.html
and a Tenma similar to this,
Tenma 72-5016 | Used Function Generator | Used Test Equipment | Refurbished Test Equipment
For speaker testing you need an amp. The computer option and burned CDR is a very usable option. Use a cheapo portable CD player as a source. The distortion from that set up will beat any function generator on THD over the audio band. At LF it's unbeatable.
Remember that only a function generator will generate proper square waves above a few hundred Hz, computer based stuff won't due to sampling limitations.
Here's a 1khz squarewave off CD (and any player will show the same result, £$10 portable or £$10000 hi end). It's rubbish but that's the way it is. Higher sampling rates than CD's 44.1Khz and results will be better but still no substitute for a function generator if you want square waves.
Here's a 1khz squarewave off CD (and any player will show the same result, £$10 portable or £$10000 hi end). It's rubbish but that's the way it is. Higher sampling rates than CD's 44.1Khz and results will be better but still no substitute for a function generator if you want square waves.
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