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Old 8th January 2012, 12:47 AM   #11
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Keep your tubes away from your computer. Go get a small signal gen that has no part of your daily tool (computer) You can find cheap tube audio gens at HAM fests for $5. Throw some new caps at it, now you have something indestructable for experimenting with.
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Old 8th January 2012, 05:41 AM   #12
dgta is offline dgta  United States
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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.
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Old 8th January 2012, 06:05 AM   #13
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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/produc...-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.

Last edited by geraldfryjr; 8th January 2012 at 06:09 AM.
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Old 8th January 2012, 09:52 AM   #14
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I bought SignalSuite for my iPod Touch (iPhone like) and while it's not much good at 10kHz it's fine for lower frequency work, it even does frequency sweeps with can show you on a scope the frequency response (rough: levelness of amplitude as it sweeps, or just LF square waves).
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Old 8th January 2012, 03:01 PM   #15
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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.)
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Old 9th January 2012, 06:31 AM   #16
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Thanks guys for the input.
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Old 9th January 2012, 06:45 AM   #17
Mooly is online now Mooly  United Kingdom
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I use an old Belco,
Belco Sig Gen. Age/Info etc

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.
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Old 9th January 2012, 07:03 AM   #18
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I just realized that the Room EQ Wizard software has both sine and square wave.
So I have the computer solution.

Yeah I will use an amp for drivers testing.

I checked out the HP 209A and it seems like a suitable choice. It is small, intuitive, and convenient.
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Old 9th January 2012, 07:19 AM   #19
Mooly is online now Mooly  United Kingdom
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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.
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Old 9th January 2012, 07:22 AM   #20
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If you want to make some simple measurements with sine/square waves GAG-810 is a good option. I can post some measurements if you are interested.
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