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-   -   Signal Generator: Which one to buy ? What to look for in a signal generator ? (http://www.diyaudio.com/forums/tubes-valves/203979-signal-generator-one-buy-what-look-signal-generator.html)

HP8903B 7th January 2012 07:11 PM

Signal Generator: Which one to buy ? What to look for in a signal generator ?
 
I want to buy a signal generator.

Could you guys make recommendation on which one to get or what specs to look for ?

I already have a Tek analog scope.
I mostly work on tube gear.
I also want to test speaker drivers with the signal generator

BZed 7th January 2012 08:19 PM

Just us your computer and some signal generator software. I would use a transformer to protect the computer from voltages in the amp.

Most generators would need an amp to do speaker testing.

aardvarkash10 7th January 2012 08:19 PM

a cheap laptop and some free software...

HP8903B 7th January 2012 09:06 PM

I am aware of the computer and amplifier option.

I was thinking of the vintage signal generators that has a large knob to dial the frequency.
I am pretty sure that those do not require separate amplifier.

SGregory 7th January 2012 09:23 PM

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.

tomchr 7th January 2012 09:33 PM

A good general purpose function generator like the HP 3312A can be had for little cash on eBay. I think I paid $100 or $150 for mine to get one that was guaranteed to work.

~Tom

Wavebourn 7th January 2012 09:48 PM

I have a pair of Wavetek 154. From 0.1 Hertz to 10 Mega Hertz. However, you know that I don't measure THD. :D
First one is connected to VCA input of the second one, to get AM signals when needed. For example, 15 KHz sine modulated by 15 Hz triangles. Or sum of 2 signals.

HollowState 7th January 2012 09:48 PM

Quote:

Originally Posted by manp111 (Post 2851074)
I want to buy a signal generator. Could you guys make recommendation on which one to get or what specs to look for ?

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 :)

BZed 7th January 2012 09:49 PM

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.

HollowState 7th January 2012 09:59 PM

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.


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