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Signal Generator-What to get???

9/8/2004 1:18 AM
BWilliamson	Signal Generator-What to get??? Alright, needed a O-scope for years but never gave in till now. So I want to buy a signal generator but again have no clue as to what to get spec wise, brand, model? any tips? thanks bwilliamson

9/8/2004 2:03 AM
Enzo	Oh, just about anything. You will usually be feeding high impedance inputs, so all the 600 ohm terminations and stuff are beyond your needs. You need something that covers the audio spectrum. if you get a function generator that goes up to 6 Mhz, that is fine, but not needed. 20Hz to 20kHz ought to do it. Anything beyond that is gravy. For your purposes, and audio generator and a function generator are pretty much the same thing. As long as it goes all the way down to the bottom of the audio band, we don't care if it also goes up to 3Mhz. I have a little battery operated box that spits out 40, 400, 1k,10k, and 15kHz. The output level is switchable from 0db to -10db to -30db. it was intended to put a level reference on recordings on tape, but it is handy for test signals. But you want something with continuously variable output level as well as continuously variable frequency. That means a volume knob and a frequency knob rather than just switches for those. Having range switches for coarse adjustment is fine, but you ned the volume control so you can set things exactly where you want. Most anything bigger than my little pocket size box will have that. WHy? If I am sweeping freqs to find buzzes in a speaker cab, I need to find the exact freq that makes it resonate. Or if I am looking for rolloff points. When I am looking for clipping or something, I need to be able to adjust the level exactly. I use sine waves almost exclusively. I don't remember the last time I switched over to square waves. Most units have sine and square, and I am not aware of a square only unit, so don't worry about it, you will get sine with any unit you chose. Ther are also triangle and sawtooth waveforms, but I can't imagine you couldn't do without those. You can buy new stuff. A quick look through MCM showed some B&K units from $200 and up. Their inexpensive Tenma house brand had them from $169 and up. They have a handheld, but it lacks the freq continuous adjust, but it is only $55. They sell an Elenco function generator kit for $41 or so. Mouser had a Global Specialties unit at $185. But look into used gear. A place I like is Fair Radio Sales. Pretty sure it is www.fairradio.com. They sell surplus, and you can get a fine old HP201 sine wave unit for under $200. Look the site over for interesting stuff. There is always eBay, You can often find serious deals there. And in your area, the amateur radio folks have what they call Ham Fests from time to time. A flea market for Ham Radio guys. LOts of real deals to be had there. The ARRL can get you in touch with local Ham clubs and stuff so you can find out when the next nearby hamfest is. My main unit on the bench is an old Leader LAG-125, but I also have a couple old Heathkits that work fine. One is tube based even. Get something basic for now, since you are just starting to equip your shop. WHen you get to the point where you want more capabiity in your gear, shop for something fancier, by then you will know what you are looking for.

9/8/2004 2:03 AM

Enzo

Oh, just about anything. You will usually be feeding high impedance inputs, so all the 600 ohm terminations and stuff are beyond your needs. You need something that covers the audio spectrum. if you get a function generator that goes up to 6 Mhz, that is fine, but not needed. 20Hz to 20kHz ought to do it. Anything beyond that is gravy.

For your purposes, and audio generator and a function generator are pretty much the same thing. As long as it goes all the way down to the bottom of the audio band, we don't care if it also goes up to 3Mhz.

I have a little battery operated box that spits out 40, 400, 1k,10k, and 15kHz. The output level is switchable from 0db to -10db to -30db. it was intended to put a level reference on recordings on tape, but it is handy for test signals.

But you want something with continuously variable output level as well as continuously variable frequency. That means a volume knob and a frequency knob rather than just switches for those. Having range switches for coarse adjustment is fine, but you ned the volume control so you can set things exactly where you want. Most anything bigger than my little pocket size box will have that.

WHy? If I am sweeping freqs to find buzzes in a speaker cab, I need to find the exact freq that makes it resonate. Or if I am looking for rolloff points. When I am looking for clipping or something, I need to be able to adjust the level exactly.

I use sine waves almost exclusively. I don't remember the last time I switched over to square waves. Most units have sine and square, and I am not aware of a square only unit, so don't worry about it, you will get sine with any unit you chose. Ther are also triangle and sawtooth waveforms, but I can't imagine you couldn't do without those.

You can buy new stuff. A quick look through MCM showed some B&K units from $200 and up. Their inexpensive Tenma house brand had them from $169 and up. They have a handheld, but it lacks the freq continuous adjust, but it is only $55. They sell an Elenco function generator kit for $41 or so. Mouser had a Global Specialties unit at $185.

But look into used gear. A place I like is Fair Radio Sales. Pretty sure it is www.fairradio.com. They sell surplus, and you can get a fine old HP201 sine wave unit for under $200. Look the site over for interesting stuff.

There is always eBay, You can often find serious deals there. And in your area, the amateur radio folks have what they call Ham Fests from time to time. A flea market for Ham Radio guys. LOts of real deals to be had there. The ARRL can get you in touch with local Ham clubs and stuff so you can find out when the next nearby hamfest is.

My main unit on the bench is an old Leader LAG-125, but I also have a couple old Heathkits that work fine. One is tube based even.

Get something basic for now, since you are just starting to equip your shop. WHen you get to the point where you want more capabiity in your gear, shop for something fancier, by then you will know what you are looking for.

9/8/2004 3:11 AM
PeteRH	Hi Brent, I bought a HP200CD signal generator a while ago after Jeff Gehring made a recommendation. These things are old and run valves (what better excuse to use one), cheap to buy, can drive from 50mV to 20 volts (enough to drive output valves) and in my experience reliable. I bought a second for spare parts and I still havent needed any spares after three years. As an added bonus I paid $15 and it had a like new Mullard 5AR4 in it. Cheers PeteRH

9/8/2004 3:11 AM

PeteRH

Hi Brent,
I bought a HP200CD signal generator a while ago after Jeff Gehring made a recommendation.
These things are old and run valves (what better excuse to use one), cheap to buy, can drive from 50mV to 20 volts (enough to drive output valves) and in my experience reliable.

I bought a second for spare parts and I still havent needed any spares after three years. As an added bonus I paid $15 and it had a like new Mullard 5AR4 in it.

Cheers
PeteRH

9/8/2004 6:31 AM
SpeedRacer	second the vote for the old HP.. I've been using the same one for the past 15? years that I bought for $40 at a hamfest. I think mine is a 200CD.. I forget the model (HP made 2 'classic' ones) but one of them puts out about 10W of power so it's good for testing OT's (which those wimpy little SS ones won't do! ) fair radio sales is a good joint as is tucker electronics if you don't mind paying up and getting a reconditioned/calibrated unit. I didn't bother with mine.. it makes a sine wave, you know?

9/8/2004 6:31 AM

SpeedRacer

second the vote for the old HP.. I've been using the same one for the past 15? years that I bought for $40 at a hamfest. I think mine is a 200CD.. I forget the model (HP made 2 'classic' ones) but one of them puts out about 10W of power so it's good for testing OT's (which those wimpy little SS ones won't do!

)
fair radio sales is a good joint as is tucker electronics if you don't mind paying up and getting a reconditioned/calibrated unit. I didn't bother with mine.. it makes a sine wave, you know?

9/8/2004 10:30 AM
Mark Lavelle	If you don't want to wait for the perfect eBay deal on one of those old tube generators (I'd like one, myself), this one has served me well for a few years now: http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=122713 I can't recall the max peak-to-peak, but it's presumably less than 9V, so it might not be good for injecting signal directly to your power tube grids...

9/8/2004 10:30 AM

Mark Lavelle

If you don't want to wait for the perfect eBay deal on one of those old tube generators (I'd like one, myself), this one has served me well for a few years now:

http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=122713

I can't recall the max peak-to-peak, but it's presumably less than 9V, so it might not be good for injecting signal directly to your power tube grids...

9/8/2004 1:00 PM
Rich Stevens	I'm using a 7-year-old Pioneer portable CD player with a CD I burned with test tones, 100 - 10 khz. I used to use it in the car, but now I have an in-dash CD player, so this lil' puppy was sitting around. It needs a rubber band to keep the lid shut. When it's not signal-generating, it plays real music CDs in the workshop through a cast-off pair of powered computer speakers. Total cost: $0 Sacrificing my remaining self-esteem in the eyes of the DIY community: Priceless

9/8/2004 1:00 PM

Rich Stevens

I'm using a 7-year-old Pioneer portable CD player with a CD I burned with test tones, 100 - 10 khz. I used to use it in the car, but now I have an in-dash CD player, so this lil' puppy was sitting around. It needs a rubber band to keep the lid shut. When it's not signal-generating, it plays real music CDs in the workshop through a cast-off pair of powered computer speakers.

Total cost: $0
Sacrificing my remaining self-esteem in the eyes of the DIY community: Priceless

9/8/2004 1:37 PM
bob p	in lieu of having a signal generator, i've always thought it would be really handy to have a CD with test tones on it. i've tried getting by with one of the Stereophile Test CDs for audio installations, but it doesn't have all of the features on it that you'd want for building/debugging an amp. i was thinking it would be a cool project to put together an Ampage Test Tones CD -- something that has tracks with all of the tones on it that you're likely to need for troubleshooting an amp, including sweeps.

9/8/2004 1:37 PM

bob p

in lieu of having a signal generator, i've always thought it would be really handy to have a CD with test tones on it. i've tried getting by with one of the Stereophile Test CDs for audio installations, but it doesn't have all of the features on it that you'd want for building/debugging an amp.

i was thinking it would be a cool project to put together an Ampage Test Tones CD -- something that has tracks with all of the tones on it that you're likely to need for troubleshooting an amp, including sweeps.

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