# Basic questions re: audio frequency experimenting



## greco (Jul 15, 2007)

If I took a sine wave output from a function generator (FG)at about 1.5 volt PTP (within the audio frequency spectrum) and put this signal directly into an *old* stereo speaker:

Would I get audio tone(s)?

Could I damage the FG? ......I'm not worried about the speaker

If I wanted to run the same signals into a small SS amp, what PTP voltage would be reasonable?

All comments welcomed.

Thanks

Dave


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## User_X (Feb 1, 2008)

You would have a massive impedance mismatch as no normal signal gen is designed to drive spkrs directly AFAIK.
Damage to your FG? Maybe, depending on its current capacity and output protection.

500mv is a big guitar signal.


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## greco (Jul 15, 2007)

Thanks User_X

....so back to the drawing board.

From what you indicated, could I run a smaller 200 to 300 mv signal into an SS amp without concerns re: damage to the FG or amp (this time I am concerned about the amp also...unless I go and buy an inexpensive practice combo.

Any suggestions for a good textbook on very basic audio electronics ?

Thanks

Dave


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## Wild Bill (May 3, 2006)

greco said:


> If I took a sine wave output from a function generator (FG)at about 1.5 volt PTP (within the audio frequency spectrum) and put this signal directly into an *old* stereo speaker:
> 
> Would I get audio tone(s)?
> 
> ...


Dave, most signal generators are designed to feed into loads much higher in impedance than a speaker. We're talking a few hundred ohms up to hundreds of thousands of ohms.

A speaker is maybe 8 ohms or whatever. When the load is so low it's very hard for the generator to maintain that 1.5volts. It would likely think it's trying to drive into a short circuit. 

This doesn't automatically mean it would damage your function generator. These kinds of test equipment normally have buffered outputs to protect against that sort of thing. 

It DOES mean that you may not get much sound out of the speaker!

So the short answer is, no it probably won't hurt anything. It just won't work very well.

Feeding an amp is a much better idea if the amp is designed to feed a speaker load. It's hard to say how much voltage it would need to drive it. If it's a SS guitar amp it would find 1.5 volts way too heavy! A guitar puts out in the range of 10-40 millivolt! However, it's always easy to cut a signal down. That's why we have pots! Take a pot of maybe 25k or so. Wire the FG output across the pot and take the signal off the wiper and the ground side. Then adjust to taste!

If the SS amp is just a power amp without a preamp stage, like a booster for your PA that is fed from a mixer, 1.5 volts is reasonable!

Hope this helps! 

Gotta go! My 80 lb puppy needs to go out and when she's that big you have to pay attention or the consequences could be big and messy!:smile:

:food-smiley-004:


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## greco (Jul 15, 2007)

Many thanks Wild Bill...

As always, I greatly appreciate your help and detailed respone. :bow:

An 80 lb. "puppy"  ............What breed of dog is it?

Cheers

Dave


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## User_X (Feb 1, 2008)

greco said:


> Thanks User_X
> 
> ....so back to the drawing board.
> 
> ...


http://www.dimarzio.com/media/content/pdfs/tech_data-quick_guide.pdf

That chart indicates pup output in mv.

Look for a book about guitar amps by Jack Darr(?) that I think has been archived online, somewhere. Once upon a time I had the hard copy and it was a good primer.


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## Wild Bill (May 3, 2006)

greco said:


> Many thanks Wild Bill...
> 
> As always, I greatly appreciate your help and detailed respone. :bow:
> 
> ...


She's a mutt! Black from her Lab side but the body and fur swirls come from Golden Retriever.

Not the smartest but certainly lovable, with a noble heart! She wants to mother everything in the world, including other dogs, people, kids, cats, chipmunks and even possum.

For some reason, she just hates squirrels! Maybe one was rude to her sometime, I dunno.

The word's out among my customers about her and many of them bring dog treats when they come by. She's gotten incredibly spoiled!:smile:

:food-smiley-004:


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## greco (Jul 15, 2007)

Well...I did it. 

One large step forward for Dave...no obvious advances for mankind. (yet...LOL)

I built an interface and sent a sine wave (at various frequencies) from the function generator to my Fender 65 watt SS amp.

Scared the sh*t out of me when it first started as the volume was low, but not low enough!! ..Mrs Greco also came flying downstairs from the kitchen....worried about me and the strange noises. It worked just fine with the volume pot on the amp almost totally turned off. 

The fun was succeeding with an idea and following through on it. Hearing the tones from various frequences and sweeping through them was interesting and fun (Yes....I really do need to get out more often).

Thanks User_X and Wild Bill 

Dave


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