Can I add a Piezo tweeter to Peavey KB100? - diyAudio
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Old 8th October 2013, 06:40 PM   #1
JayZ is offline JayZ  Canada
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Default Can I add a Piezo tweeter to Peavey KB100?

I have two 1984 KB100's. I've noticed that more current amps have piezo tweeters as well to accentuate the higher freqs. Can I add a CTS piezo tweeter to my existing KB100's? I also have a Fender KXR60 and it has a tweeter and I've attached a part schematic showing the speaker/tweeter configuration. Am I crazy?
Thanks!
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Old 8th October 2013, 11:29 PM   #2
Enzo is offline Enzo  United States
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I don't know that it is more current amps as such, but maybe larger amps that got them. A KB300 had the 15" speaker with the dual piezo horn. It's a year older.

No reason you can't.
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Old 9th October 2013, 12:00 AM   #3
JayZ is offline JayZ  Canada
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Thanks Enzo. Do the same series/parallel rules apply with a tweeter as with two speakers in series or parallel?
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Old 9th October 2013, 12:02 AM   #4
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Of course you can. If there is any treble there, it will shine.
Piezo sit across the signal source and should have a variable impedance so varied rules apply. Place one per channel is a good start.
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Old 9th October 2013, 12:48 AM   #5
JayZ is offline JayZ  Canada
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In the KXR60 schematic the 8 ohm speaker and the tweeter appear to be in parallel. From my very limited electronics knowledge that says to me that the amp output accepts a load as low as 4 ohms (assuming the piezo is 8 ohms as well). Those are the "series/parallel rules" I was referring to. I have a vague sense that piezo's behave differently than speakers in the load circuit. If not, then I'd need to add the tweeter in series to avoid damaging the amp. Correct?
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Old 9th October 2013, 02:50 AM   #6
Enzo is offline Enzo  United States
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No, piezos are not 4 ohm or 8 ohm. They are crystals. They cross themselves over, though a cap an octave below whatever crossover point might be a good idea. Ignore its impedance. ANy parallel impedances would be way up in the treble area anyway, and there is not much energy there leaving the amp anyway.

Series resistances are sometimes used to limit how much signal gets there, don;t want to shatter it. Also, it might be desired to reduce its output next to the woofer.

In an amp like this we don't generally crossover the wwoofer to piezo, we let the woofer run full range, and the piezo just beefs up the highs.
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Old 9th October 2013, 10:42 AM   #7
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I really wouldn't just put the piezo across the amplifier.
They present capacitive loads, which will result in impedance tending toward zero at very high frequencies. Not many amps will be happy with that. Better to put a resistor in series to keep HF impedance out of the gutter.

Chris
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Old 9th October 2013, 11:03 AM   #8
JayZ is offline JayZ  Canada
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Thanks! So if I found a tweeter with similar characteristics to the one in my KXR60 could I put it in the KB100 and use the same circuit and values of caps and resistors shown in the KXR60 schematic?
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Old 9th October 2013, 12:49 PM   #9
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Quote:
Originally Posted by JayZ View Post
Thanks! So if I found a tweeter with similar characteristics to the one in my KXR60 could I put it in the KB100 and use the same circuit and values of caps and resistors shown in the KXR60 schematic?
You just need a series resistor, and it's not at all critical - it will work quite happily with nothing at all, but it's certainly 'nicer' to fit a series resistor.

Something like 20 to 50 ohms is all you need, and it doesn't affect the sound in any way.
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