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Old 21st January 2011, 05:26 PM   #1
maurycy is offline maurycy  United States
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Default How to limit amp's output power when connected to small speakers?

I am building 2x15W amplifier based on TA2024. I am also building small Munny speakers based on 1" full-range Tang Band drivers to go with the amp. The drivers are only 4W RMS and 8W max so the amp is way too powerful for them.

Is there an easy way to limit the output power of the amplifier so it does not exceed the speaker specs? This setup is going to my kids room so I am afraid that they may crank the volume all the way up destroying the speakers.

Thanks.
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Old 21st January 2011, 05:31 PM   #2
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Cool Nail

Drill a hole in the front under the volume knob and insert a steel nail at such a point the volume will not go beyond 11.....
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Old 21st January 2011, 05:46 PM   #3
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1" speakers? Most of my tweeters are larger than that... I think a 3" in a cardboard box would sound better than that unit.
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Old 21st January 2011, 08:39 PM   #4
AP2 is offline AP2  Italy
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Hi,
A very simple,very good system is a 6V lamp 1,5A in series to load (or try other current).
this , (becouse thungsteno change R with current) ensures an excellent automatic adjustment of the current

Regards
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Old 21st January 2011, 08:46 PM   #5
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The "proper, but not so easy" way would be to adjust the gain resistors of the TA2024 board.
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Old 21st January 2011, 08:49 PM   #6
AP2 is offline AP2  Italy
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Hi,
What does it matter the gain? the speaker is broken for the current.

Last edited by AP2; 21st January 2011 at 08:53 PM.
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Old 21st January 2011, 08:53 PM   #7
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Quote:
Originally Posted by AP2 View Post
Hi,
What does it matter the gain? breaks for the current speaker.
Limiting the gain to prevent clipping.... does this not make sense to you?
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Old 21st January 2011, 08:58 PM   #8
AP2 is offline AP2  Italy
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Quote:
Originally Posted by theAnonymous1 View Post
Limiting the gain to prevent clipping.... does this not make sense to you?
The dynamics of the sound is not controllabie, whay do you think that just may break the clip?
If the amp is more powerful, only output current you can limiter.

Last edited by AP2; 21st January 2011 at 09:02 PM.
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Old 21st January 2011, 10:32 PM   #9
wwenze is offline wwenze  Singapore
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At 4W per speaker unless you've greatly reduced sensitivity for bass extension the reason I'd be limiting the volume is ear protection instead of speaker damage. (Teach your kids to listen at 80dB max.)

A 10k resistor in front of the 500ohm potentiometer will reduce max output power by 26dB if you don't want to play with the gain resistors.
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Old 21st January 2011, 11:51 PM   #10
Eva is offline Eva  Spain
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To really protect a speaker, the two limiting factors are cone displacement and voice coil heating.

Limiting cone displacement involves calculating instantaneous cone displacement (2nd or 4th order filter), feding the signal to a peak hold circuit and using a controlled high pass filter for attenuating low frequencies progressively when a certain displacement threshold is exceeded.

Limiting voice coil heating involves measuring rms current through the coil, integrating it over time, comparing the result to a threshold (P=i^2*R) and using a controlled gain stage to reduce signal gain progressively when the threshold is exceeded.

Obviously, this is not worth the effort for a small driver. The light bulb solution is a good inexpensive approximation because filament resistance is low at low currents and high at high currents and it does not react instantaneously to overload, allowing for large but harmless audio transients but not for dangerous sustained overload.

The optimum type of lamp may be found by trial and error.
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