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Guitar amp output power question?
I'm planning on putting a headphone jack in an older Giannini amp. I have no problem determining the correct resistor values to attenuate the signal for any given output power, but my problem is that I don't know what that output power is. It's not shown on the amp, and I haven't been able to find anything on the 'net.
The input power is 50 watts. I'm guessing that the output is about 20W (into a 12" 4 ohm speaker), so I plan on using values for a 30 Watt output.
Any comments?
3 Answers
- tom7railwayLv 78 years agoFavorite Answer
I suggest you buy resistors for output at 20,30,40 watts, they only cost pennies. Try the lowest value resistors first, and play some stuff though the amp, gradually increase the volume, and if the sound in the phones distorts, the attenuation is not enough. It doesn't take long to put in other resistors and see which sound the best without any distortion. You won't damage the phones unless you overload them heavily for a prolonged time.
I assume you know the impedance of the headphones ? It will be much higher than the amp speaker, possibly as much as 64 ohms.
Source(s): ex-electronics engineer - classicsatLv 78 years ago
Standard (on stereo systems I have repaired), is 150 ohm 1/2W or so headphone series resistor, regardless of the power output of the stereo. You could parallel 10W 8 ohm film resistor for some load.
- DONLv 78 years ago
If you start with values chosen to attenuate 30 watts to a safe headphone level, you'll be close enough.
Don
