How to minimize 150W amp to 25W

ro9397 · 2nd October 2007, 02:42 AM

Hope this isn't too dumb from a dewfus like me:

I'm considering the First Watt F4, only 25W in stereo. My preamp & system gain seem well-suited.

But very curious to hear the dynamic limits of 25W before purchasing F4. Present amp is 150W Luminance MOSFET. I have some 100W L-pads laying 'round. Can I get an idea of the output limits by inserting the L-pad at my present amp's output? How do I determine proper L-pad settings? Thanks for the effort.

Nelson Pass · 2nd October 2007, 04:41 AM

I don't think an L-pad is going to duplicate it very well, but it
won't hurt to try. I think it would take an AC voltmeter and
a test tone, and you would want to reduce the value to 40%
of the maximum level for a given tone.

Alternatively, you could get an oscilloscope and watch the output
voltage, observing that any music which does not exceed 20V
peak would be within the capacity of an F4. This is the preferred
method.

2nd October 2007, 02:42 AM	#1
ro9397 diyAudio Member Join Date: Jan 2007 Location: No. Utah	How to minimize 150W amp to 25W Hope this isn't too dumb from a dewfus like me: I'm considering the First Watt F4, only 25W in stereo. My preamp & system gain seem well-suited. But very curious to hear the dynamic limits of 25W before purchasing F4. Present amp is 150W Luminance MOSFET. I have some 100W L-pads laying 'round. Can I get an idea of the output limits by inserting the L-pad at my present amp's output? How do I determine proper L-pad settings? Thanks for the effort. __________________ Jimbolaya

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2nd October 2007, 04:41 AM	#2
Nelson Pass The one and only Join Date: Mar 2001	I don't think an L-pad is going to duplicate it very well, but it won't hurt to try. I think it would take an AC voltmeter and a test tone, and you would want to reduce the value to 40% of the maximum level for a given tone. Alternatively, you could get an oscilloscope and watch the output voltage, observing that any music which does not exceed 20V peak would be within the capacity of an F4. This is the preferred method.

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