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Old 24th June 2010, 02:05 AM   #1
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Default Pass F2 amp and FR drivers (long)

Nelson Pass designed the FirstWatt F1 and F2 (current rather than voltage) amps to drive FR speakers. On the FirstWatt site, he provided passive, speaker level EQ for the most popular drivers of the time. I finally got my hands on a F2 (clone), and am having a great time with his suggestions. Hearing good controlled bass out of 166E and 206E in .7cu.ft. and 1.5cu.ft.sealed boxes is a delight!

I understand that the first parallel resistor (R0) provides damping to improve bass nearly all the way down to Fs. Does anyone here understand how he determined R1, C1 and L1, the other parallel network EQ compensation? Are these based on T/S parameters? (this would be a great place to provide a link to that site, but my computer skills are primitive)

I'd sure like to find a starting point for some recent drivers, like the AudioNirvana lineup, or the different (more expensive!) Fostex drivers with bigger magnets and such. Maybe a simple two way using ruthlessly efficient JBL (and other) components like the pair of 15" 2220 woofs (101dB!) I own.

Perhaps I should post in the Pass amps part of DIYaudio, but I thought I'd start here.
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Old 24th June 2010, 04:02 PM   #2
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Default uhhh . . . how about a link? Pages 5&7
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Old 24th June 2010, 05:19 PM   #3
mdynac is offline mdynac  United States
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try this one....
Voyage MPD on Alix3/Objective DAC/DCB1 Mesmerize/AF4 xover
18" H-Frames
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Old 24th June 2010, 08:44 PM   #4
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What you will see is that I created a simulated loudspeaker
load based on the impedance curve of the various drivers which
guided the choices of load network to change the response
as desired. R0 sets the damping at DC and the LRC network
typically alters the response of the upper mid for either
"maximal flatness" or "best sound"

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Old 25th June 2010, 05:55 AM   #5
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Default Thanks for the reply . . .

. . . but, more importantly, thanks for the design that has me excited about DIY
speakers, again. The variety of full-range drivers have different voices that are easy and fun to play with. Relatively inexpensive, too.
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Old 25th June 2010, 06:32 PM   #6
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The variety is the best part.

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Old 27th June 2010, 05:14 AM   #7
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Default stimulate the simulation

I really have no idea how I can simulate a speaker driver load. I assume that
SPICE works well, but that is beyond my current ability.
I can measure impedance accurately, but I don't have the tools to
measure FR nor model a transducer.

I'm hoping that, perhaps, impedance combined with t/s parameters may be
enough to get me in the ballpark. If not, I'll just have to learn more, and acquire the tools needed, 'cause the fun I'm having with the F2 exploring fullrange drivers is just too good.

However, if there are ways to estimate the needed compensation, I'm willing to play around with the components to get close to a solution.

If not, I'm happy to use the drivers already suggested, and worry about other choices, later. There's already a lot of stuff to play around with.

Thanks again, Nelson Pass, for the tools you have made available to pursue this hobby with renewed passion and satisfying results.

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Old 27th June 2010, 07:10 PM   #8
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A much easier and cost effective solution is just to do one of these:


or wait until the firstwatt B4 comes out... I have heard ans seen it first hand and it's a special piece..
Randy Kunin
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