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Supplemental support information

An alternative woofer/midrange driver was developed by Seas for this application, L16RN-SL (H1480-08). It is the preferred driver when PLUTO is used without additional subwoofers.  It can be purchased from Madisound. A few circuit component changes are required for its use. They are listed on the PLUTO owner page. 

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(35)  3/28/08 Tweeter placement relative to L16RN-SL

The L16 has a continuous circular basket rim. It causes a diffraction ripple in the frequency response around 4 kHz if the tweeter is set back 7/8" as in the drawing on page 4. The tweeter should be moved forward so that the distance is 3/8" inch from the outer edge of the rubber coupler P to the rubber surround front edge of the tweeter . 
This correction flattens the tweeter response but audibly has probably only a subtle effect. 

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(34)  3/26/08  Circuit changes for SEAS L16RN-SL midrange driver (30) and tweeter boost (25)

See this page

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(33)  2/25/08  Spurious oscillation of clipping power amps

Adding 820 pF to C41, C81 and C91 prevents/reduces some low level spurious oscillation in the MHz range that is visible on the part of the waveform that comes out of clipping. This is a precautionary measure. I am not aware of any audible effects of the oscillation. The amplifier must first be clipping or be near it.

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(30)  8/22/07 New SEAS midrange driver

An alternative midrange driver is the new SEAS L16RN-SL (H1480-08). It is optimized for long stroke, low distortion and piston behavior as needed in PLUTO. It is a derivative of the W16NX001 and uses an aluminum cone. The driver can be ordered from Madisound.

On the PLUTO pcb the following component changes are required:

Change R58 from 10k to 7.5k
Change R62 from 1.96k to 2.61k
Remove R57 21.5k
Remove C57 470 nF
Remove C58 100 nF
Remove C59 39 nF
Remove C60 6.8 nF

Implement (25) below or alternatively solder a series connected 2.87k ohm resistor and 2.2 nF capacitor with one end to the junction of R28 and R29 and with its other end to a circuit ground point. This will give the same high frequency boost regardless of which input is used. Re-adjust the tweeter level if necessary with VR1.

Download and install a software signal generator Minirator MR1 if needed.

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(25)  12/29/06 Tweeter boost

A worthwhile improvement in extreme high frequency sound output can be obtained by adding a resistor-capacitor highpass shelving filter. Solder a series connected 1 kohm and 6.8 nF to the junction of R3 and R6 (at R3) and with its other end to ground (at R22). This gives a boost of 2.9 dB at 12 kHz and 4.6 dB at 20 kHz. 

Note, the added circuitry has no effect when you use the high level input J2. 
Instead, a series R-C network of 1.33k and 4.7nF would have to be connected in parallel to R6 to obtain the same boost.

See (30) above for another way to boost high frequencies.