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PLUTO-2.1 Construction 

The information presented here is supplemental to Revision 4/27/05 of the PLUTO Construction Plans. It provides the necessary additional detail for constructing PLUTO-2.1. Ignore the earlier Pluto-2 information on the owner-support page.

A - Replace the Peerless woofer/midrange drivers with Seas L16RN-SL (H1480-08) available from www.madisound.com .
Since the driver has a circular mounting rim it is not necessary to use the cardboard gasket described on page 11.  Stuff the 4" pipe uniformly with Acoustastuf by adding 85 gram for a total of 200 gram. 
The tweeter's surround plane should be set back 3/8 inch from the edge of the woofer's basket rim.

B - Crossover/Equalizer/Amplifier electronics
Use the updated material list Pluto-2.1-material list.xls

Components with new values and the two added R-C networks are circled on the schematic and in red on the layout diagram. 

Tweeter channel gain2.1 R21   3.48k R22   10k Tweeter high frequency boost R289   2.87k C289   2.2nF Tweeter notch filter2.1 R32   1.00k Woofer boost  R55, 56   8.25k R57, 60   12.1k R58, 59   21.5k C58   390nF C59, 62   100nF C60   open C61   330nF Midrange down shelf2.1 R660   1.96k C660   150nF  Midrange notch filter2.1 R62   2.61k C64   68nF C65   150nF Amplifier stability control C41, 81, 91   820pF   2.1 = changes to Pluto-2

The leads of C64 and C65 have to be bend so that the two capacitors fit into the pcb next to each other.

Tweeter high frequency boost R-C network

Midrange R-C shelf and notch filter components

The three power amplifier IC packages are mounted to an Aluminum sheet metal piece and individual heat sinks. Thermal compound is applied to the individual heat sinks and the three IC packages. The circuit will work without the sheet metal heat sink but the amplifiers can get very hot and shut down protectively at high volume levels. Adding the sheet metal will increase the amplifier reliability and avoid thermal shut-down.

2.0" tall heat sink to fit the original PLUTO base

2.75" tall heat sink for the alternative PLUTO-2.1 base

The 2.75" height of the metal piece has to reduced to 2.0" to fit the PLUTO base

Electrical test chart

        Input voltages greater that 0.645 V at 10 kHz and above will cause clipping at TP9.

The input to output frequency response without the drivers connected and measured with a 10x attenuator is the most important description of the electronic module. It should match within +/-0.5 dB. 
The spot frequency checks with the table above are primarily intended to find errors in construction.

C - Alternative cabinet construction
A larger base for easier access to the electronic module and improved heat transfer from the power amplifiers may be desirable.
Also the rubber coupler for mounting the woofer/midrange driver can be replaced by a ring of wood slats that are screwed into a standard 4" pipe coupler.

Place a strip of 3/8" wide and 3/16" thick foam tape as gasket under the woofer/midrange basket rim before screwing the driver to the ring of wood slats. The 4" pipe should be stuffed uniformly with 200 gram of Acoustastuf. When upgrading from an existing Pluto-2 it is not necessary to remove the driver to add stuffing material since the audible effect is minimal. Check for air leakage by applying a 10 Hz, 10V signal to the woofer/midrange speaker cable. If you hear puffing noise, then find its location and seal the leak with GE Silicone II Household Glue. There should be a pin hole leakage path left open so that the cone comes slowly back out, when slowly pushed in. 

The maximum amount of stuffing material in the pipe behind the tweeter is not critical, but should be at least as specified.

The internal height of the base is 3.5".

Mounting plate for the electronics Note that the electronic module described under B above works correctly also for the alternative cabinet construction.

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