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PA3 : Removing Unnecessary output lines
 

Back view of PA3 The PA3Delta series stereo power amplifiers can have their performance improved noticeably by de-soldering unused output lines.
Your DNM dealer can perform this small modification for you; damage caused by owners' desoldering may not be covered by the DNM warranty.

Under normal circumstances there should be no need to open the PA3 amplifier case, but in fixed installations it is possible to improve the performance by adapting the amplifier to suit your own speaker system. The PA3 is always supplied with all of its Tri-Wired output lines connected but if all three lines are not needed in your system the performance will suffer because of the reflective nature of the unused lines. This effect is removed by isolating unused lines and full provision to do this is built into the PA3 amplifier.

Ideally this work should be carried out by your dealer as he installs the amplifier into your system and it only needs to be done once unless you later change your speakers to a type with a different number of drive units. On the printed circuit boards Ring Pads are used to connect the Mid and High frequency lines to the external 2mm sockets on the back panel. Unsoldering the ring pads disconnects unused output lines but this change requires removal of the outer cover and removal of the power supply distribution printed circuit board.
Disassembly
To remove the outer sleeve first pull out the 4 rubber feet and undo the single sleeve fixing screw. The screw will not be tightly fixed as it is made of Nylon and it screws into a nylon bush inside the amplifier so take care not to overtighten this screw when re-fixing. The power supply distribution board (PS Dist) is the top-most circuit board in the vertical arrangement of 3 layers in the PA3. This board is retained by two nylon fixing screws which should be removed. When the two screws are re-inserted into the two nearby holes (see illustration) they will assist in lifting the pcb off its connecting pins. Turn the screws in by about one turn after they start to bite and the pcb will lift slightly along the edge nearest the heat sink. Use a suitable lever to raise the pcb in the centre of the far edge (away from the heat sink) by the same amount. Repeat this procedure a little at a time until the whole pcb comes free and can be removed. Take care not to rush and lift one edge in one go - this will distort the delicate connecting pins and make re-insertion of the board difficult. Also ensure that the pcb is completely free of all its pins before trying to lift it out for the same reason.

The Amplifier Board is now exposed. The top of this board and the bottom of the Motherboard (also exposed) allow access to the special Ring Pads (see illustration) which are filled with solder during manufacture to connect the loudspeaker output tracks to all the external sockets.

To Desolder the Ring Pads
Select the loudspeaker sockets you wish to disconnect * and find the appropriate ring pad on the amplifier board which disconnects the speaker negative line and the corresponding ring pad for the same connector disconnecting the speaker positive line on the motherboard. Use a desolder gun or desoldering braid to remove the solder on the ring pad. It is not essential to remove all the solder from the ring pad to break the circuit, the inner and outer rings tend to separate automatically as the majority of the solder is absorbed. Close inspection with a magnifying glass will ensure that the solder break is complete all round the ring and your chosen track is isolated.

*The DNM Speaker Connection System The line marked B for bass is used to drive a single wired speaker.
The lines B for bass and M for mid-range are used to drive a Bi-Wired speaker using two sets of cables per channel.
Lines B for bass, M for mid-range and H for high frequency are used to drive a Tri-Wired speaker using three sets of cables per channel.

Reassembly
When you have finished with the Ring Pad change, prepare to re-assemble the amplifier.
Unscrew the two plastic fixing screws from the threads in the Power Supply Distribution board and line up the board over the connecting pins, letting it rest under its own weight. It should lie flat and be making touch contact equally with all its pins. If it is tilted to one side then re-align it before trying to press it down. Gently press down and feel the board engage with its pins.

If more than moderate force is required and the board tries to tilt do not push harder but try again to re-position the board.
If it needs pulling off some of the pins then use the nylon screws to help to remove it, do not try to extract it using force by hand because the sudden movement that occurs when it breaks free will bend some of the pins. When the board is fully down re-insert its fixing screws in their holes and gently tighten so that it just bites, then add one quarter of a turn. Overtightening will damage the screws.

Re-fit the Sleeve, insert the fixing screw and tighten so it just bites and finally fit the four rubber feet. The PA3 is now adapted to your speaker system and ready for use.

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