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Old 8th April 2008, 06:43 AM   #1
ttan98 is offline ttan98  Australia
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Join Date: Apr 2006
Location: Melb
Default Another 4 channels Chipamp

My implementation of LM3886
---------------------------
The rest of the descriptions are in short notes:

1. 4 channels based on Chipamp cct boards with no. of mods:
a. resistors are not soldered at the correct locations they are soldered directly to 3886's pins, eg feedback 22k to pins 3 and 9. I use carbon resistors for feedback res.
b. ability to use on-board terminations which are soldered on board. This way it very easy to replace or remove the boards.
c. the 3886 is mounted on a cpu heatsink with a fan attached. the chip seldom get warm except on a hot day. I switched on the fan when it is hot day or music played non-stop, it has no problems driving 4ohm speakers.I bolt the 3886 to the heatsink without using the mica for isolation. I prefer better heat exhange and because the chassis is made from wood I don't need to isolate the chip from heatsink, hence the heatsink is set to -34Vdc.

2. The chassis is made from wood, hence no need to ground the chassis hence no ground loops hence no hums.The amp is dead silent.

3. AC power fed from external transformer which supplies 3 independent windings each carry 2*25VAC, twin windings with combined rating of 200VA. The transformer is rated at about 700VA, ie 3 separate twin windings, of 200VA, 200VA and 300VA.

4. The DC power supply are handwired point-to-point and feed from the transformer via speaker connectors. 2channels feed from one 200VA winding. Total of 400VA ratings for 4 channels.

5. I use a quad channel Alps blue pots.

6. The 4channels are used to drive a pair of 2-way speakers via a digital x-over, DCX 2496.

refer to photos here for better descriptions.

photo 1 - 4 ch. amp top view
photo 2 - 1 channel shown
photo 3 - ext. transformer
photo 4 - 2 separate windings connected to main amp.


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