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A technique for assembling our circuits

How to get rid of printed circuit boards

[Italian version]

Someome wrote me asking for some more instructions about this technique. Here they are. The process is indeed easy and straightforward, eventhough there is few people used to it, these days.

I use either a normal, single side printed circuit board or a standard matrix printed circuit board, pre-drilled with a .1" grid of holes. You can find them easily.

In case the normal board is used, copper side is used exclusively as a ground plane to reduce disturbs: components are to be mounted on the copper side. In case of the matrix board, the ones I use have instead on one side a round copper place around each hole, to enhance components stability: components in this case must better be mounted on the side without any copper.

If you want to use a normal board, you should better use anyway a matrix board as a guide for drilling and as a grid to decide where the components must be placed. I normally prepare a layout on paper, just attaching a sheet on the matrix board with adhesive tape and then forcing the components through the paper into the holes andtaking note on the paper of the component position.

So you start placing the components over the matrix board covered with paper, checking for the available space (which is never enough, as you'll find out soon). The components should be placed in general in the same order as in the drawing, that is, using a RIAA pre-amp, with passive RIAA network as an example, first the input load, then the preamplifier first stage, then the RIAA components and finally the second stage. The most important thing is to put the power supply bypass capacitors as near as possible to the corresponding stage.

Take note of the component position on paper or directly on the board, in case it is the matrix one. A warning: NEVER USE A GRAPHITE PENCIL!!!! Graphite is conductive and can easily alter the correct resistance values!!!!

In case I am going to use the normal board, at this point I attach the normal board to the matrix one and the paper, and drill out all the required holes through the paper and the matrix board, using a drill point smaller (0.8mm-1mm) than the matrix board holes. The holes must then be perfectly isolated by milling away some copper around them with a larger drill point (3mm), in order to prevent any contact between the ground plane and the component pins. In case you are interested also in obtaining a good looking board, you'll better polish the copper and protect it with a coat of transparent spray varnish. There are also some specific products for this purpose, but any varnish will do.

After you have defined the component position you must connect the components togather, following the schematic drawing (you must have it printed out in front of you!!!). You must try to use the components own connecting pins wherever possible and must isolate them accurately (either use a piece of thin heat shrinking tube or even a piece of an adhesive insulating tape) when they have to cross. Any time you complete a connection on the board check out the connection on the schematic, with a mark on each connected pin: this allows to keep track of missing connections even in case three or more pins are connected togather.

Use sockets for any dual-in-line IC: it is not very elegant but 1) there is no risk of overheating them while soldering the other components 2) the ICs remain safe up to the time you insert them and power everything up 3)if you want to test other op amps it takes a few seconds!!!

It takes some time, but in about 8 hours of hard work (and some re-work!!!) the task is completed. Then verify from the component side that all desired connections are present, and that no undesired connection is present, using a tester in resistance testing mode (be careful: if you measure a not charged electrolytic capacitor it initially appears as a short circuit!!!).

Finally, without inserting the ICs, verify that the IC supply voltages are correct. Then shut everything down, wait for all capacitors to discharge, insert the ICs, and test power supply voltages once again: first IC power supply voltages, and then the output voltages.

Connect everything to the system and hopefully everything will be working.

© Copyright 2002 Giorgio Pozzoli https://www.tnt-audio.com

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