The following is Peter Purpose’s original article detailing his mods to the Alesis 3630 compressor. It is re-posted here with permission from the author. See our full overview of proposed 3630 mods.

Modifying an Alesis 3630

to resemble something approaching what it should have been in the first place..!!

by Peter Purpose

While going through the posts at rec.audio.pro some time ago, I came across the subject line ‘Alesis 3630 famous sound quality’. It was primarily about why the 3630 is so vehemently despised by the Pro Audio fraternity and why a box that seemed to have all the bells and whistles sounded so bad, and could anything be done about it?

I followed the thread religiously, namely because I had one of the offending boxes in my rack and thought it would be a good way to dip my toes in the waters of gear modding, without the fear of destroying what was essentially a box of lights.

So armed with the pearls of wisdom dispensed by the luminaries at r.a.p. I set about finding the parts needed to turn this marvel of modern marketing into something it clearly (according to the pros) was not.

I’m not saying that if you follow these steps that you’ll have an 1176 or an LA3-A, but the quality of sound exiting the box will be vastly improved merely by swapping out a few components. 

This may be an opportune moment to inform you that if you choose to carry out any of the mods described henceforth, that Uncle Alesis will not be best pleased and will not honour any warrantee you may have remaining. I can also not take responsibility for your injury or death in the event that you’re a complete incompetent. ‘ELECTRICITY CAN KILL YOU’.  If you don’t have a rudimentary grasp of the pitfalls of working with electricity, get someone who knows what they’re doing to watch over you, or better still get them to do it.

First thing to do is get on to your friendly electronics supplier. From him/her get yourself 3 Burr Brown OPA4132PA quad op amps and sockets for same. A pair of THAT 2180 VCA’s, a pair of THAT 2252’s and sockets for that lot and what could possibly be the most important part, a 1 amp 9V a/c power supply.

Right,  get your 3630 out of the rack/cupboard/bin/attic/box and remove any electrical supply that may be hanging out of the back of it.  Find a nice container and remove all the plastic jack holders on the rear panel, pull all the knobs (ooh er mrs) from the front panel and undo all the nuts retaining the pots and put them safely into the nice container you found. Remove the rack ears and your 3630 should now fall apart nicely.

Take a moment to look at the circuit board and locate the chips marked LF347N. These are going to be replaced with the Burr Browns. Locate the chips marked DBX2150, these will be replaced with THAT 2180’s and the DBX 2252’s will become THAT 2252’s. Make a note of the orientation of all the chips. There are markings on all chips and circuit boards and inadvertently putting these things in the wrong way round will result mostly in a puff of smoke, so make notes or take pictures for reference.

Cut the legs on the LF347N chips above the circuit board with a small sharp pair of side cutters. Try to leave a bit of leg to grab hold of. The chips are worth half of nothing, so don’t worry about saving them for your grandchildren. The chips should fall off the board with ease.  If you have pets or small people, find them and bin them (the chips not the children).  Fire up your soldering iron and tin it. Hold it against each pin on the underside of the pcb and with your third hand pull the cut pins through the pcb with your cutters or small pliers. When you’ve done that lot, make sure that you can see well through all the holes you’ve now made in the pcb. If there is solder obstructing any of them, you’re going to have a spot of trouble getting the sockets in, so a solder sucker or my personal new friend de-soldering wick will have to be brought into play.  Nice clean holes? Then proceed to solder in the sockets making sure they are the right way round.

Do the same with the DBX 2150 and 2252 parts and you are virtually there. Make sure you haven’t connected any points together. Using a continuity tester here will tell you whether any adjacent points have become attracted, but some may by design be joined so it might be an idea to test all points and make notes before you even start this malarky.

 Install all your lovely new chips into their respective sockets, double checking that they are the right way round.

Now, one last thing. Get a nice thick piece of copper wire and strap all the input and output grounds together.

Admire your handywork for a moment or two and if you’ve mustered enough courage and there are no children or animals in the vicinity, introduce the new power supply into it’s socket and being careful to keep your hands well away from the pcb, turn it on.

No smoke? Then the chances are that you’ve just made your 3630 into something resembling what it should have been in the first place. Unhook the power, bolt that sucker back together and put it in the rack.

Have fun

peter purpose 2002