Alesis 3630 Compressor Mods July 26, 2011 11:55 6 Comments

Touted officially by Alesis as the "most popular dynamics processor ever made," the 3630 is a bargain bin compressor that can be polished to resemble a professional one. The circuit employs some solid design fundamentals, but by all accounts suffers from inferior components and design choices. Various mods have been proposed over the years to considerably expand the sweet spot the 3630, lower its noise floor, and remove the snaps, crackles, and pops the stock unit is prone to. Collected here are those mods that have been deemed the most successful by the people who have tried them. Many thanks go to the originators of these mods who have shared their research with the DIY community.

"The 3630 is basically a dbx compressor. It uses dbx-designed RMS level sensors and VCA gain-change chips. Problem is, most folks have not taken the time to learn how to use this box, find the sweet spots for level setting, gain reduction, gain make up and attack / release times." -Michael Joly via Gearslutz

"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... 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." -Peter Purpose via his GroupDIY writeup

"We have a really small compressor, the Alesis 3630, which is $300. That's the main one we used on Homework and Discovery." -Daft Punk via Mix Magazine

"This upgrade of the Alesis brings the VCA section up to the same spec as a DBX 1066." -"Icarus" via Sound on Sound

Please keep in mind attempting any of the following modifications will void your warranty with Alesis. 

Get a 3630

If you don't have one already, these comps can now be found for a pittance on eBay. With a little patience, you should be able to get one for less than $100. 

1. Beef Up the Power Supply

Make sure you're modded unit gets plenty of current by switching to a more robust AC adapter. This wall adapter from Line6 provides a hefty 2 amps. While you're in there, consider making these component upgrades to the power section:

Qty	New Component	Type	Position	Part #
2	220uf/35v	Capacitor	Power	C2,C3
2	2200uf/25v	Capacitor	Power	C4,C5
4	UF4001 fast recovery	Diode	Power	D1,D2,D3,D4

2. Upgrade the VCAs and Opamps

The VCA (voltage controlled amplifier) is responsible for controlling the compressor's gain and as such has a significant effect on the its sound and performance. The THAT2180 series of VCAs represent a high-quality alternative to the stock DBX2150s. Before you remove the stock VCAs, take note of their positioning so that you are sure to install the new ones with the correct orientation. The LF347N quad opamps can be replaced with a number of chips, the LME49740, MC33079P, LT1359. Make sure that the chip you order comes in the DIP-14 format. These upgrades were originally suggested by Peter Purpose in his GroupDIY article.

Qty	New Component	Type	Position	Part #
2	LT1359, LME49740, or MC33079P DIP-14	Quad Opamp	Input	U2,U6
2	2180BL08-U	VCA IC	VCA	U3,U7

Peter Purpose's modded unit. Note that the Burr Brown Quad opamps are now unavailable and must be substituted for one of those listed above.

3. Connect the Grounds

In his article on the 3630, Peter Purpose suggests connecting all of the input and output grounds via heavy gauge copper wire.

4. Replace and/or Upgrade Passive Components

Many of the passive components, resistors and capacitors, should be improved or changed to different values. The chart below was compiled by Sound On Sound forum member "Icarus" in this post.

Qty	New Component	Type	Position	Part #
2	100k metal film	Resistor	Input	R12,R54
2	1.69k metal film	Resistor	Input	R14,R56
4	2.2k metal film	Resistor	Input/VCA	R13,R42,R55,R72
4	6.2k metal film	Resistor	Input/VCA	R15,R41,R57,R73
4	240k metal film	Resistor	VCA	R27,R208,R69,R211
4	20k metal film	Resistor	VCA	R22,R23,R64,R65
2	470 metal film	Resistor	VCA	R26,R68
2	100 metal film	Resistor	VCA	R29,R71
4	33 metal film	Resistor	VCA	R209,R79,R212,R102
2	5.1k metal film	Resistor	VCA	R25,R67
2	5.6k metal film	Resistor	Knee	R83,R106
2	6.8k metal film	Resistor	Knee	R17,R59
2	2.2M metal film	Resistor	Level	R10,R52
2	10k metal film	Resistor	Level	R8,R50
2	22uf audio grade electrolytic	Capacitor	Level	C11,C29
6	10uf audio grade electrolytic	Capacitor	VCA/Level/Power	C16,C43,C6,C7,C33,C55
2	22pf metal film	Capacitor	VCA	C15,C32
2	150pf silver mica	Capacitor	Input	C12,C30
Remove	--	Resistor	VCA	R28,R70
Remove	--	Capacitor	Level	C42,C56

5. Disable the Gate

If you don't find yourself using the gate function on your 3630, you can send it and its nasty artifacts packing by simply snipping the two jumpers shown in the picture.