compressor schematic


Sorry, but sometimes you have to be cruel to be kind, 90% of the time compression is used to make bad singers sound ok, or rescue a good singer who has no mic technique.

Assuming your singer is in the latter 10%, learning a decent mic technique, ie backing off the mic for loud bits, (in a simplistic critique), will pay much better dividends, as most non valve compressors are rubbish for vocals, and if you are in a situation where you cannot afford to buy a compressor, the gigs you will be doing probably will not have one in their FX rack anyway.



2002-04-28 2:11 pm

This unit is very simple, but it may do the trick:

Here's a photo of mine, I can post the PCB layout if you want. With a PCB the project is tiny - small enough to retrofit into existing equipment.

Hope this helps,


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Hi Jbl,

Sorry about my last post, I could have phrased it more politely:) , but I had just been having an "animated discussion " about vocal compression in the pub with a couple of studio engineers!


That pcb layout is Rod Elliot's copyright, and as he contributes so generously to the diy scene I think it would be a bit unfair to copy it.

Vocal compression is also a little more complicated than just limiting, and to get a reasonable sound you need to be able to adjust the parameters of the effect, such as amplitude, threshold, and the way the compression comes into effect, (so called hard/soft knee).

Most compressors are also designed to be used as inserts from a desk, not in line, and as such need a decent signal level to work with.

I have never come across a decent diy circuit, but to be honest, basic units are not that expensive to buy, you could probably pick up one for about $100 second hand.

Once again, sorry for the last post
as pinkmouse said I am not searching to limit the singer. I just want to keep it under control and I have enough experience with compressor to know that it's something that should not be abused of. It just to keep her under control and it's normal my sytem or wathever we will put her on does not have enough power to sustain acceptable nominal level and still be able to play the loud dynamic.


2002-04-28 2:11 pm

"That pcb layout is Rod Elliot's copyright, and as he contributes so generously to the diy scene I think it would be a bit unfair to copy it."

The PCB layout is my own design. Rod Elliott has no design for that particular project - I would never copy his artwork. In fact, I mailed my design to him should he wish to include it on his site.
Compressor chip

If you are going to make a compressor, the SA571 (which I thought had disappeared as the NE571) might be a good choice.

To go better you will have to get a more complicated setup. I don't know if those designs at Rod's can get you a very good quality. There's one based on chips there, if I recall, but it's complicated to build.

Check out this schematic

Got to love Rane, they put their whole product line out there to look at. Decent, mid-range quality pro gear too.

For something simpler take a look at Paia's compressor. It isn't as refined as rane's and I think there are some obsolete parts in it. From memory the Analog Devices SSM21XX VGA's they use are no longer in production.

All that aside, it is pretty hard to justify going to all this trouble when you can buy a brand new Behringer Composer Pro for $90 plus shipping (just do a google search). This is actually a good piece of gear (unlike just about any of their digital products).