bass x guitar compressor: any difference?

[barret77]

Hello all

I'm planning to build a bi compressor (ross + orange) in the very near future;
I would like to used it both with guitar and bass.

Is it suitable to use both circuits in their stock form for bass or are there recommended tweaks - like switchable caps?

Thanks a lot!

[Mark Hammer]

I'm still not sure why anyone needs two compressors if at least one of them has finer control over attack/decay and relative sensitivity over the frequency spectrum.

One of the biggest differences between these two units (Dyna vs OS) is that one - stock - has a slower recovery thanthe other - stock.  You can easily change the response and feel of the Dynacomp via the in/famous 150k resistor and any of the different methods to vary it.  You can also change the feel of the OS as well.  Different feels tend to be more suitable for bass than for guitar (bass tends to like peak limiting more, guitar leans towards constant-volume feels).

The one area where you might want to give some thought is response across the spectrum.  Consider that "bass" can mean a lot of things, including the 5 and 6-string varieties.  Those big thick strings put out a whomping signal, which can effectively result in far more compression for the low strings than for the higher ones.  Of course theproblem that can create is that whomping the low notes for punch can end up with low notes that sound squished and wimpy.  One way to offset that is to shave off some bass content going to the envelope follower/rectifier so that whacking any string results in an approximately equal level envelope signal controlling the FET gate.

If you look at the schematic ( http://www.generalguitargadgets.com/diagrams/orangesqueezer_sc.gif ), you can see a 1k5 resistor feeding a diode.  What we want to do is make that path a little less sensitive to ultra low end.  We can do that by making it less sensitive to everything, then providing a short-cut for higher content only.  I haven't tried it myself, but I'm thinking that the following might work nicely:

1) Remove the 1k5 resistor from its spot on the board.
2) Solder a 4k7 resistor in its place.
3) In parallel with the 4k7 resistor, solder a .22uf cap in series with a 1k5 resistor.

This change will provide less sensitivity for content below approximately 480hz.  That's kind of high, but the rolloff is gentle rather than abrupt.  It should provide very similar sensitivity for content down to 400hz, and noticeably reduced sensitvity down in the 150hz zone.  You can shift that whole range down by making the cap .33uf instead.  Note that since there is no cap in series with the 4k7 resistor, that all low content will feed the diode and envelope-follower.  However this higher resistance will result in reduced sensitivity overall.  The 1k5/.22 network provides a bypass to that not unlike the bypass cap used to compensate guitar volume controls, or used for "brite" switches on amps.

If you try this, let us know what you think.

[barret77]

nice, thanks for the explanation!
I'm going to look for it.

Concerning the need to a bi-compressor, it's not really a need... It's more an "economy plus experiment" - I want to put 2 (or considering 3, since we have that nice lm386 compressor layout around) in a box to experiment the different sounds of each... Like a captain coconut only with compressors...