Bi-compROSSor, two compressors at once, why?

[octafish]

Well, I have a Mark Hammer mod style ross compressor, based on the tonepad layout, squishing away and it really out-compresses my now absent OS. However I remember a certain something in the tone of the OS that is missing in the ross. So I'm going to build an OS and pop it in the same box ala the Bi-copROSSor.
The Analogman unit has the OS first then the ROSS any ideas why this order? Arbitrary? Or is there some use for seriesed compressors?
My OS was a lot noisier than my Ross, but it was built with ceramics and carbon films whereas the ross uses metal films and poly's. Maybe my rebuild using 1%ers and yellow boxes will be quieter than my original but I can't imagine it'll be silent. Won't the noise from the OS be compressed by the ross making the pedal the hiss king?
Anyone out there familiar with this pedal? Anything to say Mike?

[transient]

Just an idea, if you use compression all the time, you could use just one switch (instead of the two switches like on the analogman unit) and wire it so that it switches between the two compressors. I have an OS, and have plans for building a ROSS as well, i would do it this way. As you said, it probably would be noisy to use both at the same time.

...
emre

[sean k]

Why not use the two as the basis of a parallel loop creater,I'm sure theres a better way to say that,so one input to two compressors and two separate outs.The orange was designed to go straight into the guitar output so it seems to make sense to use two of them in a single box instead of a making two.Also because the OS is such a simple circuit and this allows you to make use of the other half of the 4558.

[bwanasonic]

You should be able to get the OS fairly quiet, or at least I was lucky enough to end up with a quiet build using carbon comp resistors / film and tantlum caps, and without particularly knowing what I was doing. I think the OS-->ROSS order makes sense, although I never toyed with series stompbox comps.

Kerry M

[Mark Hammer]

I remember a certain something in the tone of the OS that is missing in the ross. So I'm going to build an OS and pop it in the same box ala the Bi-copROSSor.
The Analogman unit has the OS first then the ROSS any ideas why this order? Arbitrary? Or is there some use for seriesed compressors?
My OS was a lot noisier than my Ross, but it was built with ceramics and carbon films whereas the ross uses metal films and poly's. Maybe my rebuild using 1%ers and yellow boxes will be quieter than my original but I can't imagine it'll be silent. Won't the noise from the OS be compressed by the ross making the pedal the hiss king?

My sense is that the OS works a little more like a peak limiter than the Ross does.  Why do I say this?  The compression/sustain part becomes more evident the longer/slower the gain recovery.  If you are holding a note, and the gain starts to creep up again as the note is slowly dying out, it *sounds* like sustain.  The OS is designed with relatively fast time constants, such that it cuts the signal in response to the initial attack, but resumes "normal" processing shortly after the initial attack.  The Dynacomp/Ross imposes its "imprint" over a much longer interval, which is why people often comment that the OS is more "transparent".

In a sense, I suppose there is some advantage to being able to have one dynamics controller that tracks short-term volume blips followed by one that tracks longer term volume shifts.  That may produce a pleasing character in compression as long as neither device is maxed out.

One of the "problems" with the OS is that it is, in Dan Armstrong tradition, a simple-but-elegant design, which drops a whole lot of improved design possibilities in favour of the most effect with the least component-count.  One of the consequences of this is that the OS lacks any sort of decent input buffer stage, and finds all the gain in the unit concentrated in one puny op-amp.  In many respects, what it *needs* to be lower noise, is to have a high-impedance input buffer with a smidgen of gain, and an extra gain stage dedicated to the sidechain.  

Huh?  I'll explain.  There is a single op-amp in the stock OS that has a fixed gain of 23 ([220k+10k]/10k).  That gain is intended to provide a reasonable audio output level, AND as reasonable "drive" for the rectifier such that it will produce usable changes in the resistance of the FET.  If you had a gain stage of, say, 5 and a separate op-amp that took that audio signal and boosted it again for the purposes of the rectifier, then you would not be amplifying the hiss quite so much.

Certainly reducing any component-based noise in the input stage of the OS is a good idea, but at least part of why it is such a good idea is because it gets the s**t cranked out of it in the op-amp.  Divide up the signal-boosting work between two devices and the hiss may be less audible.

[Processaurus]

I made a homade bi-comprosser a couple years ago, its a great alternative to having 2 compressor stompboxes taking up real estate, plus they both are totally different.    Its been around...
I put the OS after the dyna/ross, I think the analogman one is that way.  Honestly it never sounded good to have them both on at the same time, at least through my setup.  Way too much...  A couple things I would do differently now if I were doing another bi-comprosser style box:  I've seen some really good mods for changing the release time on the dyna/ross by Mark Hammer around here.  That makes it sound better (it keeps the notes' attack) with humbuckers.  I also wished i'd put extra jacks for the option of ins and outs for each compressor, the dyna sounds awsome with distortions, and for some reason, the OS sounds really weak distorted, I suspect it might be a thing with the ouput impedance, because it sounds like it changes volume depending on where its going in the chain.  Plus its noisy as hell when it has gain added to it afterwards.  I love it for clean sounds, though.  Those are actually totally interesting suggestions Mark made about reducing the noise in the OS by dividing up gain.

[barret77]

nice finish!

[octafish]

Thanks for the replies, everyone. I haven't built the squeezer yet so I may have to try your suggestions Mark re: the redesign of the OS, the dynaross recovery switches are very usefull by the way. I saw a similar mod proposed in another current OS thread. Looks like I'll be breadboarding this one.