Rolls CL151 mic pre comp adding a 80hz low cut???

[screamersusa]

Schematic here...  http://www.rolls.com/pdf/M_CL151.pdf

I am looking to add a 80-100hz low cut as steep as reasonably possible
after C14 between the mix pre and compressor section.
Could someone point me to a circuit that will work within the unit using
its existing power scheme.

The box is really usefull as a mic preamp BEfore many vocal effects boxes because
the compressor circuits in most of them are awfull. ESPECIALLY TC helicon.
Using the cl151 before them makes them usable and you can see what the heck is going on.
TC uses an automatic adjustment that goes wacky when you get too close to the drums
or anything louder than you, and the folks at Boss don't even know how the VE20 "dynamics"
knob works or what it does...
The only thing that is seriously missing in the 151 is a pre compression low cut to make it
a compact MUST have for a gigging singer.
Thanks in advance.

[Quackzed]

i'd probably just lower c14 by ear, maybee .1 for starters then .18 or .22 if that was too much... it's not steep -6db per octave single pole low pass filter, but easy to try... if you needed steep you could remove c14 and use the 2 spots where it was to insert a dual or triple high pass filter for steep, thats a cap in series then a resistor to vb. ,then another same cap in series and another same resistor to vb, for dual and another same thing for triple etc...

like that where the furthest left top point was left side of c14 on schem and the furthest right top point was the other side of c14 and the bottom lines all go to a vb point.
but making c14 smaller by ear will probably be fine and is alot easier to try... 

[PRR]

The path through C14 does not feed the noise-gate side-chain; I dunno if that is important.

I see C27, feeding everything.

However C27 feeds a variable  resistance R11+P4, so the corner will move.

ROLLS has really-really streamlined this box, so you really can't add ANY added features/filtering.

I would break at C27, go off to any simple one-opamp low-cut filter, and back in. You have power and Vb. You may not have space.

[screamersusa]

I was thinking of a single op amp circuit. I've done the c14 trick on a VX400 and another box but
the rolloff was not steep enough. I figure someone has done this for a distortion box already with a single
supply.  (I actually wanted to use one in a distortion as well)
I would mount the filter on a bypass switch so making room won't be a problem.
I was going to just use the mackie 1400i low cut but its dual supply.
I have the switch craft xlr low cut but the freq will change if I switch from a
wired mic to wireless due to impedance. I Dont feel like modding that thing unless
dropping half of it into the rolls would do the trick with the impedance compensated for.

[screamersusa]

Im trying to keep my vocal rig down to two boxes and psu's as I play both
guitar and drums. I've done the full rack thing and it was too much to lug for
live use.

[PRR]

> use the mackie 1400i low cut but its dual supply.

Any dual-supply audio circuit can be implemented single-supply.

Especially in a low-cut filter, because the input DC-block cap(s) are already there for bass-blocking function.

[bool]

Personally, I wouldn't mess with any "addons" here.

Instead, I would only change 2 caps:

C27 to 1uF (or 2.2uF if 1uF gets too "tight")
C14 to whatewer your tests show as "OK" (I think it may be 220nF). Actually, I would make it switchable (like in some fuzz circuits, guitar fx etc), so 220nF in-circuit + 1uF on the switch

Why?

If you look at the schem carefully, you will see that the RC "thingies" around U2A, Q3 are pretty "HPF'ed" already, so I am not led to believe that killing the bass outside of the gate detector circuit (ie. with C14) will change the gate behavior in a significant manner. The compressor gets it's feedback signal downstream the C14 so all is good there.

edit: correction

[Mark Hammer]

I need some clarification here.  Is the objective to just keep any and all deep bass out of the audio and the control path (i.e., sidechain)?  Or is the objective to keep it in the one but not the other?

If the answer to the first question is Yes, then you can just reduce the values of C1-4 and C27, C14 and C18, and be done with it.  As long as you choose the cap values well, you're home.

[screamersusa]

Sorry to come back so late.. life's been busy...

The idea is to add a stable steep low cut filter to the whole circuit like in a high quality mic pre.
I'm using the 151 to feed a voice effects box (ve-20) etc and want to pre condition the mic
and SEE the gain reduction live thereby eliminating the mic pre, low cut and compressor in the vocal box.
Boss has no idea what the dynamics control does or how it works or if the low cut is dynamic or stationary.
The inputs on these voice boxes are not designed for use by a real sound engineer.
This also provides a pre conditioned clean feed when the soundguy wants one.
Id like to keep vocal warmth so a 6db may not work.