[Sch+Pics] Tire of that geriatric Ross compressor? Add a fresh young blend knob

[Processaurus]

This is a mod I recently devised for the dynacomp / ross compressor to blend in the uncompressed
signal back in.  I loved the Ross's sustain and quiet behavior, but wasn't crazy about the slow attack
that it seems stuck with, which makes a "pop" on the attack of each note before the compressor
clamps down.  This mod does wonders for changing that characteristic of the pedal (even though that
particular sound is still available, with the blend entirely to the comp side). 



Also the Ross acts as a limiter, being it tries to make everything the same level.  With heavy
sustain settings, it can lose almost all dynamics.  With a little of the clean thrown back in, its
more like a compressor.  Apparently some older rack compressors/limiters were made with this a
feature, dialing some dry signal in with the limited signal to get a "compression". 

It takes more parts than a typical mod, its more of an "add on".  It can be made on a small daughter
board though, mine is  1 1/8"x 1 1/4. Also an unintended but possibly beneficial side effect of this
mod is that the output is now in phase with the input.

Also the Hammer mods are in my prototype too:  a .001 cap in parallel with the 10k resistor before
the volume control, for a bit of treble compensation, and a 3 way center off toggle switch to select
a 33K, 10K and 150K resistors for the recovery mod.  The super fast recovery time, which makes the
notes really pop, works well with the clean blend option.  Another mod I did was change the 56k
resistor in the Vb bias voltage divider to 27K, to make the bias supply 1/2 V+, in an attempt to get
more headroom from the first transistor stage. This is important because this is where the mixer
gets the dry signal.  One could probably also get the dry signal directly from the input, without
any problems.

I'm really excited about how this sounds, especially because I've been using a stock ross clone for
a couple years now. Try it if you aren't 100% happy with your Ross/Dyna clone.  Heck, do it anyway.

Any discussion on the design is welcome, one possibly funky aspect for starters is having the wiper
of the 10K panning pot tied to 1/2V rather than ground, I was trying to save a couple coupling caps,
thats all.  Also getting the dry signal from the first transistor buffer stage rather than the input
could be questioned.  The thinking there was to present the compressor with a lightly higher input
impedance than you would get with the input feeding directly to both stages.  The overall gain of
the effect can be increased by making the feedback resistor (the 56K) of U2B larger.  The gain of
the clean relative to the compressor can be controlled with the feedback resistor  of U2A.  There
were some problems with clipping when using hot pickups with more gain coming from U2A, though. 
Maybe a rail-rail opamp would perform better here than the trusty Tl072.  The notion of putting back
2 back LEDs in the feedback loop of U2A crossed my mind as well, so if it clips it sounds like you
meant it to...


Thanks to the Barber Electronics' Tone Press for inspiration, and RG Keen's panning article at
geofex.

Happy holidays to everyone,
-Ben

[markusw]

Sounds cool!  Thanks for the mod!

Reminds me of the the "April resistor" in the "what compressor".

Merry christmas,

Markus

[petemoore]

of the 10K panning pot tied to 1/2V rather than ground, I was trying to save a couple coupling caps
  I have a Dynacomp Clone, nice box 'n switch 'n LED indicator 'n...that exhibits these characteristics for years, the 'nice sounding' pedal that 'just sits', because it's too limiting, hard to get good Fuzz to work right with it set for compclean without redialing knobs etc.
  The only 'work' I did on the envelope swing rates is twiddle the knob, which is effective [subtle difference maker of course like it should be, have to hit string and listen...], but not 'perfectly satisfying'...mostly I try to tune so I Can't hear what that knob 'does'.
  Blend Clean on this thing seems to be a great option, as does the envelope slope control mods, also the .001/10k to 'bring treble back'. That alone would help conceal the 'obtrusive envelope' the Ross/Dyna sometimes complains about.
  It's a great comp, and as a 2 knob stage comp, the MXR would do it's job very nicely...was especially 'necessary for bass ... 'Mike Rophone' left it on the whole time, two knobs was enough for a set 'n forget item that transformed his HUGE> 2x Hiwatt Custom 200 into 2x SVT cabs Bass Rig...major stage/venue rumbler, I loved switching instruments, using the Moog floor foot keys etc. into a 'tamed, trained monster'.
  It seems my Dynacomp would be suited well for bass, as the high end is rolled off to reduce hiss, and bass provides lots of input for the envelope detector, probably less 'erratic' than guitar?...more often one note at a time etc.
  This mod is sure to make my other two knobs sound more usable over a larger range.
  I think it's time now to pull the Ross from the shelf, and give it the 'thrice over' 'n DC jack...and see how it 'hangs with the gang' after a few mods.
  About the 'extra caps' near 10kpot and the 15k's...I assume the output of Ross a 'la 10k is already DC blocked, perhaps a cap between the two opamps of the mod would be needed, say between u2A output and the 15k...

[Processaurus]

Latest thing I thought of for this, since the mixer is pretty much independant of the compressor, is why does the signal that gets blended with the compressor have to be the clean signal?  One could easily insert a normally closed 1/4" jack at the point on the schematic that says "from q1 emitter" to plug something external in (like a fuzz pedal), and mix that together with the compressed signal. 

     The only downside of this is that the external signal has to be in phase with the compressor input.  If you really wanted to run with this idea, and be able to control the phase of the external signal, you could add a SPDT toggle switch and switch the .47uF input cap between the 100k before the U2a and the 15K after the U2a output.  A 1M pulldown resistor before the .47uF input cap would avoid any pops from switching upstream.

About the 'extra caps' near 10kpot and the 15k's...I assume the output of Ross a 'la 10k is already DC blocked, perhaps a cap between the two opamps of the mod would be needed, say between u2A output and the 15k...

Sure, that wouldn't hurt, and would be the normal way to do things, (see RGs panning article, thats how he has the schematic at the end of the page).  However the way its layed out now has been tested and does work fine.  In the prototype I did use a 4.7uf for the Vb supply rather than the 22uF, I made it bigger in the schematic to let less of the signal bleed into the opamp's non inverting inputs.

[Processaurus]

Here's the prototype, the insides are rough, but the rougher the better, I say.  Bought the PCB from BYOC, OMG.  The mixer is inside the electrical wrapped part (I know, so bad...).  One justs loses enthusiasm at the point when everything works and is awesome and its time to figure out a responsible way to anchor all the electronics in there.  The PCB is stuck on well, though, with that screw through the top and on a standoff.  Its insulated too with some shrink tube because the mounting hole on the PCB is used as a via for some part of the circuit.  Didn't realize that for a while because everything worked, it just sounded crummy.  Then I figured out some stuff was shorting out on the mounting screw, blaagh.  The jack in the back is for the external input to the mixer.  Those 16mm pots are great, because an unplanned jack can fit under them, if you decide to add something extra.  I was all pro and drilled little locater holes for the tabs that stick up on the pots, and then realized that they stuck out farther than the knobs I wanted to use, hence the stickers to cover up those holes.  They're made from sticker material I found in the dumpster of this place in my town that makes roadsigns for the state.  The locater holes are kinda nice though, its cool being able to tighten the pots down without trying to grab them from the back.  It feels like they aren't going to get loose over time, because any torque is on the tabs.  The box is one of the powder coated ones available from Small Bear.  $10, a real deal.  Only downside of that is I had to drill out a couple of the countersinks in the lid until metal showed, in order to ground the lid with the screws that hold it to the main box.  Not a big deal.
Still way easier than sanding & priming & painting & clearcoating & getting pissed because the paint chips.

The foam is original, straight from Jimi's favorite Fuzz Face, exhumed from his grave.

[Sindran]

I build that blen-mod and wanted to give some feedback if someone else is also interested in building it.

..Well, it does exactly what it's supposed to do.
Works really well and together with the variable recovery mod it gives tons of new sound possibilities to Ross compressor.
This mod is VERY usable IMHO.

Big thanks to Processaurus for original schematic.

[rove]

Does anyone have a vero layout for the blend mod described above? just did the more treble and input cap mods and about to dive back in and add a power jack and a larger output cap, figure I may throw in the blend circuit as I think there's plenty of room, just not sure how to lay it out.
thanks!
Paul

[markm]

I have a PCB -or- a Perf layout to offer you in my gallery, can't help with the vero though.

[rove]

Thanks, I don't mind giving it a go on perf... been wanting to try this blend circuit out for a while.
Paul

[willie.moore47]

I have a PCB -or- a Perf layout to offer you in my gallery, can't help with the vero though.

Do you still have this layout available? I'd be interested in seeing it

Sent from my SM-G903W using Tapatalk

[Ben N]

So, Jimi was buried with his FF. Kewl!

[Eparker]

I have a PCB -or- a Perf layout to offer you in my gallery, can't help with the vero though.

Do you still have this layout available? I'd be interested in seeing it

Sent from my SM-G903W using Tapatalk

Here you go willie.

https://www.aronnelson.com/gallery/main.php/v/MarkMs-Gallery/album15/album76/ROSS_Mixer_LAYOUT.gif.html


Has anyone had any issues with this blend reducing the volume? I can get a great blend but it is so quiet. Going into the mixer board it is much louder. I ended up adding this on to a keely 4 knob and it unfortunately is killing the volume.

[amz-fx]

BYOC added a gain stage after the mixer resistors on their version of the Ross, and I made a mod to it that reduces distortion. Check it out at:

http://www.muzique.com/news/mod-the-byoc-5-knob-compressor/

Be sure to use the modded resistor values for the gain stage for the cleanest sound.

regards, Jack

[ElectricDruid]

I have a PCB -or- a Perf layout to offer you in my gallery, can't help with the vero though.

Do you still have this layout available? I'd be interested in seeing it

Sent from my SM-G903W using Tapatalk

Here you go willie.

https://www.aronnelson.com/gallery/main.php/v/MarkMs-Gallery/album15/album76/ROSS_Mixer_LAYOUT.gif.html


Has anyone had any issues with this blend reducing the volume? I can get a great blend but it is so quiet. Going into the mixer board it is much louder. I ended up adding this on to a keely 4 knob and it unfortunately is killing the volume.

Increasing the 56K feedback resistor on the final crossfader/mixing op-amp stage should increase the level. The 15K/56K values compensate for the loss in *that* circuit, but don't compensate losses anywhere else. Try 100K instead for starters.

Edit: If the circuit was the right volume before the mod, and it too quiet after the mod, I'd suspect a fault. There's nothing in the crossfade circuit that should seriously reduce volume.