Ross Compressor Mods (Mark Hammer?)

[phillip]

Before I drill the Hammond B box for my Ross Compressor clone, are there any mods that I should drill the box for, other than the Ross/Dyna switch at TonePad?

I think that I'm going to add a "decay" or "attack" pot (not sure what it should actually be called...) to the pedal by changing the 150K resistor on the collectors of the FWR into a 50K resistor and a 100KB pot, as suggested by Jay Doyle.  Is this a good mod?

Any other Ross Comp. mods?

TIA!
Phillip

[Mark Hammer]

The "attack/recovery" mod does make the pedal a little more flexible. in terms of suiting it to a variety of playing styles and material.  It can be done via a pot or a toggle.  In my own tinkering, I personally found little use for anything other than the extremes of the control, but as noted, the intent is to allow the circuit to adapt better to different styles, so it's possible I don't have enough of them to warrant greater variety of attack/recovery settings.  

Those companies that have implemented a variable "attack" control for what is essentially the same circuit (see the BOSS CS-2) use a 150k pot in series with a 10k resistor.  So, the max resistance setting (longest recovery time) is 160k and the fastest recovery is set by a 10k resistance.

My sense is that meaningful changes in recovery time need to be proportionally similar.  The pot+resistor values suggested by Jay, while realistic in terms of actually being obtainable parts (I'm imagining trying to order a 150k pot at Radio Shack, here), do not really provide the degree of variation needed to produce much perceptible difference between the two extremes of the pot.  If 10k is the minimum resistance,  and 160k the max, then adding 33k or 150k on top of 10k (via a toggle-switch) will yield resistance values of 10k, 43k and 160k.  So, roughly a 4:1 change. in each position of the switch.

If you use a 3-position on-off-on SPDT toggle for this, then the sensible way to wire it up is as follows.

a) Replace the 150k resistor on the board with a 10k+150k pair in series, installed like a "St. Louis arch" with their junction pointing up; be sure to leave a little extra lead from the 150k resistor sticking out on the component side of the board, which you'll need for the other steps below.
b) Run a lead from the junction of the 150k+10k pair to the common (centre lug) on the switch.
c) Run a lead from the other end of the 150k resistor to one of the outside lugs on the switch.
d) Solder a 39k resistor from the unused lug of the toggle to the other *outside* lug.

Done.

When the switch is in the centre position, it isn't connected to anything, so the effective resistance is the sum of the 150k and 10k resistors, or 160k.  When the switch is in the side position where it connects directly to the other wire going to the board, it shunts the 150k resistor, making the effective resistance 10k.  When it is switched to the other side position, you have a 39k resistance placed in parallel with the 150k resistor, yielding a combined parallel resistance of 30.9k, which yields around 40k when summed with the 10k in series.

Voila, a simple and easy fast/medium/slow recovery control with very little modification to the board, a small footprint for installation into smaller enclosures, lower cost than a pot+knob, easily repeatable settings, and meaningful differences in settings.

Where you will notice the difference in settings will be when you try to play faster, while still maintaining pick attack.  The stock setting yields nice long sustain/compression, but at the cost of not being able to respond to new notes with any rapidity.  The upshot is that you may not be able to hear the difference until you start trying to pick differently.  To the best of my knowledge, there is no impact on any of the other tonal characteristics of the pedal, although if you feed it a noisy signal the faster recovery will mean that the input hiss comes back to you sooner.

Enjoy.

[phillip]

Thanks for your help again, Mark!  I'm glad that we have someone who knows their stuff about compressors

I'll try both methods of the attack control.  Mouser didn't have a 150K, 16mm pot like I usually use, but my handy dandy calculator says that I can put a 374K 1% metal film resistor in parallel with a 250K pot (which is wired as a variable resistor), which works out to be 149840 ohms...about as close to 150K as I can get, given the tolerance of all the parts...pots are especially loose in tolerance it seems.

I have a  SPDT on-off-on switch sitting around waiting, so I'll build the circuit in an old Hammond BB box, which is drilled for several different control layouts.

Phillip

[Mark Hammer]

I don't think you need to be THAT precise, but clearly precision is easily obtainable.

I guess my primary concern with use of a pot is that you don't want to end up with the most useful differences squeezed into 10% of the pot's rotation and the rest doing diddley squat for you.  Remember that what we're trying to adjust here is *time*, and time will most certainly be perceived in a logarithmic manner, just like volume.  That means that the *proportional* change from the leftmost setting on the dial to the middle, should be roughly equivalent to the proportional change between the middle and rightmost position.  With the switch arrangement I described earlier, it's a no-brainer.  It's certainly obtainable with a pot, but based on the actual taper the pot comes with, you may need to incorporate several parallel resistors to get the taper you need.  For example, one resistor on one leg, another on the other leg and maybe even a third straddling the two outside lugs.  If 150k was a "normal" value it wouldn't be such a problem, but once you veer in territory where parallel resistors are needed to "convert" a pot, all bets about actual taper are off.

On the other hand, 150-160k may well be a compromise value to begin with.  If you have a 250k pot right now, why don't you do a listen test to what goes on in that over-160k zone.  Who knows, maybe it is something useful, in which case we can skip all this parallel resistor crap.

[phillip]

I think I'll use your switch mod, Mark.  I thought for sure that I had a 250K pot laying around, but it turns out that it was only 25K...I knew it had a 2 and a 5 in there though

Thanks for all your help!  We should really "chronicle" all these mods for the Ross Compressor for future reference by everyone.  I have a .txt file that has various comments and improvements about the Ross Comp. that's been very useful.

Phillip

[phillip]

Mark, is the schematic below correct for your mods?  I highlighted the modified parts in red:



I've modified the TonePad layout to accept the extra leads and extra resistor, but I'll have to jumper two of the pads together...it was so tight that I couldn't get another trace in there!

Phillip

[Mark Hammer]

That is absolutely correct.  On behalf of the pantheons who are sure to ask the same question all over again...and again and again, many thanks for the drawing.

[john1056]

On tonepad all diodes are listed as 1N914, where did the 1N4001 come from? does the "a" in 1N914a matter?  

Thanks,
John

[phillip]

The 1N4001 replaces the 1N914 in the "D1" position on the TonePad layout, which is there as a reverse polarity protector...in case the battery is accidentally reversed or if the power adapter has a reverse polarity tip (I've seen that happen a lot!).

A 1N914 wouldn't last a heartbeat in that position if the polarity were reversed...especially if it was a power adapter, but the 1N4001 will last a  little longer (since it's a high voltage/high current rectifier), giving the user enough time to figure out what they did wrong.

As far as I know, the "A" suffix doesn't make a difference in this circuit, it's just very readily available.

Phillip

[bsmcc2010]

sorry to revive an old thread-just really interested in this mod.

I built a dynacomp yesterday and the only thing it is missing it doesn't give that really heavy chicken picking sound (not sure whether i need to increase or decrease the attack for that)

So i was thinking of using a 3 way toggle switch for slow, medium, and fast attack speeds. For some reason i can't view the schematic that you posted.

Any chance of posting a photo of that schematic as a layout? thanks

[Mark Hammer]

Don't have the drawing handy, but here's what you do:

Step 1:  Build a Dynacomp/Ross, as per the stock schematic, making sure to install the 150k resistor "a little high".  That is, don't snuggle it close to the board, but install it with a wee bit of component lead lifting it off the board on each side/end; just enough to wrap the stripped end of a wire around.

Step 2:  Identify the solder pads for the relevant 150k resistor on the copper side and temporarily connect a 12-22k fixed resistor in parallel with the existing 150k.

Step 3:  Play around with the pedal for a bit and determine if it actually does what you want.  Set your chicken-head to 11 and pick your brains out.

Step 4:  If Step 3 passes the test (and there is no absolute assurance it will), then you will want to install a 3-way toggle (SPDT, on-off-on).

Step 5: Solder one end of a 12k resistor to one outside lug of the switch, and one end of a 56k resistor to the other outside lug, leaving a little bit of lead so that you can bend those resistors inward a bit.

Step 6: Solder the free ends of those two resistors together.

Step 7:  Run a wire from either end of the 150k resistor on the board to the centre lug of the toggle, and a second wire from the other end of the 150k to the junction of the 12/56k resistors.  Boom, you're in business.

This should yield stock (middle) and fast/medium (two outside positions) recovery times, with the medium roughly equidistantly situated between slow and fast (in terms of ratio)

[bsmcc2010]

ok cool that sounds fine,

i was also thinking about wiring 2 different value resistors across a DPDT toggle like this:

-  - resistor 1 goes across these 2 lugs
-  - 2 wires from the solder pads go here
-  - resistor 2 goes here

might try both, see what happens.

In terms of sounds, will a lower value resistor give a mire compressed sound? or is it a larger value resistor to give a more compressed sound?

[Mark Hammer]

With a larger value resistor, the storage cap gets charged back up more slowly, yielding what appears to be longer sustain.  With a smaller value resistor, the cap charges up quickly so that the gain applied to notes n+1, n+2, n+3...etc., is pretty close to the gain available to note n that temporarily forced the gain downwards.

Hundreds of people are lined up outside a doorway, and you're standing inside the room at the other side, unable to see outside.  A person standing at the doorway shouts at the person standing at the head of the line "Down on your knees and crawl!", and immediately goes quiet.  How tall are all the other people in the lineup that enter into the room?  Well, pretty much as tall as they are.

Okay, now imagine the same scenario and the person shouting stands outside the door and shouts at the first couple of dozen people "I want you all to go down on your knees and crawl!".  As the person inside the room watching, how long will it take you to tell how tall they are?  Chances are, there will be a couple of dozen pass by before they resume their normal height.

That's the difference between fast and slow recovery times.

[Beo]

Bruce, your "Hammer" mod is here:
http://fuzzcentral.ssguitar.com/ross.php

[bsmcc2010]

ok i understand that-and i get that what people usually call attack is not attack but recovery time if that's correct?

so would you increase or decrease what people call "attack" to get a more chickin pickiny sound? and does increasing the attack mean a smaller resistor or a larger resistor?

[artifus]

so the what's the what now?!  

http://en.wikipedia.org/wiki/ADSR_envelope#ADSR_envelope

chickin' pickin' would require a slowish attack time to allow for the initial percussive attack of the note to pass through unattenuated.

http://www.soundonsound.com/sos/1996_articles/apr96/compression.html

[Mark Hammer]

Faster picking requres a faster gain recovery time which requires a smaller resistance value to permit the cap to charge up again faster.

[davidwhitcomb]

Hi.
I'm new to this Forum... Looks like this is a pretty old topic, Don't know who's still around. Just got myself a Dyna Comp from a friend.

YES. I'm finding that this pedal is very LIMITING in it's functionality (Pun intended).

Anyways, here's my Question: I'm wondering about a sorta middle-of-the-road/ minimal/ EZ mod. where I just replace that 150k resister with, say, a 100k, or 88k.
So, no switching/ pot options... Would it end up being a sorta compromise between the extreme settings? I dig the pedal, just think I'd like it permanently set to: NOT-SO-EXTREME.

Don't know if this makes sense... Thanks in advance for any advise.

d-

[davidwhitcomb]

Oh...

Guess while I'm here:

This thread is obviously about attack/ release mods...

Any one know about a mod to control/ roll back on the ratio? Just wondering, because I like monkeying with stuff.

I'm finding that this little guy is most useful to me in the almost-off setting ("sensitivity' practically all the way down)... I was already 'warned' that the Dyna Comp is not a "set-it-and-forget-it" compressor pedal... Which is what I guess I'm looking for... The obvious answer is to invest in a Boss CS.

My basic "tone" is Strat, straight into a Vox Ac15 (mostly clean), I'm hoping for something to subtly even things out a bit, while maintaining a 'clean' tone (I.E. Yes, I want to 'cheat': I want a pedal that will even out my un-even playing technique).

Thx

[Mark Hammer]

Well, I'm not dead, so I'm still here.

If you play slow, and what you want is for single notes to seem to last longer, just leave the damn thing as is.  If you often pick faster, you will likely want to reduce that 150k resistor.  I recently modded a buddy's current-issue Dynacomp (LM13700-based, not CA3080; many thanks to Jeorge Tripps for the needed info) for stock-vs-fast, with a simple SPST toggle that straps a second fixed resistor in parallel with the stock 150k.  He loves it.  Much brighter sounding.  However, it does NOT alter the compression ratio.

JC  Maillet has a few suggestions for improving the audio quality of the basic circuit:   http://www.lynx.bc.ca/~jc/dynacompSchematic.gif