Building a ross comp with attack control?

[spiderman2812]

If you were building a ross comp and wanted to add an attack control where on the board would this be done and what size and type of pot would you use? Per this lay out?
http://aronnelson.com/gallery/album77/ROSS_comp_LAYOUT_perf?full=1

[alderbody]

Run a search for Ross/Dyna comps. There's a "standard" pack of Mods for that circuit and they all make a difference.

Can't remember exactly, but i'm sure someone will post the links.

btw, here's my comp with all those mods (interchangeable)



sorry for the bad pic    I will re-shoot some new ones soon.

[Mark Hammer]

The "attack" on the Ross/Dynacomp is something borrowed from a number of other pedals, such as the Boss CS-2, and Pearl and Nobels Compressor, that use essentially the same circuit.  Jammed between 3 of the 5 transistors on the board is a 150k resistor between V+ and a 10uf cap to ground, and that 10uf cap.  When the resistance is smaller, the cap recharges up again faster after it has been essentially discharged by the envelope signal.  When it recharges faster, the circuit returns to its maximum default gain, from the reduced gain it went to in response to the sudden transient.  That's what the unit does.  It starts out at max gain, retreats in response to picking by reducing gain, and gradually creeps back up to max gain when it is allowed to.

1) This is not, and never has been, an "attack" adjustment, despite what numerous companies have labelled it as.  It adjusts the post-transient recovery...but that's longer to print on a box than "attack" and doesn't sound nearly as sexy.
2) This resistance should not be lower than 10k or so, and higher than maybe 250k (though probably lower).
3)  The impact of adjustments will depend fundamentally on your picking style.  If the recovery time is set to its default value, then you won't hear any of the initial "attack" in subsequent notes IF you play a bunch of them fast in a row (maybe that's why they label it "attack").  If you wait long enough, you WILL hear the attack of the next note.  Slower recovery times will appear to make the unit less bright in some ways, for those who like to play fast.
4) The distinctions in recovery times are generally difficult for most people to hear, especially since the inter-note interval will vary so much of the time (no one plays at exactly the same speed all the time).  Personally I found myself using the one extreme of the knob or the other, so I figured to hell with it, and went with a 3-position toggle.  It's repeatable, cheaper than a pot+knob, and takes up less room on the panel and in the chassis.  Some people LIKE continuous variability, though, and you might be one of them.  Me, I'm quite happy with fast (10k), medium (39k), slow (150k), and you might be too.

[markm]

You can find these mods detailed over at FuzzCentral.
I did a FuzzCentral ROSS Comp Layout a couple of weeks ago and sent it to Phillip and right now I'm just waiting to hear back from him as I was hoping we would want to post it on his site. 
Maybe I'll email him and see what's up.

[Jay Doyle]

1) This is not, and never has been, an "attack" adjustment, despite what numerous companies have labelled it as.  It adjusts the post-transient recovery...but that's longer to print on a box than "attack" and doesn't sound nearly as sexy.

Ummm... In other words... 'Decay'? 

Here is the short version of what happens:

Without a signal present, the 10uF cap (integrator cap) charges up to V+ through the 150k resistor because the FWR transistors (the ones with the diodes on their bases) are completely off. With the onset of a note, those same transistors turn on and turn on HARD because they are set up for massive gain (no emmiter resistors and 150k on the collector) which gives the 10uF cap a path to discharge through the emitters, this is the 'attack' and it happens near instantaneously, because the emitter resistance is on the order of around 50 ohms. With the signal removed, the transistors turn off again and the 10uF cap slowly charges back up to V+ and max gain. In between 'on' and 'off' the 10uF cap with charge or discharge acordingly controling the gain as necessary (in a lot of cases it is just easier to think about a circuit at its two extremes, in this case on and off).

SO, the attack is the discharge and is controled by the parallel emitter resistance of the FWR transistors. The decay is the recharge and is controled by the 150k resistor.

It would seem at first blush that simply adding a 5k or so pot to both of those emitters would allow you to add an attack control, and that is true, EXCEPT that in doing so you reduce the gain quite a bit as that 5k pot is turned up in resistance and will effect the action of the FWR.

To get around this, put any standard A/D network between the 150k resistor and the 10uF cap.

Hope this helps a little,

Jay Doyle

[markm]

Interesting info Jay, thanks!
Compressors really interest me considerably which is why I've built so many!
If the 10uF cap were increased in size, that would effect recovery as well wouldn't it?

[Jay Doyle]

Interesting info Jay, thanks!
Compressors really interest me considerably which is why I've built so many!
If the 10uF cap were increased in size, that would effect recovery as well wouldn't it?

It will affect BOTH attack and decay (recovery). That cap is the key to both; its discharge is the attack and the recharge is the recovery. For that reason a tant cap is my choice because of the lower leakage than electrolytics.

Keep in mind that this doesn't effect the tone at all, just the action of the gain control.

Regards,

Jay Doyle

[markm]

Interesting,
Thanks again Jay! 

[tmuka]

I put a 3-way switch in my old dynacomp tonight for "attack" control - it's nice to have some control over what sounds to me like the amount of "squish"... I think this pedal will definately see more action now in the 39K attack position!  thanks mark h, and all!

[MartyMart]

That cap is the key to both; its discharge is the attack and the recharge is the recovery.
For that reason a tant cap is my choice because of the lower leakage than electrolytics.

Keep in mind that this doesn't effect the tone at all, just the action of the gain control.

That's the reason that I used Tants in my Dyna/Ross last year, IIRC I played with that resistor/cap
area and ended up with an 82k and a 6u8 tant cap.
It seems a nice "medium" response that works well for anything IMO

MM.

[deeruss]

It would seem at first blush that simply adding a 5k or so pot to both of those emitters would allow you to add an attack control, and that is true, EXCEPT that in doing so you reduce the gain quite a bit as that 5k pot is turned up in resistance and will effect the action of the FWR.

To get around this, put any standard A/D network between the 150k resistor and the 10uF cap.

Hope this helps a little,

Jay Doyle

Can anyone explain what a standard A/D network is ?
Thanks

[merlinb]

A/D = attack / decay. A standard network has a series resistor feeding the storage cap; this controls the attack. There will also be a resistor to allow the cap to recharge (or discharge) again, which controls the 'decay'. This resistor may be to ground or to the supply voltage, depending on how the side chain works. However, the word you're looking for is not decay but release. Decay is what's used on envelope modifiers, known as ADSR (attack, decay, sustain, release). Only the first and last apply to compressors.

[deeruss]

Thank you.
Why adding another resistor if the 150K is already used to charge the 10uF cap ?
Does adding 2 resistors between 2N3904's (Q3&Q4) and ground to control the attack will reduce gain ?

Sorry I tried to resize it bu it didn't work.

[Mark Hammer]

R13 in your drawing determines how quickly C8 charges up again, after the initial transient.  The voltage/current presented from C8 determines the gain of the 3080.  So if it charges up quickly, with a lower value of R13, then the max gain is restored/"recovered" quicker.  I can't do the math, but 150k provides a long-enough charge-up time that the gain is restored gradually, to provide what feels like long sustain.  I installed a 3-way toggle on a friend's Dynacomp, to add two different parallel resistors to change the effective combined parallel resistance to around 10k, somewhere in the low 40s, and 150k, and he loves it.  When you pick faster, having the gain fully recovered before you pick the next note, allows you to hear the initial attack of the note better.  So it does not affect "attack", but just lets you hear it better.

Some folks feel they are somehow missing something by not having a continuous control, as if 3 switch positions "limits" them.  Trust me, what you hear will depend SOOOO much on your picking speed, that even if you had a 10-turn pot, you'd likely leave it at either minimum or maximum setting 99% of the time.  EHX went with a 3-position switch for the Soul Preacher.  I think they made the right call.

[PRR]

[Mark Hammer]

Looks like it will work.

[deeruss]

Thank you, it clearer now.

[Fancy Lime]

...
Some folks feel they are somehow missing something by not having a continuous control, as if 3 switch positions "limits" them.
...

For DIYing I prefer pots over switches, not because I need the continuous control (as you correctly pointed out, hardly anyone ever does, when they are being honest) but because it involves fewer parts and less soldering and I'm a lazy mufferfuzzer. But from the user perspective, a 3-way switch is often more practical.

What I like a lot in compressor side chains of this type, is a switch to change the C8 cap value. This influences attack and decay in the same way (making both shorter or both longer), which is often what I want. Short attack, short decay is subtle and unobtrusive, long attack and long decay is good for a heavily breathing "damn right I use a compressor" sound. But others like independent controls. Matter of taste, I suppose.

Cheers,
Andy

[Mark Hammer]

And that's why there are so many different compressors out there.

[rankot]

Attack unrelated, but there are lots of wise folks here, so why not to ask: in case of using LM13700 instead of CA3080, is it necessary to use that 2k trim pot which was used to balance inputs of a CA3080? What else can be removed in that case?