attack /decay MODS to orange squeezer ?

[gazza]

Hi All,

I've looked at the schems for the orange squeezer at GGG site and the discussion about altering the envelope follower.

Has anyone changed the OS envelope follower (EF), and if so what did they do and how successful was it ?  

I'm going to build mark hammer's version of the OS at GGG which includes variable gain and a 'bright recovery stage'.  I'll decide if i also need a heavier compressor after that i think, probably an optical one.

BUT I'd also like to add some form of control to alter the attack / decay in the OS.

I'm not at all sure of the best way to do this.   Is it better to try and switch the resistor values in the EF rather than the capacitor ? would pots be overkill here? should i just switch between a fast and a slow setting ?

Also,  has anyone got a schem that shows a full wave recifier in an OS ?

I've had a go at seaching this forum, but I haven't found any other schems yet.

I hope someone can point me in the right direction with all of this.  

cheers all,

Gareth.

[Mark Hammer]

Changes to the response of the envelope follower inthe OS *can* be effective in getting what you want.  Just be realistic about what you expect, since simple half-wave rectifier circuits are limited in their flexibility.

If you follow the signal from the "branch point" after the first op-amp, you will see that it goes through a 1k5 resistor and a diode, with a cap and resistor to ground after the diode.

The diode assures that only one half of the signal passes on to the FET gates.  The cap is charged up by signal, and continues passing on a constantly diminishing version of that voltage for a brief instant until it is fully discharged.  The rate at which the cap is charged up with each burst of signal is determined by what limits the current flow to it, as well as the actual value of the cap.  A much bigger cap would become fully charged to capacity at a much slower rate, and a much smaller one would be full up much quicker.  Since the 100k resistor in parallel with the cap provides a path for the cap to discharge (remember, the cap is acting like a battery here, and the two ends of this "battery" need to have a path to connect to each other), the rate at which the charged cap *dis*charges after a signal impulse is set by that resistor (and the leakage properties of the cap).

So.....if you up the value of that resistor, the decay/discharge time will be longer.  If you hold the resistance constant but increase the cap value, the decay will be longer.  If you insert a small resistance between diode and cap to limit how quickly the cap can become full of current, you slow down the attack/charge time.

The problem one acqures in inserting any variable-attack mod is that anything which restricts current flow will decrease apparent sensitivity - i.e., make the unit behave like you aren't picking as hard, hence producing less compression.  The simple solution is to compensate for that by having variable gain ahead of the rectifier.  In this case, the envelope gain section is the audio path as well.  Smart guy, that Dan Armstrong.

Personally, I try to have as much bang and variation for the fewest knobs that I can.  I love to be able to change things around, but I also want to avoid having pedal controls feel like some sort of combination lock.  So, it is exceedingly rare that I would stick both an attack AND variable decay control on such a thing, though that may be just me.  Given that the decay AND attack time are affected by the value of the cap, I find it provides a reasonable amount of variety to simply have a toggle that can pick one of 2 or 3 cap values.  In this case, being able to tack a 10uf and 22uf cap in parallel with the existing 4.7uf would provide a wide range of squish feels.  certainly the parallel value of 22+4.7=26.7uf would extend decay time/lag out enough to provide extreme squish (might be nice for cymbals, too!).  A small value pot of 500R to 1k would be reasonable to stick in between the diode and cap.

Note that the amount of squish or apparent compression a unit can provide is not only a function of how much it can reduce gain or level, but also how UNresponsive it is to any new transients.  This can not e better illustrated than by the infamous "attack" mod to the Dynacomp.  Although that mod actually alters the decay time of the critical cap in the rectifier circuit, anything you do to make it more likely that the cap will not have finished responding to the last note before the next one comes along, will create the impression of impaired attack.

I suspect one of the reasons why the OS has a reputation for "transparency" is the 100k resistor for discharging the cap.  The result of this, in theory, ought to be that gain/level is reduced for the initial transient of the pick attack (i.e., the big peaks) but the device instantly becomes ready-for-duty for anything else immediately afterwards, rather than still caught up in discharging.  In general longer decay times will increase the obviousness of the effect.

Between a toggle for decay time, a small pot for finer attack-time adjustment, and a variable gain pot to compensate for the attack control, you should be able to get a lot of different personalities out of the unit.

Hope this is clear enough.

[gazza]

Mark,

Thanks for such a clear and considered reply. Very helpful !  

Do you know anyone who has tried to put a full wave rectifier in the circuit ?  How wrong would I be if I tried to add a second diode and series resistor network in parallel (but reversed polarity) to the original diode + resistor ? Or should I run 2 parallel envelope follower circuits (ie the diode 2 resistors and cap). Should the cap be made smaller (halved) if I'm hitting it twice as often ?  

I guess I should make one first and experiment later !

I've decided to have a dan armstrong memorial weekend of pedal building and also make a green ringer.  

cheers,

Gareth.

[gazza]

Doh !   :oops:

just found the schematic for the orange squeezer +++  that has a full wave rectifier !

now I have all the info for a good weekend of soldering.  

Gareth

[Unclerny]

Hey Gazza woudl you mind posting a link to this full wave scheme?

U.E.

[rankot]

Hey Gazza woudl you mind posting a link to this full wave scheme?

It can be found here: http://moosapotamus.net/ideas/os-modified-orange-squeezer/.