Orange Squeezer

[adding_to_the_noise]

Hey, I'm working on an orange squeezer, and am planning to make both trim pots regular pots on the enclosure. From what i understand one is a level and one is an attack/release control. The problem is, the schematic isn't labeled and I don't know which on is which! Can anyone help me?

[oldrocker]

I believe that the original pot mounted outside the enclosure is a volume for the pedal and the trim pot set the compression amount off of the Jfet drain.

[brett]

Hi
IMO there's little or no point in putting the trimpot (associated with the JFETs, and usually inside the box) on the outside of the box, because it is used to get the circuit "going".  In other words, you "set and forget" this resistance.  Volume is a different matter all together, and you'll almost certainly want to control that.
cheers

[oldrocker]

I agree with Brett,  there's a kind of sweet spot to get the best sound and the rest of the trim pot travel is useless after you tweak it in to get it working right.

[markm]

I agree with Brett,  there's a kind of sweet spot to get the best sound and the rest of the trim pot travel is useless after you tweak it in to get it working right.

+1!

[jaytee]

Would these work? The 1k being attack and 50k compression.
http://i199.photobucket.com/albums/aa115/jimi_026/orsqzcontrols.jpg

[markm]

Would these work? The 1k being attack and 50k compression.
http://i199.photobucket.com/albums/aa115/jimi_026/orsqzcontrols.jpg

Not quite sure what you're doing there. 
If you want an OS with a compression control, check the Soul Preacher!

http://aronnelson.com/gallery/album76/Soul_Preacher_revision_7_LAYOUT

[Mark Hammer]

The attack control will work, but whether it will be noticeable is another thing.  More noticeable, generally, are decay/recovery controls that determine whether the gain reduction you've imposed lingers over from the previous note to the next ones.  In this case, that would be a resistance to ground in parallel with the 4u7 cap.  Something like a 10k fixed resistor in series with a 500k/1M pot would be about right in terms of providing enough range of control.  If you want more Dynacomp-like sustain, then perhaps swapping out that 4u7 cap for a 10uf or even 22uf might be appropriate, as long as you pair it up with the suggested recovery control.

The trimpot adjusts the parameters of the FET so that it becomes an automatic volume control in conjunction with the 82k input resistor and should not be reset even though the recommendations for its optimum setting might make it sound like it's the "compression amount" control.  The best way to set the degree of compression is with the drive/gain level in the op-amp itself. 

Remember that the FET doesn't change its resistance until the audio signal that passes through the diode (which will only pass one half cycle from the signal, making what's left function like a level indicator or "envelope" voltage) exceeds the forward voltage of that diode.  It is that voltage applied to the gate of the FET that sets everything in motion.  There are two ways it can exceed that voltage: 1) by you picking hard and delivering a hot signal peak, and 2) by the gain of that op-amp keeping the dying moments of that plucked/strummed note/chord high enough in amplitude to be above that forward voltage.  Of course, once the envelope voltage coming off the diode turns the FET "on", the FET's resistance drops and the 82K resistor and FET attenuate the input signal.  Like ANY amplifying device, if the signal reaching the op-amp is modest, and the gain applied at the op-amp is low, then the output signal of the op-amp will also be quite modest; in this case not hot enough to exceed the forward voltage of the diode.  At that point the FET turns "off" and the momentary reduction in level, that creates the illusion of constant volume level, ends.  The 4u7 cap hangs onto that last bit of the envelope voltage for a little while and applies that voltage to the FET so that the on/off transition is gradual rather than abrupt.  The suggested decay/recovery control allows you to vary how long the transition takes.  If the path provided to ground is lower resistance, then the cap drains off quickly.  If the path is high resistance or even open, then the cap drains off at its own internal rate or at whatever rate is feasible given all other available paths to ground.

As you may be able to tell by now, applying more gain in the op-amp itself will allow you to have the envelope voltage exceed the threshold imposed by the diode for a longer period of the note's life, instead of just the initial transient peak.  If you have enough gain in the op-amp, then even when the resistor/FET "volume pot" has turned down the input signal going to the op-amp, the output will still be hot enough for a long enough period of time to pass through the diode, keep the FET turned on and the FET resistance low. 

What kind of gain change should you be looking at?  Stock, the OS has a gain of x23 in that op-amp stage (220k feedback resistor, 10k to ground).  If you replace that 10k resistor with a 3k9 resistor in series with a 25k pot, you will be able to adjust between gains of x8.6 (suitable for applying light compression to very hot signals or line-level signals) and x57.4 (compression when you even THINK of playing).

Of course, everything has a price, and the price you pay for this is that as you turn up the gain for more compression, you will also need to turn down the output level.  Also, in the tradition of every stompbox compressor, when you stop playing the gain is applied to the full (unattenuated) level of whatever your signal happens to be at that momemt.  When the op-amp gain is set to x57, then that means every little smidgen of hiss and hum arriving at the input jack will be boosted x57.  Ouch!!    One way to offset this is to feed the pedal as clean and quiet a signal as you can.  Another strategy is to stick a small value cap (e.g., 470pf) in parallel with the 4M7 resistor on the front.  Another is to use metal film resistors for the 4M7, 82k, 390k and 470k resistors ahead of the op-amp.  Finally, if you have no plans to use the pedal for anything other than compressing electric guitar, consider sticking a small cap in parallel with the 220k feedback resistor to limit high end.  A 100pf feedback cap will roll off above 7.2khz, which should leave all the "bite" intact and tame some of the useless crap that features prominently in the hiss.  All these changes can be used together or one or two at a time.

I can verify that the mod works as intended.

[jaytee]

I see what you mean about the 50k pot it would only have an effect when the diode is conducting. I havn't tried the attack control so I don't know how much effect it has.

[markm]

I see what you mean about the 50k pot it would only have an effect when the diode is conducting. I havn't tried the attack control so I don't know how much effect it has.

You could do a search on the BB for the OS +++ which was a heavily modded Orange Squeezer.
I can't say how good it was -or- is but, it's around.

[Mark Hammer]

I see what you mean about the 50k pot it would only have an effect when the diode is conducting. I havn't tried the attack control so I don't know how much effect it has.

The trouble with that type of attack control is that it limits the amount of current in the envelope signal.  The result is that as you increase attack time by increasing that series resistance, you also decrease the amplitude/strength of the envelope signal and by consequence the strength of the gain reduction effect.  You CAN implement it without such a penalty if you you do it in moderation.  The question then becomes whether the variations in attack time which are attainable with that "moderation" are actually audible.  Could YOU hear the difference between, say, a 1.5msec attack time and a 3msec attack time?  My guess is that, on paper, variable attack time with simple half-wave rectifier circuits like this one look better than they are in practice.  They can be useful with envelope controlled filters, but less so in compressors I think.

In contrast, the variation feasible with a recovery/decay control ARE substantial and easily audible, and you pay negligible penalty for adding it.  The only sticky part would be whether the pot taper distributes the changes you consider useful in and even manner or scrunches them up together.  Happily, because the control uses a simple variable resistor instead of a voltage divider configuration, and because it is dead easy to get pots larger than the resistance values that will make a difference, it will be simple to arrive at different tapers by means of parallel resistors.  (see geofex for the secret life of pots)

[jaytee]

You could do a search on the BB for the OS +++ which was a heavily modded Orange Squeezer.
I can't say how good it was -or- is but, it's around.

What's the BB?

[markm]

You could do a search on the BB for the OS +++ which was a heavily modded Orange Squeezer.
I can't say how good it was -or- is but, it's around.

What's the BB?

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