Orange Squeezer Questions....?

[sevenisthenumber]

Here are some things I'm just wondering about??

*would it benefit in getting rid of the unused op amp?
*adding decoupling caps to the power input and to the op amp (reduces noise)?
*removed 4.7M resistor near the input (it's parallel with the 3.3K resistor?)
*use a ground plane to reduce noise?
*protection on the +9V signal?  (I'd like to put a diode in series with the power input to prevent a voltage polarity swap)  Maybe also a 12V zener to prevent over-voltage. 
*Is there a better diode to use in the place of the 1n100a?

Thoughts? 

Do you think these changes would affect the sound of the pedal?

[Mark Hammer]

You'll find a number of layouts for circuits that only need one op-amp but use a dual chip.  The reason is simple: duals cost the same as singles, and you get better prices if you buy a bunch of duals.

You can use any germanium diode istead of the 1N100.  Dan Armstrong may have had them squirting out his ears back in the day, but nowadays, the only germanium types that seem to be readily available are 1N34 and 1N270.  The key thing is the forward voltage of the diode.  It should be nice and low.  If you have a meter than can measure diodes, and have a bnch of Ge types handy, look for something with the lowest forward voltage (e.g., 210mv rather than 260).

Compressors are inherently noisy, simly by virtue of the way they work.  They cannot tell the difference between soft playing and background noise, and assume both require boosting.  If you feed no signal into the unit, whatever residual noise there might be can get annoyingly loud.  Will ground planes alter that nise level?  Perhaps, but not nearly as much as simply providing a clean input signal.

[sevenisthenumber]

You'll find a number of layouts for circuits that only need one op-amp but use a dual chip.  The reason is simple: duals cost the same as singles, and you get better prices if you buy a bunch of duals.

You can use any germanium diode istead of the 1N100.  Dan Armstrong may have had them squirting out his ears back in the day, but nowadays, the only germanium types that seem to be readily available are 1N34 and 1N270.  The key thing is the forward voltage of the diode.  It should be nice and low.  If you have a meter than can measure diodes, and have a bnch of Ge types handy, look for something with the lowest forward voltage (e.g., 210mv rather than 260).

Compressors are inherently noisy, simply by virtue of the way they work.  They cannot tell the difference between soft playing and background noise, and assume both require boosting.  If you feed no signal into the unit, whatever residual noise there might be can get annoyingly loud.  Will ground planes alter that nise level?  Perhaps, but not nearly as much as simply providing a clean input signal.

I was hoping you would chime in! ;-)

On the op Amp... I notice that the 4558P sounds more squishy and has a different "swell" than the other 4558's... Is this me or am I actually hearing this! ha! I feel like its more dramatic than the others and I like it.

Do you have a favorite diode for this circuit? Just curious!

The that I have built has an added compression control. (replacing the 1k5 with a 10kb pot as a variable resistance) I love what it does but the first 50% of the sweep is honestly nothing more than cool clean boost settings. The meat of the compression only kicks in around 65% on the pot sweep... Any advice on making this compression pot more FULL RANGE and usable in the lower sweep?

Any thoughts on power protection?

Your awesome!!! Thanks!

[Mark Hammer]

I have no basis for needing power protection, so I'll leave that for others.

No favourite diode.

The 1k5 in series with the diode limits current.  Perhaps a more productve approach to having variable compression amount is to vary the gain of the op-amp, via either the 10k to ground, the 220k feedback, or both.  I did this on mine and the squish is variable.

Consider also the components that set the time constant of the rectifier; that being the 4u7 cap to ground and its parallel 100k resistor.  A larger cap or resistor value will lengthen the decay time, which will keep the signal recovery slower in coming back.  The "transparency" that so many like the OS for is largely a function of having the volume adjustment (compression) get in and out very quickly.  Longer apparent sustain is produced by having a longer recovery time, similar to what is found on a Dynacomp/Ross or what is found on those compressors that have a variable recovery time.

Note that this does not increase the amount of compression.  It simply makes whatever compression you've applied work longer after each pick transient.

As for anything "special" about a given 4558, let's just say that there are some criteria for validating true component-to-component differences which very very few home builders are ever able to meet (myself included), and you haven't met them here, either.  So we'll just say that you heard something, but no one can say if it was substantive or not.