have any of you guys built this compressor ?

[Dragonfly]

any thoughts or build reports ?

[markm]

Yes.
Move along AC, nothing to write home about and it didn't work very well either. 

[Mark Hammer]

Never attempted it, but seeing the FET as the only path to ground from the inverting input just strikes me as trouble on a stick.  All your gain and attenuation is riding on that one lousy little FET.  Hypothetically, it WILL work, but boy oh boy will you have to pick your components carefully.

Essentially what we're looking at here is a kind of stripped-down Orange Squeezer.

[magikker]

You can strip down an Orange Squeezer! 

[Mark Hammer]

You wouldn't think so, but yeah.

The OS has a FET-based attenuator aheasd of an op-amp gain stage, rectifies the output of that gain stage to adjust the amount of attenuation.  This circuit skips the attenuation and uses the output of the op-amp to adjust the op-amp's gain directly.  Same general half-wave rectifier, same signal split on the output of the op-amp, though.  Could be improved if there was a resistance to ground in parallel with the drain-source path of the FET.

Note the 820k/10n network from drain to gate.  As Osamu Hoshuyama notes here: http://www5b.biglobe.ne.jp/~houshu/synth/PhaseFet0205.GIF   this provides some immunity to distortion, but it also tends to slow tracking.  Given that he's talking about LFO rates of tracking, I would imagine that the kinds of speeds being attempted by this design (note the .22uf time constant cap) are even faster and more susceptible to "tracking" problems by this method.

[Dragonfly]

Cool...I'll file it in the "Lauriers Handy Dandy Useless and Non-Working Circuits" folder.

Thanks guys.

[Mark Hammer]

Keep in mind that you can find a whole slew of limiter/compressor circuits on-line and in circuit collections that are really intended to keep constant voice level for ham radio operators, or some other application where no one particularly cares about distortion/coloration, sustain, or other factors important to guitarists.  Doesn't mean it's a horrible design, just that it doesn't explicitly anticipate this operating context.

[David]

Cool...I'll file it in the "Lauriers Handy Dandy Useless and Non-Working Circuits" folder.

Thanks guys.

Put ALL of his stuff there IMHO. 

[Paul Perry (Frostwave)]

Cool...I'll file it in the "Lauriers Handy Dandy Useless and Non-Working Circuits" folder.

I think there is a reason that the HD circuits are so disappointing:

1. he isn't a musician himself, so perhaps he is relying on the scope more than his ears.
2. the circuits probably aren't flexible enough (or stable enough) to cover a wide range of inputs.
3. some have the look of being tweaked until they work.. if you do this with a design containing a fet, you can end up with sonmething that only works with a few fets that just happen to have the same characteristic.

On the one hand, hats off to anyone who designs stuff & posts it - but I wish he'd post them here first, so the collective wisdom could polish them up & save people from grief. Unfortunately, a couple of 'bad' circuits can put a beginner off for life. Which is tragic.