Orange Squeezer Problem: Not compressing

[freeride]

Hey guys, I built an orangesqueezer circuit based on the schematic from generalguitargadgets and tonepad.  It was compressing when I first built it, but it no longer compresses and I don't know why.  I am a country guitar player, so I am very aware of what compression is, sounds like, and how it reacts to your playing.  The pedal is simply acting as a volume boost right now - as if the compression part of the circuit has been completely cut out.  I have messed with the trim pot inside, but all the way up still doesn't even get compression.  I thought my JFETs might have gone bad, so I've switched them out...twice.  Does anybody have any idea?  Anybody know what the DC bias points should be around the jfets?

thanks guys,

-zach

[.Mike]

I have messed with the trim pot inside, but all the way up still doesn't even get compression.

That's because the compression does not occur at either extreme of the trimpot. It occurs somewhere in the middle of the range, right as the signal transitions from silent to full volume.

There are tons of topics on biasing the Orange Squeezer. Give the ol' search a whirl, and if none of the many topics on Orange Squeezer biasing help, post back.

Mike

[StereoKills]

^This. The trimpot is extremely sensitive, and the band where the bias is correct is a very narrow one. A great technique is to have a friend help out, so one can play while one slowly adjusts.

[freeride]

Hey, dialing a spot in the middle of the extremes somewhere definitely helped.  I guess I was originally looking for a more drastic effect and passed over that spot multiple times looking for a bigger change.  It sounds pretty good as a subtle effect and adds some cool extra harmonic richness, but does anybody know a quick mod or component switch to get more compression out of it?  Maybe go from the smooth Mark Knopfler amount of compression to a Brad Paisley or Brent Mason type with the added spank?  I think it'd be fun to include a switch on there and get both out of the same pedal.  Perhaps upping the "beta" value with some new jfets or adding a third jfet in a darlington-connected style?

thanks,

Zach

[freeride]

To clarify, I'm currently using it with a strat (hence the sweet knopfler sounds!), so the pickup outputs are low meaning I don't get a lot of compression that I want for some country lead guitar.  Maybe I should just add a small op amp on a toggle switch that can boost my volume on the way into the pedal.  Does anybody have any other suggestions to get more compression while using the strat or other single coils like a tele?

Thanks guys,

Zach   

[.Mike]

To clarify, I'm currently using it with a strat (hence the sweet knopfler sounds!), so the pickup outputs are low meaning I don't get a lot of compression that I want for some country lead guitar.  Maybe I should just add a small op amp on a toggle switch that can boost my volume on the way into the pedal.  Does anybody have any other suggestions to get more compression while using the strat or other single coils like a tele?

Thanks guys,

Zach   

You can make the gain of the opamp variable, which alters the envelope detector that controls the compression.

Again, hit that search button, and dig in. Since the orange squeezer is such a common build, you will find many great resources. Pretty much anything you want to do with an orange squeezer, someone else before you already wanted to do, and chances are they posted about it.

Buried in the forum is a "technology of" article that pretty much goes through the circuit from start to finish, and there are even orange squeezer variants that incorporate variable compression controls. I know this because the orange squeezer was my second build, and I practically wore out the search button learning about it.

Good luck.

Mike

[freeride]

Through the search, two users, RG and Mark Hammer, have posted a few very good, differently worded, but right, explanations of how the pedal works, and gives some guidelines on how to alter the schematic to the way you want.  I'm going to try two things and I'll include them here for anybody in the future to check out and try.  I insult nobody's intelligence by posting this!  It's mostly for myself to talk through and make sure I understand what's happening   Please feel free to correct if I'm wrong.

Since this is a current sink-when-input-signal-is-loud effect, the input volume has a big effect in my opinion.  Louder inputs would mean Vds for the JFET is bigger, and more of the signal would be sunk to ground and not go through the op amp, granted Vgs is large enough for the FET to be on.  The current pulled down through the fet is proportional to Vds in the triode (or linear) operation mode, see a graph here:
http://en.wikipedia.org/wiki/File:JFET_n-channel_en.svg

That being said, I also understand that this pedal is a feedback compressor, meaning the amount of compression can be thought of as being controlled by the output volume, because louder outputs will turn the diode on and pull the gate voltage on the JFET up, causing the fet to be "more on" and the input current to be pulled down by the fet (limitting the amount going into the op amp and therefore the output volume...hence compression).  This is also shown in that graph on wikipedia - higher gate voltages relative to the source (Vgs) relate to higher curves on the graph and more current.   

Now thank you Mike for the tipoff and then Mark Hammer for the extended explanation about how to get some more compression by varying the gain of the op-amp and what it will do for you. 
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 [1+220k/10k =23]).  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).

Now my solution is to possibly to try both.  Add a little bit more gain in the op amp stage to open up the JFET more often by increasing Vgs values more, and boost the input signal with a variable gain stage (op amp with pot instead of fixed resistor feedback) to increase Vds and sink some volume in the beginning.  That should help to not get all of the noise from pumping up the original op-amp to x57.

Who thinks these are good ideas? ...and who just thinks I'm an idiot? lol

-Zach