Orange Smoothie Compressor Build Guide

[GGBB]

If setting the compression knob to minimum gives you the most volume, the bias adjustment might be off. Do you get noticeable compression? Do threshold adjustments work? What I am getting at is whether or not the pedal actually works - all controls - and isn't just passing signal - outside of the volume drop problem.

[mlp-mx6]

I'll recheck that too. Thanks for the guidance. I really like the idea of this circuit and I want it to work.

[GGBB]

No one has reported having low volume before. Mine has plenty - the knob is typically around the 11 o'clock position. Might be just a minor mistake - in any case should be fixable. The fact that sound gets through is a good thing. Triple-check the make-up gain section - vol pot, bright pot, R13, R14, C10, C11, C12.

[mlp-mx6]

Ok, I believe it was/is a bias issue. However when I set the bias to allow a good volume it will stutter on the pick attack, especially with humbuckers. If I lower the bias voltage to where that doesn't happen then max volume is almost (but not quite) unity gain. Adjusting the threshold control doesn't totally prevent this either, but setting that control to minimize the stutter means the compression effect is barely doing anything either. Please advise, and thanks again.

[GGBB]

Can you describe what you mean by stutter?

Where are the controls when you are adjusting bias? Threshold, attack and decay should be in the middle. Compression should also be in the middle if you are using a linear 100k pot. Then adjust according to the guide - halfway between sound drop out and distortion when listening via an audio probe at the R2-C6 junction. Volume should not be a concern here as you are not listening to the output signal - adjust to get the pedal working properly so that we can rule that out as a cause of the volume loss.

[mlp-mx6]

I'll try to record a small file, if I can attach it.

Will do on the bias readjust.  Thanks.

[mlp-mx6]

Supply voltage 12.1V.  Stuttering stops when bias is at 3.3V.  With hotter pickups I can still make it stutter a little.  Output volume is just at unity, though the control is maxed.  All others at 50% as per the bias instructions.

The two files are in here:
https://www.dropbox.com/sh/qi1eb4lzdlqptkx/AAASya1I2-P90-ZElJ8tuEsFa?dl=0

[GGBB]

That's what I thought you meant by stutter, but I'm completely baffled to hear the pedal do that. It sounds like Q2 is shutting on and off very quickly. I can only take stabs at this point. First, have you made any part or value substitutions, and have you double checked all the components including orientation of any polarized parts? Next, have you tried it with +9V power? I ask that because I've never tried it with +12V and I don't know what that might do to Q1. Do the controls change it/get rid of it (try comp and sust on min, attack and thresh full up, bandpass on)? Check the resistance across C7, which should be at least 47k, and check that C7 is good.

[mlp-mx6]

Again, thank you for taking the time.

No substitutions at all.  All part values were verified before installation.  I will recheck with 9V (8.8V, to be precise), and report back.

[mlp-mx6]

Sorry for the delay in my response.  The resistance across C7 is just over 100K.  C7 shows no DC voltage on either side of it.  Does that indicate a bad transistor?

[GGBB]

No - at 'rest' - i.e. when there is no signal - C7 would show zero-ish volts DC on both sides. With a signal present, the positive side should rise and then fall slowly (but not too slow) when signal stops. To me, it sounds like the circuit is working, but the JFET is opening and closing rapidly instead of staying open. C7 is responsible for stabilizing that so that's why I wanted you to check it. It could be just the bias setting doing it - when you adjusted the stuttering 'out' it sounded like the compressor was working, so it could be that the problem actually is just a volume problem and not the compression at all. That's probably easier to fix. So back to an earlier question then, other than volume drop does the compressor work well when you adjust the bias to get rid of the stuttering? If so, we can move on to checking the volume related components.

Please post voltages for all pins of the JFETs as well as the opamp - that might point to something. With the audio probe, compare the volume at pin5 of the opamp vs. pin 7. Pin 7 should be louder. Then compare pin 7 to output volume - it should drop a bit but not too much. It is also worth comparing volume level at the input with opamp pin 5 - turn compression to zero and threshold to max for this.

[Ben N]

Are there any more of Gord's Boards?

And, did you consider including Mark Hammer's feedback/feed-forward option; if not, why not?

[GGBB]

Are there any more of Gord's Boards?

And, did you consider including Mark Hammer's feedback/feed-forward option; if not, why not?

Yes - I have some boards - PM me.

Feed back/forward - I can't recall the exact sequence of progress on the smoothie but I think I came across Mark's Tangerine Peeler sometime after I had the basic ideas in place which came from some other posts by Mark and others. That option is easy in the peeler because it doesn't have the compression ratio control on the input like the smoothie. I opted for having that rather than the feedback direction switch because my research suggested the feedback direction change lost the classic squeezer sound, plus I thought ratio would be more useful. But I never actually tried it.