Orange Squeezer volume question

[skrunk]

Recently finished an orange squeezer and biased the fet using a precision trimpot going by Mark Hammer's info here:

http://www.diystompboxes.com/smfforum/index.php?topic=48102.0

The only issue that I have with it, and what I do not understand is that below 12 o clock
on the dial there is little or no output from the device. While I do not expect it to work from say 7 o clock, I would have expected
it to show signs of life around 9 o clock- i.e. to provide the same level that it would have being bypassed albeit with the compression added - as I understand it, the compression doesn't change as you turn the dial merely the boost?
Does it cut the signal below 12 o clock?
Sounds great at about 1 or 2 o'clock.

I understand the volume control was a set-and-forget trimmer in the original unit.
Is the volume knob simply for adjusting it to a range of different pick-ups?

[Mark Hammer]

The op-amp provides a fixed gain of 23x.  The 82k resistor, FET, and trimpot, form a kind of virtual input-level pot that is adjusted according to feedback through the diode.  Is it possible that a gain of 23x, a given FET's drain-source resistance, a given trimpot setting, and a given volume pot's taper will result in an output signal so weak that the volume pot needs to be cranked to hear anything?  Sure, it's possible. 

Consider making the gain of the op-amp stage variable to compensate.  So, instead of 10k to ground and 220k in the feedback loop, use a 330k resistor and a 10k liear pot in series with the 10k to ground, to achieve gains between 17.5 and 34.  That might help.

[skrunk]

thanks for the reply mark!
The unit works fine as far as I can tell, with plenty of gain on tap.
maybe I'm misunderstanding the function of the volume knob.

is it normal for the output level to drop quite  bit when set before 12 o'clock?

[skrunk]

I've been testing it with line level signals at various low levels and I've noticed that the louder the input source, the less relative output volume is produced by the knob.
when I run a lower signal in to it, the knob gives me more output on tap and unity gain is lower.

I imagine this is because it's just compressing more with a higher level input?

[Mark Hammer]

Uh-huh.  Which is why having a gain-adjustment that can create both greater and lesser gain can be a good thing.

[skrunk]

ok that makes sense.
thanks for the info mark, much appreciated!