Ibanez FC10 issue. When clicked "off" still hear distortion. Thoughts?

[timrichter9]

Hey all-
I have an Ibanez FC10 (which was their version of the ProCo Rat type pedal).
Works nicely when "On" but when stepped on, the "Off" position seems to
still have distortion in the path.
Thoughts?

I am handy with schematic reading (I build tube amps), but solid state stuff
gets me all mumbly-jumbly.

Thanks guys!
Tim

[g-one]

To start with the most simple stuff, is the power supply the exact one, or have you tried a fresh 9V battery if it uses one? A power problem would be much more noticeable when in bypass mode, in distortion mode a bit of extra distortion would be hard to detect.
Beyond that, this schematic should be close:

[timrichter9]

Thanks!

To start with the most simple stuff, is the power supply the exact one, or have you tried a fresh 9V battery if it uses one? A power problem would be much more noticeable when in bypass mode, in distortion mode a bit of extra distortion would be hard to detect.
Beyond that, this schematic should be close:

[R.G.]

-Was it always this way, even when new, or did it just start?

Pedals using JFETs for switching must have JFETs that have an "off" voltage on their gate that is big enough to fully turn them off. Some pedals have problems with this, either from a bug in the gate voltage circuit or by chance a JFET that needs a bigger "off" signal.

[timrichter9]

Thanks. I always wondered what JFET switching was. So what actually happens? I believe that the switch in the Ibanez -10 series pedals is a momentary switch. Is it set up so one JFET is turned on as another is turned off and then hitting the switch again reverses the process.

Tim (Dumb about solid state)

[R.G.]

See
http://www.geofex.com/Article_Folders/bosstech.pdf

[Jazz P Bass]

That schematic is not very complete.
Maybe I missed it but I do not see the switching logic.
Anyway, there are two 'n channel fet's' that are being used to switch from bypass to effect.(2SK118)
If the effect fet is not turning OFF, it will 'leak' the distorted signal.
So the first item to verify is the gate voltage of the effect fet.
Compare it to the bypass gate voltage when it is being told to turn off.

[g-one]

Yup, I noticed later that schematic does not show the switch or logic, so not sure if it's a latching switch or momentary. Unfortunately was unable to find a complete schematic.

[Dirk_Hendrik]

Late to the party. I don't visit here too often.
Ye, that schem lacks the bypass control circuitry. Since all Ibanez pedals since somewhere around 1981 use the same discrete flipflop circuit (which is similar to the same circuit used by Boss) I tend to omit it when I trace an ibanez pedal and draw the schem. It's just too standard. Therefore browse almost any Ibanez factory schem from after 1981 and you'll see the bypass control circuit. The article RG links to earlier in this thread gives the same information. I suggest to read it instead of complaining on incompleteness on something given freely.

Then,
Chances are good that your problem is not in the bypass circuit but in crosstalk from the opamps output signal into the bypass signal chain. Remember that the clipping signal is always present at the output of the opamp, regardless of wether it's bypassed or not and regardless of the level control. The proper solution is to break the connection from pin 3 of the opamp to the 10k resistor (but not the 1meg!) and add an extra switching FET in between the 10k and the pin3/1Meg junction. Next step is adding a 1Meg resistor from the 10k-Fet junction with the other lead to Vbias. Final step is control the gate of that Fet through a diode-47n to ground-1Meg network like it's used for the bypass already and control that from the "effect" line.

Like this:
http://www.dirk-hendrik.com/temp/Iba...tal-modded.pdf

[g-one]

Sorry, the comments were not meant to be complaints, just to point out that the switching was not included in the schematic.
Thanks for the schematics and your input.