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Jack Ormans "True-Bypass"

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5/10/1999 2:33 PM

Jack Ormans "True-Bypass"

Hey,

I have built the switching circuit that uses an MPSA13 transistor, It switches fine however when the pedal is in "clean" mode, the switch LED starts to come on gradually, almost like a battery charges, it only gets so bright, then it stays at that level, when I click the switch again (distorted mode) it makes the light brighter (normal) then I click it off and the process starts again,...

Has anyone had this problem?

Thanks!
Jim

5/10/1999 3:24 PM

Ormans "True-Bypass" and Fixes for It

This is one of the ills of using a darlington for this kind of switching.

From your description, you have a darlington with a fair amount of leakage. The initial switch turns the darlington off hard by sucking the base charge from the darlington into the output coupling cap of the effect. The darlington leakage then charges the output cap back up enough to cause collector-emitter leakage to light the LED.

You can do a couple of things.
(1)hand select darlingtons for low leakage
(2)parallel the LED with a resistor to make it less sensitive to darlington leakage
(3)Use a discrete MOSFET device with diode leakage pullup as in the Millenium 2 bypass.

I recommend option 3. It's less sensitive to device characteristics. To make what you have into a Millenium 2, just get a to-92 mosfet like the BS170 or 2N7000, and replace the MPSA13 with it, drain for collector, gate for base, source for emitter. Then replace the 10M? 22M? pullup resistor with a 1N914 or 1N4148 signal diode, anode to +9, cathode to gate. This works just as the earlier one did, but without either the leakage or possible clicks.

For long term protection, use a low leakage diode from ground to the gate of the MOSFET, something like the collector base of an NPN transistor or the gate/source junction of a JFET - reverse biased of course.

5/11/1999 1:42 AM

RG's Y2K Bypass PROBS.

Ok,...

I scraped the Darlington transistor switch as it caused way too many probs,..

I tryed RG's switch it works good HOWEVER, when I turn the volume up on the pedal (fet muff) it makes the LED come on (When in CLEAN mode!) what gives? I have a 100K pot there and I would like to keep it if possible. Is there any fixes? I used a 2N5457 FET for switching and a 1N4148 diode.

Please help!
Jim

5/11/1999 5:37 AM
Roger K.	>>>HOWEVER, when I turn the volume up on the pedal (fet muff) it makes the LED come on (When in CLEAN mode!) what gives?<<< Same trouble I had with the Millenium bypass. maybe the mosfet version is better. have you tried that?

5/11/1999 6:26 AM
R.G.	Try the Millenium 2. You're getting capacitive conduction to the gate of the JFET - it's actually too sensitive. The Millenium 1 does have that problem because of the very high imput impedance. The Millenium 2 solves most of that.

5/10/1999 4:41 PM

re: True Bypass

I have used this circuit several times with good success. You may have a bad transistor. What kind of pedal are you using it with?
If the output volume control of the effect is high in value like with a Fuzzface, that might cause the problem too.

i liked this version better than the fet model because it seemed to switch more positive. haven't tried the cmos or mosfet ones yet

Roger

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