orange sunshine fuzz bypass issues

[jimmy]

hi

i recently built an orange sunshine fuzz. the circuit works fine, but when the volume pot is maxxed, the bypass light comes on, only faintly, when its bypassed! im using the jack orman bypass circuit, the one with a single PNP transistor (for negative ground circuits). any suggestions?

thanks
Jim

[jimmy]

anyone? this is driving me mad!!! the light only lights up during the last tiny turn of the pot, when its NOT meant to be on. i understand that the PNP transistor acts as a switch to turn the light off when current is applied, through the volume pot resistance to ground.... which means somehow current is getting to the led when the tranny is meant to be directing all that current straight away from it. but HOW?!??!?!

cheers
Jim

EDIT - this might help eh? http://www.muzique.com/schem/dpdt.gif

[David]

Yup, that would do it.  So would a 3PDT switch.

[petemoore]

I don't understand  'light'...how it's wired.
 Are you using the millenium bypass?

[jimmy]

no, its not the millenium bypass, its the one in the picture! any ideas anyone?

[petemoore]

ok...not to be contrare', but to clarify, now I definitely can't figure out how the 'light' is wired.
 For bypass issues, I generally start at the input jack tip, and using a DMM, figure where the signal could go/not go from there [through the switch...etc.]. Getting the input jack tip to connect through the switch to the output jack tip should be fairly simple to debug.
 For the wirings shown on the link, bypass is a capability, LED indicator [is that what you mean by 'light'?] isn't, AFAIK.

[jimmy]

haha yeah, LED indicator is what i mean.

[cd]

Unfortunately petemoore has no clue what he's talking about and is leading you in circles.

Start with the bypass circuit itself.  When in bypass mode, the effect output (the volume pot - though FYI the Orange Sunshine is supposed to have NO controls) is connected to the base of the transistor.  The output resistor (from the pot's wiper to ground) pulls the input of the LED circuit to ground.  If it is too large, it's "blocking" too much of the base to ground (not enough base current), which means the transistor is not turning OFF completely, and you get a tiny, faint LED lighting up.  I'm pretty sure that's how it works - someone with a better understanding of transistors can chime in (and/or correct me) here.

Solution: get rid of the output pot (replace it with a 10k resistor to ground) or if you must use one, use a lower value pot.  Alternately, simply solder a 10k resistor in parallel with the pot wiper and ground lug to lower the output resistance.

There are other things you can do (replace the switching transistor, use a Millenium bypass, etc.) but tacking in a resistor is probably the easiest thing to do.

[petemoore]

cd, unfortunately, you're absolutely right
 Unfortunately petemoore has no clue what he's talking about and is leading you in circles.
 Well said  :roll: ... [erhaps something else causes inflammation...
 Big circles, in fact, without a schematic, and having built the OS Fuzz, not recalling anything about an LED...

[jimmy]

hi, yeah thats the hunch i had. and i also know its not meant to have any controls, but i couldnt help myself. i also replaced the second tranny emitter resistor to a pot, like the fuzzface, but it actually acts like a bias control. can get some nice squishy tones happening.

thanks
Jim

[R.G.]

cd's right. The Achilles heel of all bipolar transistor based circuits that attempt to mimic the Millenium Bypass is that they require base current. It may be small, but it's there. When the control is turned up, there is enough resistance so the PNP is not ...quite... on enough.

That's the basic reason I did the Millenium with FETs, first JFETs then MOSFETs. Used properly, they have tiny base currents even compared to a reverse biased diode.

There was a succession of bipolar based LED turner-offer-ers proposed. There was a single transistor version, then a darlington cascade, then a triple darlington cascade, all in the name of low base current, probably others. They all work under some conditions.

This is also true of the Millenium, it works under some conditions. It's just that the Millenium has far fewer restrictions on what it takes to make it work than the bipolar circuits, and far less impact on the circuit that it serves.

If you like the bipolar circuits, great. There are places where they can be made to work OK, once you understand the limitations and work around them.

[jimmy]

ahhh i see. ive been using the bipolar tranny bypass for a while now, and only had one other problem. im glad you were all able to shed some light on the situation. thanks heaps!!

[David]

jimmy -

How are you actually doing your bypass switching?  The link you provided is to the AMZ bypass circuit -- which does not include a status LED.  Is it possible you actually used Joe Davisson's "LED trick" circuit?  R.G. is assuming you used a Millenium Bypass or something similar.

I've read enough posts about bypass switching that I've decided to keep it simple.  I use 3PDT switches.  This gives you true bypass and an easy way to provide a LED status indicator.  Plus, you can't lose with Aron's pricing.

[jimmy]

well that was a stupid thing to do. well SOMEWHERE on amz there is a diagram that shows you a bypass circuit! anyone?

anyhow it has a dpdt switch set up like this:

effect in            jumper to output jack
input jack         effect out
output jack       wire to bypass circuit

the bypass circuit is a pnp tranny with a 10k to the emmiter, and 9v+ to the 10k. an LED goes between the emmiter and the collector legs of the tranny. the collector goes to ground. the wire from the switch goes to the base. it notes in the diagram you MUST have a volume control, or some sort of resistance to ground on the end of the circuit for it to work.

i dont think ive seen the 'LED trick', ill have a poke around and see what i can find.

cheers
Jim