What can be causing distortion in bypass?

[LucifersTrip]

I built a ton of fuzzes with this exact bypass/switch setup, but for a reason I can't quickly figure out, I'm getting a mild distortion in bypass mode...with or without the battery.

Am I missing something obvious?  

When the effect is engaged, it's perfect...probably one of my favorites of the many I've built...and Q2 has an hfe of 24.


thanx

[Mark Hammer]

If you're playing loud, one possibility is switch chatter; i.e., millisecond-duration (well not exactly a millisecond, but fast) openings and closures of the contacts inside the stompswitch.  Normally there is some grease inside the switch to damp the vibrations that can cause this.

[LucifersTrip]

If you're playing loud, one possibility is switch chatter; i.e., millisecond-duration (well not exactly a millisecond, but fast) openings and closures of the contacts inside the stompswitch.  Normally there is some grease inside the switch to damp the vibrations that can cause this.

Sadly, it's at low volume thru a small practice amp.   

This is really hilarious. I'm so used to seeing 90% of "troubleshooting...please help" emails stating: "It works in bypass, but when I engage the effect, I get nothing / little effect/ a bad sound". I never thought I'd ever say my effect works perfectly but I can't get bypass to function...

It's a straight line in and out and the battery's not even connected.  I doubt if  a bad jack could cause distortion?


thanx for the suggestion

[Mike Burgundy]

First off, it's a good idea to use a stereo jack to switch power on when you stick in a jack - don't switch it on when you switch the pedal in.
As for the noise - could be the switch as Mark states, could be jack contacts, guitar leads, solder joints, combination between jack and a certain jackplug (some BOSS pedals somehow dislike Neutrik plugs, however great they are) even your guitar/amp..
As any other debugging process, it can be frustrating but you will find it if you're methodical.
Verify the guitar amp and leads are fine, plugging in directly. Use both cables. Plug in the pedal (in bypass).Verify cables again. Wiggle the leads and connectors while making sound to make sure.
Switch the leads between guitar/pedal and pedal/amp, repeat.
Then:
If you don't already have them, get some alligator clip leads and verify they're ok. You'll have a lot of fun with these over the years.
Verify there are NO voltages present on any signal connection in the bypass circuit (input tip, switch terminals, etc) so the cliplead *byasses that specific connection*.
So, if the noise goes away when you clip it from input tip on the jack to output tip on the jack, it's definitely inside the pedal. If you clip it from input jack to the first switch terminal, and it goes away, the wire or solder joints you've just bypassed are faulty. If you clip it across first and center switch terminals, it's the switch. Etc.

hih

[LucifersTrip]

First off, it's a good idea to use a stereo jack to switch power on when you stick in a jack - don't switch it on when you switch the pedal in.
As for the noise - could be the switch as Mark states, could be jack contacts, guitar leads, solder joints, combination between jack and a certain jackplug (some BOSS pedals somehow dislike Neutrik plugs, however great they are) even your guitar/amp..
As any other debugging process, it can be frustrating but you will find it if you're methodical.
Verify the guitar amp and leads are fine, plugging in directly. Use both cables. Plug in the pedal (in bypass).Verify cables again. Wiggle the leads and connectors while making sound to make sure.
Switch the leads between guitar/pedal and pedal/amp, repeat.
Then:
If you don't already have them, get some alligator clip leads and verify they're ok. You'll have a lot of fun with these over the years.
Verify there are NO voltages present on any signal connection in the bypass circuit (input tip, switch terminals, etc) so the cliplead *byasses that specific connection*.
So, if the noise goes away when you clip it from input tip on the jack to output tip on the jack, it's definitely inside the pedal. If you clip it from input jack to the first switch terminal, and it goes away, the wire or solder joints you've just bypassed are faulty. If you clip it across first and center switch terminals, it's the switch. Etc.

hih

Thanx much for the suggestions. Though, I've already tried or eliminated many of those possibilities.  I will re-try some.

But first, let me clarify. I'm not getting a noise or crackle or anything intermittent. I'm actually getting a small volume boost & distortion...say, if you substituted a Q2 with hfe = 5 in a fuzz faze that should have 60-90....and the battery is disconnected.  

After connecting the battery, when the effect is engaged, it's perfect. No crackle, intermittent connection, etc...

I'm using the same jacks I've used in the last 40+ projects with the same guitar cables...The first thing I did was swap cables...same. Then, I tried the last couple
pedals I finished...clean bypass.

I clipped a lead between various spots and couldn't eliminate the distortion...even directly from tip1 to tip2.  I did try all points on the switch. The only change I got
was a slight lowering of volume (but the same distortion) when clipped between the top and bottom [input tip to 250k wiper] of the left column on my diagram.

What I haven't done:
For all my projects, I've used either mono jacks or just 2 lugs on the stereo jacks. I haven't checked any voltages since the battery's not there, but I am plugged into the amp. I haven't wiggled anything since there was no intermittent problem when effect is on or off.

I'll try some more, starting with switching amps

thanx again


Update:
Swapped amps..same distortion.
Highest voltage reading I got from ground to anywhere was .2 millivolt. Nothing.
Wiggling did nothing...perfect connections.
Checked resistance across switch lugs. I got 0's & 1's where they should be
Btw, when battery is connected I get -4.7v, -.6v on the C's of the two Q2's I switch between (mod), repectively

[Tubebass]

If your switch is really wired as shown in the schematic, your guitar will be connected to the input of the circuit even in bypass mode. Try pulling Q1, if it's socketted, or lift one end of the 0.1 uf input cap. Distortion go away now? If so, rewiring your stomp switch to a true bypass configuration should solve your problem.

[sundgist]

Have you tried (when bypassed) disconnecting the input to the effect. ie remove one leg of the 0.1u input cap. If this cures it then you would be better off wiring the switch as true bypass.

ah someone beat me to it.

[LucifersTrip]

Thanx much for the replies. I will disconnect the input if I find nothing else shortly. It's my last resort since everything's neatly soldered.
Before boxing, I tested everything but the bypass since I've never had a problem with that switch setup.

Assuming that is the problem, what is different with this circuit compared to the others I've built...for ex: Shin Ei, Fuzz Face, Fuzz Rite, Psychedelic Fuzz, Fuzz King, Sunn Buzz, Muff Fuzz, Mos Face, Os Mutantes, Tone Bender, Maestro FZ-1, etc...?

Shouldn't I be able to measure something so I can predict this behaviour?

Would I have the exact same problem if I left the end of the circuit connected?

[edvard]

The way you show it connected here I would worry about oscillation/noise if you weren't disconnecting the battery as well, and it still might happen until your 15μf cap discharged.
The only thing I can see that might be happening with the original connection is the emitter of Q1 acting as a clipping diode to ground if your pickups are powerful enough to drive it.

Other than that, I'd recommend true bypass.
You've got room for it with the 3PDT, and it would disconnect the circuit altogether, eliminating any tone suckage from driving the first transistor.
...Which brings up another question; have you plugged straight in to the amplifier?
You've eliminated the amplifier as the source, but it could be something wrong with your guitar, although you stated it works just fine with other circuits so hmmm...

[LucifersTrip]

The way you show it connected here I would worry about oscillation/noise if you weren't disconnecting the battery as well, and it still might happen until your 15μf cap discharged.

In the 1st or 2nd schematic above, or both?  What's the difference between leaving the front or end of the circuit connected during bypass?

The only thing I can see that might be happening with the original connection is the emitter of Q1 acting as a clipping diode to ground if your pickups are powerful enough to drive it.

Is the only way to test that theory to disconnect Q1 E or can I measure something? Shouldn't I be able to see a small voltage?

Other than that, I'd recommend true bypass.
You've got room for it with the 3PDT, and it would disconnect the circuit altogether, eliminating any tone suckage from driving the first transistor.

The third set of lugs is used for an led (not shown). I'll consider true bypass, but just wondering what is different here than the last 20 pedals (vintage fuzzes) I've built with the same wiring. With the battery disconnected, what else (other than pickups) could be driving Q1?

...Which brings up another question; have you plugged straight in to the amplifier?

Yes, directly into a small practice amp.

You've eliminated the amplifier as the source, but it could be something wrong with your guitar, although you stated it works just fine with other circuits so hmmm...

Yes...I plugged into the last 6 or 7 pedals I built...no prob.

thanx for the reply
=============

Note: A while ago, I did read the true bypass info here:
http://www.muzique.com/lab/truebypass.htm

Regarding, the "not true bypass" example, it states: "This type of switching can cause loss of high frequencies and overall volume"
I am getting the opposite. A light volume boost, more treble and a mild distortion.

In the  "not true bypass" example, is the battery connected or disconnected (I have to guess connected since they're using spdt)...or doesn't it matter?

[greaser_au]

Other than that, I'd recommend true bypass.
You've got room for it with the 3PDT, and it would disconnect the circuit altogether, eliminating any tone suckage from driving the first transistor.

The third set of lugs is used for an led (not shown). I'll consider true bypass, but just wondering what is different here than the last 20 pedals (vintage fuzzes) I've built with the same wiring. With the battery disconnected, what else (other than pickups) could be driving Q1?

If you're switching the supply with the FS, why not just connect the LED/resistor chain across the circuit's power input?  the LED will still show if it's on or off, but it frees the set of contacts needed to isolate the input & will answer the question very quickly...

david

[LucifersTrip]

Other than that, I'd recommend true bypass.
You've got room for it with the 3PDT, and it would disconnect the circuit altogether, eliminating any tone suckage from driving the first transistor.

The third set of lugs is used for an led (not shown). I'll consider true bypass, but just wondering what is different here than the last 20 pedals (vintage fuzzes) I've built with the same wiring. With the battery disconnected, what else (other than pickups) could be driving Q1?

If you're switching the supply with the FS, why not just connect the LED/resistor chain across the circuit's power input?  the LED will still show if it's on or off, but it frees the set of contacts needed to isolate the input & will answer the question very quickly...

david

If I understand you correctly, wouldn't I then have a resistor/diode in series with the (-) battery?  That won't effect the circuit?

I can answer whether connecting to the front or end of the circuit is causing the distortion very easily by unsoldering 1 lug...but that still
leaves many of my other questions above unanswered.

[edvard]

The way you show it connected here I would worry about oscillation/noise if you weren't disconnecting the battery as well, and it still might happen until your 15μf cap discharged.

In the 1st or 2nd schematic above, or both?  What's the difference between leaving the front or end of the circuit connected during bypass?

Second schematic.
Leaving the output connected, you'd get whatever snuck into (now) floating input amplified in the effect and mixed in with your dry signal.
Depending on WHAT was sneaking in, you'd get a nice little feedback squawk or (since the input is rather low impedance) you'd get some noise and hiss until the power supply decoupling cap discharged enough that it wasn't acting like a little temporary battery.
15μf probably won't hold much of a charge though...

The only thing I can see that might be happening with the original connection is the emitter of Q1 acting as a clipping diode to ground if your pickups are powerful enough to drive it.

Is the only way to test that theory to disconnect Q1 E or can I measure something? Shouldn't I be able to see a small voltage?

If the battery is off in bypass position, no.
A diode (base -> emitter junction) won't show any voltage by itself.

Other than that, I'd recommend true bypass.
You've got room for it with the 3PDT, and it would disconnect the circuit altogether, eliminating any tone suckage from driving the first transistor.

The third set of lugs is used for an led (not shown). I'll consider true bypass, but just wondering what is different here than the last 20 pedals (vintage fuzzes) I've built with the same wiring. With the battery disconnected, what else (other than pickups) could be driving Q1?

Nothing, which made me kind of wary of that line of thinking because normally a plain pickup output isn't enough to push diodes, BUT if you've got a very hot humbucker and the transistor is Germanium, it's possible.
If it's a silicon transistor, it'll take a more muscle than most pickups have to break it over, but it could also be damaged and/or leaky.

...Which brings up another question; have you plugged straight in to the amplifier?

Yes, directly into a small practice amp.

You've eliminated the amplifier as the source, but it could be something wrong with your guitar, although you stated it works just fine with other circuits so hmmm...

Yes...I plugged into the last 6 or 7 pedals I built...no prob.

thanx for the reply
=============

Note: A while ago, I did read the true bypass info here:
http://www.muzique.com/lab/truebypass.htm

Regarding, the "not true bypass" example, it states: "This type of switching can cause loss of high frequencies and overall volume"
I am getting the opposite. A light volume boost, more treble and a mild distortion.

In the  "not true bypass" example, is the battery connected or disconnected (I have to guess connected since they're using spdt)...or doesn't it matter?

Most folks don't have the switching circuit disconnect the battery when in bypass.
It sounds like it would be convenient; just stomp the thing off when you're done jamming.
I'll leave more knowledgeable folks to reveal the details, but when the subject comes up, it's normally frowned upon.
But hey, if it works for you, who am I to say otherwise?
Usually the negative side of power is hooked up to the Ring terminal of a stereo jack so that the plug makes the connection between the battery (-) and effect ground.
Just unplug to turn it off...

[greaser_au]

Other than that, I'd recommend true bypass.
You've got room for it with the 3PDT, and it would disconnect the circuit altogether, eliminating any tone suckage from driving the first transistor.

The third set of lugs is used for an led (not shown). I'll consider true bypass, but just wondering what is different here than the last 20 pedals (vintage fuzzes) I've built with the same wiring. With the battery disconnected, what else (other than pickups) could be driving Q1?

If you're switching the supply with the FS, why not just connect the LED/resistor chain across the circuit's power input?  the LED will still show if it's on or off, but it frees the set of contacts needed to isolate the input & will answer the question very quickly...

david

If I understand you correctly, wouldn't I then have a resistor/diode in series with the (-) battery?  That won't effect the circuit?

I can answer whether connecting to the front or end of the circuit is causing the distortion very easily by unsoldering 1 lug...but that still
leaves many of my other questions above unanswered.

Connecting the resistor/led chain across the circuit supply (say - across the 15u cap) you would have the resistor/diode in PARALLEL with the circuit (which is electrically the same as with the LED switched separately on the 3rd contact when it is on!) - you're just creating a "light to show when the power is on" rather than a "light to show when the footswitch is on"  (as the power is being switched by the footswitch, it means the same thing). in the off position it may very well introduce some small difference if you aren't using TB.  I was just suggesting an easy way to free the 3rd contact so there was no reason not go full true-bypass - sometimes life is too short to chase ghosts

I don't know what the problem really is & if you have built more of these particular things without this problem, I'd suggest you might have a component fault or a wiring error/difference. I have seen switches with physical faults that mean that they are not fully open when off...  Did you unsolder the one lug to see if it fixed it?  Beyond that, if the wiring is all correct,  you have physically removed the battery & it still does it,  an oscilloscope is what you will need to see what is REALLY going on- anything else is just a guess.

david