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PostPosted: Thu Aug 16, 2007 11:56 am 
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A lot of people seem to have difficulty figuring out how mechanical bypass switching works. To help you get a better idea of what is going on I made these diagrams. I hope they help.

First of all mechanical bypass switching is NOT an ON / OFF switch. The bypass switch only routes your signal into or around the FX circuit. It doesn't turn anything ON or OFF.

The first diagram uses a SPDT switch to bypass the signal. Pedals that use this type of bypass switching include the DOD OD-250 and Dunlop Cry Baby wah pedal as well as others. It is NOT true bypass (This is what a lot of manufacturers call "hard wired" bypass). When continuity is between lugs 1 & 2 the signal comes into the switch and goes out thru lug 2 to the output jack. You'll notice that the input signal also goes to the input of the circuit. This is why the circuit can load down your signal and cause tone suckage. When continuity is between lugs 2 & 3 the input comes to the switch and then goes into the circuit's input. The signal then leaves the circuit and enters the switch thru lug 3. And since there is continuity between this lug and lug 2 the processed signal goes on to the output jack.
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This diagram shows how you would go about adding an LED to the above switching arrangement. It requires the use of a DPDT switch in place of the SPDT switch. All you are doing here is adding a second SPDT switch in parallel with the switch in the diagram above. This also is NOT true bypass switching.
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This diagram illustrates how to use a DPDT switch and get true bypass switching. This method does not use an LED unless you want to use the Millenium Bypass circuit with it. I don't particularly care for the MB circuit because it tends to leak and doesn't always turn the LED all the way off.
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This diagram is another example of true bypass switching that uses a DPDT switch. This method however does NOT short the circuit's input to ground. I do NOT recommend using this switching method.
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In order to have true bypass switching AND a status LED you must use a 3PDT switch like this.
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
You'll notice that the two diagrams with a diagonal jumper across a pair of the solder lugs also have one lug that is connected to ground (lug 3 of the DPDT stomp switch and lug 2 of the 3PDT stomp switch). This is so when the switch is in Bypass mode the lug connected to the circuit's input gets shorted to ground. This helps to prevent turn ON/OFF pops. If this alone doesn't take care of the pops try adding pull-down resistors to the circuit (1M to 2.2M will work). Pull-down resistors may help but they are primarily for true bypass switching that doesn't short the circuit input to ground as shown in the diagram directly above the 3PDT diagram. If you still have issues with popping make sure the only thing between you and your amp is the pedal in question. This will eliminate any compatibility problems there might be with the rest of your setup. If there is only a popping issue with the pedal when used with the rest of your setup, try powering that pedal with a battery only. This will eliminate the use of a common AC power supply as the cause of the popping. If you still have a popping problem after this you may just have to learn to live with it. Mechanical switching can be prone to problems with the switch's internal contacts bouncing when they make contact with each other. That's just the way it goes sometimes with mechanical switching like this. In cases like these you may have to go with a non-true bypass pedal and live with it's associated tone sucking. In my experience turn ON pops seem to somehow be amp related. I've built several AX84 "High Octane" tube amps and have never had any of my pedals pop. However when I placed my pedals in front of an 18 Watt Lite amp I built they all make popping noises when they were turned ON and OFF. Why this is I don't have a clue.

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Last edited by Stephen on Fri Oct 05, 2007 6:40 pm, edited 4 times in total.

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PostPosted: Thu Sep 20, 2007 4:55 pm 
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i'm sitting at the dining room table reading this post and my wife just walked in and said, "you look like one of those cartoon characters that has a light bulb over their head."

thanks for this post stephen!

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PostPosted: Fri Sep 21, 2007 10:03 am 
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I have the light bulb too! Thanks Stephen! Not only does that explain the switching and how it works, it allows me to visualize and understand what the 'poles' and 'throws' are in the switches. That's eluded me since day one. And it's so basic of information that no one feels the need to explain it. Maybe I'm the only person who never understood it :)

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PostPosted: Tue Nov 13, 2007 12:44 pm 
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Thanks for posting this, very helpfull indeed !!

Cheers,

Kaycee


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PostPosted: Tue Nov 13, 2007 9:58 pm 
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Thank You so much.


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PostPosted: Sun Jan 13, 2008 10:10 am 
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THANK YOU!
"Give a man a fish you have fed him for today, teach a man to fish and he'll build stompboxes instead!"

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PostPosted: Fri Feb 29, 2008 10:41 am 
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curiosity kills, right? can you explain why this diagram shows the resistor on the neg side of the LED instead of positive? i've seen it done both ways, is there an advantage to this one?

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PostPosted: Fri Feb 29, 2008 10:50 am 
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It doesn't matter which side the resistor is on.

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PostPosted: Mon Apr 21, 2008 10:26 am 
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I wired up a confidence booster in its own housing, using a 3PDT footswitch and there is loud pop when I switch the pedal on. In your post above you say
Quote:
"If this alone doesn't take care of the pops simply add pull-down resistors to the circuit".

Can someone expand on this for me? Where would these resistors go? How many and what value(s) would I use?


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PostPosted: Mon Apr 28, 2008 5:31 am 
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How is the stomp switch wired? Does it short the circuit's input to ground when in bypass mode? If it doesn't it should.
Attachment:
p001.jpg
p001.jpg [ 59.89 KiB | Viewed 25551 times ]


Take a look at the circuit schematic on the last page of the build instructions. The only place a pull down resistor will do any good (if at all) will be by hanging a 1M or larger resistor off of the left side of capacitor C1 to ground.

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PostPosted: Wed Apr 30, 2008 7:18 pm 
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Location: West Wales ... isn't it.
Pic removed by Naz Nomad

I don't struggle with offboard wiring at all, but I'd just like to thank Stephen for this diagram.

At 2:15 a.m. it's certainly increasing my level of 'awakeness' :D :D :|


Last edited by Naz Nomad on Sat May 24, 2008 7:13 pm, edited 1 time in total.

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PostPosted: Mon May 05, 2008 6:19 am 
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Thanks a lot!

What's the difference between your 3PDT diagram and the one used at General Guitar Gadgets site

Example http://www.generalguitargadgets.com/pdf/ggg_bsiab2_lo.pdf


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PostPosted: Mon May 05, 2008 9:00 am 
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Location: West Wales ... isn't it.
Not much difference really ... if you consider each vertical line of contacts as a single switch (1,2,3 is switch A) (4,5,6 is switch B) (7,8,9 is switch C) ... It's just three SPDT switches all in one package, that all switch at the same time.

It doesn't matter if it's wired like ...

1 4 7
2 5 8
3 6 9


or


4 7 1
5 8 2
6 9 3


or


7 1 4
8 2 5
9 3 6


... it'll still function the same way.


Even upside-down works too ...

3 6 9
2 5 8
1 4 7


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PostPosted: Sun Jun 08, 2008 2:44 pm 
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Good info.


Last edited by jacksoncustomshop on Sat Jul 11, 2009 10:15 pm, edited 1 time in total.

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PostPosted: Sun Jun 29, 2008 1:50 pm 
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Forgive me for being stupid but I have a few questions (as usual).

How do I tell on a non BYOC box where the PCB input/outputs are?

The standard 'input' and 'output' I assume are where you plug your jacks into, but which connection is this from? Left Middle or Right?

If you already have an LED in the circuit somewhere do you still need to connect it to the 3PDT when modding for true bypass?

Ground is simply connecting that lead to something metal like the inside of the enclosure right? Or is it connecting everything to the negative side of the battery/AC jack?

Last thing, I built a BYOC octave fuzz and there was no resistor for the LED, why is this?

Hope you can enlighten me.

Nathan


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PostPosted: Tue Jul 01, 2008 5:41 am 
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1) Get a schematic and follow the wiring and/or traces on the PCB. If it's a pedal like a Boss you will need to eliminate the flip flop circuit that controls the bypass switching.

2) What?

3) Yes

4) The pedal's chassis is ground. The ground lead from the battery is switched so that the battery ground gets disconnected when a plug is in the input jack.

5) Because you were shorted a part.

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PostPosted: Tue Jul 01, 2008 9:50 am 
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Ah thank you very much Stephen, very helpful.
What I meant by 'number 2' was which part of the input/output jack do I connect this to eg. ring/tip/sleeve but I've only recently learnt this terminology (after the post) and referred to these as 1/2/3.

On the topic of grounding, how come on the BYOC pedals we don't have to solder a wire to the case?

Thanks again.

N


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PostPosted: Tue Jul 01, 2008 10:48 am 
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punching_sandwiches wrote:

On the topic of grounding, how come on the BYOC pedals we don't have to solder a wire to the case?

Thanks again.

N


See Stephen's response to #4. Everything is grounded to the case via the jacks, which are connected directly to the case.

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PostPosted: Sat Jul 19, 2008 9:09 am 
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Can you explain why you don't recommend the DPDT that doesn't short the PCB input to ground in the off position? Just curious. Thanks!

Edit: Never mind, I just read the post again! :oops:


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PostPosted: Mon Aug 11, 2008 6:00 pm 
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Can you elaborate on how the switching mechanisms in large production stompboxes works? I have an old DOD pedal that appears to incorporate a transistor. I'm interested in converting it to a true mechanical bypass....

Thanks!


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PostPosted: Thu Aug 14, 2008 5:06 pm 
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Companies like DOD and Dunlop use what the industry calls "hard wired" bypass which is what is shown in this diagram...
Attachment:
p001.jpg
p001.jpg [ 56.44 KiB | Viewed 25509 times ]


The only pedal I know of that uses a transistor with the stomp switch is the ProCo RAT. This is what is known as the millennium bypass circuit. It uses a DPDT stomp switch for true bypass switching along with an N-channel JFET to light the status LED. If your pedal uses a SPDT stomp switch the transistor is not part of the bypass switching.

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PostPosted: Wed Oct 01, 2008 10:03 pm 
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So I'm modding a friend's wah pedal and decided to pop open my Keeley modded wah and see what he did for modding. I decided to borrow some of his ideas as well as from this link: http://www.stinkfoot.se/andreas/diy/mod ... tep_3._the
posted here in the forum.

When it came to wiring the switch I decided to follow Keeley's lead, which is different from stinkfoot's instructions. My question is where's the ground? The way I have it wired works. I have a wire caring the signal to the switch (lug 4), but no ground wire from it. See the illustration below:
Attachment:
p001.jpg
p001.jpg [ 13.69 KiB | Viewed 25511 times ]


I have the LED ground to the lug on the output jack.

I like the fact that the pedal works and sounds better, but I would to understand what the heck the switch is doing!


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PostPosted: Thu Oct 02, 2008 10:16 am 
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Here are a couple of pics from Keeley's wah mod switch. Maybe this will help.
http://i242.photobucket.com/albums/ff13 ... Switch.jpg
http://i242.photobucket.com/albums/ff13 ... witch2.jpg


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PostPosted: Fri Oct 10, 2008 9:30 pm 
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I picked up the DOD Noise Gate 230 just last week. I want to add a DPDT switch to make it "True Bypass." How would I wire the DPDT switch with the AC jack? I should point out that I'm not using leds or the Millenium Bypass circuit.

David

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PostPosted: Sun Oct 12, 2008 4:09 am 
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Maybe I'm not understanding what it is you're asking here but a DPDT bypass switch doesn't get wired to the AC jack.

If your 230's stomp switch is wired the same way a DOD YJM308 is it will be just like the SPDT Bypass (non-true bypass) diagram at the top of this thread. See the DPDT True Bypass wiring diagram (2 diagrams below it) to see what you need to do to convert your 230 to true bypass switching.

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