Boss CE-2 Chorus/Vibrato Mod

[Joe Kramer]

NOTE: Please skip several posts ahead to the revised version of this circuit with the SPST switch.  I leave the present post intact for continuity.  Thanks--Joe


Hi!

Disclaimer: I haven't tried this yet!

Here's one possible way of doing a chorus/vibrato mod to a CE2.  The extra parts could be mounted on a small piece of perfboard and held by the lugs of the DPDT switch.  In the "chorus" setting, the DPDT switch bypasses the extra circuitry completely.  In the "vibrato" setting, when the CE2's footswitch is activated, the wet signal is passed, but the direct signal is turned off by the extra FET connected to the opposite side of the flip-flop circuit.  When the CE2's footswitch is used to bypass, you have normal dry signal again.

Here's the CE2: http://home.hetnet.nl/~chrisdus/download/ce2.gif

Sorry for my shaky-looking schemo.  If anybody tries this before I get a chance to, post your results!

Regards,
Joe



1.  Cut the trace between R21 and pin 2 of IC1

2.  Run wires to center lugs of DPDT switch.  Jumper two lugs for normal "chorus" setting.

3.  For "vibrato" setting, attach drain and source of FET to the two other DPDT switch lugs.

4.  Connect 1N914 to gate of FET.

5.  Connect .047 cap from diode to ground.

6.  Connect 1 Meg resistor to the collector of Q6.

Code Select Expand


                  cut trace
>------/\/\/\----|            |--------->to pin 2 IC1
     R21-47K    |            |
                |            |
                |            |
                |   *----*   |
                |            |
     DPDT SW.   |---*    *---|

                    *    *
                    |    |
                    |    |
                    |    |
             FET   D|    |S
                   =======
                     G^
                      |
                      |
                      |
            1N914     V
                     ===
                      |
                      |        1 Meg
                      |-------/\/\/\----> to collector of Q6
                      |
                    ----
            .047uF  ----
                      |
                      |
                      V
                   Ground






[Mark Hammer]

Aw heck, it's even easier than that.

The duplication of the FET switching circuitry, and use of the "flip" side of the flip flop (the CE-2 only uses the "flop" side) to switch the dry path is a good idea, and actually something I suggested a while back, although you've clearly done a better job conveying it (and also put in the work of doing an illustration...thanks!).  You don't need a DPDT, though.  An SPST will do nicely, in fact.  The FET doesn't really care all that much about what resistance is in parallel with its drain-to-source path.  If that resistance just so happened to be, oh I dunno, say ZERO ohms, the FET would still behave itself, except that being on or off would make no difference to pedal function.

In essence, what you end up with is a pedal that switches between all wet (flip) and all dry (flop).  The toggle serves to bypass the additional FET so that when you switch it to "all wet", you have the option of adding dry (chorus) or not (vibrato).

There is no reason for it NOT to work, although given you are in FET-land, pay attention to pinouts - they deceive, oh yes they deceive.

[Joe Kramer]

You don't need a DPDT, though.  An SPST will do nicely, in fact.  The FET doesn't really care all that much about what resistance is in parallel with its drain-to-source path.

You're right about the SPST, Mark.  I guess I just thought it would be nice to have the option of the completely stock signal path, even if the FET causes little or no change to the signal.

But now it occurs to me that the DPDT is probably going to pop without coupling caps and pull-down resistors.  With a SPST, the switch should straddle the drain and source of the FET.  When closed it simple overrides the FET, as you said Mark.  Although the SPST might also pop. . . .

I shall also heed thy wisdom, and beware the deceptive FET pinout!

Joe

[Joe Kramer]

Okay, here's the revised SPST version.  Thanks Mark!

1.  Cut the trace between R21 and pin 2 of IC1

2.  Run wires to lugs of SPST switch (the asterisks).

3.  Connect FET drain to 47K side of switch, and FET source to pin 2 side of  switch.

4.  Connect 1N914 to gate of FET.

5.  Connect .047 cap from diode to ground.

6.  Connect 1 Meg resistor to the collector of Q6.

Code Select Expand

                 cut trace
>------/\/\/\----X            X--------->to pin 2 IC1
     R21-47K    |            |
                |            |
                |            |
                |     /      |
                |    /       |
     SPST SW.   |---*    *---|
                    |    |
                    |    |
                    |    |
             FET   D|    |S
                   =======
                     G^
                      |
                      |
                      |
            1N914     V
                     ===
                      |
                      |        1 Meg
                      |-------/\/\/\----> to collector of Q6
                      |
                    ----
            .047uF  ----
                      |
                      |
                      V
                   Ground


[vanhansen]

I've been reading over this thread try to grasp it.  I have a CH-1 and from another post from Mark in the past, it states they same mods can be done to the CH-1.

In the CH-1, the resistor is R53.  Couldn't you just lift one end of the resistor and attach it to a SPDT switch?  Of course you run in to the issue where there is no output when bypassed.  I'd like to be able to go from stock chorus to vibrato and retain the output when bypassed.

[Joe Kramer]

Of course you run in to the issue where there is no output when bypassed.  I'd like to be able to go from stock chorus to vibrato and retain the output when bypassed.

That's exactly what this mod does.  With the extra FET, the signals toggle back and forth: when the BBD signal is passed, the straight signal is blocked; when the straight signal is passed the BBD signal is blocked.  This is possible because of the symmetrical nature of the electronic switch in the pedal: when the voltage at the collector of Q7 is high, the collector of Q6 is low, and vice versa.  With the higher voltage sent to the gate of the FET, signal is allowed to pass from drain to source.  With lower voltage to the FET gate, no signal can pass.

Basically, we're duplicating the same FET switch function that's already on the stock circuit on the BBD signal side, but we're putting it on the straight signal side too.  Thanks to the flip-flop switching, we can have one side off when the other is on.  Take a look at the CE2 schematic.  See where FET Q8 essentially connects to the collector of Q7?  We copy this, but add our FET after the 47K on the straight signal; also our FET connects to the opposite side of the flip-flop, the collector of Q6.      

The addition of a SPST switch practically bypasses the added FET and restores the normal chorus sound.

[vanhansen]

I think I got it.  I'm putting some mods on my CH-1 page and would like to include this one for the CH-1.

Other than part numbers, the one difference I see is that the CH-1 doesn't have the .047uF cap going to ground after the diode.  In fact, the diode off Q1 in the CH-1 leads to MONO. I see where MONO comes in to Q4 via R11 (1M) and C3 (.047uF).  I'm guessing that is where it should go and then from the 1M off the new perf circuit to Q4.

Also, what additional FET is needed here?  Another one like Q1, K30AY?

I'm also trying to visualize the switch wiring but I'm having a hard time with the forum code used in your diagrams.  I can almost see it, but not 100%.  

Does your diagram have the Drain and Source connected to the outside lugs?  

What goes to the middle lug and where does it go?  The 47k resistor?

This can still work by lifting the leg closest to Q1 and connecting it to the switch, correct?

If you don't have a CH-1 schematic, let me know and I can get one to you to look it.

I never thought I would be able to decipher this schematic.  A little of it is making sense.  It's a start.  

[Mark Hammer]

Well in fact it's a lot more generic than that.  As I'm fond of repeating ad nauseum, most commercial manufacturers who produce analog modulation or time based pedals AND use FET-based switching will almost invariably use the standard flip-flop circuit (whether discrete like Boss or CMOS, like DOD).  What is critical for all of us here is that since virtually all of these effects rely on combining wet and dry to create the effect heard, all you need to do to cancel the effect and "fake bypass" is to inhibit the wet signal from reaching the mixing stage by letting the resistance of a FET (in the way) go high.  That's it.

What this means is that they almost always use ONLY the flip from the circuit and not the flop, as discussed above in earlier postings.  So, if you want to get vibrato by interrupting the dry signal with a toggle and having ONLY the wet signal from a phaser, univibe, flanger, or chorus, you will be out of luck if you try to switch back to "bypass", because the pedal only switches the wet signal and not the dry (which will continue to be off, just where you left it).

HOWEVER, since the flop is still available for duty, you can do the above described mod of adding a FET, cap, resistor and diode to the opposite control line (and there WILL be one) and sticking the drain and source in parallel with the toggle.

[Joe Kramer]

Also, what additional FET is needed here?  Another one like Q1, K30AY?

K30AY would be nice, if you have some, but I don't.  I was going to try 2N5457 or MPF102.  I also happen to have some 2N4858 which is more of a dedicated switch FET.  Maybe Mark would have some suggestions.
 

I'm also trying to visualize the switch wiring but I'm having a hard time with the forum code used in your diagrams.  I can almost see it, but not 100%. Does your diagram have the Drain and Source connected to the outside lugs?  

Sorry about the drawing.  I wish I could post a regular schemo but I don't have the computer tools or chops right now.

As of the revision with the SPST switch:  the drain and source go to the two lugs of the switch (you only need two now),  and so do two wires from where you will have cut the trace between the 47K and pin 2 of the opamp.  Not sure if it really matters, but I think you want the drain as your "input," so that would be the 47K side.

When the SPST switch is open, the FET is in command of the signal.  When the SPST switch is closed the FET becomes overridden by the hard connection.  At that point the signal won't care whether the FET is open or closed--it hard-bypasses through the switch.

That make any sense?

If you can post or link to the CH-1, that would probably help.

Joe

[vanhansen]

Ahh, OK.  I have some MPF102's laying around.  I'll try those.  I was just thinking it would be necessary to use the same part number.

Your explanations make sense now, both of you.  I appreciate the info.

Joe, I have the CH-1 schematic here:
http://www.erikhansen.net/diy/schematics/boss/BossCH-1.gif

I also drew up a schematic of sort for this.  Let me know if this is right.  It looks to be, based off what you stated.  I did this for the CH-1.  The 47K resistor goes to another transistor, not an opamp.

http://www.erikhansen.net/diy/ch1vibratomodschem.gif

Thanks again for both of y'all's help.

[Joe Kramer]

Hey Erik!

I took a look at the CH-1.  Tell me, is this the way it works: When you only plug into output A (Mono) you get a mix of dry and wet sounds--typical chorus.  When you use both outputs, you get dry out of B, and wet out of A.  Is that right?  And when using both outputs, if you hit the bypass pedal, do you get all dry from from both outputs?

If the above is correct, shouldn't you just be able to stick a dummy plug into output B, and switch between vibrato and dry from output A?  In that case, you don't need the mod.  At most, you would maybe want to be able to flick a switch so you could go back to normal chorus without fooling around with the dummy plug.  

What I described above is basically the way the CE-3 works.  I may be misunderstanding what I see on the CH-1 schemo though.  

Let me know.

BTW, your drawing of the mod is right-on, but I'm not to sure about the connections to Q1 & Q4 as it pertains to the CH-1.

Joe

[TheBigMan]

I took a look at the CH-1. Tell me, is this the way it works: When you only plug into output A (Mono) you get a mix of dry and wet sounds--typical chorus. When you use both outputs, you get dry out of B, and wet out of A. Is that right? And when using both outputs, if you hit the bypass pedal, do you get all dry from from both outputs?

That is correct.  It's been posted in a few places (but maybe not here) that you can get vibrato from the CH-1 by using a patch cable in output B that doesn't connect to anything.  You could of course fit a switch to do the same job, but why bother?  :wink:

[Mark Hammer]

DOD has been using the J113 for bypass/switch purposes for a while.  If you can't score a suitable K30, a J113 will be a good sub.  Of course that assumes you can find one of THOSE too.

[vanhansen]

I took a look at the CH-1. Tell me, is this the way it works: When you only plug into output A (Mono) you get a mix of dry and wet sounds--typical chorus. When you use both outputs, you get dry out of B, and wet out of A. Is that right? And when using both outputs, if you hit the bypass pedal, do you get all dry from from both outputs?

That is correct.  It's been posted in a few places (but maybe not here) that you can get vibrato from the CH-1 by using a patch cable in output B that doesn't connect to anything.  You could of course fit a switch to do the same job, but why bother?  :wink:

Thanks for confirming that, TheBigMan.  I wasn't sure if that's how it worked or not.  I'll try the old mono plug trick.  And thanks, Mark, for the clarification.

Now, another question.  What if you are running the CH-1 in stereo.  Then how can you switch between vibrato or chorus?  Would the mod like what is done to the CE-2 work?

[JIG]

I took a look at the CH-1. Tell me, is this the way it works: When you only plug into output A (Mono) you get a mix of dry and wet sounds--typical chorus. When you use both outputs, you get dry out of B, and wet out of A. Is that right? And when using both outputs, if you hit the bypass pedal, do you get all dry from from both outputs?

That is correct.  It's been posted in a few places (but maybe not here) that you can get vibrato from the CH-1 by using a patch cable in output B that doesn't connect to anything.  You could of course fit a switch to do the same job, but why bother?  :wink:

Thanks for confirming that, TheBigMan.  I wasn't sure if that's how it worked or not.  I'll try the old mono plug trick.  And thanks, Mark, for the clarification.

Now, another question.  What if you are running the CH-1 in stereo.  Then how can you switch between vibrato or chorus?  Would the mod like what is done to the CE-2 work?

Will that work for that Dano Cool Cat? Mine runs the wet out of the mono out while the stereo out runs the dry signal. I run mine into two seperate amps. Will have turn one amp off and see what it does.

JIG

[vanhansen]

Joe,  I've added this info to my CH-1 mods page even though it is for the CH-1 if that's OK with you.  I also have the "plug in jack B" trick noted for the CH-1.  I'd like to figure out how to do this same thing on the CH-1 without using the plug trick, or use the plug trick but make it switchable?  It really depends on if this is possible to do even when running in stereo mode.  It would be cool.

Mark, I have the delay range mod and ring modulator mods there as well.  Thanks for letting me put it on my page.

http://www.erikhansen.net/diy/ch1.htm

[Joe Kramer]

Hey Erik,

Your page looks good.  I appreciate being given some credit--I've never been "published" on somebody's web page before!    .j,

As far as the other mods: it seems to me you could figure out just about any mod you want on these pedals by understanding the building blocks involved.  You have basically: a dry signal, a wet signal, a mixer, a back-and-forth switch, and some outputs.  You have an idea for a certain function, and then you look at which building blocks you need to realize it.  You can go a long way by simply duplicating what's already there and using it in a way that gets you what you want out of the circuit.  That's the DIY spirit!

Joe

[Mark Hammer]

In general, this mod is applicable to at least 60% of the flangers, phasers, and choruses out there.  The vast majority using FET switching ONLY use one fet for lifting the wet signal - i.e., they ignore the flop and only use the flip.

[vanhansen]

I decided to split the mods for the CH-1 and CE-2 in to two separate pages.  For anyone interested, you can check them by going to the DIY Effects and Mods link on my site (link in my sig).

Thanks to Mark and Joe for all their info and help on clarifying things.

[mrsage]

I'm sure this is possible on the CE-5, as well...

Anyone tried it?