Strange issue with Maestro Phaser...

[Projectile]

I just finished modding an old Maestro Phaser to true bypass, and added a Boss style DC jack. The battery clip is no longer easily accessible because I replaced the battery cover with a mounting plate that I used to mount the DC jack. Now I'm having a very strange issue. When I switch the pedal on I can hear the characteristic notch filter sound of the phaser, but it doesn't oscillate. It's just "static" like an eq. In order to get the phaser to start oscillating I have to unplug the input jack and plug it back in once or sometimes twice. Wiggling the plug in the jack does nothing. I have to physically disconnect it and reconnect the TS plug from the jack while the pedal is on. Then it will just miraculously start working perfectly as it should. If I unplug the DC jack for a few seconds and plug it back in, I have to mess with the input jack again to get it to start oscillating again.

I can't figure out what in the world could be going on. I don't think it's a bad connection, because the true bypass is working perfectly and it passes a signal okay. I tested the true bypass with a battery before I added the DC jack, so I know that's okay. I'm figuring it must have something to do with the DC input. It sounds like the LFO part of the circuit just doesn't want to "kick on" until I break the connection with the input jack and reconnect it. Weird.

The negative side of the DC jack connects to ground through the input jack, just like the battery did. So, unplugging the input and plugging it back in would be temporarily breaking the connection of the negative side of the DC jack, and then reconnecting it to ground, but I don't understand why that would trigger the LFO to start running.

Anybody have any idea what the problem might be? Could simply wiring the jack backwards cause this behavior? I am totally lost.


---
I can't find a schematic anywhere. This is the MP model made by Moog for Maestro, not the PS model made by Oberheim that you can find all over the internet.

[Projectile]

With some more experimenting I have determined that it is specifically when the tip of the guitar cable touches the ring contact of the input jack that the oscillator starts working. Normally the ring is connected to ground through the sleeve of the TS connector, which completes the power circuit when a cable is plugged in, but for some reason the LFO only starts to work when the tip touches the connector, and then it continues to work once the jack is slid the rest of the way in and connected to ground. It stops working again if I remove the jack, and I have to repeat the procedure of slowly inserting the jack until the tip touches and I hear the oscillator start up, and then I can push the jack the rest of the way in. If I insert the jack too quickly, the LFO never starts oscillating and the phaser just acts as a static eq.

Can anyone make any sense of this? Why would the tip of the guitar cable touching the ground wire from the DC jack make the LFO start working? I'm stumped.

Thanks.

[StephenGiles]

Do the words "leave well alone" come to mind?

[Projectile]

 I don't consider a pedal that I can still hear operating when it's switched off to be working "well". I don't care if that's how they made them back then. I'm going to mod it to true bypass so it's usable in my setup.

I also don't use batteries, period. I don't see anything wrong with adding a DC jack to an old pedal. I didn't do anything to the circuit that couldn't be easily reversed. I didn't drill any holes in the enclosure, and the pedal was already missing knobs and beat to hell when I found it in a box of junk in someone's attic, so it's worthless as a collectors item. I really don't understand your attitude. Isn't this a DIY stompbox forum? Isn't it a common procedure to add a DC jack to an old pedal? Why the hostilty, and why is it so hard to get help for a simple problem I'm having? Was my description not clear and adequate?

[JKowalski]

I don't think he was trying to be hostile.

That is a strange problem. I can't see how, but perhaps there is a problem somewhere else in the circuit, since you said it was "beat to hell" when you found it?

How long does it take to start oscillating when you have the tip connected?

Is it an open frame jack? If not, what type? Maybe there's a mechanical jack problem?


I just realized, I bet the problem is this: The pedal was probably set up beforehand to start oscillating by hitting the on/off switch, and now that you have true bypass instead, it can't start up oscillating by istelf because it needs that trigger that the non-true bypass switch gave it. I BET THATS IT. If I recall correctly, some pedals that contain oscillators did this so there was no chance of any oscillation noise bleeding into the bypassed signal.

The jack to ground thing might be starting up some weird thing that triggers the oscillator. But I can't imagine how THAT would work.

Check the schematic.

[guitarhacknoise]

Hey man,
Stephan was just trying to make you think.
Don't forget you are the one asking for help, and your response is a sure fire way to get snubbed.

Jkowalski has a good idea there, if that's not it though,
here is what I would do....
reverse all the mods, do one at a time until you realize where you went wrong.
or if that's gonna hurt you too much
take a battery snap and attach it to the jack you hacked in.....does it work correctly off the battery?
if so the P.S. may be too hot, remember this thing was designed for 9v. and loaded 9v drops to 8.whatnot. and oscillators can be touchy.
-Matthias

[guitarhacknoise]

oh crap!
I actually just processed the problem!
I'm out of whack!
you just totally mis-wired the switch!

[Projectile]

Sorry for being snippy with Stephan. It just seem that I get that dismissive attitude a lot on this forum. I thought that being as thorough and descriptive as I was in my question would have been enough of an indication that I'm not just some idiot hacking up a nice vintage pedal. I considered what I was doing before hand, and proceeded very carefully. I don't get treated like an idiot on any of the other internet forums where I am a member, but for some reason I find this place to be unusually condescending towards my questions and it unnerves me.

Thank you JKowalski and guitarhacknoise for your help. It is greatly appreciated. Your suggestions were exactly what I needed to get me thinking in the right direction and start eliminating variables.

I will have to take the pedal apart again and do some poking around. I will report back shortly with my results. Thank you.

[Projectile]

Update:

I have tested everything I could think of, and here is what I found.

-The pedal works fine with a battery
-I re-traced the True bypass mod I did, and the only change to the circuit is that the guitar signal is no longer connected to the circuit when the pedal is switched off, it is properly bypassed. The path of the power source was not affected by the bypass as far as I can tell
-If I connect a battery directly to the contacts on the DC jack, the pedal works fine, oscillation starts immediately and isn't interrupted.
-If I reverse the power leads the pedal does not work at all. No audio is passed.

From this I think I can safely draw the conclusion that the bypass switch is not the problem. I think I can also safely say that the DC jack is wired properly and working. It seems now that there is only one possibility left: The pedal just doesn't like to run off of a DC walwart. It seems that for some reason it needs to be powered by a battery for the oscillator to start. Weird.



So now here is my updated question:

Why would the pedal refuse to work properly off of a wall-wart? What are the potential differences between these two power sources? Is it likely a voltage issue, amperage, or grounding? What steps can I take to determine the problem, and then is it possible to get the pedal working off of a walwart by making some minor modifications?

I really don't want to have to run this thing off a battery. The original battery door and clip were missing when I got the pedal, so the only way to install a battery is to leave it dangling outside of the pedal. the battery door is a strange custom part that I can't find anywhere, and to make my own working removable battery door/clip would be a major pain in the neck. I would really like to just be able to run this thing off of DC if possible. I would greatly appreciate any help.

---

Also, I messed with the input jack some more and I can't really figure out what triggers the oscillator to start running. The jack is closed so I can't see what is going on inside of it. I tried shorting the connectors together in different ways with a jumper while the cable is plugged in and I couldn't replicate the behavior that starts the oscillator when the jack is plugged in slowly. I can't figure out exactly what is happening. I just know that if I wiggle the plug in and out while it's plugged halfway in, momentarily breaking and re-establishing the connection, the oscillator starts running and then keeps working all night, as long as I keep everything plugged in. I can turn the pedal on and off, it doesn't matter. But as soon as I unplug the input cable or the power cable, I have to mess with the input jack until I hear the oscillator start up again. This behavior is 100% repeatable. I just wish I could see inside the jack to determine exactly what is happening.

Any ideas?

Thanks.

[Lurco]

is this of any help? http://www.diystompboxes.com/smfforum/index.php?topic=54389.0

[Projectile]

Thank you Lurco. That was a lot of help. It wasn't specifically about the same model pedal I have, but it did point to the schematic I needed! Here it is:

http://www.dredgetone.com/Schematics/Phaser%20MP-1.pdf

In regards to that thread, the OP seemed to have solved his problem by replacing one of the opamps, but the oscillator in his phaser wasn't working at all, even with batteries. I don't want to start replacing opamps yet, because it doesn't appear that my pedal is actually broken. It just doesn't want to run off of a DC wal-wart for some reason. If I could even just figure out how to replicate the momentary connection on the jack that starts the oscillator running, I could possibly just install a momentary switch on the plate next to the DC jack that would manually start it. But I can't even figure out what is triggering the oscillator to start when I mess with the input jack. It just magically starts up while I'm slowly wiggly the TS connector halfway in and out of the stereo input jack.

[Projectile]

Update:

Sindran, who has the same pedal, has informed me that his Maestro phaser works fine with an AC adapter. So, it's not just a problem that is characteristic of these pedals. Now, I'm thinking that either this pedal just doesn't like the AC adapter I'm using, or there is potentially a problem developing with my pedal that is causing it to be finicky about the power source. Anyway, I think my next course of action is to buy the same 1spot adapter that Sindran is using (I could use one anyway) and see if that works.  If anyone else has any other ideas or suggestions in the meantime it would be greatly appreciated.

[tiges_ tendres]

What do you mean boss style DC jack?  Boss jacks are rectangular arent they?  Did you drill and then file a square hole with which to mount the jack?

Do you have a picture of the jack you used?

[Projectile]

By boss style I just mean a normal 2.1 mm DC jack wired with a negative pin and positive shell. I just describe that style of DC jack as "boss style" because I am used to most DC jacks having a positive tip and a negative shell. I was under the impression that it was Boss (Roland) that standardized the backwards wired DC jack for effects pedals, so I always heard them referred to as "boss style" DC jacks outside the pedal building community. It was probably not necessary for me to describe it as a "boss style" jack here, because almost all effects pedals use those style jacks, but I did it anyway out of habit. I thought that was what everyone called them. The one I used was from smallbear:

http://www.smallbearelec.com/Detail.bok?no=93

However, I have determined that it is unlikely that the jack is the issue, since I can connect a 9v battery directly to the jack and it works fine.

I mounted the jack by drilling a hole in a plastic plate that I am using in place of the missing battery cover and clip. It's pretty cheesy, but it works.

[JKowalski]

Okay - first, are you using mono cables for the input to this pedal? They have it set up so the battery's NEGATIVE is connected to the second contact on a stereo switch. So the circuit only turns on when you plug it in, as the second contact goes to ground, and thus the pedal circuits ground, if you plug in a MONO cable. Granted, the second contact should be shorted to ground by the output of what is was plugged into earlier anyways, but I don't know what your setup is.

That's the only thing I can possibly think of that might be causing this input jack dealio...

This could also be the cause of the battery/wallwart thing: the jack you have set up might be already connected directly to the CASE and CIRCUIT GROUND, wheras the BATTERY needs to be "input jacked" first to connect it to your ground.

[aron]

OK, I will put a guess in. Measure your wall wart. Check the voltage and you might be amazed. Try a regulated 9V wall wart and I bet it works.
(OK, I re-read, the 1 spot IS regulated. I bet this is the problem). Build a 9V voltage regulator circuit or buy a regulated power supply like the 1 spot)

[Projectile]

Okay - first, are you using mono cables for the input to this pedal? They have it set up so the battery's NEGATIVE is connected to the second contact on a stereo switch. So the circuit only turns on when you plug it in, as the second contact goes to ground, and thus the pedal circuits ground, if you plug in a MONO cable. Granted, the second contact should be shorted to ground by the output of what is was plugged into earlier anyways, but I don't know what your setup is.

That's the only thing I can possibly think of that might be causing this input jack dealio...

This could also be the cause of the battery/wallwart thing: the jack you have set up might be already connected directly to the CASE and CIRCUIT GROUND, wheras the BATTERY needs to be "input jacked" first to connect it to your ground.

Yes, I am using a mono guitar jack, and the input jack is stereo. The second contact (ring contact) of the stereo jack is connected to the negative terminal of the battery as you described. I soldered a wire from the negative pin of the DC jack to this same contact on the input connector. The positive pin from the DC jack is soldered directly to the board in the same place that the positive lead from the battery used to be connected. The positive lead from the battery now goes through the DC jack, so that the battery is disconnected when a power cable is plugged in.

The negative lead from the battery and the negative lead from the DC jack both go through the second connector on the input to ground, and they both require the cable to be plugged in to complete the circuit, so there is no way this would explain the difference.

Furthermore, I have connected a battery directly to the DC jack itself in EXACTLY the same way a wall-wart is connected and the oscillator works perfectly. The ONLY difference is that the oscillator doesn't start when the pedal is powered by a wal-wart and it does work when powered by a battery, the wiring is EXACTLY the same.

The thing with the input jack is just some sort of "trick" I discovered that starts the oscillator running with the wal-wart. I can only assume that the same "trick" would work if a battery was also connected, but since the oscillator works fine with a battery already, performing the little diddly with the input jack isn't necessary. My best guess is that the pedal is getting slightly too much voltage from the wallwart and the oscillator refuses to start because it will only start if it sees a very specific voltage range. So, messing with the input jack momentarily gives it little spikes of voltage to start it oscillating and then as long as a complete the connection immediately after it starts, it continued working. However, I have no clue what I am talking about and this is just a guess. Thanks for the suggestion though.

----

Also, Does anybody know what the little trimpot on the board does? I'm afraid to mess with it since it might be already be carefully calibrated, and I wouldn't want to make things worse. I've been told that this phaser circuit is very similar to a small stone if that helps. Thanks.

[Projectile]

OK, I will put a guess in. Measure your wall wart. Check the voltage and you might be amazed. Try a regulated 9V wall wart and I bet it works.
(OK, I re-read, the 1 spot IS regulated. I bet this is the problem). Build a 9V voltage regulator circuit or buy a regulated power supply like the 1 spot)

Thanks Aron. I figured that might be the problem. I was using the same zoom power adapter that works with all of my other pedals, but I realized that doesn't necessarily mean it's well regulated, so I ordered a 1-spot earlier today. I'll check the zoom adapter with my multimeter in the mean time. Thanks.


UPDATE:

Yup, my 9v adapter is putting out a steady 12.8 volts!!!!!  M*ther F**ker!  I guess I should have checked that first. I just assumed that since it had worked with half a dozen other pedals that it was putting out the proper voltage. I'll know better next time.

Thank you to everyone that gave me so many helpful suggestions. I'll report back when I get my 1-spot, but I assume that my adapter is the problem at this point.

Cheers.

[JKowalski]

Yeah, I have had some wall warts like that. I've even had one supposedly 9V one run up to 15 volts! Usually all my pedals work fine with the typical 12V+ that they usually put out so that hasn't been a problem for me. Just a really picky oscillator, I guess. Hope it works for you when the power supply arrives!

It would probably be a good idea to put in a LM7809 regulator in the path from the power supply to the circuit board - so you wont have to worry about it anymore.

[Projectile]

Got my One Spot adapter today. Pedal works fine now. I guess the oscillator was just really finicky about how much voltage it recieves.  Thanks for the help everyone.