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Solutions for mains-pop triggered wah-pedal (buffer?) noise?

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  • Solutions for mains-pop triggered wah-pedal (buffer?) noise?

    Hi guys, I have the following problem:

    When using my Morley Pro Series II Wah pedal, I start to get problems with audible crackles and pops through the amp, clearly caused by electrical items that come on elsewhere in the building. Worst thing is, after a loud pop when an appliance comes on, the wah pedal keeps making a loud hiss -while guitar signal drops below this noise level- until I step on the footswitch of the wah. It makes no difference whether I'm using a regulated 9V DC power adapter with it, or run the pedal off a battery. The problem is gone when I don't use the wah, i.e. guitar directly into amp or through other stompboxes.

    Some possibly useful info:
    - I use the pedal in between my guitar and amp, not in the fx loop
    - Morley wah pedals buffer the guitar signal (in both 'on' and 'bypass' mode)
    - The Hughes & Kettner 50W combo amp is run off an ungrounded mains sockets mostly (I live in a historic building with, unfortunately, very few grounded power outlets)
    - The wah pedal power supply is not grounded (battery or 9V dc wall-wart)
    - I use a strat and a les paul; no pre-amps on my guitars

    Is it possible that a peak or dip in the amp mains makes it through the instrument cable into the pedal and somehow 'upsets' the buffer in the wah pedal?

    I like the sound of this wah pedal and I also like that it has a buffer (being the first pedal in my chain). So, if there is a doable fix, I would prefer that over swapping wah pedal types and hoping for the best. Also, I'd really like to understand what's going on here.

    Thanks for your time. Let me know if I can provide more useful info. Any help would be much appreciated!

  • #2
    The problem seems to be bad soldering connections in your equipment.
    I don't see how this is caused by the building electricity.
    You are probably blaming the electricity for defects in the equipment.
    Cracked input jack, bad soldering connections, bad patch cords, etc...
    No matter HOW you arrange the order of the equipment, etc...the problem will not stop until you have your equipment serviced.
    WELL you may have a POP when an appliance comes on, but that does not explain the other symptoms.


    • #3
      Thanks for the insight. Hadn't considered bad soldering yet.

      I took my pedal to the practice room this evening and again pops in the power outlet triggered the noise from the wah pedal. This time with a different amp and grounded outlets only. I verified the triggering of the noise by power discontinuities. For example: it starts exactly when I pull the plug of another amp from its outlet, or when I plug it back in. This is 100% reproducible. Unfortunately, things like the refrigerator's cooling motor can also trigger the noise, and that might obviously switch on halfway through a song. As at home, the noise doesn't end until I step on the wah pedal footswitch.

      Could any of the components on the board have 'gone bad', or are bad soldering connections still the most likely cause?

      I've contacted Morley, and haven't had a reply so far. I don't mean to imply they won't look into it; perhaps they're just busy.

      edit: The jacks look fine. Changing cables, guitars and amps has pretty much narrowed the issue down to wah pedal internals..
      Last edited by m4j0rbumm3r; 05-20-2012, 10:39 PM. Reason: addition


      • #4
        Not that it has anything to do with your problem, but:
        I had an Ibanez Weeping Demon in for repair.
        It too, like the Morley, uses an optical trigger instead of a potentiometer/inductor circuit.
        There are two optical triggers.
        When the second one was being swepped passed, by the pedal action, there was a loud 'pop'
        It turns out that the 'wiper' was actually touching the optic device.
        When the pcb was 'snapped off' of the larger board at manufacturing, a few nubbies were left on the board.
        This in turn pushed the circuit board over too far.
        First repair I ever used a file on


        • #5
          Well, it might not be my problem exactly, but it's certainly a case of 'file under: plain weird'.

          Perhaps I should put a buffered pedal after the wah and see if the problem persists. I guess I might be able to borrow a Boss Bluesdriver or something off a friend to do that test.


          • #6
            Definitely seems like there's a fault in the Morley wah, that makes it abnormally sensitive to interference. Maybe some op-amp in there is unstable and a spike from the mains kicks it into oscillation.

            The only other simple test I can suggest is plugging everything into a good quality filtered and surge protected power strip.

            However, if your outlets are ungrounded, that could make the filtering ineffective.
            "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"


            • #7
              Yeah, I had the same thoughts about the filtered power strip and in combination with ungrounded outlets. Might very well be a waste of time and money. Besides, if the wah is faulty, I should really fix that part of my rig.
              Thanks for the input though. Your faulty opamp thought seems to make much sense, considering that the noise stays constant after an initial 'pop'. The opamp feedback might be sustaining the hiss after the initial pop.

              If all else fails, I could heat up the old soldering iron and replace the old TL072 opamps with new ones. Those parts shouldn't be expensive and I don't mind making the effort. It would still be a bit of a stab in the dark though. Do opamps tend to become faulty? I really wouldn't know.

              BTW, I noticed from their schematics (which they put on their website) that Morley don't seem to use the TL072 in their current models. Perhaps a simple price or spec improvement. I suppose might replace the TL072s with the currently used TL074s as well. I'm sure I can find a spec sheet somewhere


              • #8
                1. How old is this pedal?
                2. Has it ever been worked on/repaired?
                Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

                Oh, wait! That sounds familiar, somehow.


                • #9
                  Thanks for your input guys.

                  The pedal is fairly old, it could be 15 years or so. I bought it second hand and there have been no mods or repairs to it as far as I know.

                  I just got a reply from Scott at Morley. He was very helpful and suggested I check/replace U1 TL072 opamp, and/or the footswitch. I'guess I'll go with his directions.

                  For those interested, some additional observations:

                  - The pedal can be triggered into this weird continuous hiss only when the wah effect is off; stepping on the footswitch to engage the wah effect then ends the noise.

                  - Stepping on the footswitch again to turn the wah effect off does not make the noise reappear. The pedal is thus back into normal functioning until some new discontinuity on the power outlet to the guitar amp (note that the pedal runs off a 9V battery) triggers the hiss again.

                  - The noise can best be described as a loud hiss, very similar to a detuned radio, or a TV displaying static.

                  - Note: although the guitar amp is the only thing connected to the 230V AC power, the pedal shows the exact same problem with several guitar amps, at different locations (buildings), and with or without grounded power outlets. I verified that triggering of the hiss is by power net peaks or dips by unplugging things like the bass amp and synth power adapter from their power outlets. This definitely triggers the wah pedal into hissing. A loose contact or some grit in a jack connection would seem to me to cause brief noises at random intervals, but this continuous hiss is 100% reproducible by plugging or unplugging other electrical items from their outlets.

                  - I've changed guitars, cables and 9V batteries, and narrowed the problem down to the pedal. The pedal has worked without problems in the past, within the same rig essentially, so I'm pretty sure I'm not mistaking an original wah circuit characteristic for a fault.


                  • #10
                    Try banging on it with your fist or something to see if there is a physical connection problem which is being triggered by the line pops. If you can trigger the problem physically I would suspect a bad solder connection or the switch.
                    As far as the switch goes, try a hardwire bypass (run a wire from r1/r33 junction to the switch terminal that connects to output jack). If that solves the problem, then replace the switch. Otherwise, as the person at Morley suggested, U1 is the most likely suspect.
                    "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey


                    • #11
                      Yeah those are all good points. It's no use heating up the soldering iron before doing these quick and easy checks first. Rushing into drastic measures is a temptation to avoid

                      If the op amp replacement is needed however, I might go for a 5332 instead of the TL072 because I read here that the TL072 in general is much more prone to phase reversal, clipping and HF oscillation than the 5332, although it is cheaper and has lower current draw. Even assuming a new TL072 would do the job, a 5332 might still be marginally more reliable and a few cents price difference is obviously irrelevant.
                      Last edited by m4j0rbumm3r; 05-22-2012, 10:03 PM. Reason: spelling


                      • #12
                        Originally posted by m4j0rbumm3r View Post
                        BTW, I noticed from their schematics (which they put on their website) that Morley don't seem to use the TL072 in their current models. Perhaps a simple price or spec improvement. I suppose might replace the TL072s with the currently used TL074s as well. I'm sure I can find a spec sheet somewhere
                        After you posted this, I assume you discovered that TL072 is 2 op amps in an 8-pin package; TL074 is 4 op amps in a 14-pin package.

                        DON'T FEED THE TROLLS!


                        • #13
                          Yes I did, but good call either way.


                          • #14
                            Status update: I replaced U1, the TL072 that is, and this solved the problem. Apparently, op amps can degrade and become ‘unstable’. After very careful listening with the fresh TL072 in, plugging electrical items in and out of outlets, I noticed there is still a very quiet hiss that decays in a fraction of a second after a mains pop. This is not an issue at all, since it is so brief and completely drowned out by the guitar signal. I guess the new op amp stabilizes after a discontinuity, whereas the old one went haywire.

                            As I soldered in a dip8 socket, I might still try a supposedly better op amp type than the TL072 and see what that does. Swapping them in and out will be simple now. I might give the OPA2134 a shot. Before I was thinking of the NE5332 but I found out its lower input impedance makes it less suitable to be the first thing after the guitar.

                            I feel obliged to point out that Scott Flesher of Morley has been very helpful in offering advice on this DIY fix, especially considering that this model has been discontinued quite a while back. He offered to send me replacement parts at a low price as well.

                            Thanks to all on this board who offered advice as well. Some of you were spot on suggesting the op amp as the cause.