Home Forums GuitarPCB Build Support Apollo Trem Causes A Slight Bit of Distortion/Clipping – Buffer Stage Issue?

This topic contains 19 replies, has 5 voices, and was last updated by  Ted 4 hours, 29 minutes ago.

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    I just built the Apollo Trem.  With or without the “Kill” switch engaged I get a slight bit of buzzy distortion in the signal.  Only when I’m playing.  Everything else seems to be working fine and when the pedal is turned off, the guitar sounds perfectly clean and fine through the pedal.

    I am using a gain trimmer set to unity gain, and I have played with the settings on the BLevel and Gain to try to troubleshoot.

    I’ve tried both 9V battery and 9V adapter and it sounds the same.  Tried the pedal in and out of the enclosure.  No buzz when it isn’t activated

    In my quest to troubleshoot further, I was wondering whether it would make sense to take the buffer completely out of the circuit and just use the tremolo?  If so, I’m not sure how I would rewire the pedal to do this.

    Here are some photos- I left the wires long to make sure I’d have room to put everything where I want it, but it is a bit of a mess to work around now that I’m troubleshooting…




    Or if there are any other ideas that would be great.

    Thanks all!





    I’d shorten those wires, to avoid unwanted noise you should keep your audio signal wires as far away as possible from your power wires if you have to cross them you should do it like this

    rather than have them running like this

    Try that first to see if there is any improvement




    +1 Billy

    I agree that wire dressing is very important to avoid cross-talk. I always make a great effort to route my power wiring away from and audio wiring and when unavoidable to make sure not to run audio parallel to any power wiring.

    • Other things that I always do regardless of issue that may help:
    • Re-flow all on-board and off-board solder joints.
    • Check the IC’s after re-flowing to be sure they are properly seated and try alternate ones.
    • Tug on wiring to make sure they are all solid connections.
    • Check all socketed connections to be sure they are true.
    • Very important to visually by color band re-verify all resistors.

    Finally if you have an audio probe that could prove helpful. More info on the Guides Page.

    That I believe is good all around troubleshoot advice. I hope that helps.



    first suspect other than the usual is the socketed stuff like the opto n diode
    loose connections will often cause issues resulting in crackly noise.
    next thing would be check all the caps in the audio path.
    use the venerable jack darr <pbuh>’s “circuit disturbance test”

    whack it and see if it goes away or changes. if it does, its a loose connection. if not, suspect solder joints still… work your way thru the circuit, tapping on and wiggling each component as you go with the guitar in it, turned on, plugged into an amp. when you find the offending part, usually you can hear it.

    but first, usual suspects
    cold solder
    solder bridges
    bad lead dress
    this is a very nice circuit, but a lot of opportunities to pick up noise if not careful. if you can, i’d board mount the pots. i did, n just managed to squeeze it in a 1590b, with a couple minor issues.

    voltages are probably decent… if all these suggestions don’t help, audio probe it.
    if ya have another opamp on hand, replace the one doing the audio, the osc is likely fine

    hope that helps mate



    Very helpful suggestions, all.  I’ll get to work and post the results.  Thanks so much!  -Ted



    Okie doke.  Still working.  What I’ve done so far:

    1. Verified all the resistors by color code (that was fun) and a couple are off but not by much… think this is the issue?
      1. R8 should be 2K7.  Looks like I used a 3K.
      2. R10 should be 330R.  Looks like I used 360R.
    2. Reflowed a few suspect solder joints but not all
    3. Swapped out my TL072CP’s for two new ones
    4. Physically moved the power wires around while playing and tried to make it perpendicular to other wires if they were nearby
    5. Moved tried to move parts around one by one and tugged on wires while playing

    If it isn’t the resistors (which it might be), I guess I’m down to reflowing all the solder joints.  I don’t have an audio probe.  Yet.

    Thanks again!



    I would reflow ALL joints and also all pot and jack lugs.

    If that doesn’t solve the issue, does the distortion go away if you reduce the input level?



    Thanks, Wilkie1.  As of now the distortion doesn’t go away even with the gain trimpot set to barely audible.  It does abate a good bit when I turn the guitar volume down from 100% to about 75%.  That said, going direct into the amp I get no distortion at 100%.

    It almost sounds like a blend effect where I’ve got 90% the Apollo and 10% a crappy OD pedal.

    Back to the soldering iron I reckon…




    I cannot see from the photo but is the NSL-32 exactly that with no A, SR2 or any other extension?

    My current batch of opto-couplers are all 184 and your part looks like 683 so I thought I would ask.

    Re-flow the entire project on-board and off board.



    Hi Barry- The OC says NSL-32, then has 1638 written below it.  On the bottom of the OC it says NSL 7053…



    I believe you say that the distortion is reduced when you reduce the guitar volume.  I assume the guitar is going directly into the tremolo.  I assume the guitar is not using active pickups or any on-guitar preamp.  Under these conditions, the first stage of the tremolo should not clip and cause distortion.  Overloading the first stage opamp can cause it to distort.

    The first stage opamp bias is set by the Vb voltage produced at the voltage divider of R15 and R16.  These should be 100K resistors.  With a supply voltage of 9VDC, the Vb should be about 1/2 of 9V of about 4.5V.  You should be able to measure this also at pin 5 of IC1.  If this voltage is grossly different, the opamp may not be able to accurately process the guitar signal because it does not have enough headroom.  Distortion will result on large signals.  Measure this voltage and report the result.  We do have solutions if this is the source of the problem.




    I’ll check it out, sounds promising!  Tested with two guitars.  Both passive- one with p90’s the other with PAF-style pups.



    Reflowed everything.  Still fizzy- now working through the voltage questions…

    Pin 5 is reading 4.08 Vb.




    Vb is 4.08.  Source voltage is ??



    Sorry for the delay!  Source is measuring right at 8.99-9V from a battery source.  I measured using probes at the circuit board’s spare holes for power and ground.

    It should be noted that I’m still no pro at this, but hopefully I’m testing correctly.

    Again- thank you so much for volunteering your time and expertise to help troubleshoot.  I’m learning a lot and enjoying the process FWIW.

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