Home Forums GuitarPCB Build Support adverb clipping on transients

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  • #9872
    pinkjimiphoton
    Participant

    hey guys,

    built one of these, nice sounding box… but on real dynamic stuff i’m getting some clipping on attacks which just harshes my buzz.

    was thinking maybe a qnd fix may be an antiparallel pair of led’s in the feedback loop of q1 would do the trick most likely,  but would it be better to perhaps add a series resistance in the audio path that’s bigger than the 27k resistor spec’d?

    i can live with it, but would love to be able to put this issue aside. it is ONLY on sharp fast transients. ne5532 oa. all parts stock values, 5% metal flameproofs, mcc caps blah blah.

    other than being a smidge above unity gain when engaged, works great in all other ways.

    any ideas?

    thanks

    PjP

    #9903
    wilkie1
    Moderator

    If the signal coming in is too hot, you may be getting clipping in the first stage of the reverb block.  The first opamp stage has a gain of 7.4. (R3 200K / R2 27K).  Try reducing R3 to lower the gain a bit.  If that works, you may find that the output level is now below unity.

    No problem!  You can recover the signal level by increasing the gain on the last opamp stage. It has a gain of only ,84. (R7 6K8 + B10K) / R5 20K. Try increasing R7 first.  If that messes up the pot tracking, you could replace the pot with a higher value and adjust R7 to give you correct pot rotation.  I hope this helps.

    #10084
    pinkjimiphoton
    Participant

    thanks ray,

    i will give it a shot when i get a chance to monkey with it. been gigging A LOT. crazy times. its definitely overloading… not sure if lowering the gain to the stage will actually fix it, as i tend to run it last in line when i use effects and its gonna be slammed by fuzzes and boosts 😉

    but i will definitely give it a shot as per your suggestion… got your email, too, thanks bro… just been too balls to the walls to reply yet.

    more soon. thanks for the support 😉

    jimi

    #10190
    pinkjimiphoton
    Participant

    ok, all better. WAY easy fix.

    i did end up using anti parallel 3mm red leds in parallel with r3, the gain resistor on the first stage opamp. that helped slightly, but not enough. still, if i really hit that sucker, horrible and serious distortion.

    so first thing i did was change the opamp. i had a tl062 in there, and it was kinda noisy as well as distorting. grabbed an op275 outta the bin, first thing i grabbed. that took care of most of the noise.

    still distorting harshly on transients. so i did the no brainer move, lifted the input connection on the board, and grafted a B500k trimmer in line with it.  pin one went to the ground pad, pin 2 to the in pad, and the original connection from the footswitch to pin 3. now i can turn down the input just enough to reduce the transients and get rid of that nasty distortion… i mean, face it, a 5 volt circuit doesn’t have much of a swing before it hits the rails… reading about 78k between wiper and ground on the trimmer, which is about perfect. i can’t make it distort no matter how hard i whack that sucker now. used the volume control to bring the circuit back up to unity gain, which is roughly 12:00 now instead of off.
    sounds silken and pristine now. no noise <the series resistance of the trimmer lowers the noise floor slightly by filtering some highs just slightly> no hiss no more distortion. i took some crappy phone pics, but they’re too lame to post, really.
    so anyways, thats my q&d fix for distorting transients in the guitarpcb adverb circuit, should anyone else face the issue.

    hope it helps. rock on!

    PjP

    #10191
    wilkie1
    Moderator

    OK!  What ever works for you.   The input signal was just too much.

    #10210
    Cybercow
    Moderator

    PinkJimiPhoton – great feedback on the solution! Thanks! I’ll keep it in mind when I get around to building mine.

    #10220
    pinkjimiphoton
    Participant

    ray,

    yeah, seemed easiest.

    it couldn’t handle the humbuckers output or my pedalboard, no probs at all now.
    its got plenty of makeup gain already, so input attenuation was a no brainer

    the opamp was clipping, the brick as well.. two different issues. this took care of both with minimal circuit disturbance. the led limiter is overkill, really, but transparent enough to leave in place.

    thanks for the support!
    PjP

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