Home Forums GuitarPCB Build Support D’lay: producing unexpected (and bad) noise effect

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  • #13364
    Radical CJ
    Participant

    Hello,

    Having some issues with a D’Lay build. Clean signal passes fine, both when the effect is off, and when the effect is on.

    However, instead of producing the expected delay effect, there is no delay sound for 20 or 30 seconds of playing, and then scratchy lo-fi echo sounds very gradually slowly swell/build up and continue repeating indefinitely, over powering the clean signal. I don’t think this is even close to how a delay should work or sound, and isn’t musical.

    I’ve checked over all component values (several times). No solder bridges, re-flowed joints, etc., and PT2399 is not malfunctioning (I’ve tried a few units that I know work, always with same result when I plug them into this build). PT2399 also appears to be getting the correct voltage.

    Would appreciate any info on what might produce this strange erroneous effect? Or where might be good places to start checking voltages, etc.?

    Regards,
    J

    #13365
    Billy
    Moderator

    Hello J,

    Post some pictures of both sides of the board and offboard wiring so that it can be traced

    Pin 1 of the PT2399 should be getting around 5v

    Check the op amp voltages which should be around half the power supply 4.5v for inputs and outputs pins 1,2,3,5,6,7 with pin 4 ground and pin 8  +9v all the points on the schematic marked VR should be half power supply

    I suspect your problem may lie in the buffer / mixer area IC1A and B pin voltages will tell us for sure

    Expected voltages are also noted in the build document

    Just in case you don’t know here’s how IC pins are laid out dot or notch indicating pin 1 then down around and up in a U shape same for any number of pins

     

    #13405
    Radical CJ
    Participant

    I don’t yet have high res pics, but have taken some not quite right readings from the ICs.

    With an 8.8v supply, pin three on IC1 is around 3.6 instead of 4.4, which I guess means that R9 is not within spec (however, I don’t see how this could produce the particular problem).

    All the pins on IC2 look good, except for 7 and 8, which are too high. Above 3.5 instead of around 0.7 … Given that these both just go to ground via 100n caps, I’m not sure what’s gone wrong. Maybe a busted IC after all.

    #13407
    Billy
    Moderator

    Once we get your images something might jump out to someone

    It’s definitely a strange one which makes it interesting!

    I don’t fully understand the internal workings of the PT2399 but I’d imagine with the voltages you have on pin 7 current control 1 and 8 current control 0 it’ll have some strange affect on the output

    Hard to find any info but found this from Rob Strand, which is why I said check the op amp voltages thinking it could be a biasing issue

    I’ve been told by the manufacturers (and there’s no other way to find this out) that pins 7 and 8 are used to smooth the a biasing supply inside the modulator (MOD) and demodulator (DEM) blocks.

    the majority of the PT2399 pins ie op amp ins and outs should be vref supplied by pin 2 so half of whatever’s going into pin 1 from the regulator

    I’m assuming you mean R19 with regards to IC1 easy enough to check, with no power to the circuit, remove IC1 from it’s socket and check the resitance between VR and pin 3, I’d use the junction of R17 and 18 as my VR point

    Just on a whim I’d visually check your IC sockets too, I’ve had flimsy socket pins bend upwards more than once and cause weird issues

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