Bluelay saturating

  • Hi there,


    This is my second bluelay build, first one is working like a charm


    The build phase went seamlessly, no bad soldering, no component looking bad, I checked a dozen times


    V+, Vcc and Vb are ok


    But, when plugging in, the pedal is saturating, could be a hm-2, even with very low feedback


    Following signal path :

    - IC1 pin 1 : signal clean

    - IC2 pin 16 : nothing

    - IC2 pin 15 : little saturation, can hear effect

    - IC2 pin 14 : signal saturated, can hear effect

    - IC2 pin 13 : nothing

    - IC2 pin 12 : signal saturated, muddy, can barely hear effect

    - IC2 pin 11 : nothing

    - IC2 pin 10 : signal saturated, muddy, can barely hear effect

    - IC2 pin 9 : signal saturated, muddy, can barely hear effect

    - IC1 pin 7 : signal saturated, muddy, can barely hear effect


    Attached zip contains an audio file where you will be able to hear what it sounds like, taken with a probe on signal points above, with respect to ground


    I really don't understand what causes this saturation on IC2 stage...


    BR

  • Hi,

    Please be so kind as to provide detailed pictures of your entire build, a link to the building docs/schematics and post measurements of all the IC/Transistor pin DC voltages.

    Although you might not believe it, this:

    The build phase went seamlessly, no bad soldering, no component looking bad, I checked a dozen times

    Is the most probable cause. Always. But of course there might be another problem. We can help you if you provide the necessary information.

    Cheers, Max

    "Perfektion ist nicht dann erreicht, wenn es nichts mehr hinzuzufügen gibt, sondern wenn man nichts mehr weglassen kann."
    - Antoine de Saint-Exupéry

  • Hi Max,

    I totally agree, which is even more frustrating...


    schematics are here : https://www.musikding.de/docs/…luelay/BluelayV2schem.pdf


    please find pictures here : https://photos.app.goo.gl/H9U9KTs7U5U2M4hz8

    soldering may look dark in the center of the picture, but they are shiny from another angle


    measurements :

    - V+ : 9.1

    - Vb : 4.1

    - Vcc : 4.99


    - IC1 pin 3 : 4.1

    - IC1 pin 5 : 4.1

    - IC1 pin 8 : 8.36


    - IC2 pin 1 : 4.99


    - IC3 in : 8.35

    - IC3 out : 4.99


    BR

  • I think maybe distortion could appear in the very first OpAmp IC1a. But I don't really understand how it works. Maybe someone can explain this? My problem with understanding is, that the signal on the inverted input has no reference to VRef. The only idea how it could work is that it gets its reference from the output through R3. In that case it should be unity gain and the resistance of R3 would be irrelevant. In that scenario I don't understand the use of C16. If that assumption about the circuit is correct, IC1a should not be the reason for the distortion as it cannot amplify the signal. Same would be true for IC1b then. So in the end the only thing that distorts could be the PT2399.

  • I think maybe distortion could appear in the very first OpAmp IC1a. But I don't really understand how it works. Maybe someone can explain this? My problem with understanding is, that the signal on the inverted input has no reference to VRef. The only idea how it could work is that it gets its reference from the output through R3. In that case it should be unity gain and the resistance of R3 would be irrelevant. In that scenario I don't understand the use of C16. If that assumption about the circuit is correct, IC1a should not be the reason for the distortion as it cannot amplify the signal. Same would be true for IC1b then. So in the end the only thing that distorts could be the PT2399.


    Hi Simon,


    to avoid misunderstanding:


    (Despite of the stupid issue in the schematic, getting feeding (V+) and bias (Vb) for IC1 behind R7) ICa1 has the biggest headroom.


    IC1a as well as IC1b working as an inverting amplifier, the bias is set on the non-inverting input ("+"-input), and the OPV set its output voltage, that the voltage on "-"-input voltage is on the same voltage (Vb) as the "+"-input. Thats why, circuit around "-"-input should connected to the rest of the circuit by capacitors (C1, C4, C14).


    (C16 accelerates the NFB to keep the whole system OPA and NFB stable.)


    Same procedure in IC2---there are four OPA, output and "-"-inputs are on IC2's pins, "+"-inputs are set on 1/2*Vcc internally.


    So distortion could be happening in/around IC2 probably.


    @BR:

    I guess it could be usefull to measure the bias of these four OPAs in IC2---could you measure the voltage on Pin2 (Bias for the whole IC2) related to ground (should be 2,5V) and the voltages on the out-Pins (9, 12, 14, 15) related to Pin 2 (should be zero) or related to ground (shoud be 2,5V too).


    If there is something wrong, it is usefull switching off the device, replacing IC2 and measuring resistances to ground of all Pins 9-16 of IC2 (should be isolated).


    Hope that helps


    Torsten

  • Hi,

    thanks @all for your interest


    @Hendrixianer : just checked the solder joints you pointed out, re-soldered a couple


    @Graue_Theorie : here are the measurements :

    - IC2 2 / ground : 2.504 V

    - IC2 15 / IC2 2 : 0 mV

    - IC2 14 / IC2 2 : -3.7 mV

    - IC2 12 / IC2 2 : -1.7 mV

    - IC2 9 / IC2 2 : 1.7 mV


    I checked isolation between IC2 9->16 /ground : all are isolated

  • Hi BR,


    same answer as Hendrixianer -- looks good.


    It was an idea or a [looking into dictionary: ] suspicion


    that in one or more OPAs in IC2 the operation regime ist out of order:


    If there is a resistor from one's OPA "-"-input to ground, output voltage could be out of order. In this case output could be distorted. For instance, if output voltage of an OPA (without signal) is 4V and its maximum output voltage is something lower than 5V, distortion of upper halfwave is really probably.


    But an output offset of some millivolt is not out of order ;)


    2. You wrote, that this one is your second built of such a delay and first built worked very well---are there differencies in version, in schematic or in use?


    Greets


    Torsten

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