Home Forums GuitarPCB Build Support Too much gain using Buff N Blend?

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  • #16714
    terry
    Participant

    I completed two pedals, one multi-circuit pedal [Rat, EQ blender, Buff N Blend] and another HM-2 w/ Buff N Blend. With both pedals, I am experiencing an excessive amount of gain, so much that if either the level or gain pot is past the 3 o’clock position a nasty squeal is present. I tested all circuits [except BNB] before installation, and all functioned properly. Everything functions as expected minus the squeal. As I socketed the transistor [MPF102], is it possible I need to use an alternative transistor? Thank you for any help! -Terry.

    #16718
    Barry
    Keymaster

    What is the voltage on the Drain of Q1?

    #16720
    terry
    Participant

    If I am testing this correctly… 0.047 [DMM set to 2K ohm. Red on drain, black on source]. I am still new to this. Thank you for your time!

     

    #16724
    Billy
    Moderator

    Terry set your meter to 20V DC place your black probe on ground and red probe to the drain pin on the left nearest to the 3PDT

    #16730
    terry
    Participant

    I get 9.22V

    #16731
    Barry
    Keymaster

    Can you give the voltage now of all 3 pins.

    D:
    S:
    G:

    #16732
    terry
    Participant

    D: 9.22

    S: 4.98

    G: 3.08

    #16751
    wilkie1
    Moderator

    You are experiencing oscillation caused by overloading a device.  Can you describe how you have the boards wired together?  I would normally expect to see a sequence like this:

    Guitar (or other pedals) > RATT > BNB > AMP.  The secondary effect (the EQ) would receive signal from the SEND of the BNB with the OUT of the EQ connected to the RETURN of the BNB.  With this wiring, the output level of each device will be controlled by the VOL pots on the device.  The GAIN pot on the RATT or EQ acts like a sensitivity control and the output of the device is controlled by the VOL pot.  By setting these at a comfortable level, the BLEND control on the BNB permits adding as much of the secondary effect as you wish.  If the level of the secondary effect is too high, read the first NOTE of the Build Doc for an easy solution.

    This situation is why we discuss GAIN MAPPING.  It is important to set the GAIN and LEVELS of each component in your signal chain so you don’t overload the next in line.  Large amounts of BOOST in an active EQ can seriously overload devices.

    If the RATT and the EQ function properly alone, then there is likely nothing wrong with them. Try these ideas and see if it helps.

    #16756
    terry
    Participant

    The signal is BnB send > Rat > EQ blender > BnB return. The thing is as I mentioned in my original post; this same ‘squeal’ in present in a second pedal I built too, and that is just a single circuit [distortion] pedal, so this is where my confusion comes from. A multi-circuit pedal would make sense if it happened to be overloaded, but just a single circuit?

    #16763
    wilkie1
    Moderator

    Did you try changing R5 in the BNB as discussed in the Build Doc?  The RATT is a high gain circuit and may be driving the EQ and/or BNB into oscillation.  Does reducing the VOL of the RATT help?  As with all effects, it is not always needed to dime all the controls.

    #16766
    terry
    Participant

    Yes, I did try 3 different approaches; jumper, 10k, and 100k. The only effect it had was reducing the output [blend] signal. I thought those options would be the best scientific approach as there would be 0, min, max [suggested] resistance.

    As long as the VOL and DIST [both A100k] are not above the 3 o’clock position the squeal is not present.

    It sounds fine without anything dimed, I am looking to make sure it’s properly functioning though. Obviously, you’ll encounter feedback and white noise/hiss when pushing any effect, but the squeal is abnormal.

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