Home Forums GuitarPCB Build Support Boogie 57 GAIN pot

Viewing 4 posts - 1 through 4 (of 4 total)
  • Author
    Posts
  • #21505
    Robert
    Participant

    I checked, I double checked, I looked for previous posts and have to ask…

    The B1M pot for the gain goes from Min to MAX with the slightest turn CW. It sounds great, but something is off, no? Q1-Q4 are all biased at around 5.5 Def between 5-6. Maybe swap the Pot to an A? Was thinking associated resistors in the line might be off, but all seem to be the correct values.

    #21508
    Billy
    Moderator

    Post some nice clear pictures Robert so we can clearly see all components

    It’s easy to miss something especially in a circuit with a fairly high component count

    I know I’ve done it more than once after checking a zillion times

    A C1M or A1M should make it less severe with the more gradual distribution of resistance across the pot rotation

    Obviously desolder at the pot lugs and not pcb solder pads to minimise accidental damage

    You could of course have a faulty pot so you could check the resistance on the pot to see how it’s distributed as you turn it, put your meter probes on lugs 1 and 2 and rotate it both ways then do the same across 2 and 3 to see how gradually it changes

    With a linear pot at halfway you should have around  half the resistance

    At fully CCW between lugs 1 and 2 should be zero to a small amount of ohms and 2 and 3 full resistance as you turn it CW 1 and 2 should increase 2 and 3 decrease

    #21790
    Robert
    Participant

    Hi Billy. I’m back at this project. I did remove the B1M at the board, Just to be safe as far as the pot goes. It’s a 90 degree pcb mount pot that I don’t want to heat more than I have to. It seems fine. Range and change is as expected. I was pretty sure that i checked and rechecked all of the resistors around that gain pot circuit, but here is a pic as requested.

    No description available.

    #21797
    Robert
    Participant

    Also… My Q1-4 biasing is a little off. # and 4 goes up past 6.5 when the gain pot is down. Is the biasing based on the gain pot? I didn’t read anything about setting the gain pot before biasing the trim pot settings….

Viewing 4 posts - 1 through 4 (of 4 total)
  • You must be logged in to reply to this topic.