November 15, 2021 at 9:27 am #21505
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.November 15, 2021 at 11:24 am #21508BillyModerator
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 decreaseDecember 2, 2021 at 11:29 am #21790
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.December 2, 2021 at 1:27 pm #21797
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….
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