I boxed this last week and tested it out; sounded great (see build report over in that area of the forum). Tonight is the second time I played it and for some reason it's extremely loud, at least intermittently. With the volume and gain all the way down, there is still sound, like a clean-ish boost. Turn the gain up and its pretty bruising! I also noticed some ground-y sounds when turning the pots. I'm suspecting a dodgy joint on one of the diodes. Any other trees to bark up would be most welcome!
Carmine suddenly very loud
- Thread starter Bret608
- Start date
Got time to reflow the resistors and diodes and was able to get better joints on 80 percent or so of them; some are tougher to get to without hitting adjacent caps. Still has the issue so probably time to pull it from the box to get at the other side of the board. I did take voltages on the transistors too while I was in there:
J201:
D - 8.81v
S - 4.52v
G - 4.16v
2n1304 (NPN Ge):
E - 0.74v
B - 0.85v
C - 3.76v
J201:
D - 8.81v
S - 4.52v
G - 4.16v
2n1304 (NPN Ge):
E - 0.74v
B - 0.85v
C - 3.76v
jubal81
Well-known member
Check the resistance across the volume pot. I had to replace one not long ago.
andrewsrea
Well-known member
The 'level' control should go entirely to ground (test using a DMM continuity tester), therefore allowing nothing to go to the amp. If signal is getting to the amp with this control off, this could be an incomplete ground, quite possibly from lug #1 of the pot being broken from the internal trace (from being smacked inwards on the shaft), a poor colder joint or a broken trace.
The 'drive' control has a resistor (R1 - 10K), which prevents it from being all-the-way off. Like the level control, test it's ground by jumpering an alligator clip lead over R1, then dial it counterclockwise. It should not let any signal pass. Then go clockwise and it should gradually increase in drive. If it jumps all at once or never goes to zero, it too can be a broken pot resistive trace or a bad ground.
The 'drive' control has a resistor (R1 - 10K), which prevents it from being all-the-way off. Like the level control, test it's ground by jumpering an alligator clip lead over R1, then dial it counterclockwise. It should not let any signal pass. Then go clockwise and it should gradually increase in drive. If it jumps all at once or never goes to zero, it too can be a broken pot resistive trace or a bad ground.
Okay, here we go...volume pot pin 1 has continuity to ground. When the pot is off, there is no continuity between 2 & 3 (but there is btw. 1& 2). Resistance is 108.4k between pins 2 & 3. When turned all the way up, resistance is 2.8 ohms. Seems to check out for a 100k pot, right?
@andrewsrea, the drive pot is a bit harder to make sense of. When turned down, I get 9.4k at lugs 2 & 3 (which must have to do with R1) and 2 ohms btw. 1 & 2. I was expecting 250k somewhere I guess. When turned up, there is also 9.4k from lug 2 to 3, then 1.7 ohms BTW 1 & 2. I've got continuity from pin 1 to R1, then from R1 to ground. Does that seem right?
andrewsrea
Well-known member
Sounds like the level (volume) is functioning correctly. In the mode where the effect is engaged, you should get no signal whatsoever when it is off. At this point if you are getting signal, there is something off at the stomp switch.
For the drive fully counterclockwise (off), you should be getting <10 ohms between lugs #1 & #2 and 250K ohms (+/- 20%) between either of those lugs and #3. When the control is mid-way, you should be getting ohms measurements between all three lugs when measured to each other (lug #1 to #2, #1 to #3, #2 to #3).
Actually just got a new phone! The camera seems better. The issue is that my hands are a bit shaky for fine motor skills, which makes closeup a bit blurry (usually makes it hard to do build report without multiple tries, lol). But the new one will help with that I bet.
@andrewsrea, I would say the drive pot is internally shorted or open then. I can't get 250k anywhere; the only spot with more than a few ohms is the exact same resistance as R1.
With the effect engaged and the level all the way down, there is still signal coming through, which is at a bearable level just below unity if the drive pot is all the way down. That must be because of the 10k at R1 if the pot is otherwise bad. Turn it up even a little though and wham! Could the bad drive pot influence the level pot being seemingly unable to rein it in downstream? You mentioned the stomp switch possibly being involved but I'm not clear on how.
With the effect engaged and the level all the way down, there is still signal coming through, which is at a bearable level just below unity if the drive pot is all the way down. That must be because of the 10k at R1 if the pot is otherwise bad. Turn it up even a little though and wham! Could the bad drive pot influence the level pot being seemingly unable to rein it in downstream? You mentioned the stomp switch possibly being involved but I'm not clear on how.
andrewsrea
Well-known member
That does not sound right and your drive pot may have a short between Lug #1 & Lug #3. So that we are 100% clear, viewing the drive pot from the component side, the lugs are in this order: #3 - #2 - #1.
The measurements you see should be:
- Between lugs #1 & #3 = 250K (no matter where the variable lug #2 is in the travel, +/- %10).
- Between lug #1 and R1 = <2 ohms (the reading of the test lead).
- Between lug #1 and ground = 10K (+/-10%).
- Between lug #2 and #3, with the drive all the way 'off' = 250K ohms (+/- %10).
- Between lug #2 and #1, with the drive all the way 'up' = 250K ohms (+/- %10).
I would visibly look for the short on the solder pads and circuit traces involving the drive control, as well as the 3PDT stomp switch. This includes slight blistering of the PCB around other circuit traces. If non are detected, desolder and remove the drive pot. Measure it alone and then the empty solder pads on the PCB.