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sunking -no gain - need help

Started by joshcamp, November 17, 2011, 08:27:36 PM

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joshcamp

so, i built the sunking a while back and it has worked great until recently there has been no gain.   in fact, it seems as if the gain knob when maxed just decreases vol or tone a little. 

i checked the diodes - i replaced them with new diodes (bat41) and same problem occurs - checked orientation, etc..

i have an audio probe but since i get audio throughout the board, i'm not how i can use this to check for gain loss...

any advise ?

jkokura

Josh, so you're saying this a problem that developed?

What we need to be looking at here would be what changed. Perhaps some pictures would be helpful. Also, maybe taking some readings using a multimeter on all the IC's.

Jacob
JMK Pedals - Custom Pedal Creations
JMK PCBs *New Website*
pedal company - youtube - facebook - Used Pedals

joshcamp

yes, it is a problem that developed.   though, i noticed that the problem wasn't all of a sudden - the gain would intermittently come and go.

i just checked with the audio probe and i get a dirty tone when i touch the probe to lug 3 of the volume pot... 



joshcamp

i'll check the ic's soon

thanks for your help !

joshcamp

so here are my IC measurements:

IC1 (tL072), pin 8 = 7.3v
IC2 (tl072), pin 8 = 12.6v
IC3 (max1044), pin 8 = 7.4v


jkokura

That's a good start. We need the voltages from all the pins. You're just telling us the input voltages.

I will also note that your voltages are VERY low. You want to be seeing 8V or higher. 9V is best of course. IC2 should be seeing about 16-17V.

Jacob
JMK Pedals - Custom Pedal Creations
JMK PCBs *New Website*
pedal company - youtube - facebook - Used Pedals

joshcamp

ahh, for some reason i thought i was giving the output voltage thinking that would be sufficient. yeah, im new to this.

ive since changed the battery, here's what i get:

all pins:
    IC1    /  IC2   /  IC3
1) 4.23  /  4.2   /  8.22
2) 4.21  /  4.2   /  4.08
3) 3.23  /  4.2   /  0
4) 0      / -8.13 /  -4.04
5) 4.2   /  4.18  /  -8.02
6) 4.2   /  4.18  /  3.57
7) 4.2   / 4.16  /  5.94
8) 8.4   / 14.95 /  8.28

joshcamp

not sure how the 'cool' smiley got there.. pls disregard it !

madbean

Your supply voltage is still low. How fresh is that battery? If it's new, then you have something leeching the voltage. Are any of the ICs really hot?

joshcamp

since my last post, i switched to a 9v power supply and these are the new numbers:

IC1      IC2       IC3
4.49     4.54     9.02
4.5      4.49      4.46
3.45    4.49       0
0       -8.67     -4.42
4.48    4.45     -8.77
4.46    4.48      4.28
4.47    4.46      6.65
9        16.27     9

madbean

K, your voltages are correct. That's good. The problem MOST LIKELY is a solder bridge / loose connection / cold solder joint.

jkokura

JMK Pedals - Custom Pedal Creations
JMK PCBs *New Website*
pedal company - youtube - facebook - Used Pedals

joshcamp

so, is this the job of an audio probe ?

if yes, what's the best approach to isolate the problem ?

madbean

The easiest thing to do first is gently remelt all the solder joints. If that does not fix the problem, then you should check pins 3, 1, 5 and 7 of IC1 and IC2 to see if the problem is isolated to any of those areas.

joshcamp

yep - remelted every solder joint.   that did it !

Thanks for the help !!