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 ?
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
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...
i'll check the ic's soon
thanks for your help !
so here are my IC measurements:
IC1 (tL072), pin 8 = 7.3v
IC2 (tl072), pin 8 = 12.6v
IC3 (max1044), pin 8 = 7.4v
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
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
not sure how the 'cool' smiley got there.. pls disregard it !
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?
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
K, your voltages are correct. That's good. The problem MOST LIKELY is a solder bridge / loose connection / cold solder joint.
seconded.
Jacob
so, is this the job of an audio probe ?
if yes, what's the best approach to isolate the problem ?
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.
yep - remelted every solder joint. that did it !
Thanks for the help !!