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****FIXED****Left/Right Volume Uneven

post #1 of 13
Thread Starter 

Well, I finally got around to finishing my amp, a Ventus EZ. I then wanted to up the gain, since it was running at Unity, which kinda sucked. So I swapped out R5 and R4 for 20k Ohm resitors, to make the gain x4. In the left channel, the gain seams to be working, while the right has much lower volume. BUT, the right side (problem side) measures .15 V offset from V+ to V-, while the left measures .30. I checked everything I changed with my DMM, and all the soldering (while I soldered the new ones underneath cause I couldnt clear the holes entirely) worked, all my connections and solder pads still have continuity. I'm stumped... any ideas would be greatly appreciated! Thanks

 

EDIT: Now I'm not getting any DC Offset anywhere... maybe I just suck with this MM. Anyways, problem still there...


Edited by DutchGFX - 12/28/13 at 10:48am
post #2 of 13

If you can, try swapping the resistors you changed - left to right.  If the problem follows the resistors, try a different pair. 

post #3 of 13
Thread Starter 
Quote:
Originally Posted by bhjazz View Post

If you can, try swapping the resistors you changed - left to right.  If the problem follows the resistors, try a different pair. 
that would be a major pain but I'll try to swap them with the extra I have.. So I'll swap one at a time and see if either of them is messed up.
post #4 of 13

Well in that case!  Measure all the resistors of that value that you have and try to get as close to a matched pair as you can.  Of course, if one of the pair is already mounted, that might save you the time.  I know, sometimes squeezing in to tight spots is a pain.  I know I have an older amp that has a channel imbalance and I actually use that one less.  I think if yours is working like you want it, you'll get more out of it.  

post #5 of 13
Thread Starter 

When I check the values for 1 of the resitors I swapped out, both amp boards read 6k ohms, while it should be 20... Weird thing is that they both read this and one of them works, so it leads me to believe that this isn't the issue. The matched pairs are in each board, so I assume its some weird thing with the circuit causing the readings.

post #6 of 13

Ah.  Very interesting.  Yeah, it does sound like something else is afoot.  With four resistors to change (R4-L, R5-L, R4-R, R5-R) you may have just missed one.  Hard to say, at this point.  It is interesting that your initial impression was that your DC offset was double in one channel.  How difficult would it be to get the boards out of the case?  PM me a pic of the boards in the case (or just add it to this thread).  We'll go from there.  

 

Brian

post #7 of 13
Thread Starter 
I can take them out quite easily, and will do so today. Don't laugh though, as I soldered the resistors to the bottom of the board because I couldn't clear the solder holes. I checked continuity so I know that my joints are good tho
post #8 of 13
Quote:
Originally Posted by DutchGFX View Post

Don't laugh though, as I soldered the resistors to the bottom of the board because I couldn't clear the solder holes.

 

This sounds like a recipe for disaster. 

 

Fast & powerful amps need everything to be perfect to run well or in some cases to run at all. Don't cut corners. 

 

Go get a solder-sucker-bulb or some desoldering wick and clear the holes out. Then put the resistors in properly. If the holes are VERY small this may be hard, but things worth doing are not always easy. While you're in there fix anything else you think I would not like. 


Edited by nikongod - 1/2/14 at 8:20am
post #9 of 13
Thread Starter 
Quote:
Originally Posted by nikongod View Post

This sounds like a recipe for disaster. 

Fast & powerful amps need everything to be perfect to run well or in some cases to run at all. Don't cut corners. 

Go get a solder-sucker-bulb or some desoldering wick and clear the holes out. Then put the resistors in properly. If the holes are VERY small this may be hard, but things worth doing are not always easy. While you're in there fix anything else you think I would not like. 
I got a bulb and wick and it still didn't work after about 3 hours of trying to clear the holes.
post #10 of 13

Have you tried adding more fresh solder and then sucking? Sometimes that helps. 

 

Some people use insanely small holes on PCBs. It sort of makes sense for mass produced gear, but it makes changing parts very hard - which makes the decision questionable for DIY stuff. 

 

After a bit of effort with sucking the solder out of the holes, Plan B is even harder. 

Basically what you do is:

Trim the resistor lead to approximately the correct length. 

Tin the leads a bit. 

Hold the resistor with a pliers/tweezer. 

Hold the soldering iron to the resistor leg and press it into the hole, with solder in the hole already.

Alternate back and forth between the 2 leads of the resistor until it is all the way through. 

Take your time so you don't burn the resistor or the board.

Suck/solder wick off any extra solder.

Then re-flow the joint to make it look pretty. 

This is a last ditch effort, but better than faux-surface mounting. 

post #11 of 13
Thread Starter 
Alright I tried to add solder I tried everything. I didn't try option 2. I feel like I might have burnt a resistor out. Would I noticeif I did? Or would it be hard to tell?
post #12 of 13

Only your DMM will tell!

 

PM me a pic of the board(s) and the project.  You're so close, but I'd hate for something else to go wrong.  I may have you just ship it here to get you back up and running. 

post #13 of 13
Thread Starter 

FIXED: I was an imbecile and desoldered the IN- to GND short that I needed, then forgot to redo it. Now it sounds great, thanks anyways guys!

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