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-   -   Lighter Note Hum/Balance Problems (http://www.diyaudio.com/forums/construction-tips/229822-lighter-note-hum-balance-problems.html)

butizzle 11th February 2013 04:11 PM

Lighter Note Hum/Balance Problems
 
Hi everyone,

I ordered a Lighter Note kit from Uriah a while ago and a few weeks later received, for reasons unknown to me, a readily assembled LN. It worked fine and I went on to use it with my ESP P101. However, I noticed after a while that in a certain range of the volume pot, there was a slight hum. I found out that it could be removed by connecting the 0V center tap of the 12-0-12V transformer to the ground plane of my PSU which is to connected to mains ground. I attached the cable permanently (I'd tried it by just holding it to the contact, and after that, the hum was gone but the sound was much, much quieter and the balance pot had stopped working. I removed the cable connecting the center tap to my star ground point again, but the sound remained quiet and instead, a new hum appeared. Its volume increases with increased volume pot settings (the one I had before would only appear from around 1/3 to 3/4 of the max volume setting) and it's much louder, except on the most quiet volume settings. The balance pot still doesn't do anything. I'm very confused as to what could be causing this, since everything is now set up the same way as before I started messing around with it, but the new problems remain. If anyone has any clues (or a schematic of the LN to give me at least some orientation of what might be wrong) what might be the problem, I'd be very grateful if they could help me out. I've also emailed Uriah, but have so far not received a response from him.

butizzle 1st August 2013 11:02 PM

Well, I'm really sorry to revive this dead thread, but I assembled another LN yesterday and ended up having the same problem I had when I gave up on the last one. My op-amps get very hot and there seems to be a short somewhere after the op-amps, however I've triple-checked every solder joint and I just can't find any shorts. If someone more intimate with the design than me could take a look at my board, that would be amazing. And again, if someone has a schematic of the Lighter Note, I'd appreciate it very much if you could post it, poking in the dark like I have to do now is really no fun. I've already emailed Uriah and he's telling me to send him my amp, which I'd really like to avoid since it kinda takes away the whole DIY part of the project for me.

http://i.imgur.com/HQ6b3CL.jpg
http://i.imgur.com/f5Z6toA.jpg
http://i.imgur.com/hZbHrpg.jpg
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http://i.imgur.com/MMIRvbv.jpg
http://i.imgur.com/fGCB8o0.jpg
http://i.imgur.com/CmaGQKm.jpg
http://i.imgur.com/WLbBHLx.jpg
http://i.imgur.com/Rirq9fD.jpg
http://i.imgur.com/86FUk60.jpg
http://i.imgur.com/jJ62ycu.jpg
http://i.imgur.com/eg13u7Y.jpg
http://i.imgur.com/Ni7f23z.jpg
http://i.imgur.com/Zqdzg0n.jpg
http://i.imgur.com/v93TIr7.jpg
http://i.imgur.com/gYutzQd.jpg
http://i.imgur.com/cSdGQZU.jpg

Speedskater 2nd August 2013 05:37 PM

Do you have a schematic or a link to the schematic and general wiring diagram ?

butizzle 2nd August 2013 05:41 PM

Quote:

Originally Posted by Speedskater (Post 3582643)
Do you have a schematic or a link to the schematic and general wiring diagram ?

No, that's exactly my problem! I've written to Uriah (the designer of the circuit) and he stopped responding when I suggested he publish the schematic... I don't know if that was a coincidence, I haven't mailed him again now because I don't want to bother him too much and my last mail was only 2 days ago, but he always replied within 12h or so to the last few mails. I'm honestly a bit disappointed by this amp, since this is the second one that doesn't work (the first one was soldered together by Uriah and worked for a while, then stopped working after I made a non-critical modification (connect the center tap from the transformer to mains ground) and I never got it to work again) and I'm pretty stumped on what to do since I don't have a schematic. I think I might just build a P37 and write this off as a loss.

butizzle 2nd August 2013 11:56 PM

I can't seem to edit my last post so I'll just double post instead:

I managed to get it fixed! For some reason, my board has some weird holes milled into the bottom (see pic) and I had actually suspected the short to be caused by those, but I thought I'd ruled out when I saw that only the inner two pads shorted to ground. It turns out none of the 4 should have been connected to ground, and the inner two are actually hooked up directly to the outputs of the two op-amps, so that's where all the signal was disappearing. I ended up grinding the pads away with my dremel because I couldn't get the short to go away, I just piggyback soldered the two caps on the resistors parallel to them and now everything's working as it's supposed to (except I can't get it anywhere close to mute, might have to make some adjustments there or build a mute switch into the front of the amp that shorts the inputs to ground). The sound is great and there is no hum on the speakers that I can make out.

http://i.imgur.com/ucEbNa6.jpg

Marked in red are those stupid holes that gave me all this trouble. I initially thought it a great idea to bend the leads from the caps "into" the holes and try to solder them on which turned out to make them a pain to remove again. But oh well, everything works now.


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