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Old 21st January 2012, 03:57 AM   #1891
nezbleu is offline nezbleu  Canada
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@sofaspud, why the bridge rectifier on the lighter input? I thought that was DC, so doesn't need to be rectified. And what is D5 for?
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Old 21st January 2012, 05:49 AM   #1892
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The main purpose of the bridge rectifier is to make that input polarity insensitive. + will be + and - will be - no matter how the DC is connected. I put a large value cap across it, so the lighter plug input is quite versatile. It can accept AC also, up to about 24VAC peak (higher voltages are possible even, but then the reverse voltage seen by the diodes and the power dissipated by the regulator has to be considered).
D5 raises the output of the 7805 by a diode drop. That offsets the D6 drop (D6 blocks DC from entering the regulator output). In practical use, D6 will likely have a higher voltage drop than D5, so perhaps two diodes at the D5 position would be an improvement. Or it may not matter much; the DC-DC converter is rated at 4.5 to 9V input.
It should be mentioned also that the +15VDC output connects to the cathode of D3 on the O2 schematic. The -15VDC connects to the anode of D4 on the O2 schematic.
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Last edited by sofaspud; 21st January 2012 at 06:14 AM. Reason: added info
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Old 21st January 2012, 07:20 PM   #1893
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Hey guys. I'm starting the build of my O2's and while starting with the resistors I got to R3 & R7 (274 ohm 1%) but before I solder them I always measure them (using a Fluke 75) and all 8 measured at ~345 ohm. The color code is correct for 274. I found it's a bit off spec. Do you think it would be a problem to use them in R3 & R7 in the positive input of the 2068 opamp? (I do not care for R19 & R23 Gain of 6.5). Thanks

Last edited by Twinster; 21st January 2012 at 07:23 PM.
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Old 21st January 2012, 07:49 PM   #1894
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Hi.
I'm back to let you all know about the problem i had with my O2 not running on AC power.
With agdr's help, we managed to narrow the issue down to the U5 Regulator. So, before having a new one to trade with the supposedly dead regulator, i decided to heat the iron and remake the soldering. Guess what? It's working like a charm on AC now. I swear that i don't understand how it's working, because the solder points seemed good the first time. Anyway, it's working on AC, and that's all that counts.
But, and because i'm (not) a lucky guy, i am facing a different problem now.
I've bought a pair of Philips 9v rechargeable batteries to go with the O2. The thing is, they last about 1 hour before the amp starts turning itself on and off repeatedly, a sign that the batteries are nearly dead and need recharging.
I'll try to run 3 or 4 more charge cycles to them before trading them with something else.
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Old 21st January 2012, 07:59 PM   #1895
agdr is offline agdr  United States
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raspunsen - hey that is good news! Just curious - was it reheating the joints one of those 6 parts above that solved it-

Quote:
Originally Posted by agdr View Post
raspunsen - yep, your negative power supply is good but your positive power supply is dead.

Double check the positions of your D1, D3, C2, C4, R1 and regulator U5 match up with the symbols on the PC board, that they are turned the right way.

...... If the positions are OK and no bridges then try re-heating the solder joints on those 6 parts with your iron.
...or was it some other joint? Hard to tell sometimes visually with solder joints. Reheating suspect areas is never a bad idea.

Another suggestion, after helping jschristian44 with his issue. It couldn't hurt to solder the banded lead of D3 on the top of the PCB to that square pad around it. Turns out that square pad is a via through-hole. Soldering the top would eliminate any chance of the through-hole having issues and the solder joint on the bottom not conducting up to the top. Just on the banded end of D3, the other diodes and leads don't need it.

As for the low battery issue, have you made the two resistor modifications that RocketScientist posted in the directions? The 2.7meg resistor is now 1.5meg, as a I recall, and another resistor was changed to 33K if I'm remembering correctly. Those helped with that low battery on/off cycling issue. I think the discussion at the time between RocketScientist and people with the problem said that some batteries had the issue worse than others. Trying a different brand would be worthwhile.

Last edited by agdr; 21st January 2012 at 08:07 PM.
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Old 21st January 2012, 08:17 PM   #1896
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I spoke with NwsAvGuy about the batteries. He said some batteries are just too cheap to work with it. I use the Tenergy Low Drain batteries that he recommends and they work great.
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Old 21st January 2012, 08:19 PM   #1897
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Seems like you have given me the answer to my problem and i forgot to check it at the time... Shame on me. Guess i just assumed U5 was dead because the solder joints seemed ok.
I just heated the 3 joints of U5 and it's working fine now.
I still have the old resistors. I don't mind having this behaviour, it's a sign i need to recharge it. It's just that 1 hour seems like too short. I was expecting more.

Edit: @jschristian44: My batteries are Philips. Not the cheap kind...

Last edited by raspunsen; 21st January 2012 at 08:25 PM.
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Old 21st January 2012, 08:26 PM   #1898
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It's probably short because they are bad batteries or just cheap. I'd recommend the Tenergy Low Discharge ones.
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Old 21st January 2012, 08:37 PM   #1899
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Quote:
Originally Posted by Twinster View Post
Hey guys. I'm starting the build of my O2's and while starting with the resistors I got to R3 & R7 (274 ohm 1%) but before I solder them I always measure them (using a Fluke 75) and all 8 measured at ~345 ohm. The color code is correct for 274. I found it's a bit off spec. Do you think it would be a problem to use them in R3 & R7 in the positive input of the 2068 opamp? (I do not care for R19 & R23 Gain of 6.5). Thanks
Sorry guys, I found the problem. The adaptor clip on my Fluke was the problem. Funny that it was measuring ok with other Resistors. My bad
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Old 21st January 2012, 10:47 PM   #1900
agdr is offline agdr  United States
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raspunsen - definitely try a different brand of batteries. Not even so much bad batteries as just different. The different batteries have different internal properties. The issue causing the on/off is re-charge behavior of the batteries. After the load if removed (the power management circuit turns off) some batteries tend to "recharge" back up to a higher voltage on their own, which then turns the power management circuit back on. A different brand may not do that as much.
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