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Old 2nd December 2011, 07:45 PM   #1071
H3nk is offline H3nk  Sweden
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Quote:
Originally Posted by RocketScientist View Post
#H3nk, it's not a big deal as long as the bottom solder connections look good (shiny, good "flow", etc.). If you plan on removing and installing batteries often you might want to add solder to the top of the battery terminals as mentioned in Circuit Board Construction to add some mechanical strength to the terminals. Electrically they're fine without it.
The bottom joints looks good so it seems I have nothing to worry about. Terminals are fine as well I think. Thanks!
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Old 2nd December 2011, 07:54 PM   #1072
robodoc is offline robodoc  Germany
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I have an issue after doing the initial tests. Everything was fine up to the moment I plugged in the "sacrificial" headphones. I heard some decent pops while plugging the phones in and out. Suddenly the red LED went off and one of the 4556ad exploded and has a hole on top now.

Now - without the opa's (the U2 seems to be functional due to DC tests) the LED stays off. I can measure the raw DC voltages but thats it. The O2 is dead.

What could I try?
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Old 2nd December 2011, 08:05 PM   #1073
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I just have some comments about the discussions of DMMs a few pages ago.

True RMS DMMs are of course the best, showing the true RMS voltage for most waveforms within specified frequency range. Remember this is often only up to a few kHz or less.

Some (most?) "Semi-cheap" multimeters often used the rectified average AC voltage (measured after a input cap to remove the DC component) usinga OP-based precision rectifier. The average voltage is then multipled a with 1.11 to calculate the RMS voltage. 1.11 is the ratio between the RMS voltage and the rectified average for a sinus wave. This means that these DMMs are good only for clean sine-waves at one frequency. They will show wrong values for all other waveforms, except pure sine waves. You can easily test this by applying a squarewave with 1V amplitude at a low frequency 50-100HZ to the DMM. For a square wave the RMS voltage equals the average voltage, and hence the multimeter will show ~1.11V if it is of the averaging type. The measured voltage could be one or a few hundreds of a volt lower due to that the normally low bandwidth of these DMMs cuts out some of the harmonics of the square wave from the measured voltage.

I have also investigated several "dirt cheap" DMMs (~10-15$) of different types. If you measure a pure DC voltage with these, in one polarity they will show 0V as expected, in the other direction the one Ishow 20V(!). I haven't checked the actual PCB, but to me this means two things. First the input DC-block capacitance is omitted. Second, the multimeter uses only one diode to make a half wave rectification, measures the average and multiplies with ~2.22. I do not think they even take care of the voltage drop of the diode if looking at the numbers carefully. For the main use of these multimeters it does not matter very much. (i.e., measuring if 12V or 6VDC is properly connected in cars, boats, bikes.... and measuring if 230V is connected at home). However, I would be very reluctant to trust these for measuring any low voltage AC-signals, especially non-pure-sines or with a DC level. I showed this to some students at a lecture and the very quite amazed. Somehow, you will get what you pay for.
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Old 2nd December 2011, 09:33 PM   #1074
MrSlim is offline MrSlim  Canada
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Quote:
Originally Posted by robodoc View Post
I have an issue after doing the initial tests. Everything was fine up to the moment I plugged in the "sacrificial" headphones. I heard some decent pops while plugging the phones in and out. Suddenly the red LED went off and one of the 4556ad exploded and has a hole on top now.

Now - without the opa's (the U2 seems to be functional due to DC tests) the LED stays off. I can measure the raw DC voltages but thats it. The O2 is dead.

What could I try?
Post photos first.. so another set of eyes may notice what caused the problem..
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Old 2nd December 2011, 10:08 PM   #1075
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+1 for MrSlim's suggestion. I suspect there was lots of DC voltage on the output if you heard a loud pop from the headphones. So you might not have made the DC measurements correctly before plugging the headphones in. Lots of different things can cause DC on the output.

First verify the voltages again per Initial Testing with the 3 audio op amps removed.

If that's OK, install U1 and the op amp that didn't fail in the same socket it was in before (leave the failed 4556 socket empty). Re-check the DC measurements. If they're OK, try the headphones again and see if at least one channel works OK and plays music. If so you've at least narrowed the problem down to being in just one channel and it's likely a solder bridge or poor connection, the wrong part installed somewhere, something in backwards, etc. Detailed photos would be a big help.
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Old 3rd December 2011, 09:22 AM   #1076
robodoc is offline robodoc  Germany
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Quote:
Originally Posted by MrSlim View Post
Post photos first.. so another set of eyes may notice what caused the problem..
okay here are some photos ... the 3 audio amps removed. I will do some initial testing later this weekend. Since the LED stays off its not very promising to see anything on the output.
Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.
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Old 3rd December 2011, 11:47 AM   #1077
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Originally Posted by RocketScientist View Post

A REQUEST: For the two of you here who may be experiencing regulator problems, if you happen to have a spare 1 uF >= 16 volt ceramic cap (such as C1 used in the O2) or a 22 uF - 100 uF >= 16 volt electrolytic laying around, can you please carefully "tack solder" it across the outer two pins of U6 (the 7912) with short leads on the bottom side of your O2 board. Observe proper polarity if it's an electrolytic with the negative side on the regulator output pin. If your 7912 is genuinely dead, obviously it needs to be replaced first and any other problems corrected.

Because all my O2's, with three different brands of regulators, work perfectly I can't determine if the 0.22 uF cap could be a problem or not. If it's a problem it appears to be a very isolated problem as only 4 or so have reported any problems.
I put an order in a couple days ago for some tantalum .33uf caps and ceramic .1uf caps, I'll post my results.

Nothing else in either of my amps seems to even get warm to the touch.
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Old 3rd December 2011, 11:53 AM   #1078
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Originally Posted by cheapskateaudio View Post
I put an order in a couple days ago for some tantalum .33uf caps and ceramic .1uf caps, I'll post my results.

Nothing else in either of my amps seems to even get warm to the touch.
you really need to take some pictures of your o2

i've seen your posts in here and hf and you always dodge those requests. don't you have any camera?
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Old 3rd December 2011, 12:02 PM   #1079
qusp is offline qusp  Australia
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yes it really is kinda strange, well past kinda....its flat out wierd. are you embarrassed? what did you do to it?
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Old 3rd December 2011, 12:08 PM   #1080
rtos is offline rtos  United States
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Originally Posted by robodoc View Post
okay here are some photos ... the 3 audio amps removed. I will do some initial testing later this weekend. Since the LED stays off its not very promising to see anything on the output.
Click the image to open in full size.

Click the image to open in full size.

Looks like Q1 and Q2 might be installed backwards...
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