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Old 27th July 2013, 01:15 AM   #3361
dfy is offline dfy
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Have you checked for cold solder joints and broken cables (especially the interconnect leading to the O2, as I presume your headphones work fine on other sources) ?
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Old 29th July 2013, 11:48 AM   #3362
mt490 is offline mt490  Australia
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Regarding C6 and C7, don't these capacitors have not much more effective capacitance than the 0.22uF polymer specified on the older bill?

At 12V DC bias the effective capacitance for the Y5V grade specified would only be 0.3uF or so. Seems a bit of a muchness.
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Old 29th July 2013, 01:04 PM   #3363
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Quote:
Originally Posted by mt490 View Post
...
At 12V DC bias the effective capacitance for the Y5V grade specified would only be 0.3uF or so. ...
I thought the capacitance of Y5V dielectric capacitors depended mainly on temperature rather than voltage?
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Old 29th July 2013, 01:54 PM   #3364
agdr is offline agdr  United States
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Quote:
Originally Posted by mt490 View Post
Regarding C6 and C7, don't these capacitors have not much more effective capacitance than the 0.22uF polymer specified on the older bill?.
He specified a 50V unit, so by this chart anyway the capacitance at 12V would be down about 8% for a Y5V

Fileelta-Cap-versus-Spannung-engl.png - Wikipedia, the free encyclopedia

But those MLCCs have improved so much over the last year or so that there really isn't any point in having to buy a Y5V anymore. A 2.2uF 50V X7R at Mouser (810-FK26X7R1H225) is a couple of cents cheaper at $0.42USD and thinner (which is good for this app given where the C7 is located).

A suggestion I made way back when was probably responsible for his change in C6/C7 values. The datasheet for the negative regulator suggests the 1uF or greater for oscillation prevention, Co on the first page:

http://www.onsemi.com/pub_link/Collateral/MC7900-D.PDF

Last edited by agdr; 29th July 2013 at 01:59 PM.
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Old 30th July 2013, 05:42 AM   #3365
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Hi all. I built another O2 and it worked great. However, when I soldered a lead to the input pin 1 and then put the cover on (grounding to case like NWAVGUY said to do) I got nothing from the amp. I unplugged everything and looked. Everything looked fine with the ground lead to the case. I slid the board out and one of the batteries was burning hot.......almost melted. Visibly distorted. The other battery was fine. I clipped the ground lead off, took the batteries out and reassembled the board into case. Works perfectly. I checked all measurement again and all seems fine. I am not using batteries right now. What happened?
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Old 30th July 2013, 05:53 AM   #3366
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It is possibly the battery terminals on the PCB shorting against the case. That malfunction explains the battery behavior. Electrician's tape in a strategic location should solve that problem, or you'll need to resolder. Have a good look through the back of the unit before attaching the front and back panels... just the PCB. Reassemble with the ground to case after being satisfied there are no other parts in contact with the case.
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Old 30th July 2013, 03:46 PM   #3367
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It worked fine though (inside the case) until i installed the ground lead (nothing else changed.) Strange.....
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Old 30th July 2013, 06:21 PM   #3368
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Quote:
Originally Posted by urshurak776 View Post
It worked fine though (inside the case) until i installed the ground lead (nothing else changed.) Strange.....
One of your battery terminal (very unlikely) or a component pin is protruding too much (most likely) touching the case causing short circuit when you ground the input to case. Trim all component pins to bare minimum using a sharp nipper/cutter. Look from the sides for any visible signs. Also put some clear thick anti-static plastic(used in static sensitive electronic comp. packing) between pcb & case to prevent any shorting. Alt. you can use multiple layers of insulation tape and/or thick cardboard.

Caution-Do not use PC motherboard type anti-static packaging material. Do not use batteries until the issue is sorted out, use AC power source only.
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Old 30th July 2013, 09:12 PM   #3369
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Thanks availlyrics. I definitely want to get to the bottom of it. It is working great without batteries (I threw both of them away at work, we have a recycling company pick up batteries.) I will open her back up and see what I can find. Hopefully I will find something.
Thanks everyone for all your help. I will let you know what I find.
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Old 30th July 2013, 09:24 PM   #3370
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Quote:
Originally Posted by availlyrics View Post
One of your battery terminal (very unlikely) or a component pin is protruding too much (most likely
I could agree with that except the unit works fine with AC only and no batteries. That severely limits possible component leads in my view. YMMV.
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