Filburt
Headphoneus Supremus
- Joined
- Jun 23, 2005
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Okay, so I've been trying to use this chip as a line driver in one of my PCDPs, and I get a rather strange problem. When first installed, it mostly works OK. When I turn the unit off, I do get some noise at the end when the unit is powering down. When I tried using the chip in a test circuit, it does make some pop when turning it on, and a bigger one when turning the power off, so I'd wonder if it's related. On the test circuit, I get practically no offset (as would be expected with 200fA Ib), but when turning the chip off it does blurt out some DC or something (can't measure it very gracefully with the DMM, and I can't find my probes for the scope). However, the major problem is that when using it in the PCDP, at first everything works mostly OK, but if I leave the unit alone for an hour or so, then try to use it, the chip makes some low level noise that sort of sounds flanged or something like that. If I reflow the solder on the pins, it works OK again, temporarily. I tried playing the unit non-stop after soldering it for about 45 minutes or so, and it still worked ok. However, once I had turned it off for a bit (maybe 10 minutes) and tried to use it again, the problem came back. Real shame, since the chip sounds good.
http://focus.ti.com/lit/ds/symlink/opa2365.pdf
That's the datasheet. It's kind of an unusual topology, but I didn't see anything in the sample configurations to suggest it needed some sort of extraordinary care to use other than the usual bypassing. I have an AD8058 in it right now which has much higher Ib, Iq, and bypassing requirements on top of not being able to push as big a capacitive load, and it's working fine. In fact, this is the first op-amp I've ever used that has had a problem like this or similar in any of the units I've modified.
My intuition is some sort of oscillation, but I'm just not sure. One other weird aspect is that it seems as though if I leave the unit on pause for a bit and maybe warm things up (?) the chip will sometimes start operating normally. I just added some additional bypassing with a high quality ceramic cap (a rather difficult task that I'd rather *not* disassemble...lol) and that didn't seem to help. I wonder if the chip is just bad, but that's a pretty unusual sort of thing to happen.
http://focus.ti.com/lit/ds/symlink/opa2365.pdf
That's the datasheet. It's kind of an unusual topology, but I didn't see anything in the sample configurations to suggest it needed some sort of extraordinary care to use other than the usual bypassing. I have an AD8058 in it right now which has much higher Ib, Iq, and bypassing requirements on top of not being able to push as big a capacitive load, and it's working fine. In fact, this is the first op-amp I've ever used that has had a problem like this or similar in any of the units I've modified.
My intuition is some sort of oscillation, but I'm just not sure. One other weird aspect is that it seems as though if I leave the unit on pause for a bit and maybe warm things up (?) the chip will sometimes start operating normally. I just added some additional bypassing with a high quality ceramic cap (a rather difficult task that I'd rather *not* disassemble...lol) and that didn't seem to help. I wonder if the chip is just bad, but that's a pretty unusual sort of thing to happen.
