dasbin
Well-known member
My latest project has been to upgrade all the opamps in the Main Out stage in my MOTU 1224. I've swapped the filtering and I/V from the original JRC NJM4508's to OPA627's. I've swapped the output opamps from the same JRC's to OPA2134's. I think this should be a good combo, and both are relatively "compatible" chips, running well over a wide range of voltages. The MOTU is spitting out 17 volts each side at them - pretty high, but within limits.
Here's my problem.
The left channel works - sort of. It's full of garbage noise and distortion, but at least there's a bit of a signal coming out. However there's a 2.21K SMD resistor that went missing on that channel during the upgrade process, and I'm guessing that has something to do with it, so I'll reserve judgment on the left channel until I get a new one.
The right channel is being really goofy. It just gives me buzz. The first opamp in line (I'm assuming it handles filtering duties?) is extraordinarily hot to the touch (like, it could boil your skin if you left it on there) and measures some really weird random DC voltages on most of its pins - like 12V, 13V, 4V. I've taken the chip out, double-checked every connection, put it back in again, and checked every connection to the traces and board components. I've also checked every pin for shorts - nothing.
This opamp seems to be passing the voltages on to the next one in line (IV?) as it too measures these weird DC voltages.
I should mention that the other opamps are getting really freakin' hot too, nearly as hot as the one that's acting funny.
Any ideas?
Here's my problem.
The left channel works - sort of. It's full of garbage noise and distortion, but at least there's a bit of a signal coming out. However there's a 2.21K SMD resistor that went missing on that channel during the upgrade process, and I'm guessing that has something to do with it, so I'll reserve judgment on the left channel until I get a new one.
The right channel is being really goofy. It just gives me buzz. The first opamp in line (I'm assuming it handles filtering duties?) is extraordinarily hot to the touch (like, it could boil your skin if you left it on there) and measures some really weird random DC voltages on most of its pins - like 12V, 13V, 4V. I've taken the chip out, double-checked every connection, put it back in again, and checked every connection to the traces and board components. I've also checked every pin for shorts - nothing.
This opamp seems to be passing the voltages on to the next one in line (IV?) as it too measures these weird DC voltages.
I should mention that the other opamps are getting really freakin' hot too, nearly as hot as the one that's acting funny.
Any ideas?