op-amp locks up on powerup
- Thread starter JLavoie
- Start date
Help Support GroupDIY Audio Forum:
Yup... cheap and simple is the one cap in series with bus that combines the multiple inputs. C8 on the old schematic.
If you want more stable HPF there are caps in series with every input stage, so more caps to change but perhaps a little more stable.
How precise does the HPF need to be? You can probably live with a little pot interaction.
Pick your poison.
JR
If you want more stable HPF there are caps in series with every input stage, so more caps to change but perhaps a little more stable.
How precise does the HPF need to be? You can probably live with a little pot interaction.
Pick your poison.
JR
I'd only want the HPF on the mic input, so C8 won't help. I guess C5 is the place to be..
am I right in assuming that when the pot is up full the filter will behave as if R6 is just in parallel with R25 to ground?
I guess we could call it a loudness feature, since there will be more LF at lower volume settings
Jason
am I right in assuming that when the pot is up full the filter will behave as if R6 is just in parallel with R25 to ground?
I guess we could call it a loudness feature, since there will be more LF at lower volume settings
Jason
If concerned about HPF not changing you can make the HPF with values of C9 and C10 (input blocking caps) while there will be some interaction with mic source impedance (and I don't like making audible frequency poles with those big electrolytic caps driving 1k, but that may just be a personal problem).
Yes, pole frequency for cap in series with level pot will shift pole up for louder settings. That sounds like a feature to me. 8)
In constant voltage install systems you need to look out for high level LF that can saturate magnetics... having a HPF that gets more severe at higher level is moving it in the correct direction. I actually got a patent on a trick circuit that clamps bass boost (only at higher levels) for use in install products to allow bass boost without trashing magnetics.
JR
Yes, pole frequency for cap in series with level pot will shift pole up for louder settings. That sounds like a feature to me. 8)
In constant voltage install systems you need to look out for high level LF that can saturate magnetics... having a HPF that gets more severe at higher level is moving it in the correct direction. I actually got a patent on a trick circuit that clamps bass boost (only at higher levels) for use in install products to allow bass boost without trashing magnetics.
JR
I have this exact problem with LM4562, dual rails and 1M bias resistors. It latches to the negative rail and seems to destroy the opamp if left for any length of time. This is something that should be on the datasheet.
PS - is it really necessary to have complex verification for every post? Not to mention that three of the challenges are redundant.
PS - is it really necessary to have complex verification for every post? Not to mention that three of the challenges are redundant.
+-17V rails, and it doesn't latch every time, which caused me to miss the problem at the design stage. I've had it occur with single supply operation also, where it latches to ground. Diodes or low value resistors are NA in my case, so I'm going to try using relays to short the inputs on startup.
Surely there is a better way... some here have experience with fixing designs that are already in prodiuction. 8)
Perhaps share your pain (schematic).
maybe we can send a bill to NSC.. oops I mean TI
JR
Perhaps share your pain (schematic).
maybe we can send a bill to NSC.. oops I mean TI
JR
