I'm trying to wire up an OPA1632 differential opamp sort of like so:
A-_____|--------\-------out -
A+_____| opamp/-------out +
Anyways.. It's powered by a 9 volt battery and I've got an unbalanced microphone hooked up to the A- and A+ terminals. However, when I plug the mic in, there's apparently current leaving inputs because I can hear a static and sometimes a popping sound comming *FROM* the microphone.
Am I powering this incorrectly by using a 9v batteries 9v and Ground terminals?
Thanks
A-_____|--------\-------out -
A+_____| opamp/-------out +
Anyways.. It's powered by a 9 volt battery and I've got an unbalanced microphone hooked up to the A- and A+ terminals. However, when I plug the mic in, there's apparently current leaving inputs because I can hear a static and sometimes a popping sound comming *FROM* the microphone.
Am I powering this incorrectly by using a 9v batteries 9v and Ground terminals?
Thanks
I'm not sure what a power kill switch would do...
Anyways, I've got it hooked up again, this time with a 0v ground, however now it will amplify a line-level source but it will introduce a hum on the output AND input. If I plug a mic into the input, the popping is gone but I can hear the same hum through the microphone as if it were acting like a speaker. What could be causing this?
Regards,
Matt
ps heres an attached schematic of the *current* design
Anyways, I've got it hooked up again, this time with a 0v ground, however now it will amplify a line-level source but it will introduce a hum on the output AND input. If I plug a mic into the input, the popping is gone but I can hear the same hum through the microphone as if it were acting like a speaker. What could be causing this?
Regards,
Matt
ps heres an attached schematic of the *current* design
Attachments
MC,
Have you grounded the OPA1632 VCOM pin (pin 2) this will insure the outputs are at 0V (but you will have to operate the device with +/- DC source) - this will insure the outputs swing about 0V & therefore 0V DC on the input resistors.
If this does not help, I would try a unity gain buffer on each input - this will also gain you high input impendance.
I recently used the OPA1632 to drive a ADC front-end, the device is VERY sensative - proved horrible to use.
I had to put 2 resistors to ground on each input (Microphone end) to insure the device would work correctly with true floating inputs - I used 2x 3K3 to ground - but depends on your required input impedance - remember the load presented by the FB resistors.
Also - I had to add 470pf directly across the opamp inputs to insure stablity - even with TI published FB values. Was not happy about adding this Capacitor - but without the Cap the distortion was about 0.003% - and dropped to about 0.0002% with Cap. Could find no sign of instablity (HF oscillations) using a spectrum Analyser - however something was going on....
Notice how TI are pulling a fast one - the OPA1632 seems to be a re-badge of the TI THS4130 / THS4131 - but cheaper - even packaged at same plant....
Can the Mike drive the low input impendance presented by the Opamp feedback resistors? ( I don't know much about mikes)
Good Luck,
John
Have you grounded the OPA1632 VCOM pin (pin 2) this will insure the outputs are at 0V (but you will have to operate the device with +/- DC source) - this will insure the outputs swing about 0V & therefore 0V DC on the input resistors.
If this does not help, I would try a unity gain buffer on each input - this will also gain you high input impendance.
I recently used the OPA1632 to drive a ADC front-end, the device is VERY sensative - proved horrible to use.
I had to put 2 resistors to ground on each input (Microphone end) to insure the device would work correctly with true floating inputs - I used 2x 3K3 to ground - but depends on your required input impedance - remember the load presented by the FB resistors.
Also - I had to add 470pf directly across the opamp inputs to insure stablity - even with TI published FB values. Was not happy about adding this Capacitor - but without the Cap the distortion was about 0.003% - and dropped to about 0.0002% with Cap. Could find no sign of instablity (HF oscillations) using a spectrum Analyser - however something was going on....
Notice how TI are pulling a fast one - the OPA1632 seems to be a re-badge of the TI THS4130 / THS4131 - but cheaper - even packaged at same plant....
Can the Mike drive the low input impendance presented by the Opamp feedback resistors? ( I don't know much about mikes)
Good Luck,
John
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