I've seen a few web sites where better performance into low R loads is achieved by paralleling op amps together. Has anyone tried this?, I've tried some TI NE5532 op amps: they run hot but seem to work.
tia Mark
"Mark Harriss" = lying, PITA, criminal, artistic fool from Cairns
** Like this one:Post the damn links - you lazy, damnable ASS !!!!!!
Got a clue what an op-amp " voltage follower " is ??????
Yours wired that way ?
** Hot with a load or at idle???Idle dissipation will be about 300mW ( ie 10mA x 30 volts ).
Under full load ( 7 volts rms into 220 ohms) add another 300mW at least.
600 mW in an 8 pin DIL is hot............ Phil
Use a more suitable opamp. There are many high-drive opamps on the market. Paralelling them will not work, generally.
Try the TI website
-Andrew M
You can parallel opamp voltage followers to reduce the total noise floor, but I've never seen it done for higher output drive or any other purpose. Just use a suitably rated opamp for driving the load required, there are plenty of ones designed for driving 50ohm loads and are stable into capacitive loads etc. Or if your drive needs are greater you would typically use an external tranisistor driver.
Dave :)
It's mainly to reduce distortion into a given load, rather than increased drive capability. If you scroll down to the bottom of this page you can see what I'm after. The NE5532 gives good low distortion and I would like to minimise it as much as possible.
Thanks Mark
You shouldn't go just paralleling all of the pins, that would not be good. You could make two complete amplifiers, or voltage followers, or whatever it is, and then connect each of these to the load through a small resistor. You need to think what will happen if the DC offset of the two op-amps is not equal, in this case they will tend to fight each other, and the output resistors will help to prevent the currents due to this 'fighting' from being too high. Each op-amp must have its own feedback, taken from its own output pin, and then a resistor from the output pin to the load, then you should be OK. If you try to share the feedback connection, it will be impossible for all of the op-amps to be happy with their feedback (inverting input) voltages at the same time since they have slightly different offset errors, and so they will fight. The feedback needs to be taken from the output pin of each op-amp, not from the load, because the different op-amps will never all be happy with the load voltage, but it is possible for them all to be happy with their own individual output pin voltages, which may differ from each other by some millivolts. The size of the series resistors will need to be larger if the output referred DC offset of the two op-amps is more different, so use precision resistors. I would go for the largest series resistors that are acceptable in your application.
Unless you're driving a really low load impedance, where you are sure that the output current IS causing distortion, it all sounds like more trouble than it's worth. The only exception I can think of is if you have unity gain buffers driving cable through series resistors, where it wouldn't be much of an extra pain to do it. If you are driving cables then it is better to have some series resistance anyway so that it won't be close to oscillating.
Chris
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