Hi alec,
Thanks for the heads up.
Pin 4 goes to +6V. Pin 11 goes to -6V. The GND connection is not the same as -6V.
Yep, understood, it is (now) correctly wired.
The LM324 includes 4 opamps of which only one is being used. Check the datasheet for the pin connections.
Already checked and is correct. Op amp 1, pins 1,2, and 3.
Are you sure the lower end of the pot is connected to GND, not to -6V ?
The pot has been wired incorrectly, with the centre terminal (the wiper-pin 2) to ground. Also the centre terminal is not shorted to an outer terminal as per the diagram.
My undestanding of the diagram was that the centre terminal (pin 2) should be shorted to one of the outer terminals (pin 1), and that the other outer terminal (pin 3) should go to ground (not -6v rail). Hope this is correct.
Heat sink noted, thanks. The LM324 isn't hot.
The pot has no wattage rating, but it is wire wound and fairly chunky, so my guess is it should cope with the wattage.
However, if you want things to run cooler you could reduce the current from 100mA to 50mA by increasing R3 to 22 Ohms and R5 to 220k.
Alec, this is really useful and I will do that. Does that mean that if I increase R3 to 44 ohms and R5 to 440k the current is reduced to 25mA, with the pot dissipating .05W max?
Point about 3k3 resistor noted.
Many thanks, very helpful.
Phil.