I have a 555 timer setup in astable mode, with a frequency of about 1Hz which I measured and verified without load. Out of curiosity, I connected an 8 ohm speaker, expecting not to hear anything. However, I heard a tone, and when I looked at the signal on a scope, the frequency was about 1.4KHz. How can the frequency change like this when I have a load?
@s3c: I added a 47 ohm series resistor at the output of the 555, and re-measured the signals. I no longer see the strange 1.4KHz output. The 555 output looks normal (yellow scope trace). Should the speaker input (blue trace) be an AC coupled, reduced voltage version of the 555 output?