[sdiy] 555 noise!

[Dave Manley]

peter edwards wrote:
> I'm building a circuit with 4 oscillators (40106) that are volume 
> modulated through transistors by pulses from 4 different 555 timers. 
> That's working fine
> The problem is that when all of the oscillators are turned down I can 
> hear a loud click coming from the 555s.
> 
> The 4 oscillators are all mixing in a TL084 op amp.
> The whole circuit is running off of a regulated 5VDC.
> 
> I thought it was coming from the transistors so I disconnected all of 
> those. Still clicking.
> I disconnected the output pins from the 555s altogether. Still clicking.
> Added more power caps to op amp and 555s. still clicking.
> It seems that the clicking is EMF coming from the 555s. I don't really 
> get it though. Anybody else encounter similar problems?
> should I try powering the opamp off the pre-regulated 9 volt signal?
> -pete

Perhaps try adding small series resistors, before the caps on the power 
to the 555 and/or switch to a different type of 555.  Search the sdiy 
archives, I'm sure someone recommended quite recently to use a specific 
type of 555 which has less conducted power supply noise.

-Dave