Re: Oscillation problems WAS Re: C-Audio schematic?

gwatts wrote:

> Eeyore wrote:
> > Denny Strauser wrote:
> >>
> >> On Yahama 3K, 4K & Midas Venice, I've experienced something that
sounds
> >> like an oscillation problem. On these consoles, when an EQ gain is
> >> turned up the whole way & Frequency is swept while passing a signal,
> >> there seems to be some sort of oscillation.
> >>
> >> What is this?
> >
> > Pot mistracking due to lack of regular use. One side of the frequency
circuit goes
> > nearly open and it creates an oscillator around that EQ section..
> >
> > Whizz the Freq pot back and forth a few times and it'll go away.
>
> I've seen/heard it on brand new Furman PQ-3's, implying I don't think
> it's a worn or dirty pot, more the filter circuit going unstable due to
> the frequency related topology* changing while the gain is high.  I've
> only had it happen while sweeping and with the Q set for less than 1/2
> octave width.  Just keep the gain lower until you find the right
> frequency, then adjust the gain to suit.
>
> *  If you want to go in to poles and zeros I will, but that gets a bit
> pedantic.

Must be very poor track matching I'd imagine then. Higher Qs would
exacerbate the
problem.

Graham