ultrasonic 5532

[Happy Harry]

Hi AL ! (inline)


>From: "nss at hevanet.com" <nss at hevanet.com>
>Reply-To: nss at hevanet.com
>To: synth-diy at node12b53.a2000.nl
>Subject: ultrasonic 5532
>Date: Tue, 16 Jan 2001 14:09:34 -0800
>
>Hello list!
>
>	Well I'm glad I was paying attention to the talk about op-amps going
>into ultrasonic oscilation, as I would not have recognised it otherwise!
>I made a $10 harmonic sweetner/compressor and one of the 5532's decided
>to mess with me. It was ultrasonic, how ultrasonic? Don't really know,
>my 500khz Heathkit 10-12 could not keep up with it...
>	But anyway, question: I got rid of it by bypassing the power supply
>closer to the offending chip. Is the osc caused just because of power
>supply leads,

Yes... it can. The power supply leads are inductors at high frequencies. 
This delays the power from reaching the chip "in time"
to supply a change in output. So voltage drops. In some cases the
combination can oscillate. ESPECIALLY in a power hungry chip like the
5532 which are famous for this !!!  You just learned what decoupling
caps are for. Hopefully OTHERS will learn from your experience too !!!

or does having high impeadence feedback(high gain) paths
>have somthing to do with it?

This can contribute. Careful layout keeps outputs away (physically and
electrically) from inputs.  Two components near each other will have
some capacitance between them. Move them further apart and that unwanted 
(parasitic) capacitance decreases.

Real life components all have resistance, capacitance, and inductance... no 
matter what they are supposed to be !!!

Will they still do this sometimes when
>hooked up as unity gain inverters?

They could. Decoupling is still just as important !!!

H^)  harry
>
>	Just wondering... now
>-Al Fisher
>

_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com