[sdiy] Hum & Buzz

Ullrich Peter Peter.Ullrich at kapsch.net
Tue Sep 19 00:41:50 CEST 2017


Hi!

The 5532 oscillate quite easily if you forget to add the decoupling caps near the power pins.
I had a 10th order anti aliasing filter PCB from an AKG digital delay unit that I wanted to test.
I only got quite bad audio result, seemed distorted and noisy.
When I had a look at the output signal I saw that the circuit oscillated with about 600kHz!!!
My audio just modulated the amplitude a little bit...

There were no decoupling caps on the filter board itself, so I had to connect some at the power pins of the module.
Afterwards everything was fine and in high quality.

And an engineer from AGK told me that only two manufacturers produced high quality 5532 and 5534, the others 
are in bad quality - not useable for studio equipment. I am sorry - I don't remember which manufacturers were the useable ones... :-(
I just found the Audio Precision One measurement results and some notes regarding the pinout, not the opamp manufacturers. 

Ciao
Peter
________________________________________
Von: Synth-diy [synth-diy-bounces at synth-diy.org]" im Auftrag von "Ingo Debus [igg.debus at gmail.com]
Gesendet: Montag, 18. September 2017 18:58
An: Synth DIY
Betreff: Re: [sdiy] Hum & Buzz

> Am 17.09.2017 um 21:18 schrieb Michael Zacherl <sdiy-mz01 at blauwurf.info>:
>
> After experiencing lots of hum and buzz, as one would have with a ground loop, I disconnected the pickups and wired the two inputs to ground to see how the bare circuit would perform.
> To my surprise the hum and all other noise was almost gone.

Are you sure it’s only hum? Have you checked that the preamp doesn’t oscillate?

Ingo
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