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In Reply to: Re: okay, and the winner is... posted by eagle1 on January 31, 2002 at 07:44:50:
Hi,> I can't use OPA637 because at HF, the gain go under 5, so
> instability can happend.Well, first insert the missing 50KHz breakpoint in the active RIAA and you will find in most cases, the gain is sufficient for guaranteeing stability.
Ciao T
Follow Ups:
Hello T,Yes, I'll have to check that. I have a new circuit that take care of this breakpoint, I just need the time to try it. I still not fully understand why a 50KHz pole change so much things. Maybe it's most a phase behaviour than a relative voltage attenuation. Getting the phase right makes the soundstage real.
Regards,
Daniel Trudeau
take a look at the AD797 data sheets for ways to degrade op-amp bandwidththen, there used to be a pretty instructive BB app note called "op-amp stabilility and gettings things right for a change"
Enjoy!
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