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Forum 141

Mullard 5-10 amplifier.

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Audio & Hi-Fi

Last Post by turretslug 4 years ago

23 Posts

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Nuvistor

(@nuvistor)

Posts: 4607

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Feedback circuits are complex and could be introducing phase changes but not enough to break into oscillation.

Good call to remove that first.

Frank

Posted : 11/02/2020 12:50 am

Cathovisor

(@cathovisor)

Posts: 6415

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Or it's oscillating supersonically. I was presented with a hybrid guitar amp many years ago that the owner - following advice on a forum, I might add - decided to replace the numerous op-amps in with higher-spec ones.

When brought to me, he said that on the decay of a note, it had a "paper-on-comb" quality as it decayed but otherwise it seemed fine.

Putting a 'scope on the amp output immediately revealed the problem - a sea of green, with the amp oscillating at 100KHz. The new op-amps, with a much larger gain/bandwidth product, had made much of the poor layout and design of the pre-amp PCB and so were oscillating. Putting the original op-amps back cured it.

Posted : 11/02/2020 11:15 am

turretslug

(@turretslug)

Posts: 567

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Posted by: @cathovisor

I was presented with a hybrid guitar amp many years ago that the owner - following advice on a forum, I might add - decided to replace the numerous op-amps in with higher-spec ones.

Oh dear. What I call the "Top Trumps" school of engineering- on paper, the context-devoid parameters of one item exceed those parameters of another, ergo It's Better...

Posted : 11/02/2020 11:50 am

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