405 II (net audio upgraded) R channel distortion

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02-Nov-2019 01:10 PM

adrian

adrian

Posts: 2

Hi - My 405 II has had a gradual distortion issue over the last few months.. With a sine wave it's apparent around 800hz upwards but not when driven at a lower level.. The sine wave sounds 'raspy'! At least 10 years ago both boards were upgraded by Net Audio and have OPA627s in them... Looking at them many of the caps were changed, but not all the resistors or transistors..  I'd like to fix this problem and possibly upgrade further but I'm not sure how the previous mods might affect the Dada mods...

 

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03-Nov-2019 05:00 AM

EJP

EJP

Posts: 1669

It probably just needs recapping. Without knowing what the previous mods were in detail it is impossible to comment on them.
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03-Nov-2019 09:54 AM

adrian

adrian

Posts: 2

I think the Net Audio mods were mainly caps and replacement opamp.. All the electrolytics look new as does the opamp and some smaller caps around this..

All the semiconductors look original as do most of the resistors..


The old net-audio page is available still on the wayback machine but I can't seem to post a link  it here..

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03-Nov-2019 01:13 PM

Ton

Ton

Posts: 63

Net Audio 2008 

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03-Nov-2019 04:28 PM

circlotron

circlotron

Posts: 13

The 47uF bootstrap capacitor C10 could be failing.
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