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Classe Six Preamp MC Output not Working

Some of you may recall I decided to switch out two resistors in the MC output section of my Classe Six preamp to boost its gain for a new MC cartridge.

I've been running MM ever since I bought it but have purchased the AT ART9XA MC cartridge and followed the Classe manual directions to replace resistors R-15 and R-16 with 3830F's to boost the MC gain by 8 dB because of the XA's low .2mv output.

My tech friend did the switch yesterday, then found there's no output when the rear panel switch is put in the MC position, while the MM is fine.  I've never used the MC section, so we have no idea if it's been inoperable for years or it's a result of yesterday's resistor switch.  One thought he had is that the MM/MC switch is old and might be suffering from lack of use for 28 years.

Any ideas as to why the MC section has died?  My friend sent me pics of the new resistors in place and they look fine.  We're stumped.
keegiam

Showing 1 response by keegiam

keegiam OP
730 posts
 
Thanks all, good points.  We may have inadvertently changed some toggle switches on the front panel in handling the preamp.  I have always kept the bypass switch off and the bypass mode on balanced.

The "tech" is a friend of mine who did this kind of work in his youth and whose skill at switching out the resistors we trusted would be much better than mine.  He didn't expect to run into any problems like this.  I will discuss the front panel switches with him in the AM.  He is concerned about both the MM/MC switch and the age of the electrolytic capacitors in the MC output area.  I do have a pro at a high end shop nearby who can probably diagnose the problem quickly.

Looking back on this, it's true that it wasn't realistic of me to present you all with such an open-ended situation.  I will report back.
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