Luxman C02 Pre Phono stage issues...

[boostedb18]

Hi Guys, any idea what could be causing noise on the phono section of this preamp? With nothing plugged into it makes static noise only on the MC settings, Getting progressively worse from MC high to MC low. MM is quiet so are all other inputs. Thoughts? Advice? Thanks

 

[Raccoon1400]

It might just be picking up interference from the jacks. Does it work well with something plugged in? Does it make noise if you short the input jacks?

 

[boostedb18]

It might just be picking up interference from the jacks. Does it work well with something plugged in? Does it make noise if you short the input jacks?

Its there regardless if something is plugged in or not. I just find it really strange that its just on the MC setting. I moved stuff around, changed plugs. No dice. Its an annoying sound too, Its like listening to a blank tape. Hiss noise.

 

[Raccoon1400]

Is it in both channels?

 

[mbz]

Getting progressively worse from MC high to MC low.

Means MC Medium is also affected, right?

I had a look at the service manual, not much that can go wrong, the switch basically selects different resistors R103, 104
and 141 (68, 220, 470 ohms). Might be time to give the switch a good spray. I will try and work out what those increasing
resistor values could be doing.

 

[mbz]

They just form a filter with C115, you could visually check each and measure the R's, in circuit is fine.

Is it in both channels?

second that

 

[mbz]

Check for dry solder joints on R103, 104 and 141
and especially C115. Check C115 for corroded legs
and general health.

 

[boostedb18]

Is it in both channels?

Yup both

Means MC Medium is also affected, right?

Yup all 3

Check for dry solder joints on R103, 104 and 141
and especially C115. Check C115 for corroded legs
and general health.

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WHen checking solder joints they look ok but my eye is pretty un trained... Any way to check with a Multi meter?

 

[slimecity]

So when you say "hiss noise" - its a steady hissing?

Could it just be that the MC stage doesnt have quite enough gain for your MC cart? And you are hearing the noise floor?

Are you using a low or high output MC cart?

 

[mbz]

Pix of dry solder joints courtesy dr google



The first one is extreme, your more likely to see something like the second.

 

[mbz]

My main interest is C115, could not find in on the artwork.

Can you put the negative mm probe on the R103a, 104a, 141a common
connection and the positive probe on the chassie/ground. Measure
resistance, the mm should charge up C115 so the mm readings will
be increasing.

 

[boostedb18]

So when you say "hiss noise" - its a steady hissing?

Could it just be that the MC stage doesnt have quite enough gain for your MC cart? And you are hearing the noise floor?

Are you using a low or high output MC cart?

Yup always hissing. Even without TT plugged into input. Does not change with Input plugged in regardless of cart mounted. its not noise floor as the sound goes away on the MM setting. Only on the MC setting and gets louder each step towards MC Low. Mc low having the worst amount of noise

Can you put the negative mm probe on the R103a, 104a, 141a common
connection and the positive probe on the chassie/ground. Measure
resistance, the mm should charge up C115 so the mm readings will
be increasing.

Ill Give this a try when o get home today

 

[wmgwizard]

Make sure your switch is clean and lubed.

Try using shorting plugs in any unused phono inputs.

These units also use small connectors everywhere on the chassis for signal and power, these should be cleaned as well as they can accumulate corrosion over time.

Also loosen/tighten the screws that hold the boards to the chassis as this will clear away any corrosion that may contribute to your noise issue.