Yamaha C-80 DC offset adjustment

[redstarjedi]

Hello Yamaha Fans!

I'm using my C80 preamp a lot more these days, and and after recapping it months ago, and using it everyday for the last month, I remembered that I never set the DC offset or the bias.

• I have the service manual
• I have a volt meter
• I've set bias and DC offset on other amps

But this one is confusing the hell out of me!

Attached are screen grabs of the section that describes how to adjust the offset.

I'm not too certain where the actual test point is... I see the adjustment potentiometers. How would I use record out as a test point?


Ok, I see the bus bars and I see what I assume to be are the values they are to be set at.

What I'm thinking is that that on the B+ I put my positive lead of the volt meter there, and the negative lead on the corresponding B- and then adjust using the VR102 and VR 101 pots?

Or I place positive lead to B+ and then negative lead to E which is ground, and vice versa with the B- ?

Am i making this more complicated than it needs to be?

 

[Asmodeus2112]

Hello Yamaha Fans!

I'm using my C80 preamp a lot more these days, and and after recapping it months ago, and using it everyday for the last month, I remembered that I never set the DC offset or the bias.

• I have the service manual
• I have a volt meter
• I've set bias and DC offset on other amps

But this one is confusing the hell out of me!

Attached are screen grabs of the section that describes how to adjust the offset.
View attachment 2297710
I'm not too certain where the actual test point is... I see the adjustment potentiometers. How would I use record out as a test point?

View attachment 2297711
Ok, I see the bus bars and I see what I assume to be are the values they are to be set at.

What I'm thinking is that that on the B+ I put my positive lead of the volt meter there, and the negative lead on the corresponding B- and then adjust using the VR102 and VR 101 pots?

Or I place positive lead to B+ and then negative lead to E which is ground, and vice versa with the B- ?

Am i making this more complicated than it needs to be?

Test points are the rec out jacks. That's why you have to switch the rec out to phono and phono to MC.

This is the DC offset of the moving coil phono amp.

 

[redstarjedi]

Ok. So I just stick the prongs of my volt meter into the record out jacks ?

 

[Asmodeus2112]

Ok. So I just stick the prongs of my volt meter into the record out jacks ?

I'd probably use micro grabbers on the inside of the jack, but yes.

 

[avionic]

Hello Yamaha Fans!

I'm using my C80 preamp a lot more these days, and and after recapping it months ago, and using it everyday for the last month, I remembered that I never set the DC offset or the bias.

• I have the service manual
• I have a volt meter
• I've set bias and DC offset on other amps

But this one is confusing the hell out of me!

Attached are screen grabs of the section that describes how to adjust the offset.
View attachment 2297710
I'm not too certain where the actual test point is... I see the adjustment potentiometers. How would I use record out as a test point?

View attachment 2297711
Ok, I see the bus bars and I see what I assume to be are the values they are to be set at.

What I'm thinking is that that on the B+ I put my positive lead of the volt meter there, and the negative lead on the corresponding B- and then adjust using the VR102 and VR 101 pots?

Or I place positive lead to B+ and then negative lead to E which is ground, and vice versa with the B- ?

Am i making this more complicated than it needs to be?

Your missing this page
These are just voltage checks - no adjustments- If the voltages are off or missing . You need to t-shoot and find the problem.

The free online HFE scan is incomplete for the C-80.. Use the C-85 alignment procedure.

C-85 is the same as the C-80..

 

[redstarjedi]

The free online HFE scan is incomplete for the C-80.. Use the C-85 alignment procedure.

Oh man, thanks for letting me know, i do not have this page. i did get it from hifi engine.

It sounds great, and as long as DC offset is 0 or close to it, I'll leave it at.

Thanks!