Dc offset

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egp823

Member

• Jul 23, 2015

• #1

Can we do a Dc offset check on preamps? If yes, do I set probes on output? What are settings on control panel? Thank you.

 

EchoWars

Hiding in Honduras

Sponsor

• Jul 23, 2015

• #2

Yes you can. And you'd want NO audio through, so set the front panel controls to some high-level input (Aux or Tuner), and turn the volume all the way down.

 

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egp823

Member

• Jul 23, 2015

• #3

Would it mean that if I get a reading up to 15mv , i have a good working preamp with no problems or issues? Reason I'm asking is before i hook my preamp to my amp I want to be sure that this will not cause any problem on my newly purchased amp.Thank you.

 

Crazeehorse

Active Member

• Jul 23, 2015

• #4

Check the service manual. I believe a C-65 I just did wanted 0mv +/- 100mv to be good.

 

sregor

AK Subscriber

Subscriber

• Jul 23, 2015

• #5

FWIW most preamps have coupling caps on the outputs, so most the measurement is meaning less. However, many high end models have "direct" or "laboratory" outputs and DC check would be useful information. Check of service manual or schematic or informed technician is recommended. And if DC is present with cap coupled circuit, could be (rare) bad cap. YMMV

 

EchoWars

Hiding in Honduras

Sponsor

• Jul 23, 2015

• #6

Nearly all preamps have some capacitor to decouple any possible DC, so I'd expect you to read something like 10mV or less. But if the output side of the cap doesn't have a path to ground without a connection to an amp, it may read a several volts. On a preamp like that, properly measuring any DC at the output is a bit trickier.

 

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egp823

Member

• Jul 23, 2015

• #7

Crazeehorse said:

Check the service manual. I believe a C-65 I just did wanted 0mv +/- 100mv to be good.

Click to expand...

What does a C-85 need to be good? Thanks

 

Crazeehorse

Active Member

• Jul 23, 2015

• #8

Go to http://www.hifiengine.com and download the service manual. I wouldn't be surprised if it was the same as the c-65. You will need to create an account but its free and I do not receive spam from there at all.

 

avionic

" Black Knights "------- F-15 " Wizard "

Subscriber

• Jul 23, 2015

• #9

egp823 said:

What does a C-85 need to be good? Thanks

Click to expand...

It is what it is. No adjustment for pre-amp(flat amp) offset. Just the DC offset for the MC (moving coil) phono amplifier.

 

avionic

" Black Knights "------- F-15 " Wizard "

Subscriber

• Jul 23, 2015

• #10

Crazeehorse said:

Check the service manual. I believe a C-65 I just did wanted 0mv +/- 100mv to be good.

Click to expand...

Thats for the MC amplifier as well..

 

Crazeehorse

Active Member

• Jul 23, 2015

• #11

That explains what the manual had me do then. Thanks Avionic.

 

avionic

" Black Knights "------- F-15 " Wizard "

Subscriber

• Jul 23, 2015

• #12

Both the C-85 and C-65 MC offsets are measured at the rec.out. Not the pre-amp out.

 

avionic

" Black Knights "------- F-15 " Wizard "

Subscriber

• Jul 23, 2015

• #13

egp823 said:

Would it mean that if I get a reading up to 15mv , i have a good working preamp with no problems or issues? Reason I'm asking is before i hook my preamp to my amp I want to be sure that this will not cause any problem on my newly purchased amp.Thank you.

Click to expand...

What amp ? MX-1000 ?

 

avionic

" Black Knights "------- F-15 " Wizard "

Subscriber

• Jul 23, 2015

• #14

On the C-4 . DC offset is adjusted for 0.00vdc +/- 200mv.

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If its a Yamaha amplifier and the DC offset from the pre-amp is incompatable with the amplifier. The amplifier will just stay in protect mode.

 

E

egp823

Member

• Jul 23, 2015

• #15

avionic said:

What amp ? MX-1000 ?

Click to expand...

Yup but plan to mate this with a newly acquired cx-800. Thanks