Why are my preamps putting out 110v on the mic inputs?

[undermind]

I just got a Neumann 472-2 (V-72 follower) dual channel preamp rackmounted and was doing some troubleshooting. I was having some problems with it until I realized that some things were just installed backwards.

But the big question I have comes from the phantom power voltage on the mic inputs. Expecting to get 48v on the mic inputs, I actually got 110v. I got mad and thought there was a big problem until I checked on my other pre, a Trident S-20. Exact same reading, 110v. I thought maybe my multimeter was screwed up so I double and triple checked my settings, then tested on a wall jack and got 120 out of the wall. I also checked the reading at the power switch to the preamp before the power supply, same. So I think the readings are accurate.

I checked on pins 1+2, then pins 1+3 on the mic inputs. I got nothing keeping the red (positive) lead in pin 1 while moving the black (negative) from 2 to 3. So these readings were based on the black lead in pin 1 and the red lead in pin 2 and then 3. Same reading both places.

 

[MCI2424]

I just got a Neumann 472-2 (V-72 follower) dual channel preamp rackmounted and was doing some troubleshooting. I was having some problems with it until I realized that some things were just installed backwards.

But the big question I have comes from the phantom power voltage on the mic inputs. Expecting to get 48v on the mic inputs, I actually got 110v. I got mad and thought there was a big problem until I checked on my other pre, a Trident S-20. Exact same reading, 110v. I thought maybe my multimeter was screwed up so I double and triple checked my settings, then tested on a wall jack and got 120 out of the wall. I also checked the reading at the power switch to the preamp before the power supply, same. So I think the readings are accurate.

I checked on pins 1+2, then pins 1+3 on the mic inputs. I got nothing keeping the red (positive) lead in pin 1 while moving the black (negative) from 2 to 3. So these readings were based on the black lead in pin 1 and the red lead in pin 2 and then 3. Same reading both places.

You do know that phantom power is a DC voltage, and wall outlet is an AC voltage? How can the meter read both on the same setting?

Switch the meter to DC for the phantom reading and see what it is because there is absolutely no way an AC 110V can be there.

Also, is there a switch for a "B&K" mic setting? Some B&K mics had 130vDC phantom power. Make sure the switch is set to +48vDC.

 

[undermind]

You're right, I was reading AC and not DC.
BUT, I was getting a reading of 110v AC out of the mic inputs, and still am right now. DC is ok, a little lower than 48v but that's okay.

 

[nukeitout]

You're right, I was reading AC and not DC.
BUT, I was getting a reading of 110v AC out of the mic inputs, and still am right now. DC is ok, a little lower than 48v but that's okay.

You can't check DC voltage with an AC meter... It doesn't work... But I could see how it would give you something close to double the DC potential when measuring, since it just measures a sort of average DC and sort of doubles it (sort of). If you switch the leads around and measure AC again is it the same?

 

[undermind]

You can't check DC voltage with an AC meter... It doesn't work... But I could see how it would give you something close to double the DC potential when measuring, since it just measures the peak of one. If you switch the leads around and measure AC again is it the same?

Well, it is a multimeter, I can check both AC and DC. But I think I get what you're saying. I get (close to) the correct DC reading for phantom power. But when I switch over to AC at the same point, I get 110v reading on the meter.

Anyways, I'm not worried about it anymore. I'm sure somebody's going to come along and explain exactly why it's happening. But I'm done with it. I know you can't have DC at 48 and AC at 110. So at this point you can disregard this thread.