Please help! Ioaudio mk47 suddenly has higher self noise!?

[Khron]

Would it be safe to assume you've also swapped cables, as well as preamps / channels between the two mics?

 

[Jonkan]

Yup, everything has  been swapped  one time or another, even body tube and headgrill.  The only thing that hasn't been changed is the actual amplifier and transformer, binder connector, and the rails  which the  pcb  mounts to inside the body.

It seems I have a noisy amplifier?

 

[Alexandru marian]

In my G7 there is an slight increase in noise if the trafo can is disconnected from ground. Same for the cable outer shield.  Maybe something is dodgy but not obvious around/in the connector? 

 

[granger.frederic]

hi,
ok , first check all the wiring and then the most probable culprit is in the HiZ section , the hiz resistors on top...
in order (check noise at each step):
disconnect the relay also to eliminate it
change the 60M and 100M (R1 R2)
swap the tubes for another pair (clean the tubes as well)
change cap C1

you'll find the problem for sure

good luck
Fred

 

[Jonkan]

Thanks! But @granger.frederic theres no 60m resistor and no component designations (c1?), Are you looking at some other schematic?

Heres the schemo: http://groupdiy.com/index.php?topic=41379.0

The only thing that makes me feel ok about this whole travesty (I have spent about 20-30hours trying to find the problem now) is that I still have another mk47 that is pretty quiet, and sounds amazing. It would be easier to cope with faulty mic that didn't work at all, but it still sounds amazing, just buried underneath a slightly higher noise floor...
Cheers,
J

 

[DerEber]

Take a break and then go back to it.
We will constantly push you with ideas until it is done.
Report all you do in great detail.
This one will come back.

best,
Stephan

 

[ln76d]

Open both microphones, power up them, wait 10min.
Measure in both voltages at points marked red and note values for both.
Compare results.
At least i would start from that

 

[granger.frederic]

Thanks! But @granger.frederic theres no 60m resistor and no component designations (c1?), Are you looking at some other schematic?

Heres the schemo: http://groupdiy.com/index.php?topic=41379.0

The only thing that makes me feel ok about this whole travesty (I have spent about 20-30hours trying to find the problem now) is that I still have another mk47 that is pretty quiet, and sounds amazing. It would be easier to cope with faulty mic that didn't work at all, but it still sounds amazing, just buried underneath a slightly higher noise floor...
Cheers,
J

i was refering to the original U47 schematic
so it's 100M  resistors and 10nF capacitor
follow my method you will repair the mic for sure
good luck

 

[Delta Sigma]

Bad shielding? Have you tried swapping bodies? Have you tried listening to both mic amps outside the body?

 

[Jonkan]

Yes and yes!

About the 2mohm and 3mohm resistors, can i use 2.2 and 3.3 mohm instead? Im going to replace everything on the pcb except for the transformer and the Russian cap.  Is it OK to use 0.5w  metal film for every resistor?
Thanks!
/j

 

[ln76d]

Result should be the same as with 2M and 3M, if we ignore resistor tolerance.

 

[leitrim_lad]

Did you ever get this sorted? im having the same issue with my mic.. thanks

 

[OPR]

Sorry if this has already been mentioned.

Check that the grid resistor is grounded if it is and you still have hiss try another resistor  in that position.

Hope this helps.
Cheers
Mark

 

[mrclunk]

Jokan, did you ever get to the bottom of your noise issues?

 

[gec]

I have the same problem, did anybody solve this?

 

[mushy]

Necro thread. Anyone ever figure this out? I'm having the same issue.

 

[pasarski]

Seems like an common problem that occurs after some time, which makes me think it's probably the tube/tubes.

 

[Forcemusicgroup]

I need some direction myself as the bom and instructions have been lost

 

[garp]

I had this problem with one of mine, the culprit was the ceramic 1,5k 5w resistor that i replaced with dale aluminium body.