Jonkan

Please help! Ioaudio mk47 suddenly has higher self noise!?
« on: October 05, 2016, 05:58:13 AM »
So I  have two Ioaudio mk47 that I built. One is pretty quiet, and the other has  lately started to act wierd. Theres a lot more hiss in one of the mics.

What I have tried so far :

Clean the pcb with isopropyl 99,5%, tried not to contact the polystyrene cap.
Change tubes (even swapped with the working mic, no luck)
Swapped psu cables
Swapped psu
Flipped the capsule around and tried the other side (in cardioid of course)
Shortened the capsule wires a bit.

Still that mic is noisier, like white noise  *hiiiisssssss*

Underneath the noise the mic sounds fine.

Any ideas? The heater dropping resistor? (they seem to get pretty hot after a few days of running)?  This is the stock resistor max supplied with the kit.

Change  the polystyrene cap?

Swap capsules between mics? I also have a dale m7 cap I could try out. I'm using beez nees k7  right now.

This is driving me nuts btw!
Help is seriously appreciated.
/j


Matt Nolan

Re: Please help! Ioaudio mk47 suddenly has higher self noise!?
« Reply #1 on: October 05, 2016, 06:46:48 AM »
Check all the high impedance area components, resistors and capacitors, solder joints, wires, etc. Did you wear gloves when building those areas?

Jonkan

Re: Please help! Ioaudio mk47 suddenly has higher self noise!?
« Reply #2 on: October 05, 2016, 07:07:27 AM »
I wore  gloves when I cleaned everything, and every time I have opened up the mic to change tubes  etc.  This noise started happening spontaneously after the mic had been working  fine  for years.  Still sounds great underneath the hiss....

Matt Nolan

Re: Please help! Ioaudio mk47 suddenly has higher self noise!?
« Reply #3 on: October 05, 2016, 08:11:52 AM »
Swapping capsules may be informative. Your capsule may be dirty. If it isn't coming from the tube then it must be something upstream from there.

Jonkan

Re: Please help! Ioaudio mk47 suddenly has higher self noise!?
« Reply #4 on: October 05, 2016, 02:35:35 PM »
Thanks! Ill put in the dale m7 i have and see what happens.
/J

Jonkan

Re: Please help! Ioaudio mk47 suddenly has higher self noise!?
« Reply #5 on: October 18, 2016, 10:48:14 AM »
Update!

I put in a never used dale m7, still the same noise.

Swapped the 1k5 heater dropping resistor between functioning mic and noisy one, still no change.

Tried more tubes.

I reflowed all solder joints and tightened all screws (also a thread broke and i had to macgyver a new one with a small metal plate drilled, threaded and epoxied to the chassis, total pita...)

I replaced the 10nf polystyrene cap and gave everything else a thourough cleaning with isopropyl while it was not mounted.

I still get a small white hiss type of noise on this mic... Im almost at the point of giving up, or if someone could fix it for me for cash? Anyone know any good mic techs?

Any ideas, or randomly start replacing components?

Thanks,
J

Jonkan

Re: Please help! Ioaudio mk47 suddenly has higher self noise!?
« Reply #6 on: October 18, 2016, 08:33:26 PM »
Also, If anyone was thinking of buying equinox equ47 bodies, I  suggest that you think about it first. Mine are breaking down faster than I ever thought was possible...Alot of threads have broken in  the metal even though I have been very careful, and there are a lot of problems with fit between parts, which in turn makes it really hard to find what's wrong because 80%  of the time there's not enough electrical conduct between headgrill and  body and/or body/endbell cause the machining is not good fitting. Don't know if this was addressed later on as mine were from the first batch though.
« Last Edit: October 19, 2016, 01:34:50 AM by Jonkan »

Sredna

Re: Please help! Ioaudio mk47 suddenly has higher self noise!?
« Reply #7 on: October 19, 2016, 08:07:45 AM »
Does the hiss change in level/sound when you switch to omni mode?
Hmm... in which direction do the electrons actually go?

Jonkan

Re: Please help! Ioaudio mk47 suddenly has higher self noise!?
« Reply #8 on: October 19, 2016, 10:13:37 AM »
No, its the same in omni!

Gus

Re: Please help! Ioaudio mk47 suddenly has higher self noise!?
« Reply #9 on: October 19, 2016, 05:55:29 PM »
Have you tried a cap in place of the capsule
Another thing to check is the capsule mount to the body, does it have any resistance from the mount to the body ground?


Re: Please help! Ioaudio mk47 suddenly has higher self noise!?
« Reply #10 on: October 20, 2016, 02:15:23 AM »
Accordingly to the usual Neumann u47 capsule connection, should not be the same volume level in the cardioid and omni. Cardioid position is louder by about 6 dB because in omni the supply voltage 63 volts is divided into 2 halves of the capsule.

Jonkan

Re: Please help! Ioaudio mk47 suddenly has higher self noise!?
« Reply #11 on: October 20, 2016, 03:39:57 AM »
Gus: 2x ~60pf caps appropriate to test, or how do you do this? When I measure with my multimeter between capsule mount and body I don't get a reading at all.

o3misha: the noise is the same level, wasn't talking about capsule output. The mic works except white noise hiss in the background.


Gus

Re: Please help! Ioaudio mk47 suddenly has higher self noise!?
« Reply #12 on: October 20, 2016, 05:32:52 AM »
The capacitor is for a test so you only need one if the microphone is set for cardiod.
60pf should be good for a test.

What meter did you use for the resistance check? The reason I ask is some do not have a high input resistance. Do you have the specifications for the meter?

IIRC in the past at this forum there was a thread about a capsule mount that was somewhat conductive that was the cause of noise in a microphone build.

How many tubes did you try?

Re: Please help! Ioaudio mk47 suddenly has higher self noise!?
« Reply #13 on: October 20, 2016, 08:20:15 AM »
hi
-you could check the psu also : did you use caps for diode decoupling ? check the voltages ratings of all the psu caps, test if they are shorted ...test the psu SNR with an scope if possible , check also the resistors temperature ...
-you have cleaned the HiZ resistors/caps but they could be definitely contaminated , change all the High Impedance components
-the reed relay can be also the culprit , bypass it and hear
-if the mics still hiss with a capacitor instead of the capsule then the headamp is the culprit and vice versa
-the 6028 are not the (long term) quietest tube when they are underheated, check that as well
-check all the connectors and cable : move them mic plugged and hear if the hiss decrease or increase

hope it helps
cheers
Fred


Jonkan

Re: Please help! Ioaudio mk47 suddenly has higher self noise!?
« Reply #14 on: October 20, 2016, 06:20:12 PM »
Thanks! I swapped both psu, cable and the tubes that are in the quiet mic.  Since its quiet with the good mic, its gotta be something in that mic.  Also swapped capsules between mics.

Perhaps it's the relay? Where  could I find another one like it?

Gus:  my meter is pretty cheap so  it is  not to be trusted...

Thanks for all the suggestions, everything is very appreciated!
/j

Gus

Re: Please help! Ioaudio mk47 suddenly has higher self noise!?
« Reply #15 on: October 20, 2016, 06:57:52 PM »
Did you swap the capsule holders?
Look up some fluke DMMs for max resistance 77 87 etc. I would guess your DMM might be less

Re: Please help! Ioaudio mk47 suddenly has higher self noise!?
« Reply #16 on: October 20, 2016, 11:42:56 PM »
Body shielding identical?
Also check capsule holder isolation from the ground,
Even if it seems ok - may want to try double insulation, like covering both - holder base and the screw side with PTFE
          (including part of the screw thread with tubing)
« Last Edit: October 20, 2016, 11:58:31 PM by moomilk »

Re: Please help! Ioaudio mk47 suddenly has higher self noise!?
« Reply #17 on: October 21, 2016, 12:04:56 AM »
« Last Edit: October 21, 2016, 12:16:36 AM by Banzai »

Jonkan

Re: Please help! Ioaudio mk47 suddenly has higher self noise!?
« Reply #18 on: October 21, 2016, 03:44:23 AM »
I swapped the whole capsule +mount to the one working in the good mic, so it's probably not the capsule or mount. But just to be 100%  sure I just tried another type of capsule holder without success.

Body shielding could actually be worse on the noisy mic, the fit between metal parts is not as good as on the good mic. I got early   (i think late prototype) bodies and Skylar had some issues with the machining on these. Also the metal plate where the capsule  is mounted had to be made smaller in diameter to fit the body tube, which was the wrong inner diameter (you couldn't even slide on the body tube before this change was made)

Gonna order some extra parts from rs and start digging. Just need to take a small break from this, I really needed some success with mics (to stop me from tearing my hair and also having to repair one more damn damaged m3 thread!), so I put the dale m7 I had extra in an old adk 51st mic and put in some polystyrene caps  just for fun. Seemed to really make it less hyped in the top end. Not as nice in the mids for voice as the beeznees k7, but I can see myself using this one for some instruments in the near future  8)

Perhaps I should exchange the transformer as well, what do you think? Any suitable ones available on Rs, since I will be ordering from there soon anyway?

/j
« Last Edit: October 21, 2016, 06:10:02 AM by Jonkan »

Jonkan

Re: Please help! Ioaudio mk47 suddenly has higher self noise!?
« Reply #19 on: October 21, 2016, 10:39:43 AM »
Swapped the capsule for a 100pf cap instead (too  high  value?) ... Still noisy!

Also got some spit on the capsule so I flipped it over, since I almost never use omni. Both sides seem to work, but still...would suck  to have to send it to ben in Australia for cleaning.   Im just about ready to give up and throw this in storage and pretend like I never built two of these microphones, just one really expensive one  :'(