Low end rumble after replacing the stock capsule of an MXL V69ME

[fripholm]

It is almost like you have "accidentally" built a high boost EQ into the circuit.

I wish I knew how to do that ... "accidentally" 8)


EDIT: But wait... this got me thinking. Correct me if I'm wrong (I'm a noob, so please don't throw things at me )

Is it common with microphones that there's some kind of EQ circuit built in? What if that part of the circuit is blown and it boosts much more than it normally should? I mean, the original un-modded mic has these over-hyped, unnatural highs ... isn't that at least a sign of some type of EQ?

 

[mjrippe]

Over hyped, unnatural highs can actually be from the capsule.  When testing a prototype microphone (with no eq circuitry) we swapped in the capsule from an inexpensive condenser and it gave a hotter output but a terrible harsh high end.

 

[ricardo]

You haven't by any chance replaced the 1G resistor with the wrong part?  This would certainly give you the symptoms described.

It's not clear if the original mike had this problem and if you still have the problem when you restored it back to original.

 

[CJ]

what kind of preamp are you using?

try another preamp if you have one,

capsules do rumble, that is one reason for the shock mount,

you can play with phantom voltage levels, or micpre eq,

it is a positive feedback situation which can be very frustrating to solve,

 

[fripholm]

You haven't by any chance replaced the 1G resistor with the wrong part?  This would certainly give you the symptoms described.

It's not clear if the original mike had this problem and if you still have the problem when you restored it back to original.

I did not replace anything except the capsule and the tube (back and forth). Before I swapped the capsule for the first time, the mic didn't have this problem but it persisted after I put it back in for troubleshooting.

what kind of preamp are you using?

try another preamp if you have one,

capsules do rumble, that is one reason for the shock mount,

you can play with phantom voltage levels, or micpre eq,

it is a positive feedback situation which can be very frustrating to solve,

I've already tried different preamps. It's a tube microphone with its own dedicated PSU - no phantom voltage involved.

 

[soapfoot]

My next step would be to try physically relocating any wire lengths with a chopstick while the mic is connected, to see if the noise changes or goes away.

Like CJ said, it sounds like a positive feedback thing, and since it persists even with the old capsule, it has me wondering if something in this mic is sensitive to where a certain wire is physically positioned. If any other components have been replaced, make sure their leads are as short as possible... particularly stuff around the grid of the tube.

 

[fripholm]

...make sure their leads are as short as possible... particularly stuff around the grid of the tube.

With that in mind I replaced the thin wires which came with the new capsule by the ones from the original capsule - even the one which is mounted to the middle of the diaphragm. Fortunately, it didn't suffer any damage - but I'm still sweating

The original cabling had much thicker insulation and was placed behind some kind of shield at the height of the tube grid along the mic's frame (look at the photo to see what I mean). I placed them exactly behind the shield and even wrapped the wires in aluminium foil for even more shielding. Next, I cautiously wiggled the wires between both PCBs while the mic was connected. Except for the occasional hum, I was still getting the same amount of rumble 

 

[RuudNL]

Wouldn't it be easier (and less time consuming!) to buy a new one?

 

[soapfoot]

very odd problem you have there.

 

[mjrippe]

Wouldn't it be easier (and less time consuming!) to buy a new one?

That was my thought at one point as well, but I'd really like to see this solved and know what the problem turns out to be!

Not to belabor the point, but have all of the solder connections to the capsule, tube, coupling capacitors, etc. in the high impedance area been thoroughly de-fluxed and cleaned?  Maybe just do them all again for good measure?  Wipe down the wires with 90% isopropyl alcohol too.  Check your solder joints as well - maybe you were nervous about overheating things and made a cold joint?

 

[fripholm]

Although I didn't post for a week or so I've not given up on this. The good news is: the problem is solved ... well, sort of :-\

I decided to replace all the parts on the high impedance PCB. It took a while to get the components and to re-solder them one by one. None of the old ones (9 caps and 9 resistors) was out of their respective range but somehow the new parts brought a substantial improvement in the noise's level.

It's still there but more than 30 dB lower and therefore almost negligible (in most cases the rest will be cut off by a HP filter anyway). And the best part: the new capsule's sound is a huge improvement over the original one - really.

Thanks to all who contributed and tried to help!

 

[bruce0]

Do you have any flux remover (don't get it on the capsule).  It really can help.  When folks in this thread say "clean" it sort of understates your goal on the high impedance board.  This section is so high impedance that in some mic's there are teflon standoffs just to keep the leads off the PCB substrate because even it is too conductive.