R/E/P Community
R/E/P => Klaus Heyne's Mic Lab => Topic started by: radiovinhet on October 24, 2016, 02:52:27 PM
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Hello!
How to get a k67 capsule, working on Shure KSM 32... the original capsule was damaged... and i a have this k67 capsule that can be used on this mic, but KSM uses a pre-polarized capsule, not a real condenser, don't have any voltage to polarize the k67. There's a way to this work?
Best regards from Brazil
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A simple solution would use the phantom power directly, like in the KM8x and early versions of the U87.
Have a look at their schemantics.
The sound would be somewhat softer, cause you end up with about 40 V instead of the 60(?) of the original.
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40volts is fine, but those Shures have crappy preamps any gain in sound from a nice capsule would be wiped out by the awful grainy pre-amp - you might as well build a new preamp in it, a nice little jfet mic like the old 414 or u87 preamp not stunning but very usable.
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A simple solution would use the phantom power directly, like in the KM8x and early versions of the U87.
Have a look at their schemantics.
The sound would be somewhat softer, cause you end up with about 40 V instead of the 60(?) of the original.
Thanks, i'll try...
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...crappy preamps any gain in sound from a nice capsule would be wiped out...build a new preamp in it
I would give it a try, you got the mic and the capsule - nothing to loose here.
All you need are two resistors about 10M (both the same, but exact size doesn't matter, I suggest 5-22M) taking phantom power from both pin 2+3.
At their joint a little foil cap 0.5uf/63V, one side to ground, one to the backplate.
The diaphrag goes to the amp's input, and you're done.
This arrangement prevents the polarization voltage from reaching the amp's input, it's the most simplistic arrangement.
I couldn't find a KMS32 schematic (the only link I found seemed to be a fake), but this should work.
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WOW! Thanks a lot, i'll try... nothing to loose ;D
If works, i'll will post the results here. I have a k103 and c12 nylon to test too!
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Email shure for the schematic - they've always been really helpful, they have the attitude of devoting customer relationships over decades. I might have a contact. I'll have a look
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All you need are two resistors about 10M (both the same, but exact size doesn't matter, I suggest 5-22M) taking phantom power from both pin 2+3.
At their joint a little foil cap 0.5uf/63V, one side to ground, one to the backplate.
The diaphrag goes to the amp's input, and you're done.
This arrangement prevents the polarization voltage from reaching the amp's input, it's the most simplistic arrangement.
Cool, could this sort of simple circuit could be used in other electret mics that have had their not-so-permanently polarized electret capsules replaced with externally polarized condenser capsules? I have some old electrets lying around that are losing charge but have otherwise perfectly serviceable amplifier circuits. Also, pardon my inexperience, but 10M = 10 megohms, right?
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Cool, could this sort of simple circuit could be used in other electret mics ....10M = 10 megohms, right?
10M means 10 MegaOhms.
Depends on the type of elektret capsule that is used.
Most cheap electret microphones have the amplifier (mostly just one FET transistor with one or two resistors) built into the capsule. If you remove it there is no amplifier left or an important part is missing.
What I have done:
Open up the capsule and take out the amplifier to further use it.
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Email shure for the schematic - they've always been really helpful, they have the attitude of devoting customer relationships over decades. I might have a contact. I'll have a look
I'm trying, but no success... i need to know the valeu for C11 cap on PCB, Shure don't sent it.
I've attached an akg ck12 nylon capsule to test, feed 48v on backplate, works!!!
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i need to know the valeu for C11 cap on PCB
Why specially this cap?
You could use a cap meter.
But- if it works mount the capsule and enjoy your new microphone 😊
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Why specially this cap?
You could use a cap meter.
But- if it works mount the capsule and enjoy your new microphone 😊
The ex-owner gave me this defective ksm 32, capsule was dead... then i replace it with a real condenser, now it's works. But the electronics is all SMD (and i don't know too much about electronics), and the capacitor named c11 on PCB was replaced by a normal size 50v 1uF capacitor.. this is the only mod that i found and was replaced, sure. I need to know the original value... the mic has as 60Hz hum noise.
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...the mic has as 60Hz hum noise.
A 60Hz hum has more than likely nothing to do with internal parts modifications.
No 60Hz is present inside a correctly shielded housing. Check all metal parts and the PC-Board GND if they are properly connected to XLR pin 1.
Check your P48 supply:
Short XLR pin 1+3 with a short piece of wire directly at the preamps input connector (unbalance it). Now you can hear the noise of the unbalanced P48 feed by amplifying it with the preamp. No hum should be audible with reasonable gain settings.
It would be ideal if there is no difference in the residual noise if P48 is switched on or off. Practicality the results are better because the balancing cancels out about 30 to 60 dB of noise and hum.
But still, if exists, P48 hum could creep into the microphone, specially if something is wrong with its output stage.
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A 60Hz hum has more than likely nothing to do with internal parts modifications.
No 60Hz is present inside a correctly shielded housing. Check all metal parts and the PC-Board GND if they are properly connected to XLR pin 1.
Check your P48 supply:
Short XLR pin 1+3 with a short piece of wire directly at the preamps input connector (unbalance it). Now you can hear the noise of the unbalanced P48 feed by amplifying it with the preamp. No hum should be audible with reasonable gain settings.
It would be ideal if there is no difference in the residual noise if P48 is switched on or off. Practicality the results are better because the balancing cancels out about 30 to 60 dB of noise and hum.
But still, if exists, P48 hum could creep into the microphone, specially if something is wrong with its output stage.
I made some tests, i've changed the capacitor to another with 470uf, the hum/noise from amp it's gone... but ck12 nylon don't sounded too good, it haven't much bass, the trebles are good...
i'll try the k67 or k103 from Neumann.
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Don't forget that Shure will replace the KSM32 for a flat fee of $96, at least here in the US.
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Don't forget that Shure will replace the KSM32 for a flat fee of $96, at least here in the US.
Thanks... but i live in Brazil :-\... we pay MUCH more for less... taxes are VERY VERY VERY abusive. :'(
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The CK12 nylon capsule has excellent low end, I get 5 hz out of them easily. Wave those mics in the air and a DC coupled playback system will have the woofers follow the motion.
I suspect a too small input coupling cap or something else rather than that capsule. Polarize the back plate and the input blocking cap can be shorted out.
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Jim
I will try to replace the cap... but the hum is back... tried 10 differente preamps and i getting 60 Hz humm...
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I will try to replace the cap... but the hum is back... tried 10 differente preamps and i getting 60 Hz humm...
Because the hum is not related to C11, but to some grounding issues with metal parts of the microphone.
Wrap it in aluminum foil (simple test) and the hum will be gone.
Is the filter cap for the polarization voltage connected correctly (GND) and of sufficient size?
Shure refused to send a service manual to me, so it's hard to tell where the low range is filtered.
Have a look at the input stage, it should be very high input resistance (>60MOhm) built around a FET. If not, as mentioned above, the original capsule might have an amplifier built into. Is a wire with supply voltage going to the capsule?
A coupling cap would needs to be very small (<100pF) to affect the low frequency response, as the capsule itself is around 60pF.
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You should check the metal parts with a continuity setting on a DVM. All the outside metal parts should show an ohm or less resistance to ground. If the head assembly or body is made of plastic you know why it hums. I have a cheapo Behringer C1 mic with plastic parts, it also hums because of that.
Lining the interior with copper foil or even guitar grounding paint could help if the screening is lacking.
Every room should have a DVM. You can get one for free at Harbor Freight sometimes. Otherwise it's about 5 bucks.
If the Shure body/design doesn't work out, a cheapo 50 buck donor mic could use that capsule. I have a bunch of older MCA SP-1 mics I bought for 40 bucks, those worked out great, some of my fav's.
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C11 cap - shure don't gave me value... i put a 1000uF, before trying other values.
I've installed a k103 capsule from Neumann, it's very very bright/thin sound. But i think that this "frankenstein" mic it will be useful someday.
The lesson: akg c3000, c4000, shure and audio technica eletrect mics can use a real condenser capsule, it's easy!
Thanks for all your support.
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If you polarize the back plate you can short out that coupling cap to the jfet gate.
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Thanks, will try it!
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(The stock KSM32 makes for a pretty nice kick drum mic. Best application for it I think, and way better at it than many mics designed specifically for kick.
Not that it's a horrible mic or anything, just have a lot better mics around, so it doesn't get used as much.)
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Thanks, will try it!
Remember to reverse the pin 2 and 3 on the outputs as that will invert the polarity.