camarada78

U87i build with single backplate capsule?
« on: August 27, 2019, 03:03:32 PM »
Hi,

I have three k87 dual diaphragm but single backplate capsules laying around but i only have u87i circuit boards laying around. I could build the U87ai  from ground up using Proteus and etching but  it will be a little time consuming and dont want to buy more stuff (parts of the DC converter).

Is it possible to simplify the U87i schematic to use a single backplate capsule?

has anyone tried it?

I'm failed to see a good way to do that without having to make a whole new circuit again.

Thanks for your time. Love the forum.



Anything that is too stupid to be spoken is sung


Khron

Re: U87i build with single backplate capsule?
« Reply #1 on: August 27, 2019, 03:15:50 PM »
Long story short - no.

You have, as far as i can figure, three choices:

1) Settle for cardioid-only, or cardioid-and-omni-only

2) Make another PCB with a DC/DC converter, to provide a positive and a negative voltage for the capsule bias (as in the U-87Ai). If you insist on the lower-sensitivity "vintage" mojo whatever, you can just drop the bias voltage from the "standard"-ish 60V to 45V or so

3) Find / make / buy an insulating shim, no thicker than the stock one, to replace the stock brass one;
[ see here for visual details: http://khronscave.blogspot.com/2017/05/a-litle-k67-microphone-capsule-fun.html ]
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

camarada78

Re: U87i build with single backplate capsule?
« Reply #2 on: August 27, 2019, 04:06:12 PM »
Long story short - no.

You have, as far as i can figure, three choices:

1) Settle for cardioid-only, or cardioid-and-omni-only

2) Make another PCB with a DC/DC converter, to provide a positive and a negative voltage for the capsule bias (as in the U-87Ai). If you insist on the lower-sensitivity "vintage" mojo whatever, you can just drop the bias voltage from the "standard"-ish 60V to 45V or so

3) Find / make / buy an insulating shim, no thicker than the stock one, to replace the stock brass one;
[ see here for visual details: http://khronscave.blogspot.com/2017/05/a-litle-k67-microphone-capsule-fun.html ]

Man, you are the type of person that makes the world a better place!

Following your tips on the link I managed to fix a defective dual backplate capsule i have! And gave me confidence to repurpose a few cardiod capsules i have laying around. I think i'll make the shin out of some plastic sheets i have laying around. great stuff!
Anything that is too stupid to be spoken is sung

Khron

Re: U87i build with single backplate capsule?
« Reply #3 on: August 27, 2019, 04:41:59 PM »
That's what we're here for..(?) ;D

PS: I've been thanked before a couple times, but this is a bit much, i'm gonna blush :D :D :D
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

Re: U87i build with single backplate capsule?
« Reply #4 on: August 27, 2019, 05:15:39 PM »
Party breaker time. I am not sure it is going to work. Screws are conductive :(

Maybe, just maybe, widen the holes on backplates so that you can pull them through without touching backplate. But then, screws will be resting on just (probably plastic) tensioning rings.

I havent been lucky finding these non conductive screws-attached image.

At this point i would just go with a new DC-DC converter. Or settle with omni/cardioid?
« Last Edit: August 27, 2019, 05:25:33 PM by kingkorg »

camarada78

Re: U87i build with single backplate capsule?
« Reply #5 on: August 30, 2019, 02:37:21 PM »
Party breaker time. I am not sure it is going to work. Screws are conductive :(

Maybe, just maybe, widen the holes on backplates so that you can pull them through without touching backplate. But then, screws will be resting on just (probably plastic) tensioning rings.

I havent been lucky finding these non conductive screws-attached image.

At this point i would just go with a new DC-DC converter. Or settle with omni/cardioid?

Yeah, that is a problem. Although, if you align right you will manage to not touch the backplate, only the oposite one.  the problem i had on my dual backplate one was exactly that. It was try and error until i managed to get a good grip without shorting.
But, with another set that I took two k87 single backplate and made it dual backplate, i only successfully screwd three screws, the forth one was always shorting. I will order some plastic screws if i can find, but i'm not sure if they are m1 m1.1 or something like that.
Anything that is too stupid to be spoken is sung

Re: U87i build with single backplate capsule?
« Reply #6 on: August 30, 2019, 05:30:50 PM »
While you are there, you might want to experiment with spacer thicknes. Couple of micrometers can make enormous sound difference ;)

EmRR

Re: U87i build with single backplate capsule?
« Reply #7 on: August 30, 2019, 09:53:16 PM »
I’m pursuing option 2; will report once there’s some result.  Don’t hold your breath.....
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

camarada78

Re: U87i build with single backplate capsule?
« Reply #8 on: September 03, 2019, 04:34:25 PM »
I’m pursuing option 2; will report once there’s some result.  Don’t hold your breath.....

I am making a 87ai circuit on proteus but as i do not have a model to follow the first version was lame (i tried a single board approach). And next week i'm trying again, but now with two boards.

I have two Getwin k87 capsules i wanted to experiment to see if there is too much difference between it and the microphone parts ones.
Anything that is too stupid to be spoken is sung

 

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