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David Smith C12VR Mod Sleuthing... [message #345433]

Fri, 30 May 2008 11:45

Ron Sweet
Messages: 30
Registered: November 2006

Member

Engineers at several major NYC studios mentioned to me that the late David Smith made a wonderful mod to reduce noise of a couple of C12VR mics, and these engineers wanted the inside scoop on how he did it. So, I thought it might be fun to attach a jpg of some brief notes that I found on adjacent pages in one of David's notebooks. I post this with a disclaimer that the info and/or conclusions may be completely irrelevant to the actual mod he made, and/or it may be completely inaccurate and will cause your studio to dematerialize if you implement it. I am posting this to offer, at the very least, an interesting topic for discussion. At best, the mod approach will be in the public domain, though I would certainly not implement it without the confirmation from the Klauses and Olivers of the world, unless I had a C12VR to spare. I have no idea whether these notes represent his final design decisions, or whether he just forgot to burn the book.

I also know nothing about the circuitry of a C12VR. The interesting point for me is David's displaying measurements for a "1/2 6072" vs a "compound 6072". Assuming that a stock C12VR uses half of a 6072, could this mean that David ganged together both halves of the tube?

Attachment: c12vrmods_notes.jpg
(Size: 307.71KB, Downloaded 288 time(s))

Ron Sweet

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Re: David Smith C12VR Mod Sleuthing... [message #345438 is a reply to message #345433 ]

Fri, 30 May 2008 12:30

J.J. Blair
Messages: 12567
Registered: May 2004
Location: by the sea & sand

Diamond Member

Ron, thanks for posting this. the C12, 251 and C12VR all use only half of the twin triode 6072.

studio info

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Re: David Smith C12VR Mod Sleuthing... [message #345450 is a reply to message #345433 ]

Fri, 30 May 2008 12:59

compasspnt
Messages: 16052
Registered: December 2004
Location: Compass Point Studios, Na...

Diamond Member

Interesting, thanks.

I will soon start a thread about my and Jeff Roberts' C12VR's that we have both just had massively modified by a good friend of the Forum.

The mic's should soon be traveling home...can't wait.

Notice how there are some microphones that everyone just loves to use (47, 49, 251, etc.), and some that everyone insists upon modifying?!?

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Re: David Smith C12VR Mod Sleuthing... [message #345689 is a reply to message #345433 ]

Sat, 31 May 2008 12:02

Giles Jeremy
Messages: 33
Registered: October 2007

Member

The C12VR uses both halves of the 6072 although the second half is switched in to add extra gain.
I have a schematic if anyone wants to see it.

I believe that the 6111 circuit in the M149 parallels both halves of the the tube for lower noise so maybe that is what he did.

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Re: David Smith C12VR Mod Sleuthing... [message #345705 is a reply to message #345689 ]

Sat, 31 May 2008 13:22

J.J. Blair
Messages: 12567
Registered: May 2004
Location: by the sea & sand

Diamond Member

For real? I thought it was half, like the others. I should have looked at the schematic before shooting my mouth off. I see it now.

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Re: David Smith C12VR Mod Sleuthing... [message #346088 is a reply to message #345433 ]

Mon, 02 June 2008 10:54

Dominick
Messages: 437
Registered: August 2004
Location: New York City

Active Member

Here are pictures of one of our two David Smith modified C12VR's.
Most obvious mod is the CK12 capsule.
index.php/fa/9023/0/

Attachment: DMS C12VR composite.jpg
(Size: 255.55KB, Downloaded 732 time(s))

Dominick Costanzo

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Re: David Smith C12VR Mod Sleuthing... [message #346092 is a reply to message #346088 ]

Mon, 02 June 2008 11:04

Ron Sweet
Messages: 30
Registered: November 2006

Member

Thanks very much for posting the photos. It apparently was more than just tube work.

The same Dominick from Sony? I hope you and your colleagues have all landed in good places after the upheaval at SMS. Please give my regards all around.

Best,

Ron

Ron Sweet

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Re: David Smith C12VR Mod Sleuthing... [message #347563 is a reply to message #345433 ]

Sat, 07 June 2008 15:19

bushwick
Messages: 601
Registered: January 2005
Location: brooklyn, ny

Gold Member

Still has the transformer and unless he disconnected it, the switch on the side of the mic. You should just pull it all out and put the much simpler elam circuit in there and a proper transformer in it and be all the more happy. I have wondered if in fact the weaker link in these mics is more the amplifier inside than the teflon capsule. I would love to hear a mic modded properly with the original teflon capsule.

j

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Re: David Smith C12VR Mod Sleuthing... [message #347637 is a reply to message #347563 ]

Sat, 07 June 2008 21:33

Ron Sweet
Messages: 30
Registered: November 2006

Member

I find it interesting that when David designed a "David Smith" mic prototype, he in fact selected the teflon capsule. See it here:

http://recforums.prosoundweb.com/index.php/m/227116/16153/#m sg_227116

Ron Sweet

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