how to determine authenticity

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how to determine authenticity

Postby piercetroll » Thu Feb 13, 2014 12:54 am

I am staged to purchase a used cm47, and I have read that some people perhaps modifiy and or possibly certain parts are swapped for lesser components.. How can I be sure that the internal parts are the originals. Is there a picture I could reference or possibly tell tale signs of tampering I could be made aware of prior to purchasing?
thanks
piercetroll
 
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Joined: Wed Feb 12, 2014 11:47 pm

Re: how to determine authenticity

Postby Dave Thomas » Thu Feb 13, 2014 4:04 pm

Hi Pierce, there is no way with a used microphone to know with certainty if anything has been changed.

The probability is that the circuit would not have been changed but some folks believe that putting in a NOS 6072a will make and improvement which is not always the case.

If the tube has been changed from the original Sovtek 6072a EH then further investigation might be required. We sell the EH 6072a tubes tested for $22 each.

I have attached two picture of what each side of the circuit board in a "true" CM47 looks like.

In the later circuit boards C9 & C10 the two small blue capacitors are removed physically.
CM47internal2.jpg
CM47internal2.jpg (449.58 KiB) Viewed 10247 times

CM47internal1.jpg
CM47internal1.jpg (2.08 MiB) Viewed 10247 times



Now, someone might have changed the capsule which you can only inspect by removing the head grill.

The CM47 comes with our AK67 capsule which is a K67 type with a dual back-plate, center fed and with a 35mm footprint allowing for more holes to be drilled on each back-plate.

Here is the response with the AK67 capsule in Cardiod. Notice how flat the response is from 3-5khz and then the 4db rise at 12khz which is where we use to boast rock vocals cut with the U47.

This is the result of the extra damping from the increased number of holes in the back-plate of the AK67.
CM47 Cardiod.jpg
CM47 Cardiod.jpg (146.92 KiB) Viewed 10247 times


Here is the response of our CM47VE (formerly 47SE) which has the traditional vintage U47 response.
CM47 SE Cardiod.jpg
CM47 SE Cardiod.jpg (151.22 KiB) Viewed 10247 times



Does the microphone have a serial #?

We started numbering CM47 microphones inside about 2 years ago.

It is $135 for us to replace a capsule plus shipping.

We do have one demo CM47 at the moment that was traded back in on a CM12SE and I would sell it for $595 completely re-furbished with a 2 year warrantee.

I think it serial # indicates about the middle of 2013.

The microphone has been used sparely for less than one year as it was returned as the client wanted another CM12SE to match one they purchased earlier.

Cheers, Dave
Dave Thomas
 
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Re: how to determine authenticity

Postby piercetroll » Fri Feb 14, 2014 8:10 am

Thanks Dave, for all the valuable information, I am headed to look at the microphone this morning where I will dis-assemble the unit and have a look comparing to the pictures. I will likely remove the wind screen as well and inspect the capsule. If there is a serial number, I will post on here simply for reference. I am certainly hoping that no one has tampered with the unit as I am looking forward to dancing with it on St. Valentines Day.. (don't tell my wife) Haha. Thanks again for the prompt response, crossing my fingers, have a good day all!

P
piercetroll
 
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Re: how to determine authenticity

Postby piercetroll » Fri Feb 14, 2014 10:48 am

Ok.. so I have opened the mic, and the tube has been replaced with a jj 12ay7.. should I be concerned?
piercetroll
 
Posts: 4
Joined: Wed Feb 12, 2014 11:47 pm

Re: how to determine authenticity

Postby piercetroll » Fri Feb 14, 2014 10:56 am

Ok.. so I have opened the mic, and the tube has been replaced with a jj 12ay7.. should I be concerned?
piercetroll
 
Posts: 4
Joined: Wed Feb 12, 2014 11:47 pm

Re: how to determine authenticity

Postby Dave Thomas » Fri Feb 14, 2014 3:17 pm

Hi Pierce, I usually find the Sovtek EH6072a to be quieter but we do get a small percentage of 6072a that go preamturely noisy.

Did you try the microphone in FIG 8 the back and front should sound very similar plus the noise of the microphone should not be louder than the room noise.

It should be big and clear in the low end and there should be some sizzle up at 12khz but it shouldn't be "harsh" sounding.

Cheers, Dave
piercetroll wrote:Ok.. so I have opened the mic, and the tube has been replaced with a jj 12ay7.. should I be concerned?
Dave Thomas
 
Posts: 171
Joined: Mon Dec 30, 2013 2:46 pm


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