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[aamicrophones]

Hi Larry, I add a cathode balance pot in the Vari Mu input stage.  It helped a bit but one can still hear the effect.  

Maybe this is as good as they get and that's why the Fairchild was so much more complex.

I did get rid of the selenium "firecracker" rectifier.  

They really go out with a bad smell!!!

it sounds really good when the meter indicates no gain reduction.  

The thumping is just around the threshold point.

Cheers, Dave

[Marik]

aamicrophones wrote on Thu, 26 February 2009 05:57

I had one client who had a UM70 that we removed the capsule and put it in the CM47.   I really could not hear any "significant" difference between the M7 and the Peluso PK47 on voice and percussion (single headed tambourine). ]

Sorry, whether that M7 was seriously f..ed up, or there was something seriously wrong with your hearing.
Hopefully, you were able to put that poor UM70 back together, again.

aamicrophones wrote on Thu, 26 February 2009 05:57

What I am most proud of is our tube circuit which emulates the essence of the U47 circuit but is designed around the much more economical 6072 tube.  We use the second half as a cathode follower line driver which reduces the output impedance and give us 2-3db more headroom.  The circuit works really well with the 6.5:1 BV8 type output transformer.   By using the Blumlein cathode output line driver circuit a cathode feedback capacitor is not required and is for all practical purpose identical to the U47 circuit without using the venerable VF14.  This was my initial goal.

Priceless... in every respect.
Sorry, could not help, but comment on that one.

Best, M

[David Bock]

Quote:

aamicrophones wrote on Mon, 23 February 2009 16:22 You would not want me as a Senator as my views are to the left of Obama. then I might want you as my Senator. Mine (Clinton and Schumer) are far too right wing for me

Clinton is no longer a senator.

[aamicrophones]

Hi, of course my hearing is compromised I am 61 and probably don't hear much above 12khz anymore if anything.

However, the UM70 with its M7 definitely has a low end that rolls out sooner than a mylar capsule like the Peluso CEK367  or the Neumann K67 type.

The M7 low end roll off increases over time as the PVC membrane ages and it become brittle.   However, this M7 capsule that we tried in the tube microphone was only 2-3 years old.  

Cheers, Dave

[aamicrophones]

To Clarify about the M7.  

I do not mean brittle sounding but what I mean is that as the PVC diaphragm material ages it has a tendency to often exhibit stress fractures.  It also loses it elasticity over time and becomes stiffer and more brittle which reduces the low frequency response.

The M7 does have a subtle sonic difference in the mid range frequencies in that its PVC molecules react differently to sound pressure than mylar and the "decay" of the two materials is different.

The mylar has a slightly wider response and is a bit more precise sounding than the PVC to some ears.  However, the PVC can be "silkier" sounding on some sources.  I loved what the U47 did to the flute and soprano saxophone of Paul Horn during the recording of Jupiter Eight in the early 80's.

[Fletcher]

aamicrophones wrote on Mon, 02 March 2009 17:59

I do not mean brittle sounding but what I mean is that as the PVC diaphragm material ages it has a tendency to often exhibit stress fractures.

Only if stored improperly... over the course of 40-50 years they will indeed exhibit stress fractures.  You won't find that in a modern M-7.

[aamicrophones]

Hi Fletcher, I am not so sure about that.  

The North American Gefell distributor is in a suburb of Vancouver and I saw several M7 capsules in the shop with stress fractures when I was there a couple of years ago.  I did not ask the tech if these were new but I am sure they were not doing repair work on any vintage microphones other than Gefell microphones.

I would be surprised if any of these capsules were more than 10 years old.

I know Neumann had concerns about the longevity of the M7 back in 1959.   Having said, that we did have two original U47 microphones at Ocean back in the 80's.  One was an original Tele made in 1953 and the other was a Neumann made in 1958 and probably one of the last U47 microphones with a PVC capsule.  

These two U47's sounded quite different from each other about 4db difference in the upper midrange.  However, both sounded good and the low end sounded quite similar when used as room microphones in front of the drum kit.

We replaced the audio capacitors on one of the microphones but that would not make that great a difference in the upper midrange response.

However, it has been 18 years since I left Ocean Sound and used these microphones on a daily basis but  I heard a vocal recorded on one of them a few months ago and it sounded great.  

Cheers, Dave Thomas
www.aamicrophones.com

[Fletcher]

There is no "North American Distributor" for Gefell... there was one in Vancouver but that is no more.  As for M-7's dying, if they're stored properly, they won't.  If they're not stored properly, they will.  Again, we see a useless number of 4db in the upper midrange... 4db where?  4 db is a hell of a large difference... did you pull that number out of your ass? ... or did you measure the difference in a proper anechoic chamber?

[David Bock]

Quote:

Again, we see a useless number of 4db in the upper midrange... 4db where? 4 db is a hell of a large difference... did you pull that number out of your ass? ... or did you measure the difference in a proper anechoic chamber?

If it's anywhere between 1-5kHz, 4dB is MONUMENTAL, even without considering the 50-180Hz balance.

[compasspnt]

Huge. Difficult to believe, unless something is really broken.

[Fletcher]

Indeed 4db is monumental... huge... and frankly, ridiculous unless something is entirely broken.  I also humbly submit that all capsules must go through a measure of "quality control" whether they're made in the USA, China, Latvia, or Zimbabwe.

I also humbly submit that the consistency of machine assembled capsules should be greater than the consistency of hand built capsules as machines can be calibrated to operate within rather strict tolerances while hand built is prone to discrepancies.

While the Chinese did have "quality control" issues for quite a while [and may still to a point] I do not know of a single manufacturer of "quality" microphones that does not engage quality control testing of the capsules prior to installation in their microphones.

I'm not talking about Banjo Mart $99- specials that are built from "soup to nuts" in China [and I sincerely doubt that MXL, Studio Projects, Cascade, etc., etc., etc. have a 4db rise in the 1-5kHz range though I digress]... I'm talking about mics that are assembled in the US or EU by companies that care about their reputation and the product they put on the street.

Again I'm afraid our friend from "AA Microphones" is talking out his ass [and I have to wonder if the company is called "AA" so it shows up first in the phone book?].

Peace.

[PookyNMR]

Correct me if I'm wrong, but it appears the 4dB is in reference to the two old U47s at Ocean Studios, not the new microphones.

[aamicrophones]

Yes, you are absolutely correct.   The difference was between two different U47 microphones.  One was made in 1953 and one in 1958.   When I said, 4db difference in the upper midrange that was my best guess as an engineer with 40 years of experience recording.   It might have been 3db but definitely more than 2db.    The difference was probably more in the high end up above 6khz as one was definitely more sibilant than the other.  The midrange from 3Khz down was quite consistent and both capsule looked really good with no stress fractures.

Klause Heynes states, in one of his forum replies that the PVC capsule do in fact age quickly and that differences can be noticed even at 6 months between a new M7 and a 6 month old M7.   I doubt if I could hear that difference at 61 but there was a very noticeable difference in the upper midrange and high end between the two that we had.  I this can be confirmed by several engineers with award winning ears.

However, again these microphones were 5-6 years apart in age.  The one made in 58 lived in Toronto until 1979 and the older one lived in Vancouver all its life.  

If the PVC was not a problem for Neumann why did they go to the KK47 in 1959.

BTW, I must apologize for my comment on the M149 not having a KK47 capsule.  It turns out the microphone in question was bought used from E-bay and there is some evidence to suggest that someone installed a used K87 capsule in the microphone and possibly pilfered the KK47 for a U47 repair or clone?

I was misled by the studio's assistant engineer that it was bought new from a Canadian dealer but in fact talking with the studio owner I found it was bought on e-bay.  It had definitely be opened up before and the plastic guard on the top of the capsule was missing.   So my apologies for assuming this was the original capsule.

However, I was not impressed with the Walwart power supply of the M149.   This might be something expected from a low budget microphone but not a Neumann.

Hopefully, they have changed this on the new M149.

Cheers, Dave

[Fletcher]

Does it really fucking matter where they do the voltage regulation?  If they're doing it in the mic instead of the power supply what the hell does it matter if the thing looks like a "wall wart" or a big metal box?

FWIW I though Klaus rescinded his "time bomb" statement vis a vis M-7 capsules... and for the record, from all I've learned, the Berlin Neumann never made M-7 capsules.  It was sometime after employees from Neumann left the plant on the wrong side of the iron curtain that the K-47 and Mylar came into play... the factory that is still in existance that was [is] the original Neumann still makes M-7 capsules... I know, I've smuggled some back into the US for a couple of guys you have probably heard of who do microphone design and modification.

Other than that... this conversation is getting really boring.  You've gotten about as much "free press" as you're going to get around here... so I hope you enjoy the remainder of your life and hope that at some point you realize that the least part of the weakness of the M-149 is the "wall wart".

Peace.