aamicrophones, I have a question for you. I know that my U87ai has 3 layers of mesh in the head grill. Is there a reason your microphones don't? This isn't a criticism. I'm looking to be educated a bit. I hear people talk about this sort of thing all the time. I just figure the Neumann guys do it, why not others? My Shure KSM44 is also triple layered with mesh. Anyway, just curious.
Post by aamicrophones on May 1, 2017 14:45:58 GMT -6
Hi Vincent, there are some Neumann models with 2 layers of mesh according to Klaus. I believe the new TLM series use 2 layers of mesh. Klause also talked about the 67 head grills being changed around 1961?
Apparently, Neumann exchanged the screening with the larger mesh opening for the screen with small mesh openings. I think originally it went wide/medium/small but later something like medium/large/small and he believes this makes a difference?
There is an AES paper I read in the 70's where Neumann was comparing different layering and different spacing of head grill mesh.
I think the conclusion is that it made about a 1/2db difference at 15khz. I tried to find the article but was unable to.
The main purpose of the head grill is a Faraday Shield. It must let sound wave through but not radio waves and electro-magnetic interference (hums & buzzes).
There is also optimum mesh opening size to reduce the electro-magnetic interference.
The finer inner mesh also stop large dirt particles that are suspended in the air from being deposited onto the diaphragm. The more layers the more the SPL is reduced when it arrives at the diaphragm.
I have seen some microphone modders who believe removing the inner mesh will "improve" the sound. Now, the SPL reaching the capsule is increases and louder aways sounds better.
However, I believe that once you balance the level then the sound would be very similar with less than a db difference at 15khz.
In most of the pictures I have of the Beatles recording at Abbey Road with U47's they have added a metal pop filter in front of the microphone which would add a forth layer.
When I get some time (we are moving shipping & storage this week to a new location) I will put up a CM47ve with some pink noise and see if we can see a difference other than level with or without a metal pop filter.
The U87ai can use all the help it can get as the K87 capsules has a huge rise of about 9db at 12khz and the circuit has limited headroom compared to other microphones. That is why they use a de-emphasis circuit in the both U87 versions.
It obviously a little cheaper to make a head grill with one layer than two layers. We are very cognizant that 2 layers gives us larger SPL's reaching the diaphragm and make sure the symbiotic circuitry can easily handle these higher sound pressure levels.
Post by aamicrophones on May 4, 2017 13:20:32 GMT -6
Hi John, duhhh!!! Thanks for catching the typo. I have edited it. Crazy day as we are moving and then I just realized my passport expires the last day of the NAMM Show in Nashville so I had to get the paperwork together to re-new it.
We will be at NAMM in Nashville from July 12 to July 15th. It seems NAMM has reduced the number of guest badges which means free admission to the NAMM show.
However, I will have 6 passes left that I am saving for RGO members but I need confirmation by June 28th, 2017. We are at booth 331 which is a stones throw for our friends at Warm Audio and Matt from Roswell microphone is just across from us.
Folks don't have to buy a microphone from me just come and enjoy the show.
I have a question for you in regards to your U47 style microphones; CM47VE & CM48T.
For the CM47VE you're using the standard BV8 and you are using the 6072 tube, which per your site notes is very quiet and hifi. Now the new CM48T is using the same BV18 transformer as the CM49, but is using a more vintage style tube circuit with a 5654W tube. I'm curious about the similarities and differences between these two, and even when compared to the CM49.
Is there a reason you didn't opt for the BV8 with the vintage tube circuit for either of the U47 style mics? I have to admit, at this price point the CM48T is very attractive.
Hi Vincent, actually the CM48T I sent to you for the shootout has a BV8 transformer. My instincts as an electronics tech pushed me toward the BV18 because it has slightly more modern laminations and a higher turns ratio.
The 5654W is configured as a triode and has a plate impedance somewhere around 6500 ohms.
So, the load should be 65K in theory but with 1.2K being the input impedance of the majority of vintage preamps then the transformer should have an impedance ratio of 54.
The BV18 has an impedance ratio of 64 and the BV8 and has an impedance ratio of 42. So, the 5654W is seeing a load about 6.5 times higher than its plate impedance with the BV8 transformer.
10 times is optimum but it seems to sound a bit warmer in the lows and more "vintage" like with the lower ratio BV8 but the low frequency distortion down below 50hz does increase a couple of %.
With the BV18 it sounds probably a bit more HiFi like the Soundelux U95. I really liked the sound of the U95. I serviced a couple and thought they really stood up to the old U47's we had at Ocean they were a little more modern sounding but very musical.
We brought 16-CM48T microphones in with the BV18 transformer but they are easy for us to change here. The price difference betweem the two transformer is less than $2.
The next order will be at least 40-microphones so we need to figure our which transformer we really, really like.
Last Edit: May 12, 2017 19:49:55 GMT -6 by Vincent R.
Well aamicrophones, I'll give you my thoughts after I sing into it a few times. I wish I still had access to the Wagner U47W I had tried. That was a hell of a mic. I'm going to try and replicate what I recorded with it and I can send you some files privately. I'm looking forward to hearing it vs the Flea 47. My thoughts initially are that the BV8 will give some of the tube artifacts that people expect to hear in the U47ish mic.
Post by Vincent R. on May 17, 2017 14:32:57 GMT -6
Finally finished my crooning vocal microphone shoot out. No video this time. I actually made this recording quickly before recording the "Mona Lisa" video. Microphones are an Altec 639A ribbon mic, Slate VMS FG-47, Advanced Audio CM49, and the MK U67.
I actually have a CM48T here. My guess is T01 is the U47 & T02 is the CM48T.
I had the opportunity to get the CM48T in front of a Flea 47 yesterday as well as my Slate VMS. What was interesting to me was how different yet similar they all were to each other. The Flea sounded like I expected it to....like a real U47 with an EF12 instead of a VF14. That tube makes a difference. I have some experience with a Wagner U47W with the VF14 tube. Despite not having quite as deep a low end as the Wagner, the Flea sounded like a U47 with a similar top end and mids to the Wagner; big, warm, sits well in the mix, etc. I used to own a Peluso 2247SE. The Peluso had a much more modern top end with a little less on the bottom than the Flea, but sounded like a brighter U47; again big, warm, sits well in the mix, but could get sibilant on some voices. The CM48T has a much more even sound than I expected; Not quite as big, a bit more modern, a bit tighter, but 47ish. It had a similar top end to the Flea, but a little less low end. What shocked both of us was how good it sounded either way. For $600 no one is going to complain that this is a bad microphone. It sounds fantastic just different. I was also able to get it pretty close to what I wanted with a little EQ. On my voice I still lean toward the CM49 which gives a little more natural high end to my voice than any of the 47/48 mics did, or the U67 on anything operatic. The Slate sounds like a 47, but has some weird frequency going on that I can't pin point. It's the Chinese capsule syndrome everyone talks about when they hear it.
I'll be filming a video with the CM48T this week. Hopefully it won't take me more than a week or two to edit the song and video and post it to YouTube. The shoot out will be a little longer.
aamicrophones , I'll try to send you some samples from the shoot out in the next day or so for you to hear.
Last Edit: May 21, 2017 9:05:01 GMT -6 by Vincent R.
Hi Guys, thanks for your participation and the detailed reporting after listening to both microphone tracks. It really confirms what I am hearing with the microphones.
Microphone #1 is the CM48T. This is our BV18 transformer in the CM48T with its more modern laminations.
I have sent a CM48T to Vincent to shootout and it has our more vintage BV8 transformer.
However, our BV8 does not roll out at 40hz like the Neumann transformer or have a bump in the low end.
You can get a bit more bump in the 50hz area by reducing the value of C8 to 1ufd with the BV8.
The BV18 has a higher ratio 8:1 so it does not present as much load on the tube creating less "transformer" distortion in the low frequencies.
My design philosophy has been to reduce the bump by using a larger capacitors and a transformer with less low frequency distortion according to Bill Whitlock of Jensen.
However, both the U47 and U87 have slight bumps in the low frequency because of the capacitor and transformer inductance resonance.
I can supply the CM48T with either the BV8 (6.5:1) or the BV18 (8:1).
At some point I will try the circuit with the AMI BV8-08 transformer but at the moment the AMI transformers are $300 each which is $400 CDN.
The idea of the CM48T was to produce a microphone that would sell for <$600 that could give folks a sound that was in the U47/U48 ballpark without the buyer having to re-mortgage his house. Also, the GE/JAN 5654W 7-pin low voltage pentode is very reasonable to purchase and they are readily available costing about $8 each in lots of 100.
We are able to sell tested/selected replacement tubes for $15 each.