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Post by aamicrophones on May 17, 2017 14:10:45 GMT -6
Doug is right, the filament circuit in the original U47 with the VF14 was simply to extend the life of the tube. The plate voltage which in the case of the U47 is also the filament supply is ramped up slowly through the big wirewound resistor at the bottom of the microphone.
If you put a voltmeter on the plate/filament supply you will see it takes about 50 minutes to stabilize which allows the cathode to be heated up to approximately 2000C which yields the optimium amount of free electrons.
Underheating the cathode just means it takes more time for the cathode to get up to its optimum operating temperature. You have to let the U47 warm up each time for 50 minutes before you can listen or measure the internal tube/circuit noise.
The filament of the VF14 draws 40ma and the dropping resistor according to the schematic is 1780 ohms and there is 35 volts reaching the filament which is why it takes 50 minutes to get the cathode up to temperature.
P=E2/R 105v-35v =70v. This means the 1780 ohm resistor must drop 70v. 70x70=4900/1780=2.75 watts 4900/1500=3.2 watts. A 5 watt resistor should be more than adequate.
***** However, this math only works for the VF14 tube and not those with 6 or 12 volt filament. The EF14 draws 470 milliamps, the EF80 draws 300 milliamps and the EF800 295 milliamps. So, this resistor has to be calculated depending on the filament voltage and current.
Today, we use regulated power supplies that bring the cathode temperature up to optimization in less than 2 minutes and the filament supply and plate voltage are pulled up to the correct volatage in milli-seconds after power up.
The last U47 I serviced had a power supply that was running high up at about 121v instead of 105V. Once we changed a resistor in the power supply we got 105v after 50 minutes.
These old resistors will change the values drastically over-time from constant heating. Wirewound resistors are not quite as suscetible to the heat as old carbon resistors unless the voltage or current is increased above their design specs.
There is absolutely no regulation in the U47 supply so if the power from the utility company is higher than normal or lower than normal the U47 supply voltage will follow.
They were wire wound resistors in the U47 for the most part. Carbon resistors back in the early days of tube electronics has 20% tolerance and produced noise. Today we use 1% metal film resistors in the audio part of the circuit and 5% in the power supply.
Resistors don't have a sound other than "noise" they are either the right value to optimize the circuit or not.
Also, the only reason Neumann used fixed bias with the U47 is that back in 1947 a cathode bypass capacitor large enough to provide good low frequency results would be too large to fit inside the body.
Fixed bias does not require a cathode bypass capacitor.
In all our 9 pattern tube microphone designs we use a two stage (dual triode) CCDA circuit. This does not require a cathode bypass capacitor and produces an output impedance 1/10th that of the VF14M from a $10 tube that is exceptionally quiet when selected.
Look at the size of the 1ufd in the original U47 now imagine how big it would be if the capacitance was 100 times larger back in 1947 which is required for HiFi operation of the circuit.
What's important with capacitors is the ESR (internal series resistance). We still used oil filled capacitors today but only at Electrical Power Sub-stations. Oil filled capacitors of the kind of value used in microphone circuits can handle upwards of 10,000V.
However, the maximum voltage in a U47 should be 105v if everything is working properly. We use 2.2ufd metal film WIMA in our microphone builds with 5% tolerance having an ESR 1/100th that of an electrolytic.
If you are using a AMI BV8-08 then you must use a 1ufd capacitors because Neumann used two different winding inductances in each of the dual bobbin construction.
This rolls out the low end at 40hz with the 1ufd if you increase the capacitor value the low end will roll-out earlier. I could figure this out until I read the article on the original BV8 constructon by Oliver.
There is also a low frequency bump in the response because of the transformer's inductance and the capacitance resonating in the very low frequencies much like the low frequency bump back from a tape machine.
That's part of the U47 sound. In our BV8 version we use match bobbin windings and can use a 2.2ufd capacitor to move the resonance down into the sub-sonics and with the CCDA circuit achieve a flat response down to 20hz.
Cheers, Dave
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Post by aamicrophones on May 17, 2017 10:07:50 GMT -6
Hi Guys, Namm is July 13, 14 & 15. I will be there setting up our booth on the 12th. We will be at booth 331 which is a corner booth.
I have 6- passes to give away at this time. The cut-off day for free passes is June 28th.
Last year we had 16 passes but this year they dropped the free passes to 8 per exhibitor and we have given 2 away so far to clients.
I would need a name and e-mail address for each pass.
The doors open at 10:00AM each day to visitors and 8:00 am for exhibitors. Thursday and Friday Namm is open to visitors 10:00 am to 6:00pm and Saturday its 10:00 am to 4:00 pm.
Cheers, Dave
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Post by aamicrophones on May 16, 2017 15:51:26 GMT -6
Here is a very cool "pop" song by two of the best "pop" songwriters around in my opinion!!! I hope its not too political!!! Donald Fagan and Todd Rungren collaborating on The Man in the TIN FOIL HAT!!!
This made my day when I found it a few hours ago. ITS GREAT, TREMENDOUS , AMAZING AND ALL THAT!!!!
Cheers, Dave
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Post by aamicrophones on May 15, 2017 22:51:41 GMT -6
I agree with Jcoutou. I'm planning on trying 96 kHz next time I begin any new sessions. I've heard plug-ins can sound better at that sample rate. I'm unfamiliar with higher sample rates when bouncing. When I bounced my first 96 kHz session, it automatically converted to 48, is that normal? At, 48khz the filters are causing the high end frequencies to "fall over a cliff" at 70db/octave starting at 24khz. At, 44.1 khz the filters are causing the high frequencies to "fall over a cliff" at 70db/octave starting at 22.05 kHz. At, 96khz the filters are causing the high frequencies to "fall over a cliff" at 70db/octave starting at 48khz. To my old ears 48khz/24 bit sampling in my RADAR converters sounds as good as coming back from tape but I have less tape hiss and no low frequency bump from the record head. However, 96khz seems to sound more like the sound coming off the mixing console before it went to tape. The low frequency bump in an AMPEX 24 track was different than the bump from a 24 Track Studer or MCI 24 track. This was due to the different gap and inductance of the different maker's playback heads. That' why we always laid 1khz, 10khz and a 100hz tone on master 2" tapes that were moving from one studio to another; this way the low frequency EQ could be compensated to normalize the LF bump between different tape machines as well as the HF EQ could also be normalized. I did some guitar overdubs here at 96khz for a project that was being mixed in Sweden but the RADAR system drops from 24 tracks to 12 track at 96khz. Cheers, Dave
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Post by aamicrophones on May 13, 2017 13:08:34 GMT -6
I have the little Behringer one. It's indispensable to me. Agreed. I can't believe that I spent the better part of 25 years without one. What the $##@#$%$% was I thinking!!!!! I also agree. I still have the one I built back in the 70's when no one was building them commercially. Its a very simple circuit, 3-switches, 3-LED's, 3-resistors, 2-XLR connectors, 2 1/4"-TRS connectors and a 9v battery. If you push one button and two LED's come on you have a short. If you push button 1 and LED 2 lights you have a phase problem. This one has gone to every live recording gig with me and is still working. I think its only on its 2nd or 3rd battery. I also built one with a 7 position Rotary switch and 7 LED's for testing our 7 pin microphone cables. It has 7 LED's that than line up with the rotary switch positions and go Red, Green, Red, Green, Red, Green and Red. So, its easy to see if they swapped a wire between one side of the 7 pin Neutriks to the other or if one wire is shorting to another. Its over in our new shipping, assembly and storage building as every tube microphone cable gets tested before it goes into the flight case. Cheers, Dave
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Post by aamicrophones on May 12, 2017 15:27:23 GMT -6
OK, was it a circuit card version with a tiny transformer? Yes, that's the one. I remember the transformer struck me as being a bit small compared to the RCA, the Altec preamps and the microphone input transformer in the Ampex 350. This was over 10 years ago when I was racking a fair bit of gear for folks. The AMPEX 350 makes a great tube preamp and tube DI. You can remove the bias oscillator tubes and playback head preamp tubes. I used the headphone jack as a DI input and re-wired it so when you plugged in a bass or guitar it bypassed the input transformer. Cheers, Dave
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Post by aamicrophones on May 11, 2017 23:28:30 GMT -6
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.
Cheers, Dave
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Post by aamicrophones on May 11, 2017 14:52:28 GMT -6
Back in the day I liked to use the U47 where the neck meets the guitar and a 414 eb down by the bridge or a C451 SDC as we didn't have any KM84's. If you double the acoustic guitar part then I would pan the doubled track opposite from the first track and it sounded huge. Cheers, Dave
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Post by aamicrophones on May 11, 2017 14:43:55 GMT -6
The Altec's had 3 tubes in each module drawing 1.2 amps total to light the filaments X 8 = 9.6 amps X 6.3v = 60.5 watts just from the filament supply. 35ma plate current per module x 8= .28 x 300v for another 84 Watts. That was just too much heat for the inadequate cooling of the original studio. Here is the schematic for the Gates SA-70 it looks similar to the CA-70 without a part by part comparison it just had more modern 50's tubes I believe. I racked a couple of these up several years ago for a client. They were designed for AM broadcast and I didn't think they quite had the fidelity of the RCA or the Redd 47. I thought the low end was a bit lacking compared to the RCA, Redd 47 plus the Altec's and I did re-cap the Gates modules. My sense is because they were meant for radio announcers the let the low end roll out a bit early than if you were recording music. I think the transformers were not quite as good as the Altec, Collins and original Western Electric transformers but I never compared them side by side. We are clearing out my storage room today and tomorrow so all the spare microphone headgrills, shockmounts etc will be moving over to our new facility. I will finally be able to get to my boxes of old tubes so I will make a list of what old audio tubes I have there. Cheers, Dave OOP's that is not the schematic for the Gates I racked at it had EF86 tubes not the 6J7 in the SA-70. The modules I racked were from a Gates Studioette. I have the schematics in a PDF file but they are too big to post. Sorry for the confusion. Cheers, Dave Well there's one. Plus any parallel between CA-70 and SA-70. Anyone can send me 6J7's anytime they want! Eight 459A's would be a good winter addition, I think they are like 35mA 300VDC apiece, with 6W output capability. I got rid of a rack of Langevin 117A's for the same reason, even though they sounded amazing. Eight 6V6's, so like 4 Stalevel turned on at all times. OOP's This schematic is not the schematic of the Gates tube preamps I racked as it shows a 6J1 tube and the Gates I racked has a 9 pin pentode in the front end so it must have been a model made after the SA-70. Cheers, Dave
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Post by aamicrophones on May 11, 2017 14:27:47 GMT -6
I have used an RCA BA-2 back in the 90's and it sounded really warm and smooth sounding. I probably have some 6J1 tubes kicking around here somewhere I would give away to a good home. I had a 8- Altec 459a tube preamps in a rack back in the 70's. We ended up selling them as they sounded amazing but they heated up the control room too much as we hadn't anticipated the gear creating so much heat. The Altec's had 3 tubes in each module drawing 1.2 amps total to light the filaments X 8 = 9.6 amps X 6.3v = 60.5 watts just from the filament supply. 35ma plate current per module x 8= .28 x 300v for another 84 Watts. That was just too much heat for the inadequate cooling of the original studio. Here is the schematic for the Gates SA-70 it looks similar to the CA-70 without a part by part comparison it just had more modern 50's tubes I believe. I racked a couple of these up several years ago for a client. They were designed for AM broadcast and I didn't think they quite had the fidelity of the RCA or the Redd 47. I thought the low end was a bit lacking compared to the RCA, Redd 47 plus the Altec's and I did re-cap the Gates modules. My sense is because they were meant for radio announcers the let the low end roll out a bit early than if you were recording music. I think the transformers were not quite as good as the Altec, Collins and original Western Electric transformers but I never compared them side by side. We are clearing out my storage room today and tomorrow so all the spare microphone headgrills, shockmounts etc will be moving over to our new facility. I will finally be able to get to my boxes of old tubes so I will make a list of what old audio tubes I have there. Cheers, Dave Well there's one. Plus any parallel between CA-70 and SA-70. Anyone can send me 6J7's anytime they want! Eight 459A's would be a good winter addition, I think they are like 35mA 300VDC apiece, with 6W output capability. I got rid of a rack of Langevin 117A's for the same reason, even though they sounded amazing. Eight 6V6's, so like 4 Stalevel turned on at all times.
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Post by aamicrophones on May 11, 2017 13:53:25 GMT -6
MBHO MBD 219 SC Dynamic Hypercardioid Handheld Oooooooooooo. This is something I need to check out now. COMING SOON!!! The Advanced Audio CM54 live vocal microphone. Here it is being field tested in Portugal. Maria the singer told me the sound guy loved it and preferred it to the Neumann KMS-105. Here is a picture of the prototype The head will fit on or CM1084 pencil microphone and has a super-cardiod 22mm capsule. The super-cardiod head grill will be about $95 and the complete CM54V with its class "A" fet transformer coupled 414eb type circuit will sell for $229.00 These are in production as we speak and we expect to have stock by July to introduce them at Summer Namm in Nashville. I will have several vocal samples by the end of the month from the prototype that I have here. Cheers, Dave aamicrophones.com
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Post by aamicrophones on May 10, 2017 19:14:09 GMT -6
I like the V78's I have re-built for folks better than the V72 but the V78 has at least 7 capacitors in the audio chain and the Redd47 has 4 capacitors. This is a case where less is more in my book.
The Red circuit is quite elegant with a fat/present sound.
I have used an RCA BA-2 back in the 90's and it sounded really warm and smooth sounding. I probably have some 6J1 tubes kicking around here somewhere I would give away to a good home.
I had a 8- Altec 459a tube preamps in a rack back in the 70's. We ended up selling them as they sounded amazing but they heated up the control room too much as we hadn't anticipated the gear creating so much heat.
When we built Ocean "proper" in 1979 we use a 1 ton air conditioner for the control room and a 2 ton for the studio. Each control room and each studio had their own air conditioners.
Cheers, Dave
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Post by aamicrophones on May 9, 2017 23:52:20 GMT -6
These were all done with the Dizengoff D4. Don't know if this helps, but there it is.. ("All Again") hasn't been mastered yet, so it's not as loud as the other tracks, turn it up a bit. The third track is from my friend Dusty Wright's new album, it's a song we co-wrote. https%3A//soundcloud.com/martin-john-butler/long-road-back-masterhttps%3A//soundcloud.com/martin-john-butler/all-again-mix-10https%3A//soundcloud.com/martin-john-butler/life-is-hardThat's the Redd 47 type sound. The Disengoff D4 is their take on the REDD47. That's an amazing price if they all sound that close to the original as the once I have heard. That's my favourite tube preamp circuit and what I have heard from tracks cut on the D4 is pretty convincing. That's negative feedback at its finest. I have re-built V72 preamps and they don't sound anywhere as good as the EMI Redd 47 to my ears. Rubber Soul seems to mark for me a noticeable improvement to the sound in Beatle recordings to those previously recorded with V72's. Below is the console that the preamp was designed for and it recorded Rubber Soul, early Pink Floyd and probably Sargent Pepper. This one was saved from the dump by David Stewart the manager of British Grove and completely restored for Mark Knofler. Dave told me Mark loves it on guitars. Dave let me peak inside and twiddle knobs. The lower console is the one Mark bought from the EMI Studios in Lagos that recorded Band on the Run. These consoles are both working on opposite sides of a 72 channel Neve V88 in British Grove Control room A. The big brother of the console below was at Abbey Road and recorded The Wall and it just sold for several million dollars!!!!!!! So, if you can get the same sound for under $1K its a no brainer. This console still had the same Redd 47 preamp circuit but the module had a different model number and the EQ was a bit more sophisticated. Anyway you can't go wrong with the D4 as it is literally a new version of a "classic" sounding tube preamp. Here is a prototype of my homage to the Redd47. This has been on the back burner for a while as we have been putting the MT8016 into production. The 2047 can go back up on the workbench next week as I have some input transformers I really want to try with the circuit and finally got the 2db per step gain switches. Cheers, Dave
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Post by aamicrophones on May 9, 2017 21:19:14 GMT -6
Hi Guys, the original U87 has a transformer with a 5:1 ratio (200 ohms) and can be strapped at 10:1 ratio (50 ohms) The U87ai has a transformer with a 7:1 ratio. Here are the schematics for the U87 made before 1988 and the U87ai made after 1988. Both microphones have the same single class "A" fet transformer coupled circuit running from the same supply voltage but the polarization circuit is quite different. The original U87 has a polarization voltage of 46v while in the U87ai the capsule is polarized at 60v yielding more output from the capsule and a bit more upper midrange lift. I have serviced many U87's and U87Ai's and to my old ears the original always sounded better, (once the issue it was sent in for is resolved). The original U87 always seemed to sound warmer and smoother. The U87Ai just sounds brighter and more sizzly to me but some folks do like that sizzle. You never have to brighten a U87ai or a U87 in my experience but it never sounded as good to me as adding 3db at 12khz with the Pultec to the U47. Having said that, I like to stay away from EQ whenever possible!!! Because the output of the capsule is a few db higher from the 60v polarization the single fet amplifer has to handle this extra output and the circuit is already at its limits. So, the U87ai has less headroom than the original U87 which had a lower output from the capsule and the original U87 has 3db less transformer loss than the U87AI. Even at 69 I can still hear at least a 3db difference in headroom between the two microphones. I agree with one of my hero's the late great Roger Nichol's who stated on the liner notes of Katy Lied that, "Individual microphone EQ is frowned upon". I have never had a problem hearing the vocals and background vocal parts on a Steely Dan recording and they are usually more complex than other rock & roll recordings. The legendary Al Schmitt would first change the microphone or microphone position rather than resort to EQ. When I worked once with Bill Porter he was very concerned about where the artist was positioned in front of the U47. He moved the snare microphone rather than ask for it to be EQ'd. At Ocean if a producer wanted a brighter microphone the C12 or C414eb would be pulled out first rather than a U87. One very famous producer brought in a Sanken CU44 which is very bright and we had several other tube condenser microphones to choose from including 5-U87's. They only had U87's at Little Mountain and Bob Rock would come over to Ocean Sound to cut vocals on one of our U47's. Vincent, used my CM49 quite successfully and only rolled out the very low end and the very high end above 10khz to move it back into a more 50's soundscape. He never had to EQ anything in the midrange frequencies. Knowing, the REDD 47 circuit it would be difficult to bypass the built in negative feedback. You design a negative feedback amplifer for maximum gain and then, as you add more negative feedback, the gain (output) level is decreased. So, it is quite possible that when you gain the Redd down to +4dbu you are adding the maximum amount of negative feedback. Someone mention the U87 sounded good through a Neve 1073 which has two gain stages utilizing negative feedback. Our MT8016 transformer coupled preamp also uses two stages of negative feedback and it makes my TLM103 sound much more palatable to my old ears. I have built up a Redd47 circuit and it does something really nice to whatever you put into it. The one problem I see as a microphone builder is the more circuitry you put inside a microphone the more parts there are to fail. Just one tube inside a microphone produces a fair bit of heat. You can always patch into another preamp if one fails, so I am not sure about putting all my eggs in one basket? However, I have spent most of my life with a single microphones connected into a single microphone preamps. The track on the Redd site sounds really good and its a lovely sounding room. However, someone building their first studio could buy two tube microphones and a 2 channel preamp from us for that kind of money. Also, the microphone is also only competing with an acoustic guitar on the track I heard. I would want to hear a bit more "spark" when the bass and drums kick in. The one advantage the Redd has over all others is you are bypassing 30' of microphone cable or more in some cases. I would love to hear the Redd microphone directly patched into my IZ Technology A/D converters. I will have to resurrect my Redd 47 project. It will work brilliantly with the 6:1 transformer we are currently using in our MT8016. Cheers, Dave aamicrophones.com
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Post by aamicrophones on May 5, 2017 14:53:31 GMT -6
Seems like a lot of folks like the sound of the Chandler over all others. What I expect you are hearing is the negative feedback used in the Redd 47 preamp used in the microphone. The Redd 47 preamp had 24db to 52db of negative feedback in 6db steps.
I built one up one day with a Neve 1073 input transformer and it did make everything you put into the preamp sound really punchy, full and smooth. I still have the prototype here but its on the back burner at the moment.
There are some advantage to negative feedback in audio amplifier circuits.
1) Negative feedback can increase the stability in high gain situations.
2) Using negative feedback can reduce noise in thre amplifier chain
3) Negative feedback can decrease non-linear distortion is multi-amplifier stages.
4) The bandwidth of an amplifier can be increased with negative feedback.
5) An amplifier with negative feedback will have an increase in its input impedance. This is helpful when you are coupling a condenser capsule into a microphone circuit. If for arguement sake we say an LDC condenser element has a capacitance of 70pf then it will have a reactance of 22 meg ohms at 100hz and a reactance of 113K ohms at 20khz. This capsule would have a reactance of 52Meg ohms at 40hz and you would need to load it with 520 meg to have a flat response down at that frequency.
6) Negative feedback also reduces the output impedance of the circuit so a lower ratio output transformer can be used. The REDD 47 had an output transformer with a 7:1 ratio.
So, I suggest that is what we are hearing in the Chandler microphone, which to my old ears sounds like the Chandler is smoothing out the transients a bit.
Negative feedback will reduce gain so usually two gain stages are required.
We use negative feedback in our MT8016 solid state preamp which has two 30db negative feedback gain stages that are coupled in tandem.
The gain of each stage is brought up together and like the Redd 47 microphones just seem to sound better through the MT8016.
Cheers, Dave
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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.
Cheers, Dave
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Post by aamicrophones on May 3, 2017 14:16:27 GMT -6
Lynn, is a lovely guy who was very impressed with our CM67se and Sweetwater's recording Studio bought a couple on his recommendation.
Sweetwater actually approached us about them becoming a dealer for our microphones at Namm last year but my feelings were at this time, if we increase sales to that extent we couldn't keep up the quality control.
How we shootout microphones here in my studio is how we use to comp tracks back in the day. I record say, four different microphones at the same time from the same source through the same preamp each on separate tracks of my Radar.
The tracks come back up on the MCI/Sony MXP3036 and the lighted channel on/ mute buttons on the console switch completely silently. If you have one channel up and all the rest off then hitting two buttons at the same time will turn off one and engage the other.
You can switch within milli-seconds and really compare. I find with this method you can really hear the subtle differences between microphones that are very close sounding to each other.
It takes a good amount of time to get the levels balanced even with the P&G faders. I tried this once with a Pro-tools controller and couldn't get the resolution I was use to getting with analogue P&G faders.
If one source is even slightly louder than the other it often will be the one you pick out as sounding better. I don't really call the Vintage King video a true shootout. For, example the Bock sounded a bit better than the Tele but the Bock seemed to be louder to my old ears.
All you have to do is move a few milliametres of the microphone and the sound will change. I also disagree with the notion that Cardidod is good enough for vocals.
Now, most of the time I use Cardiod but put the microphone in OMNI and some good gobos around the microphone and you get no proximity effect plus a microphone can handle 6db more level in OMNI.
Most of the Beatle vocals were cut in OMNI I suspect because the room sounded so great. I will ask Ken Scott if I see him at NAMM. Ken bought some of microphones for his recording College in London.
I thought the SOYU popped too much on just a short spoken word to be trusted on a recording without a HD pop filter. Maybe, it would fair better if were hung and angle back to let the blast of air pass under the capsule.
I am not a bit fan of bottle microphones either for that reason as you have such a short distance between the grill and capsule. I probably would never build or use one even if they sounded better than any other microphone.
They just remind me of Hitler spewing Mein Kampf while the U47 shape reminds me of John Lennon singing "Give Peace a Chance" but that's just my "child of the 60's" sensibilities.
This has nothing to do with audio quality but KARMA is very important to me.
Lynn also did and interesting comparison between my CM87 and his U87AI. He was quite impressed how close it was for 1/10th the price and wrote about it in one of his posts.
He had a great Forum much more like RealGearOnline than Gearslutz.
I am glad RGO has come along to fill in the gap.
Cheers, Dave
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Post by aamicrophones on May 3, 2017 12:48:59 GMT -6
Hi Guys, I don't like to "kick a man when he's down" but there is a real flaw in the Avantone CV12 and the TNC ACM-1200 circuit.
As, others have noted it uses a economy Chinese K87 capsule which is skinned with 6 micron mylar and we do use selected versions of this capsule in our CM47Fet microphone. However, the CM47fet like the U87 uses de-emphasis to reduce the drastic rise above 10khz that an 87 capsule is noted for. Select and de-emphasize is the secret with the K67/K87 typ capsules.
There is no de-emphasis in the CV12 circuit and it also is fitted with an economical single bobbin transformer.
The circuit has a cathode output stage but was implemented incorrectly to provide the HP filter option.
Whoever, designed the HP filter broke the direct connection between the plate of the first stage and the grid of the 2nd to insert a switchable capacitor value to roll-out the very low frequency content.
The CF output stage now has to be biased with a resistor network and this reduces the headroom by nearly 1/20th and the result is the positive going waveform distorts much sooner than the negative going waveform.
You can clearly see this if you put a sine wave into the circuitry or put it in front of a kick drum and you will see the top waveform square off much, much sooner than the bottom waveform.
We can check the integrity of the microphone audio circuity by disconnecting the capsule and inserting a sine wave, pink noise or music source into the input grid of the first stage.
Now, its typical for a class "A" tube circuit to be a little asymmetrical but the CV12 circuit is way beyond the norms of good tube design.
What we do is put the CV12 circuit back to being a class "A" CCDA tube circuit that we use in our 9 pattern tube microphones, I move the HP filter postion to the cathode output section just before the output transformer.
This is a slight trade-off as different preamp loading of the microphones output stage can cause the HP filter to vary slightly but the CCDA circuit has a 600 ohm output impedance so its much more forgiving than a single stage circuit with a typical 10K to 15K impedance.
So, when you couple a capsule with a 9db rise at 12khz into a circuit with reduced headroom and a economical output transformer then it will sound blurry and grainy even with moderate sound pressure levels to say the least.
When you put someone like Vincent in front of it with his incredible pipes, it won't matter what tube you put in, it its not going to reproduce correctly the sound reaching the microphones capsule and would not be a useful audio tool in my experience.
The sound will also vary much more drastically between pianissimo passages and fortissimo passages even with Vincent's excellent microphone technique compared to a "properly" designed microphone circuit.
My sensibilities are more inclined to save the money on the chrome headgrill, red sparkle paint and wooden case inside the road case and optimize the circuit but that's just my philosophy.
We are just in the process of moving our storage, assembly, testing and shipping to a slightly larger but modest facility that will give us more room to assemble preamps and get microphones ready for shipping.
I will keep my shop here for R&D and the Studio for testing microphones in the "real world". Folks will still be able to drop my my home looking out over lake Okanagan and try out some microphone in the studio.
Once we get organized after we complete the move then I could find my notes on the CV12 circuit and the changes that we made and put them up in a post.
The "baby does not have to thrown out with the bath water". Simply removing 7 components, moving the HP filter to the cathode output stage, replacing the capsule and tube bring the microphone into the "world class" realm.
You can also keep the K87 type capsule if you just want to upgrade the circuit, if you place a 1000pf from plate of the first stage to ground it will tame the rise of the 87 capsule. If you want it more C800 like then use a 330pf to 470pf.
Cheers, Dave
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Post by aamicrophones on May 3, 2017 11:22:30 GMT -6
I just had a brand new Avantone CV12 here. Stock it sounded rather poor I thought. I opened it and found that they use a chinese K87 type capsule. I had assumed it would at least be edge terminated. I changed out the capsule and replaced the EH 6072 with a GE JAN 6072. The difference was quite dramatic. It ended up sounding like a great microphone. I had two TNC ACM-1200 microphones. They are essentially the same mic as the Avantone CV-12. I sent both to aamicrophones . One became an Advanced Audio CM12le, the other a CM251. The capsules were both changed to Dave's AK12 style capsules, and the circuits upgraded. The difference was huge. More balanced sound, more low end, bright with no hasrshness. They can be a nice platform for upgrades.
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Post by aamicrophones on May 2, 2017 0:40:56 GMT -6
So I'd sound like an electric guitar if I sing into a 57?? By that metric, singing into an RE20 either makes you sound like a kick drum, Trombone, or Stevie Wonder. Pyscho-acoustics is an amazing phenomenon. I worked with a very well respected producer once and he said, the snare need to be a bit brighter as I am loosing it in the mix. I reached over to add 2-3 at around 3.3K on the Neve 1073 EQ but I didn't engage the EQ as I hadn't had time to clean the noisy EQ gain pot. So, I planned on engaging the EQ after I turned the pot. Before I could engage the EQ the producer said, "that's better, its punching through now". My old friend Laurie Wallace who won a Grammy or two working with the Hudson brothers in the early 70's had some great stories. On day he is recording a Country Band to 8 track. The guitar player lays down a guitar track which is well played but doesn't really work with the song. Laurie's asked him to do redo the guitar part but the guitar player is adamant that its one of the best solo's he has ever played. So, without raising the tension in the room Laurie decides to move on to another tune. After the band leaves for the day he copies the guitar solo to another machine. The guitar solo track is also shared with tambourine in the chorus. The next day they are recording the tambourine part in the chorus before the guitar solo and Laurie leaves it in record erasing the guitar solo while banging on the tape machine with his fist and yelling, "the damn tape machine won't come out of record." He tells them how sorry he is but they will just have to re-record the guitar part. The 8 track was a Scully and it had huge red record indicator lights that you could see through the studio window. Laurie was recording Maria Muldar and every time the track went into record she would get nervous and you could hear it in her voice. I was the Tape Op and Laurie knew I was a tech and said, "Dave, stand in front of the tape machine and remove the record lamp." So, I quickly removed the record lamp on the vocal track. Laurie hits the talkback and say's "Maria let's just run through and rehearse it one more time before I record it". They roll back and Laurie puts it into record but no red light and the slight quiver in her voice is gone. I am in control room "A" at Ocean Sound and we are mixing a 22 minute cartoon that has to be finished and out the door by 4:30 pm. We take 45 minute lunch break around 12:30 to let a local rock band do a piano overdub on the C7 that was miked up with two C414eb microphones. My ex-partner had arranged this "free session" for one of his publishing company bands. I had the assistant mike up the piano while we were starting our mix. We work on our mix until the rock guitar/keyboard player arrives about 12:30. The piano is tuned at least once a week and more often than not a couple of times a week but the rock band guitar/piano player is convinced that the piano is a bit pitchy, doesn't sound as good as the last time he played it and it needs regulating. He's only playing 3 F**CKING CHORDS. On the previous Sunday I had recorded and opera singer and a 14 year old Korean piano prodigy who was already at the Piano Conservatory Advanced level. I still had the DAT recording in the machine. I had let this very shy Korean teenager play a solo piano piece from memory which was Chopin's Fantaisie Impromptu a very difficult piece but perfectly executed by this young girl. After several failed attempts the rock "god" managed to get through the part and came in to listen to his mediocre playing and said, "that the best I can do with the current condition of the piano." This was my beloved Yamaha C7 Grand that he was slagging. This was the piano that KD Lang and Roy Orbison has worked out their vocal parts on for CRYING without a word of complaint. We had to get back to the cartoon mix, if we didn't get it finished before FEDEX arrived at 4:30 then somone was going on a RED EYE with it to LA. This was not going to be me if I could help it plus I had missed out on lunch and 45 minutes of hearing bad piano playing was making me cranky. So, as ROCK EGO is going out the control room door I couldn't resist hitting play on the DAT and saying, "That's strange cause I though it sounded pretty good on Sunday when I recorded this and the player never complained but she was only 12". We have given advertising executives dummy faders so they can mix dialogue/FX and music on one or two occasions. So, they would quit calling out fader moves as we trying to get the jingle mixed. Bring up the Fx here it really need punch to get the listeners attention or the fade needs to be longer "really cause its a 30sec radio jingle" Push up the name of the product and make it pop Push up hook line where they sing the name of the car dealership Can I hear it on the big monitors instead of the 5" speaker on the Studer 2 track? "Sure cause those 15" JBL's and bi-radial horns really relate to the 5" TV speaker in a 1980's TV." We actually in some cases would mess-up on little part of the mix so the advertising executive could say, "Yes it was me that made that hook line pop out!!!!" I find engineers often have to take the rap for a lot of stuff that isn't really their fault. You call up the drummer and guitar player to make sure they have new heads on their drums and new strings on their guitar. But when they arrrive at the studio you find they are all completely dead and they expect you to fix it with EQ. The vocalist could do take, after take, after take but if the engineer missed one punch he could be fired from the session. Back in the day there was no undo, if you erased a part it was gone for ever. By the time we got to 24 track we could take several vocal parts and then comp them later but working with a 8 track tooks some pre-thinking. Cheers, Dave
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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.
Cheers, Dave
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Post by aamicrophones on Apr 30, 2017 20:51:32 GMT -6
Is it possible that some mics do not sound good in a different tracking room? Sounds stupid but it seems that happened to me today... Absolutely, for example the K67/87 capsule in the U87 has an anomaly. In Cardiod the rear rejection is about -20db from 100hz to 2khz except for 400hz and 800hz which are only -10db at 5khz. By 100hz the rear response start to drop and is down only -10db at 25hz and the rejection start to drop past 2khz and is down if you use them in a live room with lots of reflection getting to the rear of the microphone then 400hz and 800hz the "honky/nasal" frequencies will be more pronounced. The U87 is a microphone bodes well with a reflection screen as it can greatly improve the sound when used in rooms with lots of reflection coming back to the microphone. Our friend Joe Carrell in Nashville likes to use them over drums and re-called that in two tracking room in Nashville there seemed to be more midrange 'honk' both these rooms had low ceiling while in studio with higher ceilings they sounded much better. In our AK67 capsule which has more holes drilled in the back-plate than the K67/k87 the rear rejection is -18db at 400hz and -17db at 800hz on average. Now, this is where mike placement and placement of the instrument in the room can make a big difference to final sound. Cheers, Dave aamicrophones.com Cheers, Dave
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Post by aamicrophones on Apr 30, 2017 20:24:23 GMT -6
Are you going to put some AA K47 capsules in them? I was thinking if I buy some Thiersch M7 down the line for a project like this, it would be wise to pick the Mylar versions for these reasons of long term failure in PVC. Hello, yes we are going to replace them with the AA K47 capsules. They belong to a radio station in Eastern Canada and they can only afford to spend $300 a microphone for repair. It a good 3 hours to get each one apart replace the capsule and then put them back together so the pattern switch still works. Cheers, Dave
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Post by aamicrophones on Apr 30, 2017 19:17:44 GMT -6
I have the drum kit pulled out of the studio at the moment but will try and put it back up tomorrow and set up the CM414 and CM1084 as overheads.
I was using the CM1084 with the vocal (super-cardiod) head grill for a live vocal/un-plugged rehearsal today. It worked really well.
Cheers, Dave
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Post by aamicrophones on Apr 28, 2017 16:24:30 GMT -6
I used to work on those when they were popular in LA 20 odd years ago. They have a Russky metal jfet and a small thick film audio circuit board. If that goes SOOL. There is a crappy el cap that should be changed and three .015 uf ceramic disc caps used for the bass roll-off switch. A Wima .047 MKP-2 100V polyfilm cap fits nicely. These are also rf sensitive. Remove the ceramic caps off pin's 2 and 3 to ground and replace them with surface mount caps soldered across the pads on the rear of the circuit board. Hi Guys, the UM70's are lovely microphones but BUYER BEWARE they have M7 capsules which are prone to failure. I am just repairing two UM70's for a local broadcaster and both capsules have failed. Here is the schematic and you can see the hybrid circuit board in the triangle and the capacitors that Jim Williams spoke about. The microphones are transformer coupled. You can put signal in at point G to see if the circuit is working. The most common problem I have seen with these microphones is failing M7 capsules. Both microphones here have working audio circuits. Especially, as these microphones get older they will experience more capsule failures because of the PVC material changing it consistency over time. The UM57 is another lovely microphone and I repaired one a few years ago and was very impressed. I thought it was a better option to the U47. The also have traditional M7 capsules so there will be a huge difference as these capsules age between individual M7's. The one I worked on had a very nice sounding M7 but the tube was going noisy and it was easy to replace. Gefell used a EC92 which is a 7 pin triode with a plate impedance of 10K ohms. You can buy military grade NOS EC92 tubes for $6. The circuit is very elegant and simple with self biasing of the EC92. AMI makes a replacement transformer for $195. The parts to build this circuit with high tolerance components including the tube would be about $50 plus the AMI transformer. We use a similar circuit in our CM48T tube microphone but I choose to use a GE/JAN 5654w tube which is a military grade pentode that we strap as a triode like the U47 circuit. The 5654W gives us a plate impedance of about 6.5K ohms and it works really well with a 6.5:1 ratio transformer which was used in the U47 and U48. A properly working M7 capsule will be 4db noiser than a properly working K47 type capsule. This is hard to notice on close vocals but when used for distance miking or on instrument with low volume it would become noticeable. Case in point, you don't need to use a VF14 tube to produce a U47 type sound. In haste, as I have to pack up for a percussion gig tonight. I do have a file with our CM48T compared to a lovely sounding U47 with a M7 capsule and you can hear the difference which is quite subtle. The M7 does yield a slightly more velvet or lush sound but it would be hard to notice at all in the mix. They are incredibly close but I am using a slightly more modern transformer. However, we can fit them with the more vintage BV8 type transformer we use in our CM47VE. The slight difference are a result of the M7 and transformer. To me the CM48T sound 1/2 way between a U47 and M49 fitted with a K47 type capsule. What happens with the PVC diaphragm in the M7 is that it looses elasticity over time and becomes tighter and tends to smooth out some of the transients in the vocals or source. While K47 types remain much more consistent over time. Yes, there is always a trade0off. I will link the files of our CM47 compared to a nice sounding U47 at sometime tomorrow. Cheers, Dave aamicrophones.com
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