Microphone design tutorial part 2

Here is a complete dissection of a one of CAD's best microphones.  This one is made in America and has the original OS 110 capsule that CAD manufactured in it's facilities in Ohio.

I hope we can have a cool conversation about this microphone, because it is literally amazing.  I've put it up next to all different Neumann's and Telefunken's and to me just takes the prize for best sounding male vocal mic... even an original Neumann U47 with K47 capsule that my buddy owns.

Here are the pics







































This took me a bit of today to take these pictures... I hope we can really learn something from this mic's design.  I don't know any other company using opamps for the amplifiers...

Thanks,
min

It looks like they took some real pride in their work back in the day.

Thanks for the great pics!

Here is the schematic and a link to the owners manuel.  I was hoping someone would ask for it....   But I guess the name CAD doesn't really interest people.

It should because this mic is amazing!  Better then any U87 I ever tried 

http://dl.dropbox.com/u/13352325/DIY/E350man.pdf

http://dl.dropbox.com/u/13352325/DIY/E300-350%20schematic.pdf

A strange circuit - specially that output attenuation stage R10/12 and R11/13, throttling down the signal by some 30dB just before the output XLR.

Maybe a simple way to to reduce output impedance?

Or to ensure relatively stable turn-over frequency of the HPF across different micpre input impedances?

Maybe a quick-and-dirty way of getting rid of an originally intended but too-expensive 5:1 output transformer?

Or simply a wrongly notated schematic?

Jakob E.

Price wasn't the factor.  At least I don't think.  The mic sold for over $1000 a mic in the mid-90's and in Europe a lot more, if I'm not mistaken (I'm the second owner of a matched pair).  I believe none of their Equitek series used output transformers.  Even now they don't.  The mic has a real solid tone to it.  I can post some audio clips.

I personally thought the design is genius... 

Price is always a factor. That said, I don't think the designers wanted a transformer; people who prefer IC opamps over discrete parts are unlikely to feel love for iron.

There are a couple of unusual things about the circuit. Opamps aren't too unusual. AKG and Neumann use(d) IC opamps in certain models; some mics use circuits that are essentially discrete opamps. The Peus/Boré Neumann book has a chapter on opamp circuits.

One problem with opamps, especially when you want to use more than one, is that they may draw more current than P48 has available. And many preamps don't even give you full P48 specifications anyway. So about 5 mA is usually your design limit, and then you lose some in conversion for IC friendly voltages. CAD thus put in batteries as a kind of buffer. Personally, I think there's not a whole lot you can do with an opamp (in a mic circuit) that you couldn't do with a discrete circuit.

What is unusual is the pattern switching after the first stage, also the use of DC servos. And, as Gyraf said, the output stage looks weird.

I once reviewed one of the successors that had essentially the same circuit. I liked it, but it didn't strike me as a very memorable sound. I do remember that it sounded very clean. So one thing that may teach you is that you like clean better than colored. So maybe forget about tube and go solid state.

The capsule is essentially a K67 knock-off. According to the manual, it is a little bit larger, though. I'm not sure, but I think CAD models used Chinese capsules. The one in the mic I reviewed looked like a 27 mm Tenlux capsule.

mista min said:

Here is the schematic and a link to the owners manuel.  I was hoping someone would ask for it....  

Click to expand...

I would have, but I just assumed you didn't have it. I thought you were looking for help rev. engineering a schem from the pictures.

Although I haven't used one, I consider this a remarkable mic from a couple standpoints: It's made in America. And it's an entirely new design, i.e. not based on a classic mic. I recall Fletcher from gearslutz praising early versions of this mic, until shoddy capsule QC turned the purchase into a risky one.

Thanks for sharing. I will study the schematic.

CAD models now use Chinese Capsules and their mics are made by Felio, except their E100s, which is made in America.

The E350's capsule is not a chinese one.  It has been manufactured in their clean rooms in Ohio.  That's one of the big deals about this mic is that it has a great capsule.  The drilling in the capsule is pretty much the same as a KK67, but I don't know if it's an exact clone.  I'm not gonna take it off to check because I don't feel I'm ready for that step with one of my favorite mics.  However, it may very well be.


This mic is the last thing from clean.  It has a real vintage sound to it and more meat then a 1970's U87.  It really sounded like a U47 without some of the harmonic content.

Here is a clip from our churches Christmas concert.
It was recorded using:
1x CAD E350 (for Vox about 2 meters away on cardioid pattern into a Soundcraft GB8 with the mix down being recorded straight into wavlab... it's the churches setup).
2x custom wide cardioid SDC's that the church owns (inside the piano one at the treble side of things and the other pointed at the bass section, all going into the same GB8 preamps)
1x Audio-Technica AT4041 (under the piano into the same board with the phase-inverted.)

I had prepared the things for live use during the concert, but I muted them during her performance because it didn't need amplification, but I still got a recording

Excuse the noise as this is a live sound thing, not really meant for recording... converters were bad   I did use a bit of noise remover, but it didn't really effect the vocals or the piano too much.

Still the artist shines and the mic captured it.... there is some eq around 3 kHz from the earlier performances and on the piano too.  With the piano panned a slightly.

https://dl.dropbox.com/u/13352325/MICC%20Concert%202010%20-%20Amanda%20-%20%22O%20Holy%20Night%22.mp3

http://dl.dropbox.com/u/13352325/MICC%20Concert%202010%20-%20Amanda%20-%20%22O%20Holy%20Night%22.wav

p.s. Oh, I did put a buss-compressor on it just to tame the picks when she hits the loud notes... hope you enjoy

p.s.s. Kato, no I wasn't trying to reverse engineer it.  I just wanted to share this mics crazy quirks, because believe me it sounds great!

Whatever sound this mic has must come from the capsule. The circuit is very linear and clean.

Bahh... I didn't like how I expressed my idea so I decided to rewrite it....  I understand what you mean by the circuit being clean.  But linear is something that is applicable to tubes too, right?  Why would a tube be none linear?  Forgive my lack of knowledge here.

Thanks for posting!

OPA 2107 input amp... not the lowest noise at 8nV/sqrt Hz...but the large capsule should have high output, and its
transformed acoustic resistance pressure noise might still predominate along with bias resistor noise. Some other CAD
mics (M179) use the higher still noise TL072.

Gain of 1 or 10 for that input amp...

Servos? (TL062)

Looks like it could be much lower distortion than say discrete source and emitter followers.

Must take a ton of current. The 9V batteries are nicads?

Les

A tube circuit can be fairly linear. Older classic mics tried to be as linear as possible; those mics were designed for broadcast - rock & roll wasn't even invented.So they were as clean as was possible back then. That said, a simple tube circuit with little or no negative feedback is not as clean and linear as a modern solid state or even opamp circuit. So tube circuits do have more nonlinearity.

These days, tube circuit often exaggerate the nonlinear component. People want "a tube sound". Or what they think is "a tube sound".  That's why you often find hi gain tubes such as the 12AX7/ECC83, expecially in budget mics.

Modern solid state mics often use fairly complicated circuits with lots of negative feedback. They're not just clean, they're squeaky clean. And often the max SPL figure is very high, so these mics remain clean, even when it gets very loud. Depending on taste and application you may or may not like that squeaky cleanness.

I believe they are NiCad, but when replacing NiMH are acceptable replacements.  Not sure if Lithium ones would be ok, because I don't know jack about those...

Random bit about replacing the batteries...
http://www.cadaudio.com/images/downloads/CAD_battery_instruction.pdf

Thanks Rossi,  I appreciate the explination.  That's how I understood it, but you said it better then how I thought it.

Here is a clip of the E350 during a shoot out we did looking for a good vocal setup.  We tried several preamps and revolved around 3 mics and decided to keep the GML 2032.

These clips are into the GML 2032 and a UA 1176 reissue.  You can here the 1176 sound in it all, but I hope this also helps understanding this mic a bit more.
1970's U87 with original KK67 capsule
https://dl.dropbox.com/u/13352325/DIY/Mista%20Min%20shoot%20out_Neumann%20U87.wav
U47 with original KK47 capsule
https://dl.dropbox.com/u/13352325/DIY/Mista%20Min%20shoot%20out_Neumann%20U47.wav
CAD E350
https://dl.dropbox.com/u/13352325/DIY/Mista%20Min%20shoot%20out_CAD%20E350.wav

Levels are close, but not perfectly level matched... especially on the U87.

Notice the shape and mesh of the grill and the mount for the capsule.  I have not heard this microphone.

Gus what exactly are you trying to say?  The grill shape/design and mesh is great.  Why?

I'm impressed by the conical mount under the capsule, thus removing any sound reflections under the capsule.  First time I've ever seen that.

The basket is more or less U67 style, with the angled flat surfaces, which is supposed to be very good, again minimizing reflections/interaction, from the grill <--> capsule.

My one experience with a CAD mic was performing onstage, in Ohio in fact, and it was exceedingly clear and clean sounding and picked up everything.  It was really annoying from a performing perspective.  Totally the wrong application -- live sound -- and I was quite miffed with the sound crew for picking such a live studio mic which made things prone to feedback, foot noise, sounds from across the stage, etc.  I asked them to change it and they wouldn't.  Maybe they were recording the feed...  

The name CAD seems like the worst marketing choice ever...

I never even thought about that... crazy....

It was always just normal to me. 
The grill is larger, longer, thicker and wider then a U67's allowing for room inside the basic. 
This mic is massive, it's bigger then a U47 shortbody.


The conanical design is even in the newer ones... but these use a chinese capsules... I've never used them before.

Now I've been thinking about this for a while and I just wanted to ask... Rossi, you said

Rossi said:

A tube circuit can be fairly linear. Older classic mics tried to be as linear as possible; those mics were designed for broadcast - rock & roll wasn't even invented.So they were as clean as was possible back then. That said, a simple tube circuit with little or no negative feedback is not as clean and linear as a modern solid state or even opamp circuit. So tube circuits do have more nonlinearity.

These days, tube circuit often exaggerate the nonlinear component. People want "a tube sound". Or what they think is "a tube sound".  That's why you often find hi gain tubes such as the 12AX7/ECC83, expecially in budget mics.

Modern solid state mics often use fairly complicated circuits with lots of negative feedback. They're not just clean, they're squeaky clean. And often the max SPL figure is very high, so these mics remain clean, even when it gets very loud. Depending on taste and application you may or may not like that squeaky cleanness.

Click to expand...

Now... do you think this is the case on this one... I mean... well, I kinda know it is because of the design.  I don't know enough to explain it, I just know that opamps allow for extra amounts of negative feedback because of the ability to get more gain.  Right?  Idk, that's what CAD says in their statements, but where is the negetive feeback?  Could someone explain this?  If this mic is using a K67 clone or drivative, so to say, wouldn't it need some sort of eq to make it sound the way it does?

This mic does not get the sharp esss at 7-8 kHz like a TLM-103 (a mic with a flat response circuit and a K103) or a Nady TCM (I mention the Neumann because it has a great capsule )  And has bass out the ass!  So much smooth great sounding bass response it's crazy

Forgive my ignorance, I just don't understand how this mic sounds how it sounds if the capsule is similar to a Neumann K67/K87.... Please help me understand...

Thanks! ???

Read up on opamps.
There is a metric tonne of resources around the web for this.

This one is pretty good:
http://hyperphysics.phy-astr.gsu.edu/hbase/Electronic/opampcon.html#c1

If that doesn't do it for you, try this:
http://www.allaboutcircuits.com/vol_3/chpt_8/1.html


Also...a tip to make your threads more readable...make large images thumbnails so that your thread doesn't take forever to open.

You can do it like this:

Well, the links are great skylar!  Thank you!