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News » LDC condenser microphone

The AKG C414 LDC Condenser microphones Posted on November 02, 2019

IF YOU HAVE FOUND THIS PAGE THEN YOU MOST LIKELY ARE LOOKING FOR INFORMATION ON THE AKG C414 AND IT’S MANY VARIATIONS OVER 40 YEARS:

The AKG 414 is dual sided LDC solid state multi-pattern microphone. Unlike the U87 multi-pattern microphone which has two electronic variations since it was released in 1968, the 414 has had nearly a dozen incarnations since its first inception as the C414 comb in 1971.

These variations have significantly changed the sound and circuit designs over the last 4 decades garnishing many opposing opinions on its sound.

All versions of the C414 from the “EB” to present day were fitted with a 4   pattern variation switch on the front of the microphone which allowed the polar or directionality of the microphone’s pickup pattern to be switched between OMNI, CARDIOD, SUPER CARDIOD and FIGURE 8.

All version since the C414eb featured a -10db and -20db attenuation switch plus a 75hz and 150z low cut. Also known as a rumble or HP filter. This HP or low cut filter will reduce the proximity effect which is the phenomenon of the low frequencies building up as the source is addressed closer than 30cm from the front of the microphone.

The first changes from the 414 comb to the 414eb were more subtle. Within 5 year of its inception the size was reduced and the more durable XLR 3 pin connector became standard. But for all practical purposes the capsule and circuit remained the same except for an improvement in the bass response by redesigning the output transformer in the 414eb compared to the 414 comb. The C414eb was released in 1976 and I remember buying a matched pair for our studio, Ocean Sound located in Vancouver circa1977 at a price of $400 each CDN.

WHAT ADVANTAGE DID THE 414eb HAVE OVER THE U87 FOR MUSIC RECORDING?:

The 414eb proved invaluable on acoustic instruments and it could be placed very close to the hammers of a grand piano or used as drum overheads because of the extra headroom and dynamics that is provided by the -10/-20db pad switches and the 2 stage emitter/follower circuit.

The emitter follower circuit used in the early 414 microphones increased the headroom of the electronics compared to the venerable U87. This improved transient response of the 414 on percussive sources allowing the 414 to be used over the hammers of a grand piano. This was very useful when the piano and drums were recorded in the same time in the same room. The emitter follower circuit had a much lower output impedance compared to the single FET circuit used in the U87 allowing a transformer with 14db less loss to be be used. This means the first stage of the 414 required 14db less gain to provide the same final output level as the U87.

The 414eb microphones were often favoured for percussion recording and drum overheads. Several examples can be found on-line including Paul Horn and Ralph Dyck’s Jupiter 8 album that this writer recorded in 1980. Track #5 the title track called Jupiter 8 features an original 414eb on all the percussion overdub. This is a good example of an early 414eb on different percussion as the conga, shaker, scraper and wood block was all recorded in one take with the 414 in the centre of the room.

WHAT IS THE DIFFERENCE IN SOUND BETWEEN A U87 vs the 414EB?:

Both the U87 and 414 had an extended top end above 10khz but rather than de-emphasize the high frequency rise with active EQ like the 87 circuit the 414eb had an amplifier circuit that could more easily handle this extended HF response. The U87 was a bit more mid forward having more rise at 3khz while the 414e did not start to rise till and octave later but having a greater rise above 10khz creating an “airy” sound signature.

The c414 offers and alternative for acoustic guitar recording compared to the U87. For example, the difference between a U87 and 414eb on acoustic guitar is a bit like the difference between a Martin D28 and a Gibson J200. The Martin sounds wonderful on a simple folky/blues arrangement but in a pop tune the jangle of the J200 helps the guitar sound cut through a busy mix.

Likewise, the 414 tends to capture more of the pick striking the strings sound while the U87 captures more of the body. The 414 would often be used on BG vocals as it tended to let the vocals cut through the mix even though they were mixed further back in the track. This wasn’t always the case but it gives the reader a closer idea of how the 414 could be used in a recording situation.

WHEN DID THE SOUND OF THE 414 CHANGE MORE SIGNIFICANTLY?:

In the late 70’s the capsule’s construction was dramatically changed to drop the price and time taken to manufacture the very complex CK12 capsule.

Recording professionals including this writer believe that the sound of the original 414e and its class “A” discrete solid state circuit provides a sound signature that is often preferred for music recording and drum miking compared to later variations of the 414.

The sound of the original CK12 seems a bit more open and the use of the teflon pressed capsule seems slightly darker sounding than the original 414eb microphone. Engineer/producer Hugh Padgham preferred the 414eb to record the vocals for Sting’s “Every Breath You Take”.

By 1980, the 414eb-P48 was introduced which optimized the 414 power circuit for 48 volt operation. Earlier versions could be powered from 9-48v by changing a jumper wire inside the microphone. The 414-P48 power circuit re-design increased the signal to noise ratio by 6db to take advantage of modern digital recording techniques with its better noise ratio.

The 414eb-P48 remained in production until 1986 when the C414B-ULS was released. The 414b-ULS circuit reduced the noise floor even further but the this contributed to the microphone becoming even darker sounding compared to the early 414eb with its CK12 capsule. The 414b-ULS had a more “compressed” an less clear sound compared to earlier versions.

However, the 414 remained popular as it was still more affordable than the more expensive U87 which costs nearly 3 times the price of a 414.

In 1993 a capsule with a brighter response was added to the 414 and a transformerless circuit was introduced. This model became the C414 TL-II. It was a brighter, sounding microphone with a better transient response but again fell slightly short of the sound produced by the earlier 414eb versions. It was characterized by some engineers as sounding too bright.

The latest C414 XLS/XLII versions have the brighter teflon capsule. AKG has improved the capsule mount in the new version but the circuit still remains transformerless with surface soldered components making the microphone nearly impossible to repair but much cheaper to manufacture.

The current list price of the C414XLII is $1549 USD but the microphones can can be purchased at a street price around $1000 with shock-mount.

The 414 still remains a multi-pattern solid state LDC microphone which has become a workhorse of the recording business. However, recording engineers still look for alternate versions that more closely represent the more favoured sound of the original 414eb manufactured in the early 70’s.

On the left is the early CK12 capsule which was very time consuming to manufacture having over 50 individual parts. On the right is the Teflon 2072z which has a slightly “darker” response curve.

HERE IS A PICTURE OF AN EARLY C414EB

Here is a picture of the darker ULS which still incorporated an output transformer and components that are soldered through the circuit board.

CAN A MORE ECONOMICAL VERSION OF THE VINTAGE 414EB BE DESIGNED WHICH INCORPORATES THE MUSICAL SOUNDING CLASS “A” TRANSFORMER COUPLED CIRCUIT AND THE “AIRY” CAPSULE RESPONSE OF THE ORIGINAL MICROPHONE?:

 

Designing the Advanced Audio CM414 multi-pattern professional LDC microphone.

The Advanced Audio CM414 features a dual diaphragm edge fed brass capsule with a response within 2db of the original CK12 capsule used in the original 414eb. The Advanced Audio AK12 capsule has the same “airy” lift found in the original 414comb and early 414eb microphones loved by recording engineers.

 

 

CAN A COMPLEX EDGE FED CAPSULE BE MADE TODAY THAT HAS THE “SOUND SIGNATURE” OF THE ORIGINAL CK12 WHILE REMAINING COST EFFECTIVE TO MANUFACTURE?:

Modern CNC “computer controlled milling machines” allow nearly twice as many very accurate holes to be drilled in the capsule’s back-plate negating the need for two resonator disks that have to be accurately hand fitted and aligned under each of the mylar diaphragms of the original CK12 capsule. This gives the Advanced Audio AK12 capsule a response which delivers a very similar sound as the original capsule while allowing its to be manufactured for much less cost than the vintage CK12 capsule.

 

 

 

 

The body of the CM414 is also manufactured via computer control milling machines reducing production costs significantly plus the construction is much more ergonomic and efficient in its construction. It much faster to fit the capsule and circuit board components into the CM414 body. The CM414 also uses more reasonable priced rugged metal toggle switches compared to the custom made switches used in the original 414.

LEARNING FROM THE EXPERIENCE OF USING THE 414EB:

While reviewing the use of the 414eb on sessions over a 20 year period we discovered the -20db pad was never used. So, in the design of the CM414, only a -10db pad was incorporated for use with high SPL sources. It is possible to use the CM414 just a few centimetres above a snare drum with just the -10db pad. This is because of the CM414’s emitter/follower circuit having 14db more headroom than a U87 before its 10db pad is engaged. Also, the more complex 3 position HP filter switch was replaced with a much more economical and sturdy SPST metal toggle switch engaging a roll-off frequency of 10ohz, 1/2 way between the 75hz and 150hz roll-off frequency of the original 414. Also, we discovered that hyper-cardiod pattern was under utilized and the CM414 was designed with just 3-patterns like the U87. This also means a lower cost and more rugged 3 position metal toggle switch could be used to choose the polar pattern.

These design considerations allow for a microphone to be built that accurately captures the sound signature of the vintage 414eb microphone for a price of $379 complete with a HD shock-mount and flight case.

The CM414 has high quality components that are solder through on the circuit board and can be much more easily and economically replaced than modern day surface soldered components. The CM414 also uses high quality and more expensive tantalum capacitors in the audio chain just like the original 414eb and the U87 vintage microphones.

The CM414 has become a popular choice for percussion, grand piano, vocals from professional to project studios alike.

 

U47fet Microphone versus Affordable Alternative Posted on November 02, 2019

U47fet MICROPHONE VERSUS AFFORDABLE ALTERNATIVE

 

IF YOU HAVE FOUND THIS PAGE THEN YOU MOST LIKELY ARE LOOKING FOR HISTORY OF THE NEUMANN U47fet :

The U47 FET was developed and designed circa1969 as the source of tubes for the now famous and still popular U47 & U48 microphones started drying up.

During this time period, the “Cold War” and resulting “Space Race” had caused rapid advancement in electronic technology. During the late 60’s, now reliable and high quality silicon transistors were starting to be manufactured very economically compared to more costly tubes. Very “HiFi” and quiet audio circuits could now be manufactured with transistors instead of the older tube technology.

Considering this, along with the new trend of placing microphones very close to instruments and voices in Cardiod…Neumann decided to re–engineer the U47fet as a solid–state, single-pattern microphone, designed around a “state of the art” Field Effect transistor (FET) with 5 additional silicon transistors.

This new FET microphone circuit will now do the work of the tube in previous designs; matching the very high impedance capsule to the final low impedance balanced 150-200 ohm output of modern recording microphones.

The newly designed U47fet was in full production by early 1972 and it provided a welcome alternative the use of dynamic microphones for close recording of instruments that can deliver high SPL’s.

Although, the U47fet could be used easily to record an acoustic guitar, producers often preferred the brighter U47, U87 or AKG 414eb to the U47fet. However, It was lovely sounding on upright bass or in front of the guitar or bass amp.

FET CIRCUITS VERSUS TUBE CIRCUITS

A tube’s input and output impedances are much higher than we see in early transistor circuits. The output impedance at the transformer is typically 200 ohms.

However, with the development of the field effect transistor in the early 60’s; which has a much higher input impedance compared to early silicon transistors it was possible to built professional condenser broadcast and recording microphones with solid state devices. Modern field effect transistors could now offer better noise and gain figures than a single vacuum tube and were easier to power.

The typical FET “transconductance” or impedance to gain ratio is many times higher for a FET compared to a tube. This means that a FET can yield 94db more gain than an equivalent single tube circuit and provide a better signal to noise ratio than an equivalent tube circuit.

However, the tube is still used today for condenser microphone circuits because impedance matching is more important than obtaining maximum gain in typical condenser microphone circuits; plus tubes can take and incredible amount of “abuse” from excessive input levels or excessive power supply voltage variations compared to any solid-state device.

In a way the FET circuits are more detailed and with a slightly faster transient response than tube circuits while the TUBE circuits are more “forgiving” with a overload characteristic that is more “compressor” like than hard IC clipping.

Solid State circuits must be able to provide more “headroom” or maximum output before distortion compared to a tube amplifier to be preferred in listening tests.

Here is a reference to an AES Paper from 1973 comparing tube circuit to solid- state circuits in audio gear. This is a fascinating study and the full study is well worth reading for any enterprising recording engineer. All the findings are verified scientifically with double blindfold testing.


THE PAPER ASKED:

TUBES VS TRANSISTORS: IS THERE AN AUDIBLE DIFFERENCE?

Engineers and musicians have long debated the question of tube sound versus transistor sound. Previous attempts to measure this difference have always assumed linear operation of the test amplifier. This conventional method of frequency response, distortion, and noise measurement has shown that no significant difference exists. This paper, however, points out that amplifiers are often severely overloaded by signal transients (THD 30%). Under this condition there is a major difference in the harmonic distortion components of the amplified signal, with tubes, transistors, and operational amplifiers separating into distinct groups.


THE CONCLUSION OF THE STUDIO STATED:


“Vacuum-tube amplifiers differ from transistor and operational amplifiers because they can be operated in the overload region without adding objectionable distortion. The combination of the slow rising edge and the open harmonic structure of the overload characteristics form an almost ideal sound- recording compressor. Within the 15-20 dB "safe" overload range, the electrical output of the tube amplifier increases by only 2-4 dB, acting like a limiter. However, since the edge is increasing within this range, the subjective loudness remains uncompressed to the ear. This effect causes tube-amplified signals to have a high apparent level, which is not indicated on a volume indicator (VU meter). Tubes sound louder and have a better signal-to-noise ratio because of this extra subjective headroom that transistor amplifiers do not have. Tubes get punch from their naturally brassy overload characteristics. Since the loud signals can be recorded at higher levels, the softer signals are also louder, so they are not lost in tape hiss and they effectively give the tube sound greater clarity. The feeling of more bass response is directly related to the strong second and third harmonic components which reinforce the "natural" bass with "synthetic" bass [5]. In the context of a limited dynamic range system like the phonograph, recordings made with vacuum-tube preamplifiers will have more apparent level and a greater signal to system noise ratio than recordings made with transistors or operational amplifiers.”


THE TECHNICAL DETAILS OF THE U47

The U47 FET’s circuit was far more complex than any other Neumann fet microphones designed in this post tube era including the U87 and KM84.

The later U89 microphone featured a similar circuit to the U47fet but with a different capsule than either the K67 or K47.

However, in the U87 and the SDC, KM84 circuits a single FET impedance converter directly feeds an output transformer with a 10:1 ratio. But, in the U47 FET/U89 circuit the FET is buffered from the output transformer by 5 silicon transistors configured like a discrete OP amp to provide a class A/B output stage.
A sixth transistor serves as a voltage regulator to ensure the circuits working voltage and capsules polarization stays consistent at 43V allowing the 48v phantom supply a 10% working tolerance.

The U47fet circuit uses negative feedback to reduce the HF response of the K47 capsule much like a “HF limiter” giving the U47fet a tighter more controlled sound.

Although the FET model incorporated exactly the same K47 capsule as the original U47, the revised internal electronics, contributed to a darker sound signature in the Cardiod pattern compared either to the U47, M49 or the U87. Nevertheless, the U47 FET became a reliable “go to” workhorse microphone and it was highly regarded in high SPL settings whether in front of a kick drum, over the Timpani’s or in front of the bell on a French horn.

It was a favourite of mine in front of the kick, on trumpet, trombone, upright bass and the low end of a grand piano, or on a vocal where a U47 or C12 is a bit bright, or you have an overly sibilant singer and don’t want to resort to an even darker dynamic or ribbon microphone.
The U47fet was well regarded in its ability to handle extremely high sound-pressure levels. It can handle an SPL level of 147dB with the 10dB pad switched in. For, comparison a U47’s distortion will start to increase with levels above 120db. Although never as popular on vocals as the original U47…it sounds a little more “compressed” and has a slightly flatter response than the original 47 (which has a much broader 5dB presence boost) — the FET 47 was still quite usable in this role too, particularly for male vocals and speech. Its modest 2dB of presence boost between about 2 and 5 kHz is enough to aid clarity and intelligibility in a mix, while the gentle proximity boost adds a degree of body and warmth. (SOS July 2015).
Here is the schematic of the U47fet courtesy of RecordingHacks

U47fet Schematic

 

Note: the 5 transistors are all dc coupled. C10 protects the output transformer from passing DC and R13 is providing negative feedback to the transistor circuit.
T4 & T5 provide a class A/B NPN-PNP transistor output pair. A similar circuit is used in the output stage of the Neve 1081 modules.



IS THERE AN ECONOMICAL ALTERNATIVE TO THE U47fet? DESIGNING THE CM47fet AND CM47fetCE

 

You can still buy a true Neumann U47fet (collectors edition) for a sale or street price of $3999. However, today it is possible to build a FET/LDC microphone that will handle high SPL’s with a similar frequency response and sound on dynamic instruments for much less money than the new U47fet.

Having used and serviced U47fet, U47’s, U87’s and the AKG 414eb microphones in a professional studio setting during the 70’s and 80’s I was familiar with the overall functions, use and circuitry of these microphones.

The U47 were the GOTO microphones and probably responsible for over 75% of the recording duties during my tenure at Ocean Studios in Vancouver thru the 70’s & 80’s.

The U87’s were relegated to voice work and string instruments. The 414’s were able to handle the level of drums percussion and being placed close to the hammers of a Yamaha C7 grand piano.

The U47fet was and great sounding work horse in front of the kick drum, in front of loud brass instruments, on an upright bass or on the bass amp and for the low end of a grand piano. It was also used for vocals and if the vocalist was overly sibilant or harsh for the U47 then it was the U47fet next and then a SM7.

The U47fet was not as open as the U47, U87 or 414eb. Plus, it could only be used in Cardiod and it could have proved useful in OMNI.

The CM47fet is not a direct clone or copy of the U47fet.

But it was designed to exhibit the same type of headroom necessary for extreme “close miking” situations and the recording of loud sources.

It has a switchable OMNI option plus a -10db pad and HP filter.

The stock CM47fet actually uses our AK89 (original k67/k87 curve). The CM47fet uses a de-emphasis circuit similar to the U87 to tame the extreme rise in this capsules response above 10khz.

The stock CM47fet, even though slightly brighter than the original U47fet works as well as the U47fet in front of the kick drum. The CM47fet can be used in very close proximity to toms, snare drums, hand drums, percussion instruments and in front of any instrument speakers.

It uses an original AKG 414 2-stage class “A” type transformer coupled circuit with K67 de-emphasis added and has nearly 14db more headroom than a U87 circuit.

The CM47fet also comes as a CM47fetCE. This features our AK47 capsule with the de-emphasis circuit and has a response curve nearly identical to the original U47fet but with a true class “A” circuit.



TECHNICAL DETAILS OF THE CM47fet & CM47fetCE

The CM47fet uses a 414eb class “A” type circuit, which reduces the amount of semi-conductors from a FET and 5 silicon transistors to a FET and a single silicon transistor configured as an emitter follower. This keeps the CM47fet circuit class “A” but with a lower output impedance.

Because the emitter follower circuit has such a low output impedance and no gain it can more than adequately drive a 2:1 ratio output transformer instead of the 10:1 used in the U87 and the 9:1 used in the U47fet.

When a level of 0dbu is measured on the input side of the 2:1 transformer then a level of -6dbv is measured on the output.

When a level of 0dbu is measured on the input side of the 9:1 transformer then a level of -19db is measured on the output.

The 2:1 transformer has just over13db less loss than the 9:1. This allows us to decrease the gain of the first stage by 14db and allows the use of a medium mu FET to be used instead of the high gain 2N3819 in the U87.
This increases the headroom and reduces the signal to noise ratio.

The U47fet can deliver a final output from the microphone of -5.5dbv before the onset of distortion.
The CM47fet can deliver a final output from the microphone of 0dbv before the onset of distortion. This is nearly 6db better than the U47fet.


       
The shootout mic positioning (above)


MICS INCLUDED IN THE SHOOTOUT:

A) Vintage U87 pre-1988 which is a lovely sounding specimen ($3500 new)
B) Advanced Audio CM47fet which sells for $295 with mount & case
C) Advanced Audio CM87se which sells for $595 with mount & case
D) Vintage AKG 414eb P48 which is in lovely condition ($1000 new)

                         
The microphone set-up was lowered and placed in front of our Tinker acoustic guitar.(above)

 

These microphones were patched directly into the Jensen transformer coupled preamps in the MCI/Sony MXP3036 console.Channel 1 is the AA CM47fet, Channel 2 is the Neumann U87, Channel 3 is the AA CM87 and Channel 4 is the AKG 414eb P48.The output gain of the CM47fet and the older U87 set to 200 ohms are nearly identical. A new U87Ai will have the same output level as the AKG414eb while the CM87se has 3db more output level than the original U87 but 3db less output than the AKG 414eb P48.

                              

                                          

 

The outputs from the microphone preamplifiers appear in the patchbay of the MCI/Sony 3036 console and they were patched directly into the multi-track inputs 1-24 of the RADAR 24.


                     

 

HERE ARE THE RAW, UNTREATED AUDIO CLIPS FROM THE SHOOTOUT