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Curio's - Calrec, some "Old Favourites" and more !


The mid' 1960's

Times were changing and technology had moved away from the use of  valves, to that of the modern semiconductor. With the emergence of the new "Field Effect Transistors" (FET's), then the very Hi-Impedance input stage of a condenser microphone, could now be designed around an FET, rather than the traditional valve.

In 1965, tests were being carried out by Calrec, into the use of FET's in their microphone designs.

Calrec had finally arrived in the modern world of semiconductors, saying a fond farewell to the "Calrec" valve years.


The Calrec CM652, from the 600 series microphones.

Let us not forget .....

Prior to the FET range of microphones, manufactured by Calrec, there was the relatively less well known CM450 "Dynamic" microphone. Very similar in size and appearance to the Calrec CM650. Maybe the CM450 was not the best dynamic microphone ever made, but one that was very suitable for PA and general Studio use.

In the case of the CM450, then the "4" stands for the 400 series, using the "Dynamic" principle of operation. The "50" standing for "Cardioid" polar pattern, as is the code used on their capacitor capsules e.g CC50 being a Cardioid capsule with a flat frequency response. It is worth noting, to avoid confusion, that although the dynamic capsule element of the CM450 is fitted inside a metal windscreen, it has a "Flat" frequency response. Unlike the later "CC56" capacitor type capsules that incorporate a bass roll-off.

Introduction of the FET condenser (Capacitor) type microphones

The first FET microphones manufactured by Calrec, would be the very popular "Fi-Cord" 600 and 650 microphones. These microphones, together with the 700, 800 and 900 series, were all designed and manufactured by Calrec, but originally distributed by "Fi-Cord" and therefore labeled as "Fi-Cord" microphones. The design and technical specification of the microphones, catered for most demands required by the "Potential" end user. Also, the variation in designs, allowed the various models to work on the many different powering arrangements available at that time.

The Capsules used in the Calrec/Fi-Cord FET microphones, would be a smaller diameter than that used in their valve models i.e. The capsules employed in the C41, FC1200 valve microphone etc, were somewhat larger in diameter than that used in the 600 series and all other Calrec/Fi-Cord FET type microphones. Of course, this would mean a change in tonal quality, but the FET microphones would still retaining that familiar Calrec sound. The design of the capsules would still be of the same general principle, only on a slightly smaller scale.

Note - See "Calrec - The Valve Years" for more information about Fi-Cord.

600 series

Designed with the "Amateur" and "Semi-professional" user in mind, the 600 series offered microphones with fixed capsules. Capsule types available were, Omni, Cardioid, and Cardioid with bass roll-off, the later mounted in a wire mesh windshield. Despite the fact that only 3 capsule types were available, this would prove more than sufficient for most uses. Throughout the many years since their introduction during the mid' 1960's, the 600 series gathered very many fans and followers. Indeed, many examples are still in use today.


From a service engineers point of view, the Calrec 600 series is a nightmare. The Hi-Impedance areas of the PCB, being totally encapsulated in epoxy resin. Therefore, should any component fail within that area, then the PCB was rendered un-serviceable, and a replacement PCB would be required. That would not have presented a problem when the microphones were still in production, as the PCB's were readily available. However, in the current day, it is not financially justifiable to have new PCB's produced  and "Populated" with the required components, to enable these microphones to be serviced. Having said that, not all faults are in this part of the circuitry, and should a fault lay outside of the "Encapsulated" area, then the PCB/microphone can still be serviced/repaired.

The method of construction was also to cause problems during servicing (See Later paragraph's - "Construction Problems").

One of the disadvantages with the 600 series, is that of the powering arrangement and the type of audio output, used by the microphones. The "Professional" type 3-pin connector, similar to that of the "Din" family, carries the common "Earth/0v", +48v power and an "Un-Balanced" audio output. The +48v feed not being Phantom derived, but a single rail supply. This would not have presented any problem back in the 1960's, as the microphone used it's own PSU and "Phantom" powered systems were only just coming into being. Now however, those engineers who still use the 600 series microphones, would probably like to use them on "Phantom" powered systems. Without the disadvantage of an "Un-balanced" audio output and the requirement of having to use Calrec's "Special" power supply units.

There are various methods of over coming this problem of powering the 600 series microphones.  I manufacture a "Conversion Lead", a nominal length of 4 Mtr's, to overcome this problem. This then allows any 600 series microphone to be connected to a "Standard" +48v phantom powered microphone input. If required, the lead can then be extended up to a maximum of 50 Mtr's, by the use of any "Balanced" cannon to cannon microphone lead.

A new PCB, using the same "Front-end" as in the 600 series microphones, but with conventional "Balanced" output, thus allowing the microphone to work on "Standard" phantom powered microphone is currently under design. This will then be retro fitted into the 600 series microphone's that require such modification.

Note - All semi-conductor "Calrec" microphones used the Suffix "C" or "D" to donate the type of connector used i.e. "C" for "Cannon" type and "D" for "Din" (Touchal) types. Alas, some models with "Cannon" types of connectors, such as the 600 series for example, might not be wired to the "Standard" one expects to find. Always check first !!!

The "Ferrograph" C651 microphone ?

A Calrec microphone that never made it into production, was the C651. This microphone was specifically designed for use, with Ferrograph series seven tape recorders, thus being sold under the "Ferrograph" name. The circuit, was based around the CM600 series, with a few minor modifications to the power rail and output level/impedance matching. As any "Ferrograph" series seven and "Super" seven, owner is aware, there is a Octal multi-way "Auxiliary" connector on the connector panel of the recorder. This provides the +48v supply required by the "Ferrograph" C651 design.

The idea of the "Ferrograph" C651 microphone, all fitted nicely into place ..... Ferrograph were sent 3 samples for evaluation. But sadly, the project never got beyond that stage. Why, who knows ?
However, user's of "Ferrograph" series 7 and super seven machines, could/can still use the Calrec 600 series microphones, with a few small modifications etc.
The "Orange Hypercon" microphone

This microphone, manufactured by Calrec, was designed for stage/vocalist use. Manufactured for the "Orange Music" company, based in London. A company known for the famous "Orange" PA amplifiers of the 60's/70's.

Cosmetically and mechanically, the "Orange Hypercon" was very similar to the Calrec CM656, but used a "Tighter" Cardioid capsule. The polar pattern almost being a hyper cardioid, hence the name "Hypercon".

Judging from the amount of these microphones that I have received for servicing, sales of the microphone must have been quite good.

Note - The "Orange" amplifiers, designed by Matthew Mathias, were made by Cliff Cooper in Huddesfield (Gt. Britain), a town very close to that of Hebden Bridge, home to Calrec microphones. It's a small world !

A "Simms-Watts" microphone

Yet another microphone manufactured by Calrec, was designed for the famous "Simms-Watts" London based music company. Alas, I have little information on this product and as yet, I have never had the pleasure of seeing one "In the flesh". However I do have a picture, showing a typical example.

700 series

Lesser well known, is the 700 series of "Self contained" battery powered "True" capacitor microphones. Rather than the "Electret" types so often found today. The 700 series microphones, were based around the two different "Pre-amplifiers". One being the CB7C, with a "Cannon" type connector, the other being the CB7D, with a "Din" type connector. Both types used in conjunction with the CC75* series of inter-changeable capsules i.e. Omni, Cardioid, and Cardioid with bass roll-off, the later being mounted in a wire mesh windshield. Thus offering great versatility and making the 700 series ideal for use with portable recording equipment.

The battery consisted of 6 x 625 type "Button" cells, giving a total of 7.5v. For ease of use, these could be "Stacked" together and fitted inside the case of an old AA size battery. This would then fit neatly into the microphone.

As the power source was only 7.5 volts, then some form of "Step-up" system was required, to give around 50volts, to "Polarize" the capsule. A minature DC to DC converter would be used for this application. Much of the design work, for the DC to DC converters, was assisted by Peter Baxendall.

Although the 700 series was an excellent design, "Battery" powered microphones were not so eagerly accepted by the potential end user's, as Calrec had anticipated. Sales of the 700 series, would prove to be very disappointing. 

Note - External powering of the 700 series is possible, but involves the fitting of a "Shorting Link" in the place of the normal battery. The microphone is then powered from an external source, much like the 600 series. In the case of the 700 series, "Earth/0v", - 7.5v power and an "Un-Balanced" audio output.

800 series

Very similar to the 600 series microphones i.e. Using the same, fixed capsule design. The important difference, with the 800 series, being the use of a transformer coupled "Balanced" audio output, therefore allowing the microphones to work on +48v "Phantom" power. Making these microphones ideal for use in Radio, TV and Recording Studios.

900 series

The 900 series is also very similar to the 600 series microphones i.e. Using the same, fixed capsule design. However, the 900 series was designed for use on "Modulation Lead" powering. (DIN 45 595 standard), also known as "AB" or "T" powering. Whereby the nominal 12volt supply is feed directly to the send/hot and return/cold wires of the "Balanced" output of the microphone. This being a system of powering used by many of the "European" countries at this time. This method was employed by many other microphone manufacturers e.g. Neumann's KM70 series and some of the Sennheiser models. The 900 series microphones would be ideal for use in "European" Radio, TV and Recording Studios. Not forgetting the compatibility with portable recording equipment, from companies such as "Nagra".

The 900 series, was manufactured between 1973 - 1980 . Just like the 700 series, sales of the 900 series, would also prove to be a disappointment.

1000 series

There are 2 "Versions" of the 1000 series microphones i.e. The "Original" types, with detachable capsules, and the "Later" models, with fixed capsules.

"Original" 1000 series

The "Professional" 1000 series, was to replace the older "Fi-Cord" (Calrec) FC1200, FC1200a and the "Original" Calrec CM1050, which were all valve (Nuvistor) type microphones. The design of the 1000 series, employees a separate body (Pre-amplifier) together with a detachable Capsule. The body i.e. CB1000, contained the Impedance converter/Pre-amplifier for the associated Capsule. This PCB, being held in place by locking screws mounted in the cannon socket assembly. The microphone worked on "Phantom" power and therefore the audio feed was in "Balanced" form. The output connector being of the now "Standard" cannon type, as opposed to the "Professional" Din type used on the 600 series.. 

A choice of  Capsules were available for use with the CB1000 body e.g. CC1050, cardioid type.


Again, from a service engineers view, these "Early" examples of the 1000 series, used the best "Construction" design/technique, employed throughout the entire history of Calrec microphones. The microphone being very easy to dismantle i.e. By simply undoing 3 small screws around the socket end of the microphone. Somewhat different to other Calrec microphones produced throughout the years, whereby a special jig is required to "Break" the glued seal, used to hold the assembly together. All of the components, mounted on the 1000 series PCB, are easily accessible for service purposes. Access to the capsule is quite straight forward, to allow for cleaning etc. A great design !

"Later" models of the 1000 series and "Construction Problems"

In an attempt to keep costs down, the later models of the 1000 series were to utilize, fixed capsules. There were 3 different models available;


Hand Held Omni i.e. Built in Pop Filter




Bass Roll-off Cardioid




Alas, later models of the 1000 series, along with the majority of the other models, were to use the "Glued Together" method of construction (A service engineers complete nightmare), rather than the screwed together method of the "Early" 1000 series. It proves to be so easy to damage the housing tube, when dismantling the "Later" 1000 series microphones. Therefore requiring a new housing tube to be fitted during reassembly after repair/servicing. Not only was the case "Glued Together", but ..... an expanding brass "Locking Ring", holding the PCB and Capsule in place, was also glued into the microphone housing tube. The glue needs to be completely removed from the expanding ring, to allow access to the locking "Grub Screw", which  often proves very difficult to undo. So, when the housing tube and lock ring are completely free of any traces of glue, the PCB can finally be withdrawn from the housing tube, to enable the required work to take place. All of this "Messing About" being very "Time Consuming" and not very cost effective, but it still has to be done !

When a microphone of this type is serviced, then during "Final" reassembly of the socket to the housing tube, a modification is carried out. This involves drilling and tapping a hole in the socket assembly, together with a locating hole in the housing tube. Then using a small grub screw, to hold the microphone parts securely together. Thus, if required, the unit can be easily dismantled for future servicing etc.

The internal assembly of the microphone i.e. PCB and Capsule, is "Pushed" together and held under tension via a "Brass" expanding ring. This "Brass" expanding ring, used on many of the various PCB's used in Calrec microphones, expands sufficiently via the grub screw insert, therefore not to warrant being re-glued back in place.

Finally, the 2000 and 2100 series

Like the "Original" 1000 series, these microphones used separate bodies (Pre-amplifiers) and capsules. Alas, the PCB was not held in place by screws, but rather by being "Glued" in place like the "Later" 1000 series. A choice of two bodies were available, both being "Phantom" powered. One being the CB20, designed specifically for +48v working, and the other being the CB21, designed to work on supplies between 7.5 v < 52v. The circuit (PCB) of the CB21, employing a DC to DC oscillator, to provide "Constant" HT potentials within the microphone, over a very wide supply voltage range. 

A choice of no less than 5 different capsules were available for use with the CB20 and 21 bodies;


Hand Held Omni i.e. Built in Pop Filter


Studio Omni




Bass Roll-off Cardioid


Bass Roll-off Cardioid mounted in a Wire Mesh Windshield




Many of these microphones, were to be purchased by the BBC.  A excellent recommendation, if ever there was !

"Valve" version of the 2000 and 2100 series

The FET CB20 and CB21 microphone bodies work very well. However ..... a "Valve" version would be a very welcome addition. Therefore, after spending many hours designing, and carrying out an apparent endless amount of listening tests, a "Valve" version of the CB20 and CB21 microphone bodies, is now available.

For more information on the RMB-2021, please refer to the "Replacement Microphone Body" page.

Other "Calrec" Microphones - "Talkback" and "Test and Measurement"

During the many years of microphone production, Calrec also manufactured "Talkback" and "Test and Measurement" microphones. 

Below is a list of some of "Talkback" microphones, and the CM15 "Test and Measurement" microphone, that Calrec manufactured. The later being used by Klark Teknik, known as the AT1, for use with there excellent spectrum analyzer unit. The list also gives details of the respective powering requirements and other information.




+7.5 to +52 volt "Phantom" / Also known as the AT780 / Uses 2100 series PCB


+7.5 to +52 volt "Phantom" / Uses 2100 series PCB


+48 volt (Not Phantom) / Uses 600 series PCB


+9 to +24 volt "Phantom" / Also known as the Klark Teknik AT1


Powering requirements are unknown / Mini-mixer Microphone


+7.5 to +52 volt "Phantom" / Uses 2100 series PCB


+48 volt "Phantom" / Cardioid with bass roll-off / Mounted on 100mm stem


+48 volt "Phantom" / Cardioid with bass roll-off / Mounted on 200mm stem


+48 volt "Phantom" / Cardioid with bass roll-off / Mounted on 300mm stem


+48 volt "Phantom"


+48 volt "Phantom" / Cardioid with bass roll-off


+48 volt "Phantom" / Cardioid with a flat response


+48 volt "Phantom" / Cardioid with bass roll-off / Mounted on 450mm stem


Many of the above microphones are identical, both cosmetically and sonically, to their "Conventional Use" look-a-likes. The main difference being in the way the microphone is physically mounted to the associated Mixing Console.

The "End of an Era"

During the late 1980's, Calrec discontinued the manufacture of "Conventional" microphones. Only to continue production of the "Soundfield" microphone. 

Production of the 1000 and 2000/2100 series, together with the servicing of Calrec/Fi-Cord microphones, was taken over by an ex-employee, Keith Ming i.e. "Hebden Sound". Sadly Keith passed away in 2002 and production of "Hebden Sound" microphones ceased.

There was continued production of the Calrec designed CM1050 and CM1051 microphones, for a short time, by David Anderson of "Bridge Microphones".

My connection .....

I had known Keith for many years, and we would refer "Clients" to one another, as you do. Over which time you build up, not only a working relationship, but a personal friendship.

Sadly, Keith was only too aware of the condition of his health. He approached me some months before he passed away, asking if I would be interested in  taking over the servicing of Calrec microphones. This I willingly accepted.

I was to be given many folders of "Documentation", relating to Calrec microphones e.g. Circuits, together with a wealth of "Historical" information about the design and testing of various microphones throughout Calrec's long history. Without this vast background of knowledge, I could not have written the information contained within the "Calrec" pages of this site.


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