Electro-Voice Microphone Catalogue

Here is a scan of an old Electro-Voice catalogue, probably from the 1950s or early 60s, featuring a wide range of microphones. It includes the multi-pattern Cardak, which appears to have been the flagship model, and the V-series ribbon mics. There is no date on the document, but at this point in time the V1 would set you back US$27.50, and the multi-impedance V3 was $50. The Cardak II would set you back a whopping $75!

In the velocity microphone description I was amused to read that "the woven housing allows the sound to pass through without reflection". This neglects to mention the whopping magnet located at the rear of the ribbon! All of the dynamic ribbon mics were available in 50, 200, 500 ohm and high impedance models, which reflects the plethora of input types around at that time.

The second page deals with carbon and crystal microphones and accessories. The bottom of the page was uppermost in the box, and consequently is somewhat grubby.

Cadenza Crystal Mics - a mystery solved!

This Ebay auction has solved a little mystery for me!

Cadenza Crystal Microphone

Cadenza was a British brand remembered primarily for their 'Rocket' ribbon microphones. They are still quite common, and I have repaired many of them in the course of my work.

Cadenza microphone with ribbon element

Most of the Cadenza mics are grey or pale blue in colour, and have a removable stand. However, I have come across three or four of these mics with black bases and a fixed stand. These often have a crystal element rather than a ribbon motor, and I and speculated on their origins in a previous blog entry. When I first encountered one of these, I had thought that it was some kind of DIY 'repair' job, but having seen more than one, it seemed more likely that they came out of the factory this way.

Crystal element in a Cadenza body

Until now I had never seen an advertisement, manual or box that could confirm the existence of a Cadenza Crystal microphone. The photos in the auction show the original packaging, marked 'Cadenza Crystal. So this was indeed a Cadenza product, using the same body as the ribbon microphones.

I like the triangular box!

Thanks to Benchmark Collectibles for permission to use this photo.

MOTM: Melodium / Radiodiffusion model R

Here is a rare and magnificent microphone: the Melodium type R (number 12).

The microphone is dated 31.12.40, which makes it 72 years old at the time of writing! The mic was made by Melodium for the national broadcaster "Radiodiffusion Nationale", which would have been the French equivalent of the BBC. This is particularly fascinating as it dates the manufacture to during the period of occupation in the Second World War. I was surprised that microphones were still  being manufactured during that period, but I suppose that the government needed to broadcast their propaganda, or perhaps this one was stolen and used by Le Resistance!

 

There is a bit more about the history of the French national broadcasters here, and it seems that Radiodiffusion Nationale began in 1939 but was subverted by the Vichy government in 1940. It was replaced or perhaps rebranded in 1945 after the end of the war. There is more history here for our Francophonic readers.

Inside, the mic is very similar to the 42B, with the same magnets and motor assembly, but the internal grills are different, using a wider mesh and cloth.

The high pass filter section of the mic is also different to its square cousin.  Instead of the three way rotary switch on the 42B, this mic uses a metal bar to bridge a terminal inside the base of the mic, and it just as 'Music' and 'voice' settings. A hole in the bottom plate lets you see whether the jumper bar is engaged or not. It is a more reliable arrangement, but you need a screwdriver and spanner to make the change. I guess the guys at the radio station did not want the filter to be engaged accidentally, causing them to wonder where the bass had gone!

Remarkably, the ribbon on this one was still intact, and after cleaning the motor the mic sounded very good indeed, with a big bottom end and nice proximity effect to make voices sound richer and fuller.

New parts for the old microphone.

The mic arrived without some parts, so we made replacement brass washers and thumb nuts on the lathe. They look really smart, and in a few months will be a lot less shiny!

Melodium 12 side by side with the 42B

In comparison to the 42B, the model R has a bit more bass, although this could simply be due to the differences in tension and mass of the ribbons. There are other small differences to the high frequency sonic signatures, primarily due to the differences in grill shape and mesh. 

Frequency sweeps for Melodium R (red) and 42B (Blue)

The mic is now back home at Kore studios, in good company!

Oktava mod FET biasing

Here's one way to bias the FET on an Oktava microphone....

Our good friends at Valley Wood Studios in Leeds had followed one of the popular projects for upgrading Oktava MK319 microphones, which involves changing a handful of resistors and caps, along with the field effect transistor (FET). After the mods one of the mics was about 3dB louder than the other.

This kind of thing is normally due to variations in the FET's characteristics, and to optimise the modification, it is necessary to adjust one or both of the bias resistors (R7 and R8 in the PDF document). Between them these set the gain of the mic, and the bias point for the FET, which gives the best noise performance.

I often do this by hacking a decade box into the circuit, and in this case we put the mic in our test chamber so that we can tweak and scan as we go along. At the end of the tweaking the pair of mics were well matched, and noise free.

We celebrated with tea and biscuits!

Cadenza Mic Transformers and Mounts

Xaudia now supply drop-in upgrade transformers for Cadenza ribbon microphones.

Xaudia transformer (left) and original Cadenza tranny

The original transformers had a tapped winding made to give an output impedance of either 30 ohms or high impedance, neither of which is ideal for interfacing with modern equipment. Our upgrade transformer gives an output of 300 ohms with a good original ribbon, which gives about +10 dB compared with the 30 ohm connection. It also has a lower DC resistance and noise floor.

The transformer is supplied in a mumetal shielding can of the same dimensions as the original, and slots into the base of the mic below the motor assembly, as shown.

Cadenza on a stand!

And here is a funky adapter that we made for a customer, to mount his Cadenza onto a normal mic stand. It recycles the plastic connector and locking ring from the original tripod mount.

Cadenza mic stand adapter

*Or other impedance values on request.

Reslo RV and UR microphone variations

Reslo RV ribbon velocity microphone.

The RV was one of Reslo's earliest ribbon microphones - possibly their first production model, although I am not sure if the UR series came before or after. They share parts so it is hard to pin down which one came first.

Inside Reslo RV mics

The two mics shown have the same frame for the ribbon, but the magnets are very different. I believe the mic on the right to be the earliest RV design, or at least the earliest I have come across, and it uses a single cast magnet with quite a complex shape.

Reslo RV magnets

The mic on the left uses two simple horseshoe magnets at the top and bottom, attached to a pair of metal pole pieces, and this really sets the style for all subsequent Reslo ribbons - later models have three magnets but use a similar layout.

The UR model has a similar construction but has a rear mounted transformer. This is effectively blocking the pickup from the rear of the mic, giving it a more cardioid pickup pattern. It seems likely that 'UR' stands for Unidirectional Ribbon, although I have not seen any documentation to support this.

Reslo UR magnets and rear-mounted transformer

But the story doesn't end there. Many of the RVs that I have worked on have a later, smaller motor which is essentially the same as found in the RB model. Keeping common parts with the later models must have kept costs down.

Reslo RV mics with different motors.

Until very recently I had only ever seen 30 ohm versions of the RV and had assumed that they were all low impedance. However, the one on the left, which came in recently, has a high impedance transformer, and measures around 6.5K ohms with the original ribbon.

Reslo mics don't have serial numbers or dates on them, so it is hard to make a definitive time line for the development, and always if you have any further information we would love to hear from you.

Bang and Olufsen BM5 manual

Here is the manual for the B&O BM5 stereo microphone, in English.

M320 and M360: Beyerdynamic's ugly ducklings

We have TWO microphones-of-the-month for May. Both are cardioid ribbon microphones from Beyerdynamic. We see a lot of M260 models, but the M320 and M360 are bigger, uglier and much less common too.

Beyer M320. Do not stick it in your kick drum!

The M320 makes good use of plastic for the body, and has all the style of a brick! A Beyer catalogue* from 1965 called it a "heavy-duty dynamic type for show business use", and the switch allows the use to select 'music' or 'speech' settings, the latter giving a bass attenuation of 12dB at 50Hz.  Because of its appearance and a vague resemblance to the AKG D12, it is tempting to thing that this is designed for inside a bass drum. It is not.

The M320 has the same motor that is found in the M260, but is connected to a large rectangular chamber below the mic via a tube. I have not been brave / stupid enough to cut open the chamber to see what is going on inside, but one assumes a series of interconnected tubes forming an acoustic labyrinth.

Beyer M320 inside

Although the M320 is called 'heavy duty', the M360 is much more sturdy, with a metal housing and grill. The catalog calls it a "dynamic unidirectional studio microphone with ultra-modern styling". Again, it is as elegant as a 1980s Volvo, but at least form follows function in these mics!

Beyer M360. Ultra-modern?

... or just ugly?

The M360 is slightly larger and like the M320 it also has an acoustic chamber below the ribbon motor. I was fully expecting to see the same motor in this mic as is found in the other Beyerdynamic ribbon microphones of the same era, so was suprised to find something quite different. Rather than being assembled from four small magnets glued together, the M260 has a larger cast magnet with two copper coloured pole pieces which may also be a magnetic alloy.

Beyer M360 motor

Although the motor is wider and deeper, it still accommodates the same size of ribbon. And the magnetic field measures around 5000 Gauss, which is similar to a 'normal' healthy Beyerdynamic motor. So I am really not sure why this uses a different motor. Perhaps it was an early production run. The transformer and switch (on/off) are housed below the acoustic chamber below the microphone.

In the photo above, the ribbon is fully corrugated, but another specimen (below) had a standard Beyer ribbon, which seems more likely to be the original.

Both mics sound good when working properly, with a cardioid pickup, a relatively flat response and a bit less proximity effect than you would find in a figure-8 ribbon. They use the typical tiny Beyer transformers, which in the case of the M60 at least is wound for a full range response.

*Here is the full Beyerdynamic catalog from 1965, at the excellent Coutant website.

Huge heavy Meico dynamic mic

Here is another big old dynamic microphone, this time made by Meico.

Meico Dynamic microphone

The big ferrous magnet inside the mic bring the weight up to nearly 1.5 Kg!

This one is certainly a heavyweight!

The badge is very cool though, and the star and wings look like it might be inspired by Soviet artwork of the era!

Like Mexico, but without the X....

According to this eBay seller, the mics were made in Congleton, and they were used as announcer's mics in boxing matches. I have found nothing to confirm or deny this, so as always if you know more than I do, please get in touch!

But if it fell on your head, then it would certainly be.... a knockout.

(Sorry)

Oktava ML16 ribbon microphone dissected

Here is an Oktava ML16 from 1968. Back in '68, man had not yet been to the moon, and you could not buy a Russian microphone in Western Europe! 

The early Oktava ribbon mics are nicely designed and generally sound good, although it seems that smoke-free regulations did no apply to old Soviet studios and stations, and the old mics often benefit from a good clean and a service. 

The ML16 is a bi-direction model, and the ML17 was its cardioid partner.

Sometimes it is easiest to strip a mic down completely and build it again from scratch to make sure everything is cleaned, tested and working properly. 

At the top of the photo you can see the brass blasts shield to protect the ribbon, the internal grills and the ribbon clamps. Across the middle are the outer grills, some wiring and the motor and magnet themselves. At the bottom we have the lower housing and the toroidal output transformer.

Then it can all go back together again, and with a new ribbon it works first time!

MOTM - Toshiba Type K multi-pattern ribbon mic

Last month I posted about a Toshiba copy of the RCA BK5. Here we have Toshiba's take on the RCA77 DX....

Toshiba Model K

The Toshiba model K was one of the later Japanese ribbon mics. By this point they had really mastered the technology and were producing high quality microphones to rival to the American mics. It is slightly shorter than an RCA 77DX, but is equally heavy and well built. I very much like its stubby looks and slotted grill holes.

Rear of the model K, with pattern control

The model K was designed to broadcast standards, and this specimen was obviously made for NHK (Nippon Hōsō Kyōkai, or Japan Broadcasting Corporation), which is Japan's equivalent of the BBC. Like most Japanese ribbon mics, this has a 600 ohm impedance and gives a strong output.

Inside the mic, the motor is based around a single strong horseshoe magnet, with the ribbon held between two chunky pole pieces.

Like the RCA 77DX, there is an acoustic labyrinth made from a series of holes with connecting channels, which goes up and down the centre of the mic. Two thick wires take the signal from the ribbon, through the labyrinth, down to the transformer below.

Acoustic labyrinth in the middle of the mic

The pattern control uses a choice of baffles to partly or entirely redirect the rear of the ribbon into the acoustic labyrinth. This turns the mic into a pressure transducer when the rear baffle is closed, giving a more omnidirection pattern.

Pattern control on the Toshiba type G.

It differs from the RCA design: the 77DX has a a cam shaped copper plate that allows the rear vent to be opened by incremental amounts, whereas the Toshiba has three discrete positions, which are labelled...

• N (fully closed - non-directional)
• B (fully open - bidirectional or figure 8), and 
• U (a small opening - unidirectional or cardioid)

And in an attempt to beat the Americans, on the bottom of the mic there is a switch for a 6 position variable frequency high pass filter - the RCA77DX only has three!

High pass filter switch

Update 27/5/13... this is how the filter affects the frequency response....