MOTM – Tannoy Ribbon Microphones Part 2. Cardioid ribbons

Tannoy’s Cardioid ribbon microphones

As well as the bi-directional microphones described in my previous post, Tannoy also produced several cardioid models. In the picture below, the mic on the left is the MD422. I don’t have a model number for the centre and right hand microphones, but they are the same basic microphone inside, with very different grills and bodies.

The internal design of these two microphones is very simple, with a huge heavy horseshoe magnet providing both the magnetic field and creating an internal cavity to help control the pattern. The ribbon pole pieces are simple rectangular steel plates screwed into position.

There is a layer of felt behind the ribbon. I also expected to see the cavity behind the ribbon stuffed with horse-hair or cotton wadding, but in this example it was completely empty. There is a small transformer in the base of the microphone – in this example the output impedance was 2000 ohms, but I’m sure that other output options would have been available.

Despite the size, the output level is rather low.

The MD422 uses the same ribbon motor as the Type 2 bidirectional mic, and we can safely assume that they were contemporary models.
As well as these large cardioid microphones, Tannoy also produced this smaller directional model which looks rather like a dynamic mic:

The motor inside this mic is reminiscent of that from the STC 4104 lip microphone. It uses the same base and connector as the MD422 and MR425 models.

Update March 8th 2015

Tannoy were developing directional ribbon microphones from the mid 1930s onwards. I have never seen this model on the bench, but this sketch appears in Wireless world in September 1937:

Tannoy and the Houses of Parliament

Tannoy ribbon microphones were used in the British Houses of Parliament. According to Chris McClean’s article for the Institute of Professional Sound, twelve ‘brass barrel’ microphones were fitted by Tannoy in 1951, and the system was further upgraded in the 1970s, again by Tannoy, with a system than lasted until 1991. 
Here’s the problem: I have seen several of these brass-barrel Tannoy mics on sale that claim to be ex-Parliament. Too many, certainly more than twelve, and some at very inflated prices. Either Parliament kept a huge number of spares (which is possible, I guess), or this model was not exclusive, and was sold elsewhere. I have heard anecdotally of these being salvaged from church PA systems, and also the Canadian government.
Additionally, I have seen, and bought, Type 3 bidirectional Tannoy mics that claimed to be ex-HOP., although when I asked for documentation as proof of the claim, the seller was unwilling or unable to do so. Were these fitted in the 1970’s refurbishment? Again, it is possible, but I have yet to see any proof of this claim. If you know better than please get in touch and show me!
The lesson here, as always, is Caveat Emptor, particularly when buying used microphones.

Update March 8th 2015
Thanks to one of our readers for sending in a link to this announcement in Tape Recording magazine (1962, issue 5). This adds to the Houses of Parliament microphone debate.

The article announces two new ‘Slendalyne’ ribbon microphones from Tannoy – a cardioid and a bidirectional version. Yet the cardioid version looks very much like the brass-barrel mic that was supposedly installed into the Houses of Parliament 11 years earlier! This sentence is particularly intriguing: ‘Although they have manufactured microphones for internal use before, this company has never made their instruments available to the public before‘. The statement is not quite true as their earlier models were widely available. But this implies that these specific models had previously been supplied to select customers, and became available widely from 1962 onwards.

Thanks to Tom McCluskie, Jamie Neale of Real World Studios, and Marco van der Hoeven of Vintage Mic World, and everyone else for sharing information and photographs of their microphones.

Tannoy Ribbon Microphones Part 1


This is my attempt to round up and discuss the various ribbon microphones that were made by Tannoy. I have split this survey across two posts, with part 1 describing Tannoy’s figure-8 microphones and part 2 focusing on their attempts at cardioid ribbons. Finding firm dates and model numbers is a little tricky as they are rarely marked on the microphones themselves, and so there is a certain amount of educated guesswork involved. If you know more, please get in touch!

Update 8th March 2015
Several kind and knowledgable readers have sent in links and articles with dates and model numbers. I have added these where possible. Thanks to all!

Figure-8 ribbon microphones
Over the years Tannoy produced three main models of bidirectional ribbon microphone, with some variations around those types. I have called these types 1, 2 and 3 in order of production.

Type 1
The BBC technical team reviewed this mic in 1947 and applied their usual exacting standards, rejecting the mic for broadcast use. But as usual the benchmark mic for comparison was the BBC Marconi AX model, which cost many times more, and in fact these mics can sound warm and rich, with an overtly vintage tone.

These mics are heavy with a cast body and large cylindrical magnet. I have come across mics with different output impedances, usually 50 ohms, 600 ohms or high impedance.

Type 1 variant
In response to the BBC comments, extensive changes were made to the motor design, although the body remained the same. The magnet structure is completely changed, with what looks to be a single cast magnet. I have never actually seen one of these on the bench, but Seth at the 2 Track Mind blog has written a nice post about his microphone here.
Type 2 – MR425
The Type 1 mic was succeeded by the type 2 or “Pitchfork” model, which is much smaller and has a completely new motor design. This model seems to date from the early 1950s and was available in different colours with different mounting options.

Most of these models have a 600 ohm output, and give a full well balanced sound. This is my favourite figure-8 Tannoy, partly because this was the first Tannoy mic that I owned, but also because it has a good response and a very usable signal / noise output.

The type 2 motor is simple but nicely made, with two tapered magnets either side of the ribbon, and the adjustable pole pieces allow one to set the ribbon tension.

Update – this model has been identified as the MR425, and it was briefly mentioned in Wireless World in May 1952:

Type 3 – Slendalyne
These mics are smaller again and use a lot of plastic in the body, which can be prone to cracking. The grills are stamped metal, and the connector is a simple DIN plug without a locking ring. They are a lot less common than the types 1 and 2, although perhaps not as rare as has been suggested by some sellers.

The magnets in these mics are made from a ceramic material which allows a smaller, lighter microphone than its predecessors.

Update: This microphone has been identified as the Tannoy Slendalyne model which appeared in Wireless world in June 1962:

In my next post I will describe Tannoy’s cardioid ribbon mics.
Stay tuned!

2-Track Mind’s Tannoy mic restoration

Here is a nice article by Seth at the 2-Track Mind blog, describing how he restored a very early Tannoy ribbon microphone. Seth went to great lengths, building his own corrugator and refinishing the mic, and the results look great. I played a tiny role here and was able to supply a little brass mount so that he could put it on a stand.

The mic itself is quite unusual, and the motor assembly (above) is different to most of the other Type 1 Tannoy ribbon mics that I have seen. Below is the more usual look of these mics inside, with a large cylindrical magnet and simple flat pole pieces:

It is becoming clear that Tannoy made many different variations on their ribbon mics. I feel a big Tannoy blog post coming on…

MOTM Tannoy MD422 cardioid ribbon mic

Here is Tannoy’s cardioid ribbon microphone – the MD422.

Tannoy MD422 ribbon mic, front

Firstly, Tannoy lose a point for the name. ‘MD’ should surely mean “microphone dynamic” in any sensible society! Perhaps the D stands for “directional”? Who knows, but it puts them at odds with other the Sennheiser MD421, and it is just plain confusing.

Tannoy MD422 ribbon mic, rear

Whatever the D stands for, the mic itself has an industrial look, and this one is finished in a bronze-ish coloured paint. To the best of my knowledge this is the only cardioid ribbon model that Tannoy ever produced, and it uses an acoustic labyrinth to provide the necessary back pressure to the rear of the ribbon. The chamber is the black cylinder in the photo below.

Tannoy MD422 ribbon mic, chamber
Some of the parts were made to a budget, or perhaps a short production run, with thin stamped metal for the base and top cap, along with two layers of off-the-shelf mesh to protect the mic from dirt and wind.

The ribbon assembly and magnets are the same as found in the type 2 Tannoy ‘pitchfork’ microphone, which would have saved costs by sharing components.
Tannoy MD422 inside, showing ribbon motor

The MD422 was subject of a BBC technical report, which concluded:”..this microphone has nothing to commend it for use in the Television Service“. That assessment seems rather harsh, but at the time the Corporation’s selection criteria were flat, uncoloured responses and good signal/noise performance.

In the report, the bi-directional BBC-Marconi AXBT was used as a comparison, which was much more expensive, a different pattern, and therefore a tough benchmark. Cardioid (and non-directional) ribbon mics generally use an acoustic chamber on one side of the ribbon to apply pressure, and this damps the ribbon motion, reducing the output compared with its natural bi-directional response.

Drawing of the Tannoy MD422 from BBC technical document.

Unlike my mic, the BBC’s example had a yoke mount rather than a fixed base, although there are mounting screw holes in the side of mine.

Despite my irritation with the model number, and the BBCs damning assessment,  I like this microphone very much. It has a gentle warm tone. More importantly, it was an attempt at technical innovation, which is always to be celebrated.

Reslo transformers vs the WEE monster

This little dinosaur sculpture was made out of waste winding coils, stripped mostly from old Reslo and other microphone transformers. 🙂

So why are we stripping transformer coils?

Some older ribbon mics were originally wound for 30 or 50 ohm output impedance, and tend to give a low output level when connected to modern recording equipment.

Many of these low impedance mics, including Reslo and Tannoy ribbons,  can be rewound for a modern 200 or 600 ohm input, raising the output to a more useable level, and avoiding noise from having to crank up the preamps.

Bobbin from Reslo transformer with secondary winding removed.

The old Relso 30/50 ohm transformers have an inner (primary) winding consisting of just 12 or 13 turns of thick (0.8 mm) enamelled wire, and a secondary winding of 152 turns of 0.4 mm wire. The thick wire of the inner winding ensures that the primary resistance is low, which keeps noise to a minimum.

Reslo transformer rewound for 600 ohm output

Re-winding the transformer involves removing the outer winding from the original transformer and replacing it with sufficient turns of a thinner gauge to reach the desired turns ratio and output impedance. Usually the original primary winding can be kept in place. The transformer is then reassembled and dipped in wax to fix the windings and lams in place.

This makes the microphone much more usable in a modern studio – transformers can be would for 250Ω, 600Ω or any other desired output impedance.