Melodium 42B replacement magnets

Eleven Melodium 42Bs in for service at Xaudia

We now stock magnet assemblies to replace weak or cracked magnets in Melodium 42B ribbon microphones. *

Replacement magnet assembly for Melodium 42B ribbon microphones

The horseshoe type magnets found in some of these mics tend to hold their field well and rarely fail. However, I have occasionally encountered examples where the magnets have cracked and lost some of their strength. This may happen if the mounting screws are overtightened or the microphone has been abused.

Around half of the 42Bs use block magnets with a carrier bar to complete the magnetic loop. These are more prone to losing their field especially if they are removed from the microphone for some reason. It is hard to predict how these will behave. Luckily we can measure them and see if they are up to scratch. A healthy microphone should show above 3000 Gauss in the ribbon gap to give good signal to noise performance.

In this example, the field is down to around 2400 Gauss, which is at about 80% of where it should be. That amounts to 2dB loss of output – not yet a disaster but may be heading that way. With the new assembly in place we measure around 6000 Gauss, which is up + 6dB on a ‘good’ stock Melodium 42B.

*Magnet failure is rare. A bad ribbon is the most common cause of a weak signal in these microphones, and would be worthwhile testing the ribbon before embarking on any kind of magnet service.

Melodium RM6 XLR conversion

It’s nice to keep things original, but better to make them usable. Let’s face it, the definition of a microphone is ‘something that records sound’, and not ‘a chunk of metal that lives in a box’. 🙂

Like many old connectors, it is hard to find good quality used Melodium connectors, so here is a nice simple XLR upgrade for a Melodium RM6.

I removed the base of the microphone and cut off the old connector on the lathe. Then I turned a Neutrik XLR socket to fit into its place.

Solder three wires back in place and this RM6 is now ready to record music!

Melodium 42B XLR mod

The old Melodium 3 pin plugs are getting very hard to find, and quite expensive when they do show up. This is a pragmatic approach to the problem, and allows an XLR to be connected directly….

The Switchcraft connector could be painted to match the mic, but I don’t mind the nickel either.

MOTM – Melodium RM6

As promised (or threatened), MOTM is back, and December’s microphone of the month is the Melodium RM6.

Although much much smaller in size than the Melodium 42B, the RM6 takes some of its design philosophy from its predecessor. The motor assembly has horseshoe magnets above and below the ribbon (like a tiny RCA 44BX), and an inductive filter with multiple cut-off frequencies. It also has an obsolete and hard to find proprietary connector, albeit a different one from the 42B.
The body is made from cast metal which has a tendency to crack, and the first challenge is to get inside the mic without damaging it. There are three tiny metal pins pushed through the mic that fix the grill to the lower body of the mic. These need to be pushed all the way through the mic so that the grill can be removed, and usually these can be found stuck to the magnet, although one will inevitably go missing!

To remove the mic completely, the connector must be unsoldered and the switch tip removed. Once inside, we see something that looks like the Easter Island statues!

The ribbon is hiding behind the baffles, and the motor requires quite a lot of disassembly before the ribbon can be accessed. The ribbon itself is about 1.8 mm wide, so a bit fiddly to fit. Like most mics of a certain age, half the problem is that the ribbon has become oxidised and stiff, and the other half is small particles of wild iron that that have become stuck between the pole pieces, preventing the ribbon from moving freely.

Removing the strong magnets made cleaning and re-ribboning a lot easier! The transformer and filter inductor are housed in a mumetal can, screwed beneath the motor assembly and above the filter switch.

As usual, the mic sounds best without the high pass filter engaged, although I can imagine it being useful to compensate for proximity effect when close micing some instruments.

There doesn’t seem to be much information about this mic available on-line, but I have scanned an old Melodium catalog featuring the RM6. There is also a French language review of the RM6 over at Audio Fanzine. They seemed to like it, and gave the mic 9 out of 10!

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!

Melodium 93C & 530C measurement microphones

Melodium was a French manufacturer of microphones and other audio equipment, probably best known for their excellent model 42B ribbon mic.

The Melodium model 93C is a small diaphragm condenser measurement microphone that was on the market in the 1970s. Although the data sheet is not dated, the frequency plot is marked 03-73, which pins down the measurement, if not the manufacturer, to March 1973. The specimen on the bench was actually stamped with model number 530C, but seems to be the same microphone.

Melodium 530C measurement microphone

The 93C / 530C needs a 13V to 18V supply to operate, and a battery pack was available.

Melodium 530C with battery pack

The mic is not compatible with phantom power, but a simple converter can be built. In this case it was built into the old battery pack, with an indicator LED replacing the on-off switch.

Melodium 530C with modified supply to convert from phantom power

Once the power is sorted out, the mic is quite sensitive, with a very hot signal which may even need padding for louder instruments.  The mic seems nice and flat up to about 8000 Hz – here’s the result from our little test chamber, which doesn’t go much past 10KHz anyway.

Frequency plot for Melodium 550C, referenced to Beyer measurement mic

When I wired this one up according to the manufacturer’s data sheet, I found that the mic was out of phase with our reference mic, and indeed the data sheet claims that the ‘Angle of phase rotation 180C to tension’.

Here is the manufacturer’s data sheet for the Melodium 93C.

Thanks to Santiago Calvo Ramos for sharing.

Melodium 42B rebuilt

A few weeks ago we received this rather forlorn looking box of Melodium bits for service!

Melodium 42B stripped down to parts

The good news was that all the important parts were there, and despite some corrosion, the magnets and the transformer were on good shape, which meant that this vintage gem could be restored to some of its previous beauty.

Melodium 42B repaired and re-ribboned

The mic was stripped down and all the parts cleaned up in the ultrasonic bath. Then the magnets and some other bits were painted to stop the rust returning, and the motor reassembled. Dino (the owner) wanted to retain the vintage look of the mic, so the grills were straightened, de-rusted and then given some clear lacquer rather than being refinished. New grill cloth gives some protection against pops and wind blasts.

Then it was put back together and a new cable fitted with XLR output. And of course a new ribbon. The mic looks pretty damn cool!

Thanks to Dino Jakobsen of The Why Project.

Melodium 42B Stand Adapters

Xaudia is pleased to announce this little gadget

Melodium 42B stand adapter

Anyone who has ever tried to put a Melodium 42B on a mic stand knows that it is challenge, if the original adapter is missing – which it often is.

So we have made some replacement adapters. These are machined from 1 inch (25 mm) solid brass bar, and fit snugly inside the yoke. There is a shoulder to support the weight of the heavy microphone, and a recessed band to accept the thumbscrew. The base is tapped to accept a standard 3/8″ mic stand thread.
Melodium 42B with Xaudia stand adapter

The Melodium 42B can now be securely mounted on a stand. Problem solved!

Transformer assembly line!

This week we have been building lots of little transformer moxes to match vintage 30 ohm ribbon mics to modern mic preamps. Correct impedance matching can deliver a +12 dB increase in level without noise penalty or loss of frequency response, which is welcome for many older microphones. Here is how a Reslo RV microphone behaves with and without the transformer:

Frequency response plots for Reslo mic with and without an impedance matching transformer

They are suitable for many old microphones including the following:

  • Reslo RBL and RB 30 ohm models
  • Melodium 42b
  • Grampian ribbon mics (including GR1/L and GR2/L)
  • Cadenza ribbon microphones (wired for low-Z use)
  • RSA & Selmer ribbon mics
  • STC 4033
  • Altec and Western Electric ribbon microphones

More information.

Mic of the month – Melodium 42b

Our Microphone of the Month for May is the magnificent Melodium 42B ribbon microphone.
Evolving Melodium 42b – serial no. in the 1700s, 4300s and 6600s (L to R)

The Melodium 42B was conceived as a French alternative to the RCA 44 family of microphones, and is in its own way every bit as good as the more celebrated RCA mics. At 32 cm high and 14 cm wide, and weighing 2.65 Kg, the 42b is a huge microphone with a large ribbon (68 mm long by 4.2 mm wide) and big powerful magnets*, to give a strong output with low noise.

We have been lucky enough to have four of these through the workshop, and have had the opportunity to observe some for the finer details that have evolved during the production of these beauties. Over the years the grill of the 42b has been refined, with the holes becoming larger, and a solid unperforated band appearing across the bottom of the microphone. Later microphones have a three pin connector at the rear, whist early models are hard-wired.

The magnet structure has also changed over time – earlier models have U-shaped magnets above and below, whereas the later microphones have four block magnets, arranged in pairs and connected by metal plates to complete the magnetic circuit.
The photo on the left shows the later style of magnets. The transformer and inductor are in the circular metal can below. Some models have a rectangular can, but the transformer and inductor inside are similar, at least in the ones we studied. The transformer has a ratio of 1:14, giving an output impedance of 50 ohms**

There is also a facility to adjust the ribbon tension, which should be mandatory on all ribbon mics!

Here’s a short summary of the changes with serial number:
  • 1500 – Small grill holes, fixed cable (no connector), U-magnets with North marked, rectangular transformer case
  • 1700 – Small grill holes, fixed cable (no connector), U-magnets, circular transformer case
  • 1900 – Small grill holes, fixed cable (no connector)r, U-magnets, square transformer case
  • 3400 – Small grill holes, connector, U-magnets (unmarked), rectangular transformer case
  • 3700 – Big grill holes, connector, U magnets, rectangular transformer case
  • 4300 – Big grill holes, connector, U magnets, rectangular transformer case
  • 5100 – Big grill holes, fixed cable (no connector), U-magnets, rectangular transformer case
  • 5300 – Big grill holes, connector, U magnets, rectangular transformer case
  • 6100 – Big grill holes, connector, U magnets (North is marked), rectangular transformer case
  • 6600 – Big grill holes, connector, block magnets, circular transformer case
  • 8000 – Big grill holes, connector, block magnets, circular transformer case
The latest serial number that I know of is number 9250, on the Coutant website, which has large grill holes and a connector.

The 42b has a three-position switch on the front which is used to select “Speaker”, “Voix”, and “Musique” modes. In the first two positions an inductor is switched in parallel with the output transformer which causes the lower frequencies to be rolled off.

Above is a frequency plot that I recorded in our anechoic mic testing chamber (well, more of a walk-in cupboard really!). This was recorded at 40 cm distance from the sound source, which is a concentric full range speaker, using a swept sine wave technique.

The bottom end boost due to proximity effect is pronounced, even at this distance, and the effect on the sound is very musical when capturing acoustic instruments. Of course sometimes you don’t want or need the proximity boost, and the switch conveniently corrects for this at speaking and singing distances.

If you are lucky enough to come across an old Melodium 42b but are disappointed with the sound, it may well have an oxidised ribbon and will need cleaning. The strong magnets are prone to attracting little shards of iron, which stick to the magnets and interfere with free motion of the ribbon.

* It is worth noting that the magnets on these microphones can fade with time – a healthy 42b should have a magentic field between the pole pieces of around 4000 Gauss. One of our microphones measured at just 1500 gauss and it was necessary to replace the magnets with suitable modern alternatives. If you have a Melodium with a weak output it may be worth having the field measured and the ribbon checked. Xaudia can of course help with all those things.

**  For optimum results with modern equipment a matching transformer is recommended.

Here are some Melodium links on the web:

Updated 9/10/14 with additional serial numbers