The Xaudia Blog

22-11-2012

Film Industries M8 XLR mod

Film Industries M8 ribbon mic with XLR
In the days before XLR became the standard microphone connector, most manufacturers made their own custom connectors. The British companies Reslosound, Grampian, Cadenza and Film Industries all followed this practice.

I guess at the time it was a good idea and meant that the company could earn extra revenue for spares and replacements, but 40 or 50 years down the line it is becoming increasingly hard to find good quality  connectors for these mics.
Here is a humble Film Industries mic that arrived without a connector. It was converted to XLR at the owners request. With a bit of care the new connector can be fitted without spoiling the look of the mic. Now it is good to go back into service. Better than being stuck in a box!
08-11-2012

Italian ribbon microphones

Today we took delivery of some interesting microphones from Italy. Here they are with some other resident Italians.

Geloso double ribbon, Framez, Do-Re-Mi 351MN, CM, Magneti Marelli MC46, Riem and Meazzi

From left to right we have ribbon mics by Geloso, Framez, Do-Re-Mi, CM, Magneti Marelli, Riem and Meazzi.  On closer inspection it seems as though some of the different brands came from the same factories.

The motor of the Do-Re-Mi mic is the same as the Framez, and the Riem is a skinny version of the Meazzi. We also know from previous research that Framez and Meazzi were related companies. Magneti Marelli made 74B copies under license from RCA.

We know less about the RCA-shaped CM microphone. In fact nothing at all about it, other than it is a fairly standard design, made for public address use.

It seems as though there was once a a thriving ribbon mic industry in Italy, with numerous brands and models, but I don’t know of any modern Italian ribbon mics.

Update: I found this ad for the Riem ribbon microphone, from the magazine Selezione Radio, Feb 1952.

03-11-2012

Ribbon mic patents

Here are some more ribbon microphone related patents, both US and British, from the 1930s, 40s & 50s.




The diagram (above) is from one of the patents, and may be the first tube ribbon mic!

Harry Olson, Marconi, July 1932.  
Improved ribbon mic with tube amp and better housing. Possibly the first tube ribbon mic! 
Olson, Marconi, May 1933. 
Directional microphone with velocity and pressure components connected in series.
Otto Kolb, September 1933. 
Ribbon mic with 1 to 1.5 micron ribbon and holes in the pole pieces for improved air way.
Andrew Swickard, Bell Telephone Labs. July 1936. 
Ribbon microphone with both velocity & pressure sections
Thomas Julian, GEC, March 1944. 
Improvements in ribbon microphones.
Horace Duffell, Radio Gramaphone Development, June 1947
Adustable magnet pole pieces. 
William Cragg, Standard Electric Corp. December 1945. 
Velocity microphone with ribbon supported along its edges
Helmuth Eckardt, Bell Telephone Labs, May 1949. 
Describes a 3-zone ribbon to eliminate distortion and improve frequency response. 
Donovan Shorter & Hugh  Harwood, BBC, March 1953
Improved ribbon microphone design. Looks very much like the STC / Coles 4038!
02-11-2012

The Trashcaster Lives!

Finally the Trashcaster guitar is finished. This started life as some parts on ebay – an old vox body and broken scratchplate, a Squire neck, hardtail bridge and knobs from a Jazz Bass. Add some paint and a pair of home-made pickups…. behold the Trashcaster!
Xaudia ‘Trashcaster’ guitar
The Trashcaster has custom wound big single coil pickups, with coil tap and phase switches, a blend pot, and normal tone and volume knobs. Wiring the blend pot was fun. You have to get the turn direction right otherwise all of the sound disappears! With these controls the guitar has a wide range of tones, and the out of phase sound Nashville tone is definitely something unique!

I have strung this for Nashville tuning, which is the same as the high strings on a 12 string guitar. So when played along with a guitar in standard tuning, it fills in the holes and sounds a bit like a 12 string, but with micro timing difference there is more of a chorus sound to it. You have probably heard this effect on countless records without knowing it.

A couple of coats of clear lacquer helps the slide-on decal blend in. But perhaps I should have called it the ‘Nashmaster’. Too late now! The last job was to file the nut to take the narrower gauge Nashville strings, and to do this you really need a proper set of nut files. They are not cheap but I found these ones on ebay for around £40, and they did the job quickly and accurately.

27-10-2012

MOTM The Italian Job

I have no idea who made October’s microphone of the month. But it is quite a beast, dwarfing the SM57 that I have used as a geologist’s hammer*.

Italian ribbon microphone by an unknown maker

This one came from Italian ebay, and has a whiff of DIY about it. Except that if it is, the work quality is very high. It could well have been a project for an engineering degree. Or perhaps a prototype from a professional workshop?  Some parts of the mic are well thought out, but ultimately it is let down by the transformer and low magnetic field.

The microphone body is based around brass tubing with an imposing chromed grill and chromed bells at each end. The base is fitted with a (horrible) 4 pin CB-radio style plug. The yoke is nicely bent aluminium with a turned base and wingnuts.

Italian ribbon mic – motor and magnets

Inside, four large cylinder magnets are clamped between two heavy blocks of mild steel, and the ribbon motor sits at the centre. There is a hint of the RCA 44BX in this approach, and the ribbon is of similar dimensions to that mic. The ribbon itself is clamped with sturdy brass blocks. These magnets here are not really strong enough for the job and the measured field in the ribbon gap is around 1000 gauss – a bit low really. Perhaps they were once stronger than this.

The transformer has its own internal can for extra screening, and the connections to the tranny primary are made with heavy copper for very low resistance. Good thinking!

Ribbon mic transformer

The transformer itself looks home-made from recycled laminations. Although the thick copper wire for the primary is a sensible choice, the inductance is a rather low 24 microHenries and there is no chance of reproducing a full frequency range. These lams look familiar – I have seen similar ones in Thiele microphones for the power transformer, and also, I think, in Geloso amplifiers

Domed end cap of the mic, with striped output leads

The maker, whoever he was, has used brass, mild and stainless steels, copper and aluminium for the construction. Parts are turned, milled, brazed, folded and domed. It looks more and more like an engineering workshop project designed to showcase the maximum number of skills, and in that respect it does a very good job.

Better laminations or a new transformer would show the true potential of this mic, as would some stronger magnets to boost the field. I will try that!

If anyone out there knows more about this mic, I would love to hear from you.

* Geologists often use their hammer in photographs as a way of denoting the scale of rock formations and features.

20-10-2012

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.