The Xaudia Blog

20-12-2012

Reslosound and the Incomparable Ferrograph

The Incomparable Ferrograph brochure
Here is an old Ferrograph brochure whoch arrived with a Reslo ribbon microphone. Built like tanks, Ferrograph made arguably the best reel to reel tap recorders through the 50s and 60s, and it seems that they had a formal agreement with Reslosound as the two names often appear together in catalogs.  The final page of the document shows the Reslo RB microphone, along with accessories including matching transformers and stands.

The Reslo microphone sold for 11 Guineas at the time of publishing. (1 Guinea = one pound and one shilling. Only the British could come up with such a bizarre coin!)
18-12-2012

Quick-change guitar for pickup testing

One challenge when building prototype pickups is testing them quickly. It is easy enough to make the electrical measurements such as inductance, resistance and capacitance, but they don’t really tell you how the pickup is actually going to sound. Sooner or later they need to go into a guitar.

Squier by Fender Jagmaster ready for surgery
Changing a guitar pickup isn’t a big job, but it still takes time. Usually the strings need to come off, the scratch plate removed, a bit of soldering, and then back together again before tuning. If you add a cup of tea then you can easily lose an hour.
So I wanted to make or modify a guitar to act as a workhorse for pickup testing, which would allow for quick pickup swaps without having to take the strings off. The obvious approach is to put the pickups in from the rear of the guitar – which means cutting a hole through a guitar and finding an alternative way to mount the pickup.
 

This Squier Jagmaster guitar makes a suitable victim for surgery. It was fairly cheap, the neck is straight  and plays well, and the strat-style trem cutout means that I don’t need to remove a huge amount of wood.

The first job it to strip the Jagmaster down, removing the strings, scratch plate and the existing hardware from the front of the guitar, and the tremolo system from the rear. Then off with the neck to keep it safely out of the way when the jigsaw comes to play.

Once everything is out then I measured up and cut two aluminium rails that will act as mounts for the new pickups. These were filed round at the ends to fit the existing routing, and drilled and tapped for mounting.

Then came the dirty work.  With a jigsaw I cut through the body to make a humbucker-sized hole. You can see just how thin the wood is between the pickup and the tremolo routings – just a few millimetres.

After the jigsawing, the hole was cleaned up with a wood file. The rails were then screwed into the body at the top of the guitar – the holes countersunk so that they don’t get in the way of the pickups.

One more job – the bridge no longer has springs to keep it under tension. A block of wood locks it in place instead. The guitar can now be put back together.

Now the pickup can be fitted from the rear with two screws attaching it to the aluminium rails. Screw terminals are also used to connect the wires to the output sockets for the ultimate quick change experience. A brass plate will cover the mess.

Rear of ‘quick change’ Jagmaster with locked tremolo and pickup mount

Now it takes two minutes to swap a pickup! Time for some rapid prototyping. And here’s the front of the guitar with a hexapup fitted from the rear.

Jagmaster with Xaudia pickup fitted.
16-12-2012

Lustraphone VR53 microphone documents

Lustraphone was one of several British companies making microphones back in the 50s and 60s. The catalog includes product sheets for several microphones and also some accessories such as mic stands and matching transformers. I was lucky enough to come across some old Lustraphone catalog pages, which included a product sheet for the VR53 ribbon velocity microphone and several other microphones. The catalog probably dates from 1952 or 1953. Note the four digit phone number!

Lustraphone VR53 ribbon mic data sheet front

Lustraphone VR53 ribbon mic catalog, reverse

Although the catalog mentions 20 ohm and 500 ohm models, I have also seen high impedance models of this mic. The frequency response is claimed to be “substantially maintained to 14000 Hz”. From experience, I would say that ‘substantially’ is used loosely. The BBC have a bit more to say about this mic in their R&D reports.

As well as the VR53, the catalog also includes

VC52 “velodyne” noise cancelling microphone
C48 moving coil microphone
C51 dynamic microphone
C151 telephone microphone
AGC496a – Automatic gain control, which looks to be some kind of tube limiter.

I have uploaded a PDF of the full catalog here. (10 Mb).

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.