Racking a pair of Ward Beck M480 preamps - Part 1

Ward Beck M480 preamp modules

I recently acquired this pair of Ward Beck M480 input modules. Ward Beck Systems, or WBS, have a great reputation, and so I am very keen to get these racked up as microphone preamps. The modules have four switchable inputs, and a parametric EQ section too.

I have not yet found a copy of the M480 manual, but the Ward Beck Preservation Society have the manual for the later variant, M480C. The pin assignments look the same although the later 'C' revision has some additional features such as a switchable phantom.

The modules are very neat and clean inside, and use 44 pole PCB edge connectors. Luckily I had three gold plated connectors in the parts bin. These were salvaged from some scientific equipment that I pulled from a skip. It pays to recycle... and never throw anything away!

Although the modules are in great shape inside, the front panels and knobs are very dirty from years of sticky fingers. Naughty engineers!

The collet knobs can be removed by popping off the coloured caps, and then loosening the central locking nut. Then the black control panel can be prised away from its glue. In both cases they are destined for a long zap in the ultrasonic bath, which will clean them up nicely.

WBS M480 stripped down for racking

The modules will be mounted in a standard 19 inch rackmount case, and the construction makes this very simple. The existing aluminium front plates can be used as templates to drill the holes in the new front panel, and the black screen printed control panels can be mounted over these. Then it just needs a ±24V power supply and we will be ready to go.

Part 2 to follow soon, when the new case arrives

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!)

You can download the whole brochure here (7 Mb)

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.

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).

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!

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.

1934 RCA PB90 ribbon mic time capsule

Look what's on the bench today....

RCA PB90 ribbon microphone from 1934

This is a beautiful RCA PB90, in complete original condition, but need of a little loving care to bring it back to its former glory. Here's the output transformer....

RCA PB90 Ribbon mic transformer, 1934

It's date stamped 21st September 1934! 78 years old.  The mic shares a birthday with Leonard Cohen!

That's amazing.

Grampian microphone documents

Here are links to some manuals and documents from Grampian Reproducers Ltd.

Grampian DP4 dynamic microphone manual.

Grampian price list from June 1976.

Instructions and wiring guide for Grampian microphones.

Product line short catalogue from February 1968.

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! 

GB391340.pdf

Olson, Marconi, May 1933. 

Directional microphone with velocity and pressure components connected in series.

GB405497.pdf

Otto Kolb, September 1933. 

Ribbon mic with 1 to 1.5 micron ribbon and holes in the pole pieces for improved air way.

GB414907.pdf

Andrew Swickard, Bell Telephone Labs. July 1936. 

Ribbon microphone with both velocity & pressure sections

US2141420.pdf

Thomas Julian, GEC, March 1944. 

Improvements in ribbon microphones.

GB592492.pdf

Horace Duffell, Radio Gramaphone Development, June 1947

Adustable magnet pole pieces. 

GB641897.pdf

William Cragg, Standard Electric Corp. December 1945. 

Velocity microphone with ribbon supported along its edges

US2510079.pdf

Helmuth Eckardt, Bell Telephone Labs, May 1949. 

Describes a 3-zone ribbon to eliminate distortion and improve frequency response. 

US2608265.pdf

Donovan Shorter & Hugh  Harwood, BBC, March 1953

Improved ribbon microphone design. Looks very much like the STC / Coles 4038!

GB738864.pdf

Look who is really answering your enquiries...

Xaudia customer services!

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.

Inside the EF40 vacuum tube

Here's a broken EF40 pentode tube. I dropped it, so took the opportunity to take a peek inside. The construction is intricate and quite beautiful.

Inside the EF40 tube, glass envelope removed

EF40 pentode with screen removed

EF40 with getter, mica insulation and plate removed

EF40 showing grids heaters and cathode

Vacuumtubes.net have a good description of how tubes work, and this diagram from shows all the parts:

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.

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.

Trashcaster guitar (part 3) - Red or Dead

After stripping off the pink paint from my Trashcaster guitar, I found some traces of the original paint underneath. The guitar had once been a nice shade of fiesta red. I also found this photo of an old Vox Consort on the interweb...

I'm pretty certain now that my body started off as a Consort like the one above. It looks like someone cut down the pickguard, which was presumably damaged like the one in the photo. 

After stripping and sanding back to the wood, I sprayed the body with several coats of red nitrocellulose lacquer from Rothko & Frost (who give an excellent service). These lacquers are nice to use as you can build up several thin coats in a day. The Trashmaster now looks rather smart!

The paint is just transparent enough to let a little of the grain show through. For a high gloss finish it should be given a few layers of clear lacquer, but I'm aiming for the less shiny look of budget 60s guitars so will probably leave it. The scratchplate is less than mint, and so a perfect body may look a bit incongruous. The replacement chrome control plate came from a Fender Jazz bass, adjusted slightly with a file to take off some pointy edges.

The extant screw holes in the body didn't fit a standard neck plate, so I've used these ferrules and screws from StewMac. They work very well and solve the problem. Also, the original tremolo bridge was missing. I have replaced it with a used hardtail bridge from ebay (£6!), and machined a brass block to fill the hole where the vibrato spring must once have been. Perhaps that will give a little more sustain too.

Nearly done, and what the guitar needs now is a logo to stop the headstock looking quite so naked. Rothko & Frost also supply custom vintage style logos for a very fair price, and here is one that they printed for the Trashcaster. It now just needs a couple of coats of clear lacquer to protect it, and everything can go back together again.