Our mount-a-mic adapters received a nice review in Sound-on-Sound magazine this month. These little gadgets are designed to make it easy to mount any mic with an XLR fitting. You can read the full article here.
Here’s a new video of our friend Jose Estragos from Spain, using his Reslo RVs in his song ‘Buscandote’.
Enjoy!
The STC 4033 cardioid microphone was a stalwart of British broadcasting and an early solution to the the challenge of making a cardioid directional mic. The 4033 contains both dynamic and ribbon elements, and in cardioid mode the microphone blends the two transducers together via a capacitor and inductor – you can read more about the filter and switching circuit at the wonderful Coutant.org website. The mics are still quite popular with some recording engineers, but of course there are no spare parts available after half a century or so.
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| Omni and Figure 8 suming to a cardioid pattern – from SOS website |
I was recently asked to repair a 4033 with a cracked bottom bell, which is made from some kind of zinc alloy. When I took the microphone apart it became clear that the casting had collapsed into several pieces, only held in place by the rest of the microphone. The job looks like a challenge, and we like a challenge.
It isn’t clear how this became so damaged but it is possible that the alloy itself was at fault. Zinc Pest is a notorious cause of failure caused by impurities in zinc alloys, particularly those from the 1930s and 1940s. Like this one.
The alloy is pretty much impossible to solder or weld back together, and I don’t believe that any glue would be strong enough to hold when the mic is bolted back together. A new part is required but impossible to find, so we need to make one, or at least persuade somebody else to make it. Metal casting requires specialist skills and equipment, so I asked Abbey Casting to copy a good part from another 4033, and they did a fantastic job to produce this part in bronze.
The raw casting needs various holes drilling and tapping, but with a little work we have a perfect fit.
The 4033 is not the easiest thing to work on – everything is tightly packaged and the transformer is set in wax into the stem of the mic, so I had to use a hot air gun to dismantle it. Whilst the mic is apart it makes sense to replace that Hunts capacitor* with a nice NOS Mullard, and re-solder all the old joints to lower noise and improve future reliability.
With the new part in place I can put it all back together again. The casting could be painted or powder-coated to match, but in this case the owner prefers to see the bronze. These are 50 ohm microphones and work nicely with our impedance matching transformer boxes.
Thanks to Liam at ToeRag Studios & Richard at Abbey Casting.
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 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.
Tannoy and the Houses of Parliament
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.
Introduction
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!
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.
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.
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!
Ev of Vashion Island sent in these pictures of his wonderful tube ribbon microphone and has kindly agreed to share the photographs and description on this blog. The mic is a little bit of a mystery as it appears to be similar to an early Marconi design and the RCA PB17, yet has no maker’s mark and is different in many details.
The mic is clearly influenced by Harry Olsen’s design as described in his 1932 patent and the magnetic field for the ribbon is provided by an electromagnet, which is very rare and only usually found in the very earliest ribbon mics; this approach became redundant very quickly as strong permanent magnets became available.
As I have not inspected this microphone myself I will use Ev’s description and photographs – Ev’s comments are in italics:
“The outside diameter of the cylinder is 4.75 inches or 210mm. The cylinder is aluminum. the top end cap and plate are machined aluminum. The hemispherical bottom cap is also machined aluminum.
The yoke mount is steel flatbar (I believe the PB17 yoke mount is made of cast metal).
There are three transformers including the one for the electromagnet.
Instead of having three UX864 tubes it uses two unknown tubes, one has 5 pins with a wire attached to the top, and the other is 6 pins.
The resistors are made by Morrill, Germany. The transformers and capacitors have no makers marks that I can see. Whoever made this microphone obviously knew what they were doing. I wonder if this was a prototype made by RCA, or perhaps it is European (because of the German resistors)?
The bell…. is definitely cast aluminum. The inside plate at the connector end of the mic is also cast. The acorn nuts at the connector end fit a 7/16″ SAE wrench perfectly and the bolts with the wing nuts are US threads.
Note the tiny piece of threaded stainless steel pipe bolted to the plate (to the left of the connector in the picture). I thought it might be a jack, but I think it is only a pipe. There is what appears to be a ground wire soldered to it inside the mic.
The number 13 etched beneath the bottom right connector blade corresponds with the number imprinted on the connector itself inside the mic.”
Here are the Beebs in action as drum overheads, and for recording a string section…
He was using them to record the French band Watine at a country house in Sussex, working out of this amazing airstream mobile studio supplied by Yellow Fish.
We will link to the music as soon as it is published.
Here is our first Microphone of the Month for 2015. This Shure Stratoliner looks like a Zeppelin airship or perhaps Flash Gordon’s space ship. But is it a crystal, ribbon or dynamic microphone?
I had always thought that the Shure Stratoliner series were crystal microphones, and indeed the 708 model does have a crystal element. But although this 508C uses the same body, it is quite a different microphone inside.
This one says ‘dynamic’ on the label but it is really a rather strange ribbon microphone. Here is the business end of the mic with some kind of flat ribbon in place, possibly made from kitchen foil.
Once we remove the ribbon and clean the motor, we can see a series of slots right behind the ribbon. These make an acoustic cavity and help to control the directional pattern.
The motor design is quite basic, with two cylinder magnets behind the ribbon, covered in felt. The transformer is mounted behind the magnets.
This construction and slots behind the ribbon also do odd things to the frequency response. Here is the published response chart from the Shure 508a user manual:
Even the published chart is pretty bumpy, and it seems that Shure were willing to sacrifice fidelity for directionality. And the mic does sounds peaky – definitely one for the vintage / special effects shelf in your microphone locker.
These HMV and EMI ribbon microphones show up quite often for repair. The models are identical, just branded differently, and very often they come complete with wooden box, which survives decades in a damp shed or attic better than cardboard.
It is rare to find any paperwork with these but I was lucky enough to come across an HMV 2350 complete with brochure and manual
The manual confirms that they were designed to drive a 20 ohm line. I have found that most of these mics measure around 15 ohms and have really low output. A suitable matching transformer makes a big difference to the usability of these microphones.
PS, some of you might recognise this mic from Marvel’s Captain America movie – it was used by Howard Stark in the scene where Steve gets his treatment!
Here is a scanned review of the Reslo RB miniature ribbon microphone,
The review is written by Fred C. Judd, who was an early champion of both electronic music and DIY audio electronics. You can hear and buy some of Judd’s creations at this bandcamp page.
This article arrived with a microphone but I am unsure which magazine it was originally published in. Perhaps “Amateur Tape Recording”, of which he was technical editor. If you know more, please let me know.
