We are excited and a little bit proud to announce the launch of MoMics.Org, our little on-line Museum of Microphones.
The museum of microphones is and will forever be a work in progress. At launch we have over two hundred microphone exhibits in the collection along with over two thousand individual photographs and documents, and over a hundred sound recordings. The collection will continue to expand over the coming months and years, including additional sound recordings when we find time to make them, and more documents as and when we come across them.
Hopefully you will find something of interest and everything is free without a paywall or advertising. Take a tour but try not to get lost and stay all day!
The 1970s saw a mass extinction of British companies that produced ribbon microphones.
Don’t look up!
At the start of the 1960s there were at least seven significant and well established makers of ribbon microphones in the United Kingdom: Cadenza; Film Industries, Grampian, Lustraphone, Reslosound, ST&C, and Tannoy. Some of these companies like Reslo and ST&C had been in the business of producing microphones since the 1930s, yet by 1980 all seven had either ceased trading, sold their interests, or abandoned the market to focus on other products.
Timeline of British Ribbon Microphones ’60-’81
Tannoy stopped making ribbon mics in the early 1960s but continued to produce speakers and public address systems with such success that they became a household name – synonymous with unintelligible announcements at railway stations throughout Britain. SimonSound, who made the Cadenza microphones, disappeared in 1967. Perhaps the booming home recording market was already saturated at this point, and Cadenza was undoubtedly had the weakest design – evolutionary forces dictated that it would not survive. Similarly, Lustraphone had to all intents and purposed ceased making ribbon mics by 1971 – some new models such as their mythical 4-50 model were promoted but never appeared, and the company had vanished completely by 1973. Film Industries soon followed in around 1974 – their M8 models had been sold unchanged since the 1950s. Reslosound thrashed around for a few years, spitting out various new dynamic models, a new logo and even a condenser microphone. They finally ceased trading in 1978. Grampian hung around for another year before extinction.
British Ribbons and other models
So what happened? The British economy faced severe challenges in the mid 1970s, which led to a deep recession. Oil prices were sky high due to conflict in the Middle East, which was compounded by the Miners strike. This led to rampant inflation, power cuts, and a three day week for many workers to save electricity. The knock-on effects of this were high unemployment and reduces consumer spending.* It took nearly four years for the UK’s GDP to recover back to pre-1973 levels.
Arguably, some British manufacturers had not invested sufficiently in product development and were still selling the same technology that they had developed in the late 50s or early 60s. For example Film Industries M8, Lustraphone VR64, Reslo RB and Grampian GR1 were all essentially unchanged from 1960 through into the early 1970s. Meanwhile, new imported models from Shure, Neumann, Beyer and others were smaller, lighter and had better signal to noise and frequency response. And these new mics came with standard XLR or DIN plugs, which meant that the user did not need a different cable for every microphone. This combination of recession, reduced consumer confidence, and high quality imports squeezed the last breath out of the British ribbon microphone industries.
Did ST&C see this coming? They sold their microphone division to ITT in 1971, and then on to Coles Engineering in April 1974. Coles are still making the classic 4038 and other microphones to this day. Perhaps their focus on professional studio and broadcast rather than home taping made them more secure than others, and their contracts to provide the 4038 and commentator mics to the BBC surely helped.
Reslo, a.k.a. Reslo (Sound) Ltd., a.k.a. Reslosound, was a British manufacturing company who made audio equipment and produced A LOT of microphones between about 1937 and 1978. In just 40 years they went from making primitive carbon button style mics through ribbons to modern looking electrets and handheld dynamics. In the middle were the ribbons that we associate with the brand, including the RB and CR models used by a well-known beat band from Liverpool. 🙂
Reslo mics are by far the most popular brand that we see in for service at the Xaudia workshop, and I probably work on a hundred or more Reslo mics each year. The RB model is the commonest, making up perhaps 90% of those that come in for repair or for our popular Beeb (BBC) upgrades.
Although we have good documentation for many of these microphones, most of the original manuals and promotional material are undated, so we have to work a bit harder to find dates for Reslo products.
I have attempted to summarise when the Reslo models were made by trawling through numerous old magazines, looking for advertisements and reviews. The nice thing about magazines is that the issues usually have dates, which gives us a snapshot of which microphones were available at that point in time. Wireless World and HiFi Yearbook proved especially helpful.* The results are in the spreadsheet below – we may have missed a year or two either side, but these dates are broadly accurate to the best of my knowledge. Information before about 1960 is scarce and should be considered less reliable than that for later models, and we have almost nothing from the wartime years from 1939 to 1945. Additional documents may come to light in the future which can expand our time line. Let’s hope so!
Timeline for Reslo microphone models. Click it for the full size PDF version.
The earliest models appeared around 1937 and include the LC, a carbon mic, and two dynamics, the PR** and PMD. By 1946, with a world war in between, these three models have vanished and the VMC dynamic mic has appeared.
We can see that the RV ribbon microphone was available from around 1949 through to the mid 1950s, when it was superseded by the hugely successful RB and related models (including the SR1 and VR), which were in production until 1973. The end-address CR model (which is really just an RB in a different shell) was launched around 1959 and received a face-lift in 1965 to become the CR2. Amazingly, the VMC and VMC2 dynamic microphones were in production right up to 1968, by which point these heavy paper cone dynamics were very old technology and sonically no match for an imported shiny new Shure or Neumann!
In hindsight, 1973 looks like a year of revolution at Reslosound, with many of the old models, including the RB and CR series, being retried. Several new dynamic models were launched, along with a new logo and even an electret condenser for the first time. The only ribbon microphone left in the 1974 line-up was the MR1, which used a repackaged RB motor with a smaller transformer. I surmise that they were trying to modernise their range to compete with imported mics from Germany and the USA.
Hello John, got a new logo?
But it didn’t work. Sadly, by 1978 Reslo had ceased to exist.
You may have noticed that many RCA microphones have (at least) two names. Generally they have a model number with one or two letters before or after the number, for example 44BX or KU3A. But all RCA products also have an MI number, which is short for Master Item.* The MI number is usually four or five digits and may or may not be followed by a letter, and may contain extra information such as minor improvements or a different finish. A major change might involve a whole new number For example a shiny black and chrome RCA 77D is MI-4045-E and the improved 77DX is MI-4045-F. However the broadcast grey version of the 77DX was considered sufficiently different to become MI-11006-C.
I took a little tour through some old RCA product catalogues and attempted to correlate the microphones’ common names with their MI numbers, and track any minor revisions across the years.
The 1930s saw a rapid development in ribbon microphone technology but documentation from that era is hard to find. (That is a big hint – if you have any old RCA catalogs then please share them widely). We have a 44A manual from 1933, and by 1936 the early PB series and related microphones were already being phased out, with only PB90 left in the catalog The longevity of the 44B/BX and 77D/DX models is notable but expected, with each being in production for around 20 years. Other models appear only fleetingly – the 77B and C models appear only in 1948, and the B1 and C1 only in 1950. Some models such as the SK-50 and KU2 do not appear in any of these documents.
From 1968 onwards RCA introduced a new look, retiring the old red meatball logo in favour of a three letter graphic with a modern stylised font.
We recently made some recordings of some of our oldest microphones, tracking a 125 year-old Martin 0-18 acoustic guitar. The guitar is very special – it was build in 1900 before Martin began selling guitars with steel strings*, and has a very lightly-built Adirondack spruce top and rosewood back and sides. It would have originally been fitted with gut strings and now has a set of Aquila 900 nylon replica gut and silk. I love the warm tone of this elderly little guitar.
The microphones in question are all quite ancient too, with the exception of the BerZerker from Extinct Audio which we put up for reference. The recordings are below with a description of the microphones. Most are ribbon microphones but we added an STC dynamic into the mix too. All were run directly into a UA Apollo 8 preamp and recorded into Logic with no further processing except that the tracks are normalised when bounced down.
1. Melodium Type R, serviced with new ribbon.
2. National model VM-11 (a replica of an RCA PB type) serviced with new ribbon
4. STC 4021C with VIE grill. This 15 ohm low impedance mic is connected via an Extinct Audio matchbox.
5. RCA PB144 with original ribbon in place.
6. National VM-1 serviced with new ribbon.
7. Toshiba Type C with new ribbon.
8. Siemens ELM 24/III cleaned and serviced with new ribbon.
All of the recordings have merit although some of the older mics have higher noise levels than one would expect from a modern microphone. The VM11 was particularly hissy. As one would expect, the BerZerker had by far the highest output level and needed substantially less gain than the other microphones. I was especially impressed with how good the STC 4021 sounded in this context, and the Siemens mic was impressive too considering it is now around 95 years old.
Finally, we made a mid-side recording with the Siemens ELM24/III as mid and the Melodium type R as side. This has a little bit of reverb and compression added for fun.
And so it is fairly easy to make nice sounding recordings with very old microphones, although it helps if they are properly maintained and serviced. For those interested, the pieces of music is roughly “Birds flew over the spire” by Gary Ryan. You can hear a much better performance by Beatrix Novak here. She’s a better guitarist but we’re better at fixing microphones. 🙂
Our Microphone of the Month is the RCA KU2a, which was one of the earliest unidirectional ribbon microphone.
The KU2a is often known as the ‘Skunk’, because of the distinctive white stripe along the rear of the microphone grill. Marking the rear of the mic may seem a little counterintuitive, but this gave the boom-operator a clear indication of where to point the microphone, aligning the stripe with the actors or other sound source.
Unidirectional microphones were a real challenge for the early film industry because the common transducers of the day were generally bi-directional ribbons, or omnidirectional carbon or dynamics.
In the KU2a, directionality is achieved in a cunning manner. The ribbon is divided into two, with the top half acting as a normal figure-8 ribbon microphone. The lower half is sealed at the rear and is connected to an acoustic chamber, which makes the ribbon behave as a pressure transducer, with omnidirectional characteristics. These elements combine together to give a cardioid directional pattern.
This approach causes a bump in the frequency response at around 5kHz, which is attenuated, to a degree, by use of an RLC filter network, which is housed in the base of the microphone. The manufacturer’s frequency response chart shows the effect of the filter…
The transformer can also contains the inductor for the filter, with a capacitor wired besides it.
Updating an old STC 4033 microphone for use in a modern recording studio.
I have always loved the looks of the STC 4033A microphone, but as far as cardioid microphones go, it might be considered an evolutionary dead end. The 4033A is an example of a dual transducer mic, which was designed back in the 1930s when uni-directional (i.e. cardioid) patterns were needed for film set use, but most ribbon mics were figure-8 and most other microphones were omnidirectional. STC solved this problem by combining both of those elements. The front of the ribbon is in phase with the dynamic capsule and adds to it, whereas the rear of the ribbon is reverse phase and cancels. Add these together in the right proportions and we get a cardioid microphone.
Omni plus figure 8 combine to give a cardioid pattern
At least that is the theory. In practice this works well enough in the mid range but veers away from cardioid at the high and low ends of the frequency range. To compensate, the 4033 has a filter network which rolls off the top end of the ribbon when combined with the capsule. A switch at the rear allows the engineer to select either the ribbon or capsule by itself, or the combined output. (BTW We recently built a few replica 4033 microphones at Extinct Audio – in this case we prioritised tone over pattern and omitted the filter network).
Wiring diagram for STC 4033A microphone
The Western Electric and Altec version of the 639 birdcage microphone, and the Western RA-1142 all used a similar approach to the 4033 , but these mics were soon superceded by other simpler cardioid dynamic and ribbon mics. The dual element cardioid mics were became obsolete curiosities, although they have developed a bit of a cult following in recent times.
I have recorded some great electric guitar sounds with a 4033, with the ribbon softening the tone, whilst the dynamic capsule can add some welcome bite at the top end. The low sensitivity and output level are well suited to louder sources and it doesn’t matter for this application if the mic has a little noise, as the amp noise will always dominate.
There are still some good working examples out there, but, as a jobbing microphone technician, I see a lot of these which are in poor shape and need a lot of work. That is not surprising after 80 years or so – I expect I’ll need a service too when I get to that age! They do tend to be a bit noisy, and they have a low impedance output, with the ribbon and dynamic elements having outputs around 25 ohms, and the combined mode is about 50 ohms. Often these are best used with a matching transformer.
Often the best way to approach a really old mic in poor condition is to do a complete rebuild, rather than trying to fix numerous small problems and then finding others. And that also gives the opportunity to make some changes, so that the microphone is more suitable for use in a modern studio setting. Common problems with 4033s are broken output pins, noisy, stretched or broken ribbons, flaky paint, erratic switches and bad capsules. Luckily the mic on my bench this week had a good capsule, and the other issues can be solved.
For this mic I decided to split the ribbon and dynamic outputs into different channels, bypassing the switch and filter section. Each channel gets its own transformer so that the outputs are both 300 ohms. The output impedances are now the same as a modern Coles 4038, and any good modern mic preamp will work nicely with a 300 ohms source. Adam at Extinct Audio re-finished the microphone for me and fitted new grill cloths, and I added a 5 pin XLR socket to carry the two outputs. Everything was re-wired and the ribbon replaced.
So now we have a modernised 4033 with two outputs, both at 300 ohms, which can be recorded onto separate channels and mixed together to taste. Each channel can be given separate equalisation or compression. I made a couple of recordings to show how this works.
Firstly, a little bit of speech to introduce the microphone and hopefully demonstrate how the two transducers sound, separately and together.
4033-ST Speaking:⬇️
And then some acoustic guitar:
4033-ST Ribbon only: ⬇️ The ribbon element is quite dark.
4033-ST Capsule only: ⬇️ You can hear that this is quite a bit brighter than the ribbon.
If we put those together and get a little creative it can sound like this:
4033-ST Ribbon and Capsule mixed:⬇️
The track above has a little bit of compression and bass cut on the ribbon element (to control my sloppy playing), and a plate type reverb on the dynamic capsule to give it a feeling of space and depth.
The result of this is that we now have a microphone with a sufficently low noise floor to recording gentle acoustic fingerpicking, and the two outputs makes it versatile and opens some creative doorways, such as blending the sounds to taste ands addding EQ, dynamics or effects. One can also pay for a stereo effect. And the ribbon motor and dynamic elements themselves remain unchanged, so the sound is very close to that of a classic 4033A. Best of both worlds? Maybe.
I like this one so much that I am keeping it, but will be offering a few for sale soon as well as upgrades as a service.
PS the guitar music is an excerpt from “Kinkachoo I Love You” by Phillip Houghton.
The ML19 ribbon microphone from Oktava is still a little underrated and I think this is one of the best sounding end-address cardioid ribbon mics.
Based loosely on the RCA BK5, the ML19 has a wider ribbon and is a little warmer in tone with a good bass response, without being overly dark or woolly. It is great for upright bass and horns and any source where you need rear end rejection. It also sounds rather nice on acoustic guitar.
Here is a short acoustic guitar recording I made with a spaced pair of Oktava ML19 cardioid ribbon microphones.
The tune was played (by me!) on an old Levin flat top acoustic with silk-and-steel strings, and recorded into a UA Apollo 8 preamp with 57 dB of gain, using Logic Pro. There was no processing aside from normalising the file. I pointed one mic at the 12th fret and the other at the lower body. However I suspect a crossed pair might sound really good here.
These mics don’t age well and it is worthwhile getting them serviced if that not been done. Generally they need new cables, new ribbon and perhaps most importantly the internal foam should be cleaned out and replaced.
The Lustraphone VR53 was first made in the 1950s and would have been used with either an old reel to reel tape recorder or valve PA system, with lots of lovely background hiss.
The V53 has two (probably) ferrite horseshoe magnets and some rather hefty steel pole pieces, The result is a weak field which conspire with the long ribbon to give a weak, flabby sounding signal. It is a very dark sounding mic even for a 50s ribbon, and maybe for some recordings this is the sound that you need! But for most users the signal to noise and output are too low for our expectations of modern recordings, and the lack of top end limits its use to special effects duties or spiky sounds where you really want to kill the top.
However these microphones are very stylish and it would be nice if they sounded as good as they looked. Fortunately, the VR53 is ripe for modification because…
(a) it is not a very good microphone, so there is a lot of scope for improvement,
(b) it is (still) relatively inexpensive, probable because of (a) and…
(c) it is common so we don’t need to worry about hacking a rare antique. I would not do this kind of thing to an old RCA 44bx
The limiting factor here is really the weak magnetic field. If the field can be increased then the output level and signal to noise will improve and the bottom end response will be tamed a little, giving a less flabby sound. I have posted previously about machining the old pole pieces to make space for some booster magnets. That worked well but milling the old steel parts proved to be very time consuming and so expensive to do, and sometimes the old parts would fall apart. I don’t really like machining ferrous materials here in our workshop because the combination of iron filings and strong magnets can cause trouble later.
Now we have a simpler magnet upgrade which works just as well, or better but is much quicker to fit. Adam at Extinct Audio and I designed some small steel holders to replace the old pole pieces. These are screwed in place and then new Neodymium magnets simply slide into these holders and the magnet upgrade job is done. I measured 6500 gauss in the ribbon gap which is a hefty improvement and is comparable in field strength to something like the Coles 4038. Then it just needs a new ribbon and putting back together – I generally replace any perished rubber parts at this stage.
These microphones were available in different impedances but the transformers were well made. If the microphone has the 200 or 600 ohm transformer then it can be left in place and the microphone will work nicely with modern equipment, although we can squeeze another 2 or 3 dB out with a new transformer. The result is a substantially higher output and signal to noise performance, and more controlled bass response which lets the top end shine through. The new ribbon also helps with the highs.
For comparison, here are two short recordings of acoustic guitar made with the stock microphone with old magnets and ribbon
And here is the modified version at the same gain settings. Be warned this is much dB louder and you might want to turn your headphones down now!
You can easily imagine the product development meeting at AKG back in nineteensixtysomething…
Or something like that. It is certainly true that AKG made some great microphones (too many to list) and a lot of nasty ones (also too many to list). The AKG BX10 and BX20 spring reverbs have become studio classics. And so if any company was well positioned to make a microphone with a built in reverb, it had to be AKG. The result is the AGK BX11, which is a battery powered dynamic microphone with a built in single spring reverb and a battery powered circuit which uses five germanium transistors to amplify the signal and drive the reverb spring.
AKG DX11 echo microphone
There are some major shortcomings to this design. It is impossible to use this as a hand held microphone because the spring just rattles around. The microphone capsule is not great quality, battery life is short and the germanium transistor circuit is noisy. And although the microphone element is certainly not of hi-fi quality, and the spring is ‘boingy’ rather than lush, none of that matters because it is quirky and fun and offers something unique.
AKG DX11 capsule and circuit board
The owner of this one had enquired about converting the mic to run on phantom power, but that was not trivial because the circuit has a positive ground, and I also had doubts over whether we could supply sufficient current with phantom. The output of the microphone of the DX11 is unbalanced 15K ohms or unbalanced 200 ohms.
AKG DX11 spring reverb
I added a small Neutrik 10:1 transformer to drop the unbalanced 15K output down to a balanced 150 ohms*, which makes it a bit more compatible with mic preamps and mixers, and wired to a normal balanced XLR output. The transformer fitted in neatly in the cavity behind the capsule. (*You could use a 1;1 transformer from the 200 ohm output).
DX11 circuit hacks – Click on the image to see a bigger version.
After a bit of initial testing, I came to the conclusion that reverb is better than the microphone, and so, after a discussion with the owner, we decided to fit a line input to the reverb circuit. The microphone capsule itself has a measured output of 250 ohms, so it was easy to hack into the circuit at that point, via a switched mini-jack socket. Now one can run other things into the reverb, such as a better dynamic or ribbon mic, a quiet line input or a guitar via a DI box.
Here is a picture of Adam from Extinct Audio test-driving the DX11 reverb (on the bench) with a Jazzmaster guitar…
