|Reslo PR ribbon microphone|
Here are a bunch of scanned information sheets published by Reslosound for various dynamic and ribbon microphones in their range.
He discusses several vintage models in his collection, including RCA KU3, Coles, Melodium 42Bs and a nice mention of our upgraded Reslo Beeb ribbon microphones. Here are Marc’s words about the Reslos.
It’s always great to see and hear how our customers use the microphones we send out.
The recording in the video/sound clips is just the Beebs, no other mics at all, and just a touch of EQ and compression. It is an impressive result from just two microphones. Of course, you need a good kit as well as good microphones, and being a great drummer helps too!
Here are some further sound clips from Joe.
Pop duo Layla Lane kindly shared their video of their cover of ‘In My Life’ by the Beatles, which which extensively used a Reslo RB microphone with Xaudia’s ‘Beeb’ upgrades.
The guitar, piano and all the vocals were recorded with the Beeb connected into an Ampex 350 preamp and Urei 1176 compressor. You can read more details about the recording at their youtube page.
Layla Lane are Heday Ikumo and Valerie Stern, who together have written music for Coca-Cola and Mello Yello commercials, recorded a song for the Ashton Kutcher film Killers, toured Japan, and produced/wrote songs for big Japanese artists such as Sunplaza Nakano-kun and Yoko Oginome.
Thanks to Saro Tribastone for sharing his band Cordasicula‘s new album Aria ca Spira.
Cordasicula come from south-east Sicily and are inspired by the traditional music of their own island, as well as the southern Italian regions of Calabria, Campania and Puglia.
Saro explained to me that “all these styles, mainly defined by their rhythm, are coming from those areas where 2500 years ago we had Greek people living there, globally known as Magna Grecia (Big Greece).” Their songs are a mixture of original compositions with some traditional tunes, and collectively they have a beautiful, haunting and slightly melancholic quality.
Many of the instruments were recorded with one of our customised Reslo ‘Beeb’ ribbon microphones. The Beeb was used to record the Greek Tzouras, violin, cello, double bass and Battente guitar for the album. For those who like technical details, they were tracked through a DAV BG1 preamp and Mytek Stereo 192 ADC converter. It is nice to hear the Beeb working so well with these traditional acoustic instruments. Here is a photo of the Pier Paolo Alberghini playing double bass, with the Beeb microphone up close to the sound hole.
Marilena Fede’s voice was recorded with an AKG C414B, again using a DAV BG1 preamplifier.
Saro has kindly allowed us to share the Spotify playlist for the album, which should appear below.
I have said many times before that we have fantastic, creative customers, and it is always nice when someone takes the time to share what they are doing. Sometimes their stories are amazing!
Here’s a video clip of James playing his drums and skins, recorded using two of our Reslo ‘Beeb’ microphones as top & side mics in a Glyn Johns arrangement, along with a CAD M179 in cardioid in front of the kick drum.
I think these really do sound fantastic, with a classic yet contemporary tone. I could imagine these sliding very easily into a mix without need for much processing.
Here’s a new video of our friend Jose Estragos from Spain, using his Reslo RVs in his song ‘Buscandote’.
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.
Here is a scan of a ‘manual’ from 1973 for the Reslo MR1 ribbon microphone, which was the successor to the popular RB model.
I say ‘manual’ – really it is just two sheets of printed A4.
Reslo are of course best known for their ribbon microphones, particularly the RV and RV models, However, it should not be forgotten that over the decades they made many dynamic microphones, and even some condensers too.
|Reslo VMC with base station|
The earliest Reslo dynamics seem to be the VMC and VMC2, with the initals standing for Velocity Moving Coil. These had a big heavy permanent magnet and a paper diaphragm, and are really rather lo-fi devices. These two models are more or less the same inside, although the VMC was hard-wired, and the VMC2 had a new grill and an output plug.
|Reslo VMC2, with output connector.|
In the late 1960s Reslo made a range of more modern light hand-held dynamic mics. The UD1 used a Japanese-made capsule which sounds rather good, of comparable quality to the Shure mics of the era. I have seen transformerless 200 ohm models, and also a dual output 30 & 600 ohm version with a transformer in the body to convert the impedance.
|Reslo UD1 microphones|
The UD1 was apparently used by Bob Dylan at the 1969 Isle of Wight festival! Here is an advertisement scan from the Reslosound blogspot….
The advertising also mentions a high impedance model, although I haven’t come across one yet.
Some of the UD1 mics were hard-wired to the cable, and it was also supplied with a Reslo connector, and later a 3-pin din plug, with different impedance options available through the different pins. They are wired like this, with one side of the capsule and transformer primary wired to the output socket.
In addition to the UD1, there was a short stubby version that used the same components, and would often have been used with a gooseneck adapter. Pictured below is also a smaller dynamic mic for use with a tie clip.
These models appear to have been replaced in the 1970s by the Reslo Superstar range, which were essentially the UD1 with an updated body and grill. The Superstar was supplied with a DIN plug – I have converted this one to XLR.
|Reslo Superstar 80 dynamic mic.|
SJT, May 2014
Like all of our ‘Beeb’ mics, this features an upgraded 300 ohm output transformer, new ribbon and XLR socket. This special edition as well as a switchable high pass filter inductor to balance the proximity effect when used close to sources.
The custom camouflage colours makes it suitable for undercover operations, and even better for guitars and drums!
Our Microphone of the Month for April is this rare oddball from Reslosound: the NC-RB.
This was Reslo’s attempt at a commentator’s lip microphone, and appears to be cobbled together from spare RB parts. The upper body and head are from an RB, but the head is rotated through 90 degrees and screwed to another chopped-down head. The lower body-stroke-handle is a straight aluminium tube with a switch which terminates in a normal Reslo output socket.
Inside the head is a rotated RB-style motor. The magnets face the speaker, to provide some pop protection for the ribbon at the rear.
Behind the ribbon I found this metal baffle, which should control the pickup pattern and tweak the frequency response. There is also fibre glass and felt wadding for more protection.
Overall it is a strange little mic. The ribbon runs horizontally, which is generally considered a bad plan as, if it sags, it will droop into the metal pole pieces. They must have been a way of producing a lip mic without the expense of re-tooling for a completely new design. I have only ever seen this one, although I know of a customer who owns another.
What does NC stand for? “Not a Coles”, perhaps?
This batch now have their own metal badge, which looks great. In addition to the usual chrome and hammertone mics, we also have some rather smart looking black microphones, which have a tough powder-coating finish.
The sound is still the same 🙂
When I plugged it in, the mic gave a very lo-fi sound – even more distorted than one would expected for this era. On investigation, there were some metallic particles sticking to the diaphragm, preventing it from moving freely. The paper cone had also become detached from the diaphragm.
|Diaphragm from a Reslo VMC2|
|Reslosound VMC2 magnets|
|Reslo VMC with base station|
For comparison, here is a Reslo VMC with announcer’s base station. Note the difference in the grill, with five horizontal slats, as opposed to three vertical.
This one is labelled RVH – the ‘H’ means high impedance output.
I have also seen and serviced RV models with a Philips badge.
|VOX badged Reslo RB|
The common Reslo RB models were also sold under the VOX and GEC brands. This Vox mic is identical to the Reslo badged model, apart from the badge.
|GEC badged Reslo RB|
The GEC mics are painted black and given the model number BCS 2378, but it is simply a Reslo
We have just shipped this rather lovely set of Reslo microphones to Thomas at Le Lupanar Studios in Belgium. He will be recording a brass section with two of our ‘Beeb’ Reslos, and a pair of upgraded cardioid Reslo CR mics on goosenecks.
His studio is still under construction but Thomas has been making a photo diary of the project – from the pictures so far it will be an amazing facility in a great location! How’s this for soundproofing…
Good luck with the building, and we will watch with interest as it all comes together.
|Reslos at St Peter and St Paul Church, Kimpton|
Organ recording with Beeb Reslos – Andy Wright.
The recording was made with the mics plugged straight into a Tascam DR100 mk 2 and recorded in wav mode, then compressed to mp3 in Soundforge.
In the eighties and early nineties Hyperion Records used the organ to record classical music, including string quartets, piano solo and the Kings Consort doing The Four Seasons. Eventually Luton Airport, about 8 miles away, got too busy!
The Reslo RB mics are perhaps most famous for being used by the Beatles in their Cavern Club days. As a young photographer, Andy was assigned to one of their early gigs, and here are some of those photos at the Daily Mail website.
|One of Andy’s photos of the Beatles|
The MR1 was an attempt by Reslosound to re-invigorate the classic RB model for a 1970s market, whilst trimming down the cost of manufacturing parts and assembly.
|Reslo MR1 and RB models|
The MR1 (left) has the same format as the RB, with the ribbon element and magnets housed in a tilting head attached to a cylindrical body that contains the transformer. The grills are now flat, rather than domed, and the custom pivot screw is replaced with a standard hex socket bolt.
|Reslo MR1 and RB|
The MR1 still usesd Reslo’s custom 3-pin connector, and still makes ground contact through the body only. One assumes that this was to ensure backward compatibility with their older mics and cables, but it seems like madness that they did not take the opportunity to switch to using XLR connectors, which were very well established by this time.
The classic stamped brass badge on the RB is replaced by a printed foil sticker that hides the join between the barrel of the mic and the cast base of the pivoting head. The sticker shouts ‘Reslo MR1’ – note that it no longer says ‘Reslosound’ – in a very trendy 1970’s style font, with fattened letters typical of the era. I am also 1970s vintage, and the label reminds me of watching programmes like Magpie on TV in my childhood!
|Magpie – classic 70s font!|
The ribbon and motor assembly (top in the picture below) is exactly the same as the RB, but the transformer is smaller. Over time, better understanding gave rise to alloys with higher magnetic permeability, enabling smaller transformers to be made with the same inductance properties. The RB mics used a EE24/25 size core (pictured below the motor). The MR1 has a narrower body and a smaller transformer marked 4414.
|Top to bottom… Reslo MR1 motor, transformers from RB, MR1 and Xaudia|
Xaudia, as you might expect, make a suitable replacement transformer (bottom) for upgrade and impedance matching duties. 😉
Compared to the RB, I see very few MR1s, and can only conclude that they were not a great success. By the 1970s, good dynamic mics were becoming the first choice for home recording, and professional recording studios would probably favour condenser microphones for many applications. Reslosound Ltd. disappeared sometime in the 1970s, and this must have been one of the last models that they produced.
|Reslo RV ribbon velocity microphone.|
The RV was one of Reslo’s earliest ribbon microphones – possibly their first production model, although I am not sure if the UR series came before or after. They share parts so it is hard to pin down which one came first.
|Inside Reslo RV mics|
The two mics shown have the same frame for the ribbon, but the magnets are very different. I believe the mic on the right to be the earliest RV design, or at least the earliest I have come across, and it uses a single cast magnet with quite a complex shape.
|Reslo RV magnets|
The mic on the left uses two simple horseshoe magnets at the top and bottom, attached to a pair of metal pole pieces, and this really sets the style for all subsequent Reslo ribbons – later models have three magnets but use a similar layout.
The UR model has a similar construction but has a rear mounted transformer. This is effectively blocking the pickup from the rear of the mic, giving it a more cardioid pickup pattern. It seems likely that ‘UR’ stands for Unidirectional Ribbon, although I have not seen any documentation to support this.
|Reslo UR magnets and rear-mounted transformer|
But the story doesn’t end there. Many of the RVs that I have worked on have a later, smaller motor which is essentially the same as found in the RB model. Keeping common parts with the later models must have kept costs down.
|Reslo RV mics with different motors.|
Until very recently I had only ever seen 30 ohm versions of the RV and had assumed that they were all low impedance. However, the one on the left, which came in recently, has a high impedance transformer, and measures around 6.5K ohms with the original ribbon.
Reslo mics don’t have serial numbers or dates on them, so it is hard to make a definitive time line for the development, and always if you have any further information we would love to hear from you.
Reslos are best known for their ribbon mics, but they made some dynamics too.
|Short, stubby and dynamic – The Reslo PGD|
The PGD appears to be made of leftover parts from the RV ribbon mics. The base of the mic is the same, complete with swivel mechanism, and the grill looks like a cut down version of the RB too. As usual it uses the annoying Reslo plug.
|The head on the RGB could be tilted for best pickup of sound.|
|Reslo PGD – aluminium diaphragm|
Like many early dynamics, it has a pressed aluminium diaphragm, which is heavy and stiff compared to later polymer film designs. Consequently has a quite lumpy response. Here is a frequency plot for one mic – other examples may differ!
|Frequency sweep for Reslo PGD mic.|
Here is a scan of the manual for the Reslosound LMT series of line matching transfomers. If you have one, it might be useful! Many thanks to Lee Ackerly for sharing this.
Edit: link fixed 2nd March 2014
When home recording with reel-to-reel tape machines was a popular hobby, back in the 1960s and 70s, many recorders had only high impedance inputs. However, the low impedance microphones of the time could be used with a longer cable without signal degradation, and so most manufacturers offered matching transformers to plug that gap.
Other transformers were also available to match medium and high impedance microphones to low impedance inputs, and so on. But the Low-to-High is by far the most common.
Here is a scanned manual for the Reslosound LTU1 line matching unit, which was used to connect 15Ω to 50Ω ribbon microphones to a high impedance tape deck. This was superseded by the LMT, which is essentially the same thing in a smarter metal can.
|Reslo impedance matching transformer.|
|The Incomparable Ferrograph brochure|
The Fostex printed ribbons are rather odd microphones, using a membrane with a metal track suspended in a magnetic field to generate the signal. Although they have a natural figure of 8 response, their sound is more like a moving coil dynamic than a ‘true’ ribbon microphone.
This one was probably once used as a donor mic to fix a broken one – it arrived without a capsule assembly.
|Fostex printed ribbon mic|
Sadly, Fostex UK were unable to supply a replacement part, so for now at least it has been converted into a Frankenphone ribbon mic.
I used a spare ribbon frame from a Reslo mic, with a pair of small neodynium magnets glued to the frame, which gave a field of around 6000 Gauss (normal Reslos are around 4000 gauss). The new ribbon assembly fitted neatly into the old mount, needing just two strips of foam to hold it in place.
|Fostex transformer and switch unit|
The Fostex transformer and filter switch were still present, but were designed for the Fostex printed ribbon capsule, and are unsuitable for a ‘real’ ribbon microphone. I wound a custom 1:34 transformer for the job, which works nicely. The mic has a full range output and sounds pretty good!
|Reslo SR1 studio ribbon microphone|
The advertising at the time claimed 30Hz to 20kHz – although doesn’t qualify that with a dB range.
|Reslo SR1 (top) and RB microphones|
Extra sensitivity comes from using a longer ribbon and an extra magnet, and the mic is consequently about 1/3 as long again compared with the more common RB. By necessity the SR uses a different ribbon frame from other Reslo microphones. The mic below came complete with its original fibreglass stuffing – which protects the ribbon, damps any ringing of the shell, but seems to muffle the sound a little.
|Inside the Reslo SR1|
|Reslo SR1 output connector|
The RB microphones are quite notorious for grounding problems, as the mic body is only grounded through mechanical contact at the plug. The SR1 deals with grounding in a better way. The output socket has a hole drilled in the centre with a small wire pushed down and soldered to one of the lugs (see photo, by the green wire). When the mic is reassembled, the long screw that secures the connector makes firm contact with both the mic body and the central wire, giving a good solid ground. This works well, and I now use this approach to ground troublesome Reslo RBs too.
|Reslo SR1 transformer, being re-wound|
|winding arrangement for SR1 transformer|
The SR1 was available in both 30/50 ohm and 250 ohm versions, and used the same laminations and bobbin as the later RB transformers, but with a more sophisticated winding configuration. The SR1 transformer has a 5-winding construction, with two primary windings alternating between three secondary windings.
Thanks to David Pumple for sharing photos and information. The SR1 advert is from http://reslosound.blogspot.co.uk/.
Xaudia have a limited number of Reslo RB microphones for sale, with upgrades and modifications inspired by the BBC. We call these “The Beeb.”
|‘The Beeb’. Modified Reslo microphones by Xaudia|
They recommended a number of modifications, which included….
Xaudia have recreated these mods and added a few more of our own. “The Beeb” has an XLR output, and new 1.8 micrometer ribbon. We also ultrasonically clean these before re-assembly to remove 50 years of gunk. And we put a (removable) sticker on them, so you know that they are 300 ohm mics.
|Reslos with XLR upgrade|
We have a very limited number of these mics for sale. Alternatively we can upgrade your own mic to these specifications. Please get in touch for details.
Those who follow this blog may have noticed a certain amount of Reslo-related activity….
|Xaudia R-series transformers – Reslo upgrades & repairs|
Our new Reslo upgrade transformers are the result of this work. They are made here in our workshop in York, UK using high quality German laminations and teflon insulated silver plated lead-out wires.
They outperform the original Reslo units in terms of resistance noise and frequency response, giving less noise, an extended bottom end, and better impedance matching into modern equipment.
Primary DC resistance 22 milliohms.
Primary Inductance >620 µH at 1KHz, >2.0 mH at 100Hz.
Frequency range <20Hz to >65 KHz.
Ratio 1:32 (available in 1:12 to 1:40, as required).
Some Reslo RB mics have a transformer with a split secondary that gives the owner the choice of either a 30 ohm or high impedance output. Often these mics get dismantled and rewired, so here is where the internal transformer wires go….
For a 30 ohm output, yellow is the ‘hot’ output, and should eventually end up at XLR pin 2. White is cold, and goes to pin 3.
The green wire should not be grounded, but this sometimes happens by accident if the plug uses one of the pins for ground. The result is a high impedance path to ground from the output, which can act as a filter and give a weak output and weird frequency response.
Last month I wrote a post discussing reslo microphones with red and black labels, and spent some time describing the transformers inside. Since that post I have measured more transformers, and the larger data set is beginning to show some definite trends.
|Transformers from Black label mics – type 10202|
Perhaps the most revealing transformer characteristic is the primary inductance. The DC resistance is also important in terms of noise, but seems pretty consistent across the measured transformers – usually around 50 mΩ for the primary and 1.2 ohms for the secondary. DC resistance should depend on the thickness of the wire and the number of turns used for the winding, and this seems to be common to the transformers although occasionally the leads may become oxidised.
Measuring the inductance is a little hazardous as it is dependent on the frequency at which the measurement is made. For most of the transformers I have measured at 1kHz and also 100 Hz, but the first few were just measured at 1kHz. The inductance at 100 Hz is usually around 3 times that measured at 1KHz.
The graph shows the measured inductances at 1kHz and 100Hz when available (circles). The transformers marked with crosses were just measured at 1kHz, and the 100Hz value extrapolated from behaviour of the others.
Another way of looking at the transformer data is the relative cut-off frequency (fc) – the ribbon and transformer primary winding form a high pass filter. Assuming the ribbon has an impedance of about 0.3 ohms, then we can calculate fc. We use the value measured at 100Hz as this is closer to the frequencies of interest.
The transformers have a wide range of inductance / frequency values, but fall broadly into two classes. All but one of the transformers from the black label microphones show fc values of between 20 and 50Hz, whereas the red label ones have a much wider spread. About half of the reds are very similar to the blacks, but the others have a much higher fc value – between 70 and 110 Hz.
Many of the black label transformers are marked “10202”, and are occasionally painted in blue, pink or purple. These are sometimes found in red label mics too. The transformers with lower inductance have a ‘sandwich’ of laminations with darker ones in the centre, and these are often marked “SE 4402”.
|SE 4402 type Reslo transformers|
So it seems that we are somewhat closer to the truth about the red and black Reslos. The black ones are more consistent, and have a better chance of having a deeper bass response. Some of the red ones are just like the blacks, but about half the reds have a different, lower inductance transformer. These were probably designed for speech, and are not inherently better or worse than the others. However, if you are trying to record the lower frequencies of a bass instrument, or a fat electric guitar, then you may feel that the mics with the lower value for fc are more suited to the task.
We have spare 10202 black label transformers in stock, and also make replacement full range 300 ohm transformers for Reslo RB mics. So if your Reslo doesn’t sound up to scratch, then get in touch!
|Red and black badges on Reslo ribbon mics.|
Are black label Reslos better, or even different from red ones?
There is a rumour that occasionally appears on the internet concerning the relative merits of Reslosound RB microphones. Some of the mics have red labels, and others have black ones, which has led to speculation that the mics must be different, and one type must sound better than the other.
Normally it is stated that the black badged ones are better. Most rumours have some basis in fact, so let’s investigate!
|Reslosound RB microphone dissected|
Over the past couple of years I have serviced around 50 Reslo mics, with both colours of badges. Here are some of my empirical observations…
The black ones are less common than the red ones, but they are by no means rare. I don’t have exact figures but perhaps 75% are red, and 25% black. I will be keeping note from now on!
Edit 29/11/2013: I wanted to correct this figure as I have seen it regurgitated on ebay a couple of times. Having seen a hundred or so more since I wrote this, I really can’t say that one is more rare than the other. I would probably guess that they are equally common.
2. There are at least three styles of red badges from different periods.
3. Some later mics (red and black) have a white plastic ribbon holder. The older mics have black bakelite holders. This should not affect the sound.
Recently, I had seven 30/50 ohm Reslo RB microphones on the bench, and I took the opportunity to examine the transformers. Although the basic construction is the same, the transformers are quite different in looks, and have different inductance values! Some have a striped core with two metals, the middle often being darker or rusty, suggesting a higher iron content.
|Reslo transformers (left to right) A, B, D, E, F|
Impedance and resistance values
This is hardly a statistically significant data set, but here goes…
A. Lp = 0.463 mH, Rp = 84 mΩ, Ratio = 1:12, fc = 103 Hz (purple)
B. Lp = 0.434 mH, Rp = 56 mΩ, Ratio = 1:12, fc = 110 Hz (pink)
C. Lp = 0.470 mH, Rp = 56 mΩ, Ratio = 1:12, fc = 102Hz
D. Lp = 0.533 mH, Rp = 52 mΩ, Ratio = 1:12, fc = 89 Hz
E. Lp = 0.204 mH, Rp = 63 mΩ, Ratio = 1:13, fc = 234 Hz
F. Lp = 0.214 mH, Rp = 63 mΩ, Ratio = 1:13, fc = 223 Hz
G. Lp = 0.454 mH, Rp = 49 mΩ, Ratio = 1:12, fc = 105 Hz
Where Lp is the inductance at 1KHz, and Rp the DC resistance of the primary winding.
The mics are supposed to be 30 to 50 ohms output, and so from the ratio we can estimate the impedance of the ribbon and transformer itself to be around 0.3 ohms. The ribbon impedance and transformer inductance form a high pass filter, and so we can calculate the frequency, fc, at which the bottom end response drops away.* This handy tool means that we don’t have to get out our calculators.
* It must be noted that the inductance of a metal core rises and frequency drops, so the cut-off frequencies will in reality be somewhat lower than these values. However, they should be comparable to one another.
What we can say for now, from our very limited data set, is that the three black label transformers, and two of the red ones, have substantially higher inductances and lower cut-off frequencies than the other two red ones. This difference in bass response is likely to be what some users hear as ‘better’. However, it cannot be said that a red label mic always has less bass response than a black one.
The two transformers with purple paint have higher values than the ones with pink paint!
My feeling is that the later Reslos have ‘better’ transformers than the early mics, and that the colour is more cosmetic than diagnostic. But I shall keep adding to this list as more Reslos come into the workshop, and it will be interesting to see what trends develop.
And finally, if you are reading this and once worked for Reslo (or Grampian), we would love to hear from you.
Update 12 May 2012…
In 1961 the BBC R&D group studied the Reslosound RB microphone and recommended that the transformer be replaced with one of higher inductance. It seems plausible that the later Reslos were revised to use a different transformer following that study. You can read the BBC report here.
Stewart Tavener, Xaudia, First posted 24 April 2012, Latest update 12 May 2012
Pete Gardiner is a singer/songwriter and acoustic guitar player based in Newtownards, Northern Ireland and his new album ‘Songs at Sunset’ was produced by Paul Steen, who used a Reslo mic on the vocals alongside a Shure SM7b.
Paul bought one of our Xaudia upgrade transformers for his Reslo RB ribbon microphone, to give the mic an output of around 250 ohms. Paul fitted the transformer himself and used Ward Beck preamps for the recording. Paul said….
“I recorded with the reslo and an sm7b but the final edit ending up being 99% reslo. The sm7b is heavily compressed and dialled in on occasion for choruses etc.”
This is the ‘official’ wiring information from the Reslo RB brochure…
As you can see, different models had different wiring conventions and required different colour coded cables. This can cause confusion, particularly if the mic has been separated from its original cable in the 40 or so years since manufacture. The most important thing is to check the mic and cable wiring and make sure that they match!
Unfortunately, grounding the mic by connecting the cable screen to the body of the plug does not work well, and these mics are prone to hum. For the low impedance models, it seems sensible to use pins A and B for the balanced output, and pin C for ground. The ground must also be connected to somewhere to the body of the mic and/or to the shell of the cable.
The dual impedance models are particularly problematic, in that pins B and C were used to select either low or high impedance output. This means that if one pin is used as a ground then one part of the transformer will be grounded and some of the signal lost. It is therefore important to disconnect the high impedance leg inside the mic and rewire to match the cable.
I found this ribbon / magnet / motor assembly inside a Reslo RBL microphone…
..which is very different from the usual Reslo motor design.
I have never seen this type, and I don’t know if it is an attempt by Reslo to upgrade or modernise the old design, a transplant from another make of microphone, or a good quality DIY repair job. It remains a mystery!
This little dinosaur sculpture was made out of waste winding coils, stripped mostly from old Reslo and other microphone transformers. 🙂
So why are we stripping transformer coils?
Some older ribbon mics were originally wound for 30 or 50 ohm output impedance, and tend to give a low output level when connected to modern recording equipment.
Many of these low impedance mics, including Reslo and Tannoy ribbons, can be rewound for a modern 200 or 600 ohm input, raising the output to a more useable level, and avoiding noise from having to crank up the preamps.
|Bobbin from Reslo transformer with secondary winding removed.|
The old Relso 30/50 ohm transformers have an inner (primary) winding consisting of just 12 or 13 turns of thick (0.8 mm) enamelled wire, and a secondary winding of 152 turns of 0.4 mm wire. The thick wire of the inner winding ensures that the primary resistance is low, which keeps noise to a minimum.
|Reslo transformer rewound for 600 ohm output|
Re-winding the transformer involves removing the outer winding from the original transformer and replacing it with sufficient turns of a thinner gauge to reach the desired turns ratio and output impedance. Usually the original primary winding can be kept in place. The transformer is then reassembled and dipped in wax to fix the windings and lams in place.
This makes the microphone much more usable in a modern studio – transformers can be would for 250Ω, 600Ω or any other desired output impedance.
This week we have been building lots of little transformer moxes to match vintage 30 ohm ribbon mics to modern mic preamps. Correct impedance matching can deliver a +12 dB increase in level without noise penalty or loss of frequency response, which is welcome for many older microphones. Here is how a Reslo RV microphone behaves with and without the transformer:
|Frequency response plots for Reslo mic with and without an impedance matching transformer|
They are suitable for many old microphones including the following:
Another typical day at the Xaudia studio & workshop…
Outside the studio …. flowers, blue sky and cows.
And inside, in the basement workshop…. a Reslo production line!
We see a lot of these little British microphones. The original ribbons are quite thick and have an unusual ‘square wave’ corrugation. Very often these have oxidised and become noisy, and after 50 years they usually benefit from a clean and a fresh ribbon.