One of our readers sent in these photos of an unidentified ribbon mic motor. It looks like an attempt at a cardioid pattern, with the magnet and transformer located behind the ribbon. Presumably the original mic was a circular, end address arrangement.
If you recognise this or have any further information, we would love to hear from you.
Thanks to David for sending this in.
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.
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| 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”.
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| 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!
Here is a tube microphone that we put together for Jørn Christensen of Rodeløkka studio in Oslo, Norway. Jørn wanted a steampunk vibe… and that’s exactly what he got!
The good old BBC have made many of their research and development reports available through their website, spanning 1944 through 1996.
1945
The Crosley ribbon velocity microphone.
1953
Lustraphone VR53 ribbon microphone
The design of the PGD and PGS ribbon microphones.
The EMI microphone Type 2351E.
Tannoy microphone Type MD. 422.
1956
Design of the PGD and PGS Ribbon microphone Part 2
1958
RCA BK5
1961
Reslo RB
1965
Beyer M160
(Thanks to Santiago Ramos for sending the links.)
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| Failed magnets in a T-Bone microphone |
The coating around the magnets had peeled away, allowing the rare earth magnets to oxidise and expand. This process of course destroys the ribbon too. The magnets can be replaced, but may not be worth the expense.
I have seen a few microphones that look like this, and the worrying aspect is that it seems to happen spontaneously, possibly because the coating on the magnets was not of high quality, or perhaps they were scratched or cracked on installation.
Nearly all manufacturers now use neodynium magnets for their microphones, and I fear a epidemic in the future.
April has been hectic! We have been repairing microphones, installing a new coil winder, and developing some new & exciting products. And suddenly it is already the 30th and just time for a very brief MOTM.
This month’s mic is a beautiful and very old French LEM ribbon mic, probably from the 1930s….
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| Very old LEM ribbon mic |
Inside, it is very similar to the smaller Amperite ribbon mics, with a large fibreboard frame supporting the ribbon, and a pair of (rather weak) magnets behind.
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| Old LEM mic deconstructed |
The mic has a classic design, with brass sides, a folded steel grill and a cast steel yoke. These solid-sided microphones look strange now, but I guess the thinking at the time was that figure-8 microphones didn’t pick up sound (or reflections) from the sides, which allowed for a very simple construction. The ribbon itself is positioned right at the front next to the grill, with a metal plate across the magnets at the rear, so there is some attempt at making the mic more directional.
The transformer had failed due to insulation breakdown, but with new magnets, a fresh ribbon and repaired transformer, the mic has a reasonable output and nice vintage tone. And it looks great!
Cadenza ribbon microphones are quite common, but there seem to be more microphones than there are connectors for them. The mics were originally supplied with an integrated stand & connector, which was ideal for desk recording, but not very effective for hanging over a drum kit.
The XLR has the added advantages of making a good earth connection, and also gives a way of mounting the mic on a stand as it can be slipped into a standard mic clip. I think elongating the base makes the look more elegant too.
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| 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!
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| 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…
1. 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.
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| 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…
Black labels
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
Red Labels
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
We have just installed a second Meteor ME307 coil winder at Xaudia, for rewinding ribbon mic transformers, pickups and making new parts.
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| Meteor ME307 with electronic controller |
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| Marvin the paranoid android from the original TV series of Hitchhiker’s Guide to the Galaxy |
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| Marvin the Meteor coil winder |
Marvin even has a brain, although perhaps not the size of a planet. It has more sophisticated controller than our existing Meteor winder, which just has manual controls and a foot pedal. The newer model has preset adjustable ramp, speed, idle, and also a reverse wind setting, which is very handy and removes much of the human element from the winding. Let’s hope he isn’t bad tempered like his namesake !
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.”
