There’s a mystique around ribbon microphones due to their being expensive studio-grade items, which has led more than one experimenter down the rabbit hole of making one. [Catherine van West] has posted her experiments in the field, and it makes for an interesting read.
The recipe for a ribbon microphone is very simple indeed — suspend a corrugated ribbon of foil in a magnetic field, and take the voltage across the ribbon. But that simplicity hides some significant issues, as the foil is much thinner than the stuff you might roast your turkey under. Such lightweight foil is extremely fragile, and the signwriters leaf used here proved to be difficult to get right.
Then when the microphone is built there’s still the exceptionally low impedance and small voltage across the ribbon to contend with. The choice here is a transformer rather than a FET preamp, which surprised us.
The result is by all accounts a decent sounding microphone, though with some hum pickup due to difficulty with shielding. Should you give one a try? Maybe not, but that hasn’t stopped others from giving it a go.
One wonders if a second loop of wire in series, wound “the other way” aside/above the ribbon could act as a “humbucker”, cancelling the magnetically picked up hum.
Somebody else wonders if a current amplifier would be more cost effective than an $80 transformer feeding a voltage amplifier, but I don’t see where anybody has tried that. I’d also see what a cheap transformer with a one turn added primary would sound like.
You’re right that a low impedance input amplifier is preferred for this application. But a current-feedback amplifier is generally better known for high speed than low noise. Is there one you have in mind that would perform better in this application than, say, a LT1028?
Hams put audiophiles to shame with Thier power cords
filters on the power cords might actually help. Nothing excessive but the usual 20 turns on ferrite might help.
They would be fine for filtering out RF interference (cell phones for sure), but not so good for 60 Hz fields.
60 and 120 Hz notch filter on a power line should be enough to attenuate most of mains hum, at least for typical home usage scenarios.
A 60 Hz filter on the power line would do a good job at attenuating the actual desired power too.
You’re right of course, I thought she said noise got in through the mains, not that mains hum was the main concern.
Have to say I skimmed the article, it looks great but that website layout is a… Choice.
This is very cool
I wonder if I can make something similar with the copper tape I have lying around. Feels like it just might be too thick
I am thinking more along the lines of the paper backed aluminium foil that you can find as a wrapping for gum sticks, some candies, and cigarette packets. It can usually be peeled off with ease, but maybe it’s possible to keep the paper backing on for creasing and then remove it with water or alcohol?
I played with gum stick aluminum foil when I was a kid and made car models (I used it for automotive “chrome”); unfortunately, I don’t remember how I removed it from the backing. Today, this sort of material is commercially available, metal and thickness unknown: https://www.megahobby.com/products/original-chrome-bare-metal-foil.html
What a relief to find a link to an actual write-up, and not a godforsaken made-for-clicks video!
So many things to comment on the build, but I will just note that her reference to Horowitz & Hill is spot-on. They say why a FET preamp is not suitable for super-low input impedance like this, why a bipolar input amp is better (lower noise at low impedance than a FET), and why a transformer (as she uses) is even better (better impedance match yields better SNR).
Doubleplus cred points for using a Lundahl transformer.
In college 20+ years ago the radio studio had a 77DX microphone. Then it makes you sound on air is so distinctive I can pick one out easily to this day listening to broadcast radio. I’d be at least $1 the NPR studio still uses them for some stuff.
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Honestly they sound a bit muffled to me but it warms my heart to hear. I went to an alumni event recently at the station and the same exact microphone was still in use. I don’t know when they got it but It’s entirely possible it’s been in continuous use since the 60’s. Maybe they are “fragile” but considering how hard college kids were (are?) on the hardware that’s really saying something
Sounds like they’re pretty fragile.
https://mynewmicrophone.com/differences-between-dynamic-condenser-ribbon-microphones/
I just read most of that linked article and thought of a possible improvement to ribbon mics:
If I understand correctly one huge downside is that there’s only “one (half?) turn” of wire moving inside the magnetic field leading to “very low electrical levels” (too lazy to properly formulate that part).
What if the wire ribbon would instead consist of many wires connected in series through static connections outside the magnetic field.
Basically a strip of ribbon paper with lets say 10 parallel electrical conductors on it and 9 wires outside the magnetic field connecting those 10 parallel strips in series (plus the two primary connections).
Now if the ribbon moves you get 10 times the output compared to single conductor ribbon mic.
I’m sure there’s some combination of carrier material and conductor that would work – from paper to kapton tape and from enameled wire over aluminum foil to vapor deposited or painted silver or something.
Congratulations. You’ve just described a moving coil dynamic microphone, but with a more complicated geometry and poorer flux and conductor utilization.
Right. One wonders why one can’t go optical though.
Quantization. Photons are noisy purely through counting statistics. If you try to get enough of them to get good counting statistics and low noise, then you have a thermal problem.
Whoa! moving coil dynamic & ribbon microphones work on/with the same fundamental physics? What a surprise.
You know, moving coil dynamic mics are just speakers – so lets ditch all the mechanical and sound sensitivity differences and shit all over it…
The reason she’s having so many interference issues is because it’s a 3d printed case with absolutely no shielding. The screens on ribbon microphones are metal, and the cases metal, for a reason. Shielding matters, a lot, for audio.
I don’t understand how someone so supposedly versed in electronics, audio, etc. could miss this.
I have a pair of birdcage mics. I even reset the ribbon in one that was bent and weak and now they both sound identical. Touchy! Wonderful for my deep voice. As for the RCA 77’s in an NPR studio, WBAA had em but they had to go when NPR pressed a uniformity edict on member stations. One particular mic must be used by all stations. Gone are the voices and the mics that made radio great, now it’s whiny over modulated kindergarten-teacher-talk with generous amounts of vocal fry. Make mid-Atlantic great again.