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Contact: larrykillip"*replaceandinsertAT*"gmail.com

NEW!! Flickr slideshow installing a new ribbon in an RCA 77D - click to view lots of "how I did it" pix

ML52 Octava Russian ribbon mic

This is the "Motor' from the Russian Ribbon Mic ML52, these are ribbons I am replacing from original. One has been fitted, the other has just been laid into the channel ready to be tensioned and clamped. Took me several tries and a few broken ribbons before I succeeded, it's brain surgery Jim!. The original ribbons have broader corrugations, these had opened up a bit and both ribbons had gone slack. These new ribbons sound fine now. 

A homemade ribbon crimper, well made by Juerg Oswald from Switzerland, complete with "RCA" branding.

This little thing is called a " Paplin Quilling Crimper Tool " and they're about $12.50 on ebay.

Thanks to Kristof for suggesting this as a crimper

My homemade crimper using "Meccano" gears..rough and ready but it works.

A great Youtube video showing the manufacture of an AEA RCA44 copy.

Some comments/hints below kindly sent from Dave Royer of Royer Ribbon Microphones

Dave Royer wrote:

Our techniques are somewhat different,
but for a "so-so" microphone, like a Reslo, your approach is
perfectly reasonable. The techniques you describe bring back memories. . .
I have a couple of hints, by the way. . .

1. Many less expensive ribbon microphones will profit from a
transformer replacement-- the RCA Varicoustic has a particularly
good transducer and a particularly bad output transformer.

2. If you are familiar with the technique for measuring the resonance of
a speaker, a similar technique can be used to measure the resonance
of a ribbon microphone's ribbon-- that's how you get consistent results.

3. Ribbon microphones will give their FLATTEST response with a load
that is at least five times the nominal impedance of the ribbon-- RCA
specified that their ribbon mikes work into UNLOADED input transformers.

More Comments from Dave Royer:

1. For corrugating ribbons, get yourself a couple of gears
and make a jig so you can pull the strip of foil between the lightly-meshed gears,
like running a sock through a wringer-- this has been the usual way to do the job.

2. With skinny little ribbons, glue ONE END of the ribbon to the end of
a broom straw; then you can poke the broom straw through the transducer
(prop the clamping blocks up with another broom straw) and pull the ribbon through with less cussing.

3.  With a mike like a Varicoustic, with a pot metal case, use THREE wires to
make the connection to the ribbon-- the BOTTOM of the ribbon connects to the output transformer with ONE wire; the TOP of the ribbon connects to the transformer with TWO pieces of wire, connected in parallel.Twist the three wires
together between the transformer and the bottom of the ribbon, then run the two
wires going to the top of the ribbon ONE ON EACH SIDE OF THE RIBBON.
That way, you will get a hum-bucking effect-- with a Varicoustic, the hum pickup
is unacceptable if it is wired the usual way; it is very satisfactory if wired as I suggest.

May 2012 Dave Royer adds:

I need to clarify something. . . It seems like my comment about "measuring the resonant frequency of a speaker" has been misunderstood.  What I meant in my original post about re ribboning microphones was to connect the microphone you are re ribboning in series with a resistor and then feed the output of an audio generator to the microphone/resistor combination so you can monitor variations in the microphone's impedance with frequency. Poking around with an ohmmeter is liable to get you into trouble as a few people have noted!

Information below is from my original page..and is here for reference only

How I replaced microphone ribbons in the past using signwriters aluminium leaf

This article describes how I replaced ribbons in my ribbon microphones using dexterity, patience, a few common tools, and signwriters aluminium leaf. This is difficult material to work with, make no mistake and the results can be unpredictable but if done carefully and probably a few tries, the mic should be up and running as good as it ever was and in some cases better.

Here is my technique for making a new microphone ribbon:

Material:

Obtain some signwriters aluminum leaf, mine was called "Schlage aluminum loose leaf" but many other brands are out there. It is sold by any reputable signwriter's supplies shop. It comes in approx 5" x 4" sheets interleaved with kraft paper. 25 sheets equals a 'book" and one book costs around $10 US. Sometimes this material is also called "Silver Leaf" or "Imitation Silver Leaf". Some Silver Leaf is actually Silver so you need to be sure you get "aluminum".

Here is an online store selling Aluminum Leaf. 

"Richard" emailing from the US informs me:

Richard successfully replaced the ribbon in his RCA Varacoustic MI-6204-C and say's the results were excellent.

Cutting the ribbon, leave kraft paper on        Imparting corrugations                               Or use plastic gears..very gently

Make the ribbon:

Next, take a deep breath, hold it in, do the following and don't let it out till you're done. Also accept you may break ribbons before being successful.

On a small piece of flat glass place one sheet or piece of sheet of aluminium leaf (still sandwiched in the kraft paper it came in).

Take a good look at the mic to be repaired and gauge the width and length of the ribbon. remember the ribbon has corrugations in it so needs to be longer than you think. I always cut mine way over length first up.

With a small steel rule and a very sharp one sided razor blade cut a strip through all sheets (kraft and leaf that is). The size virtually being determined by eye or measure and mark if you can. I go by eye. Usually we're talking about a 3 or 4 millimeter gap. The ribbon needs to be a close tolerance in the gap but not touch the sides. You can slip the ribbon into the gap while it is still sandwiched, and test for fit. Might take a couple of cuts to get right. I cut mine over length.

When ready, get some methylated spirits or isopropyl alchohol and dampen the glass plate lightly, lay the still sandwiched ribbon onto the wet plate. Now very carefully you can peel away the top kraft paper revealing the aluminium. I use a cotton bud also wet with meths  I have had an email from one experimenter who tells me he prefers working with the ribbon dry, so over to you, I find keeping it wet stabilizes the ribbon and I can handle it better.

If you haven't made a ribbon crimper (see pic above) then you will need to find something that has a serration moulded in, something about 15 to 25 corrugations per inch or even slightly less is fine. I use an older camera lens. No matter that it's circular. Original ribbons were passed through a set of gears.

Now for brain surgery! Wet the corrugations with meths, use the wet cotton bud to pick up the aluminum leaf away from the kraft paper left under it (the aluminium will simply cling to the wet end of the cotton bud. Don't sneeze right now!! Now lay the aluminium onto the wet corrugations longitudinally until the whole strip is laying there and fairly straight.

With a soaked (meths) cotton bud gently roll over the strip one end to the other thereby imparting the corrugations into the aluminium. Yes, sometimes I break the strip at this point but if done carefully it works ok.

Prepare the hardware, both ends ready to receive the ribbon. Some mics are adjustable with tiny screw adjustments, make sure there is room to tighten your ribbon with those after assembly. If it is adjustable then it is easy to mount the ribbon as you don't have to get the tension right immediately.

Also make sure the gap and magnets are very clean. Small iron filings cling to the gap and I use plastizine or blu-tack to press into the gap and pull away any clinging filings or debris.

With a soaked cotton bud get the ribbon at one end (still laying on the corrugations) to cling to it and begin lifting it off gently so it ends up hanging from the cottonbud.

Important to clean the connection posts very well as any resistance here will affect the ribbon impedance considerably and reduce sensitivity. I check this later by measuring with my digital ohm meter, should read about .7 ohms +/- .5 depending on ribbon length and material.

Attempt to lay the ribbon very carefully into the prepared gap, trying to lay the loose end across one connection ledge then down through the gap and finally laying the other end onto the other ledge. You must be careful about keeping the ledges wet also so the ribbon can move otherwise it will stick.

I wear magnifying glasses to help me see so I can gently position the ribbon and centre it in the gap. Once centered you will probably need to very carefully drag one end through more or less to get the tension about right. Too tight and you lose all your corrugations, should be about level when laying the mic horizontal, you want to keep it's resonant frequency as low as you can. It can be  loose but with very little sag, certainly not too tight.

By the time you have it in position (if you've made it this far!) you will probably have flattened out the corrugations a little. That's ok, so long as there is still some corrugation left in the strip. 

Clamp both connection ends down and cover the gap with material gauze or similar as soon as possible to stop any foreign matter getting into this precious gap.

Try the new Ribbon:

Try the mic! Remember they always have low output, and if your mic has an output impedance of only 30ohms (as they often did) then consider a replacement transformer. If the mic is worth it then a serious ribbon transformer will also be worth it.

A good transformer can make a huge difference in the quality of a ribbon mic.  This supplier in the US has Lundahl transformers, and the service is very good. The ribbon mic unit is: LL2911     I recommend this transformer! http://www.kandkaudio.com.

If your finished result sounds "honky" then the ribbon is too tight and you're hearing a high resonant frequency from the ribbon.* See Dave Royer's comments above. 

If there is a lack of bass then maybe the ribbon is too loose. There is a method for setting the resonant freq of the ribbon therefore getting the tension right, trust your instincts, a little sag is ok as is a slight flattening of the corrugations as you install the ribbon. it is a question of what kinda looks right will be right. You're trying to get the resonant freq of the ribbon to around 30 - 50hz so that's obviously not a tight ribbon. You can use an audio sine wave generator and feed the signal into the secondary of the mic transformer, observe the ribbon oscillating..especially as it reaches resonant frequency around 25 - 50hz. At some point the oscillations will be most obvious. This is where the resonant frequency is. Watch the Youtube video above for more.

It's ok to do the "light breathe" test, hold the motor with the ribbon in front of your face and very gently breathe across it, observe the flutter, it should be a gentle flutter that doesn't seem too taught. Vague instruction I know but a tight ribbon is obvious and a loose one is too, a just right ribbon is minimal movement each end with a moderate flutter in the middle. It is also well known that the impedance of the preamp used reflects back into the mic and affects the impedance of the ribbon so it is important to use a preamp that suits your mic.*See Dave Royer's comments above

In my studio some mic pre's like the ribbon more than others. I have a small Allan & Heath mixer and the pres on that love my ribbons...but my Presonus ADL600 is not so keen despite it's variable impedance switching. It is well known that a mic pre's input impedance/reactance can reflect back into a passive ribbon mic and affect perfomance. A new trend is for some mics to have a built in buffer amp keeping the ribbon mic internals separated from the outside world. The Cloudlifter does this and is a great way too boost the output of a ribbon mic. I use one often.

You also need to know what output impedance the transformer is, some old ribbons are very low impedance (30 ohms) and some others are high impedance (up to 50k). Either of these will produce a low output into a modern low impedance mic pre which is usually about 200/600 ohms. A real life example of this is the original Coles type ribbon branded as an "STC" is often only 30 ohms whereas the later release as a "Coles" is 200..much more suited to everyday mixing desks and recording interfaces.

I have always tested transformer approx impedance with an ohm meter measuring dc resistance however the following was pointed out to me:

I don't think you should suggest measuring the DC resistance of a transformer with an ohm meter. The DC meter current can leave a residual magnetic field which will cause distortion.
If the core is Mu metal, its magnetic properties can be permanently changed.

Ian DuRieu
The Leon Audio Company

Lundahl transformers talk of degaussing the core after DC measurement, (an old tape demagnetizer??) so maybe there is a way back!

An impedance meter would be best for testing, however not many of us have these things, If your mic is known to be good but you're getting a very low output then likely you have a 30 ohm output transformer.

If you still want to proceed to check the dc resistance of the transformer output first disconnect one of the primary wires to the ribbon or you might damage it. In general a 200ohm impedance will read about a tenth of that as DC resistance. If the transformer output reads 800 to 900ohms or so then it is likely a high impedance output meant to work into a valve circuit. Simple way around this is to obtain a high to low impedance converter, or in the case of 30 ohm outputs (very low) companies like Sowter make a suitable 30 to 200 ohm converting transformer. This will make a difference with a ribbon, matched correctly it will come alive. Ideally the primary should read about .22 ohms and the secondary maybe 20 - 50 ohms dc resistance. Certainly if the output side reads more than say 500 ohms then it's a high impedance transformer. Once again though..bare in mind some mic pres simply work better with ribbons than others despite supposed impedance matching. .

Links:

The Cloudlifter I have one of these and it's great for bringing ribbon or dynamic mics with low output up to a decent working level.

A great article written by Ty Ford, interesting bits of info plus insights into some ribbon mic history. Ty knows his craft, his homepage is well worth a visit.

AEA Ribbon Microphones and parts for RCA Mics - Wes Dooley

Royer Microphones

Build your own Ribbon Mic Do-It-Yourself Ribbon Microphone tutorial by Rickshaw records. Excellent article for a very small fee guiding you all the way, plus links to materials required.

Check out Bob Crowley's (Crowley & Tripp) blog