The Electrovoice PL10 is a cardioid dynamic microphone which looks very much like a cut down version of the popular RE20. It has no transformer or filter circuit but it still sounds excellent. These omissions presumably kept the price down.
Just like the RE20, the foam that holds the capsule in place can cause trouble. Over time this can degrade into a sticky pulp and then the capsule becomes loose and rattles around and may eventually destroy itself. This microphone needs new foam and a good clean right away!
The microphone body is in three parts – grill, body and base – which are screwed together and some kind of glue applied. I had to heat the threads and apply more force that I would like to break the glue and get the microphone apart. That was the hard part of the job, and once opened it is easy to remove the foam with a bit of isopropyl alcohol. As always, care must be taken around the diaphragm to avoid damage. The metal parts went into the ultrasonic bath and cleaned up nicely.
Once back together, the PL10 is an excellent sounding dynamic microphone. The PL10 should be a cheap alternative to an RE20, but in fact they are scarce, and prices on eBay and Reverb may be higher than an RE20, which is a bit daft.
Here are some comparison frequency sweeps of the two mics conducted at around 25cm from the source (as usual take with a pinch of salt.)
These old Elctrovoice ribbon mics look great but sadly the sound rarely lives up to expectations.
I have worked on a few of these over the years and there are several things that let these microphones down – happily they can all be sorted out with a bit of thought.
EV V2 clamp with through-ribbon bolt!
Firstly, and perhaps most annoying are the ribbon clamps. EV used thin plastic clamps to insulate the ribbon from the body of the mic, and the ribbon is secured by a central screw that goes straight through the ribbon. The old EV ribbons are quite thick and were supplied with (even thicker) copper end terminals, so that they could just be screwed in place. One problem is that tightening the screw twists the ribbon, pulling it into the side walls of the motor. It also does not make very good electrical contact, especially with a new thin aluminium ribbon. And the clamps are flexible too so the ribbon is not held securely.
New ribbon silver clamp
A better solution is to make new stiff metal clamps. These could be made from plated brass but I tend to use solid sterling silver to avoid the need for a plating process. One clamp must still be insulated from the body of the microphone to avoid shorting out the ribbon.
Rusty old magnet.
The next problem is the weak magnetic field. Replacing the old magnet with a new neodynium one can boost the field around five-fold, which gives a corresponding increase in output. With stronger magnets the steel screws can jump into the ribbon gap and wreck a new ribbon, so it is best to swap the screws out to some brass or stainless ones.
EV V2 transformer.
The old transformers are not great and lack bass but that’s an easy thing to sort out! And finally the old plugs are getting hard to find so we can put an XLR on the rear.
XLR fitted to EV ribbon mic
Voila! With new clamps, ribbon and magnet we have a healthy signal with plenty of bottom end!
Here is a scan of an old Electro-Voice catalogue, probably from the 1950s or early 60s, featuring a wide range of microphones. It includes the multi-pattern Cardak, which appears to have been the flagship model, and the V-series ribbon mics. There is no date on the document, but at this point in time the V1 would set you back US$27.50, and the multi-impedance V3 was $50. The Cardak II would set you back a whopping $75!
In the velocity microphone description I was amused to read that “the woven housing allows the sound to pass through without reflection”. This neglects to mention the whopping magnet located at the rear of the ribbon! All of the dynamic ribbon mics were available in 50, 200, 500 ohm and high impedance models, which reflects the plethora of input types around at that time.
The second page deals with carbon and crystal microphones and accessories. The bottom of the page was uppermost in the box, and consequently is somewhat grubby.
Here’s an early Electrovoice velocity ribbon mic, model V1. These are great looking microphones, but the early versions are rather crudely made and this one, like many others, suffered from low output due to weakened magnets.
The motor of this model is based on a single cylindrical permanent magnet, clamped to a pair of metal plates which make up the pole pieces of the assembly. Because of the positioning of the magnet, the magnetic field is uneven, with a significant difference in field between the top and bottom of the motor assembly. In our example we found that the field varied from around 700 gauss at the bottom to 1000 gauss at the strongest point. This is very low for a ribbon mic, and, along with the oxidised ribbon is responsible for a low, noisy output.
Fortunately, we have sourced some very powerful cylindrical N42 neodynium magnets of a suitable size and shape, which are a perfect replacement for the original weak magnet.
With the new magnet the field is increased by a factor of around four, to about 3000-3200 gauss, a much healthier figure which should lead to an increased output and much improved signal-to-noise performance.
Now it’s time to cut a new ribbon, reassemble the microphone, and do some listening tests. In the meantime, we made a rather attractive bracelet from some of the spare magnets.