Friday, January 11, 2008

How is in charge of buying your toner?

If you work in an office or business like we do, you are bound to get cold callers trying to sell cleaning services, wall to wall carpet, financial advice, local magazine advertising, and, our "favorite", toner for copiers.

Every call center in Mumbai seems to have our number and wants to sell us toner, which we use little of. We pay very little attention to it and try to get off the phone and back to mic making as soon as we can. It has been busy! But we did take a time out to look at two imported Chinese ribbon microphones a company wants to sell to us: One is the ubiquitous lollipop style you see everywhere with that "head" shape like a D-104. That one is under $30 in quantity and the quality reminds us of the Argonne mics that the Japanese used to make. They were very inexpensive and looked pretty neat, and they did put out sound.

The mic you see here being tested in front of the Hofner is one of those very familiar pill shaped ribbon mics you see all over ebay, except this one has a 12AX7 in it, and an outboard power supply. The design is simple, and uses a small transformer into the grid of one half of the tube (the 12AX7 is a dual triode), then another transformer out. Pretty cool for only $100 in quantities, we thought. But the sound is, well, like a very boomy, hard room, though the noise isn't bad. I think this explains why this particular model isn't being seen much these days. You get a lot to play around with though: A nice case, a power supply with filament, bias and enough B+ to give you a shock, a suspension mount, two cables, and of course the mic, which is delightfully easy to take apart by unscrewing the bottom. I think I could make a ham radio transmitter out of it!

It would be easy to get sidetracked into fiddling around with these mics and they do seem to call for significant mods. We also get asked by others to modify these mics and put in "the good stuff", but we have to explain that it isn't worth putting a hemi in a Yugo. My sister-in-law once had a Yugo. I was quited amused when she and her mother pulled up the drive in this minimalistic conveyance, which she said "won't do over 60, but it seems fast". As I recall, it was a light yellow color, which was somehow appropriate.


Anonymous said...

How about a close up?

Bob Crowley said...

Of the Yugo? Or do you mean the mic? Click on the image for a pretty hi res closeup of that mic.

go3daudio said...

Looks a lot like the standard Chinese R84 knockoff, with the metal plate covering what appears to be the same motor assembly. Is it?

Bob Crowley said...

It's like the ML15 (I think that's the one) at least. I haven't taken aprart an 84, but I did see a picture of it open once and thought it was derived from the Russian ML15 or similar, with that 8-shaped motor.

In any case yes, this is the exact same as the Nady etc. types. I'm serious about doing something with that power supply. Even though the B+ may only be good for a few mils, it should be possible to make a modulated oscillator with some RF output. I think that would be a lot of fun.

The plates are designed to be combined acoustic resistance and high frequency resonators. I think a lot of people misunderstand how they are supposed to operate. The acoustic resistance is like a high pass filter, and the resonator corrects for high frequency rolloff if it is positioned correctly and has the right geometry. All that is moot in this design. I have one of the Nadys which is very dark and veiled sounding, not a very transparent mic. One thing it has going for it is the hf rolloff which can really make a harsh horn sound smooth. This has that same sound but a big boominess even at a distance. The ribbon seemed about OK so I assume it's in the amp or transformers.

Larry Killip may have one of the very old Russian mics. I cannot remember if it was the ML15 or another model.

Stay tuned for a new release at NAMM.

go3daudio said...

In my tests, stripping out all the "blast protection" (screens, plates, extra basket) around the ribbon assembly had a much greater effect on the low frequency response than on the high frequency response. I expected the opposite to be true.

Bob Crowley said...

Right - An acoustic resistance in the near field acts like a high pass filter. In other words, it doesn't do much to the high frequencies, but it does attenuate the lows. Olsen discusses this at length in his book "Acoustical Engineering". In it, he develops equivalent acoustic circuits comprised of resistance, capacitance and "intertance", and uses these in various configurations as series elements and as phase shift networks. If you study Olsen and Chladni together, you can start to get a feel for why certain violins, drums or guitars, for example, sound the way they do. Microphones behave in similar ways, just on a smaller scale.

Bob Crowley said...

It's spelled


bad typign skills herre

Bob Crowley said...

Did it again!!??! yikes


it seems once the mistake is learned, it cannot be unlearned. Inert, like my head is today. Must be due to NAMM. Not being there is mind numbing.