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N1NKM's
Ribbon mic page 3 |
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HOMEBREW ribbon microphone GAMMA
Others in this series:
ALPHA UNIT (Page 1)
BETA UNIT (Page 2)
DELTA UNIT (Page 4)
Latest updates: 1/6/07
Beta unit modified. Preamps on both the Beta & Gamma units upgraded with low-noise transistors & a few other component changes/additions. (At some point, I will split this page into two or three seperate pages. Stay tuned!)
1/1/2007
A third unit has been constructed, and used on-air. (Gamma Unit)
Reports are that it sounds BETTER than my D-104!
It sounds quite good in the headphones, as well!
Scroll down, down, down....
12/27/2006
Beta unit preamp upgraded. New transformer in Prototype, now called Alpha unit.
Both are awaiting low noise transistors.
GAMMA UNIT!
(Best audio quality, by far!)
| Gamma unit ribbon (motor) front |
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As you can see, this unit is quite small! (Quarter for scale.) Also notice that this ribbon is not even corrugated! I tinkered with it, trying various tensions, and it sounds the best with the tension such that the resonance is below normal voice frequencies. (I'm guessing maybe less than 30Hz.) The thing that is so amazing, though, is how incredibly GOOD this thing sounds! I used it on the air via the "Alpha Unit"'s preamp and original transformer. I've just constructed a new preamp for this, which will be the GAMMA UNIT when fully completed. (More pics of the complete unit are coming later.)
| Gamma unit ribbon back |
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Notice that the copper foil connection tabs are simply MELTED INTO the small plastic frame. :) That frame is a small bracket used to mount mini-blinds to a window frame. ;) This unit also uses magnets salvaged from a dead computer HD. These are different, in that this magnet structure uses 4 discreet magnets. They have a small gap between them, but each piece has uniform polarity facing the ribbon! This is the best configuration, and may explain the drastically better audio quality!
In both views, above, you can see the seperate magnets. The ribbon only passes between the "lower" pair. The upper pair is simply unused.
Here are pics of the new preamp. (It has yet to be used on-air. I just wanted to get this online ASAP!) The input transistor is standing way above the rest, because I'm going to replace it with a low-noise unit as soon as I can.
| Gamma unit preamp front |
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(Click pics for large view. Use browser BACK button to return here.)
| Gamma unit preamp back |
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This preamp is the same schematic as the Beta unit. The twisted wires coming off the transformer connect to the copper foil tabs on the "motor" unit.
The two transistors to the left in this photo have been replaced with the low noise units, which are in small metal cans.
| THE GAMMA UNIT V1.0! |
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Here it is! The Gamma Unit... the GOOD-SOUNDING one! If you heard me on the air New Year's Day, 2007 (or after) talking on my HOMEBREW RIBBON MIC, then THIS is what you heard. :) This is the unit that sounds better than my D-104, according to several reports. :) It is fed through the AGC unit you see below. The PTT button is on that board. Eventually, I'd like to get a footswitch or other box with the button on it, and mount this mic to some kind of stand. For now, it works nicely if I hold it nice and still. :)
The Gamma Unit now has the low noise transistors & V2.2 preamp. It sounds better with less noise! :)
Ribbon Mics AGC Unit
| AGC amp for ribbon mics |
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No schematic, yet. It uses an LM1458 (dual 741 op amp) and an LED/Photocell for the AGC cell. (It's the thing wrapped in black tape.) The transistor drives the LED. Parts are "hanging in space" as I was still refining this thing when I took this pic. The trimpot sets the bias to the transistor, which affects the maximum possible gain. More bias = more leight (at idle) from the LED. More light = less gain. That's how the AGC works. The more signal, the brighter the LED, the more the gain drops, to keep the output fairly constant. :)
I've pretty much abandoned this project, so I have done no additional work on it in some time. Sorry... no schematic. I may scrap this, and start from scratch with a TLC272 preamp, instead. I was also tinkering with a tube-based AGC, but haven't touched that in some time, either.
"Stay Tuned!" ;) There's still MORE TO COME!!
(I will keep updating this page as I make progress with these units. Check back often.)
Others in this series:
ALPHA UNIT (Page 1)
BETA UNIT (Page 2)
DELTA UNIT (Page 4)
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