Monday, December 14, 2009

The latest project, complete.

Not bad for stuff I had laying around, and a lot of eyeballed measurements and hand-tooling.

What is it? A desk mic converter to use with a PA system. The particular microphone that was in mind has a switch, but it's inconvenient... mount it here, plug in and plug the stand into the amp, and the black pushbutton is a momentary on switch. Fully internally shielded but without caps, it may ping a little on active/release but that's ok, it's a PA mic after all.













This was made almost entirely "from whole cloth" btw. The only prefab items are half a walmart craft plaque, a cast-off mic clamp, and the lid to a canister of tea. Well, and the switchgear of course... but the neck started as a piece of aluminum angle trim, and the bottom cover was bent and trimmed by hand.

I like it, honestly. Looks a little unusual due to the brass 'muffin' but that was a necessity as the switch was too long to mount flush in the base, and that was a quick'n'dirty solution. Neck's not perfect either but looks very organic... I bent that up in the small vise and hammered/filed away until I was happy. It's only painted because the metal was soft enough to scar up a little.

4 Comments:

Blogger The Tarquin said...

Damn, nice work! The audiophile in me is aching to know what kind of system this is going to be hooked into. What kind of amp are you going to be running it through? What kind of mic do you plan to use?

Do you have a particular PA system in mind that you need a mic for, or are you just just building one in case a mic-less PA system ever wanders your direction? :-P

But seriously, awesome work. It looks good, and the overall finish is particularly impressive for using found/off-shelf parts.

1:04 PM  
Blogger Dr. StrangeGun said...

It's for the PA system at the range... if I can get the wire run before the end of the year.

Nothing special... I eBay'ed an old 'Champion' (I think) 100W single channel PA amp and I've got two 6.5" two way outdoor weather resistant speakers to hook to it. I don't have the specs in fron tof me but they're ~93db/1w/1m so that amp should be able to provide for around 112 decibels without taxing things too much. It'll be around forever too, it's a good old two stage class A with huge honking transformers and no capacitors in the output path, everything's inductance matched. Those transformers somehow manage to pump to the point where it'll run a good 10-15 seconds after power interruption, and slowly taper off to nothing.

The mic is a freebie, cheap old multipurpose Ratshack hi-Z with an 1/8" plug on it (hence the jack and socket). Sounds good enough though.

I did discover a problem with my build though... threw everything together and discovered that you can play buzz-theremin on that can lid, it gathers enough RF and there's just enough ungrounded signal path in the switch body to make it buzz when you get within 1/8". Touch the base at the same time and it stops... if I felt like it, a piece of aluminum foil on the inside of the hole for the cap and touching the inside of the base would be enough to get it perfect, but it's not a bad enough problem for the effort.

The finish on the mic arm is steel-silver appliance epoxy paint sprayed in a too-cold room, then rubbed to get the loose stuff off and turtle-waxed to avoid any more powder shedding. The base is craft-store gloss acrylic paint, which worked WONDERFULLY and I'll be keeping some of that stuff around permanently. The cap... came that way. All I had to to was be careful to not collapse it when I press-fit it into the base.

The cable was a compromise, the longest stretch of anything I had was some 58 ohm shielded line off of a length that I think at one time in the 80's had BNC connectors on both ends and shuttled signal between test equipment. Good wire, given the age that stuff was expensive and it shows. Tinned ground strap, foil underlay, REAL teflon internal insulator, nice soft central conductor that doesn't break for bending it around to solder...

7:33 PM  
Blogger Roberta X said...

Very fine!

WV: gypertia. Insulating material from the 19th Century?

7:11 PM  
Blogger drjim said...

Kinda has a nice SteamPunk look to it!

3:49 PM  

Post a Comment

Subscribe to Post Comments [Atom]

<< Home