My $5 DIY Tube Mic!!!

Howdy Folks, I thought I would share a small Project that I did today durring a couple hours of free time and inspiration that I had.....

I had a Bunch of cheap Electret elements laying arround and some 6418 Sub Mini tubes from a Project that I never started so I thought I would see if I could make a Tube mic out of them useing the body of an old Dynamic that I killed....

Here are a few Pics of the mic and the Curcuit (slightly modified version of someone elses design)...



The Mic has a very nice nice warm sound with a very detailed low end but the high end is a bit lacking probably because of the crappy capsule.... I am actually very pleasantly surprised that this $5 in parts makes such a nice sounding mic and with a better quality capsule it sould sound much better....
The mic has an extremely hot output so you don"t need hardly any gain before clipping so a 10db pad switch could be probably added pretty easilly....Also the Transistor I used was the BC550C but Others could also be used .....

The PCB is only 1.5in x 1.2in and should fit in the body of most regular mic bodies but could also be redesigned to be smaller, PCB design isn"t my strong point....

So if anyone needs a useable Tube mic that can be made for about $5 in parts this is a Pretty good and easy project to do and it is probably one of the only tube mic designs that run off of +48v Phantom power.....


Cheers

Interesting!

Yeah, this is pretty neat. I pieced together the schematic from your PCB, so I think I have it right that the 4k2 resistors are for a condenser element with an internal FET. Is that right? And what is the max voltage for the mic element that you are using?

Hi , Yes the Capsule connects to the 4.2k resistors and the Capsule is Unmodified so it has an Integral fet , I"m sure the curcuit could be changed to work with a Linkwitz modded capsule or with a fetless capsule, I just wanted it to be small enough to fit in my mic body with the fewest parts....

I believe the Voltage at the Capsule is about 3 or 4v, It could be raised by lowering the Value of the 4.2k resistors.....Most electrets I believe have a max Voltage rateing of 10v....

I"m sre there are a Lot of Mods that could be done to improve this curcuit but I just wanted to get it to work before I worked on any Improvements...I was also thinking about makeing another one useing other non working Dynamic I have but this time trying to use the Dynamic capsule as well as the electret capsule and put a switch in to change between a Tube Dynamic mic or a Tube condenser mic....I have never heard of a Tube dynamic mic before but that doesn"t mean it wouldn"t work or sound good so I think I will try it, Maybe this time I will use a Bigger body which will give the the space so i can use all film caps and improve the curcuit a Bit.....

Cheers

which capsule did you use? the panasonics have very detailed top ends..

It wasn"t a Panasonic WM61 or anything good like that....It was actually taken out of a Toy that was used as a Listening device, It was like $1 at the Dollar Store...I think it might even be a Cardioid capsule because I get a Proximity effect.....

I actually have some better capsules arround somewere but I will have to dig them out somewere but when I do I will try them out in this mic....


Cheers

That;s cool!
I was thinkin (always a dangerous prospect) you could mod that into a piece of spyware. Battery operated with a TX chip.
But who would want to do something as highshschool as that?
Unless there was money involved, like in the big D, and I don't mean Dallas.

Whats that blues song I heard today?

"I Think Your Husband Is Cheating On Us"

:razz:

Can you post a sample?

This is probably a stupid question, but could this circuit be used with a polarized capsule so that you can modify the pattern like HV tube condensers? I guess you'd have a 24-0-24 type polarization or something?

[quote author="blandman74"]Yeah, this is pretty neat. I pieced together the schematic from your PCB, so I think I have it right that the 4k2 resistors are for a condenser element with an internal FET. Is that right? And what is the max voltage for the mic element that you are using?[/quote]

Can you share the schematic? Any time saved drawing schematics is time I can spend building gear!!! Thanks!!!

Here it is. I suggest minion weigh in on it, in case it's wrong.

Hi, Here is the actual schematic:




I"m sure there is a way to mod the design for regular Condencer capsules that require a Higher Polarizeing voltage but since I don"t have any I didn"t try it.....

It is a Pretty simple project and only takes me a couple hours to throw one together....

Cheers

Yep, yours looks better. But it seems like the PCB has pin 4 of the tube connecting directly to the element *through* the 4.2k, and not like you have it in the schematic. Actually your schematic looks correct, so could there be an error in the PCB?

Yes, It could be an error on my PCB, But the PCB Works so I guess that it is not a critical error.....

I have to re-design the PCB anyways because it is a Bit small to fit into some of my Mic bodies so I will probably make the PCB much thinner but longer so it fits better but this time I will make sure I don"t make that mistake again....and thanx for pointing it out....Like I said PCB design Isn"t my strong Point, even though I have designed a LOT of PCB"s, This is probably why about 30% of my Projects don"t work properly (PCB mistakes).....

If any of you Build this mic please tell me your impressions of it....


Cheers

would love to try this with a panasonic i have laying around. anyone suggest a revision for that capsule?

thanks

I redesigned the PCB in case anyone want to use it....



The PCB is now 0.86 in x 2.6 in so it should now fit a lot better in even the thinner Mic bodies.....Also the error is also corrected....

I found a couple Panasonic WM61-AY Capsules arround so I am going to try to build one tonight useing this better capsule....


Cheers

would anything change schematic wise using that capsule? if not ill try tonight too.. point to point though as im not very good at double sided etches.

thanks

it's not a double sided etch. It's parts layout on one. The bottom one is what you would etch from...

Well This isn"t a double sided etch, The one pic is of the Copper layer and the other is just the stuffing guide so you know were what parts go and what there orentation is....

The curcuit will work with any 2 terminal Internal fet Electret capsule, So allmost any Electret capsule will work without any mods to the curcuit...

It might work with a Capsule that doesn"t have a Internal fet like a TSB165 or a TSB2555A but with a lower output....I might try Modding a Capsule tonight and see if I can get it to work with a Linkwitz modded capsule....

Cheers

PS: Pin 1 of the Tube is at the top(by the 47k resistor) and pin 5 at the botom(off of the 100r resistor) on this new layout.....

cool thanks, yeah should have looked closer. i found these tubes for a buck a piece. gotta buy 10 though http://www.piexx.com/index.php?main_page=product_info&products_id=33 most places are 13 or more each!!

thanks again!