DIY "Sidekick" Speaker mic

[bitman]

Hello all,

I am making one of those speaker mics for kick drums and want all the low frequencies to get to my preamp, but block the phantom DC from getting to the speaker. How big a blasted capacitor do you think I should go for and does it need to be non-polorized?

Thanks in advance

:Ron

 

[skipwave]

What about a transformer?

This subject came up over at the TapeOp forum:

http://messageboard.tapeop.com/viewtopic.php?t=45929

 

[adamasd]

Antique electronic supply has a tube output transformer with a 600ohm primary, should work well. Its made by Hammond as a replacement for some old collins gear. Fairly cheap to if I remember correctly.

Edit: Here it is, item number P-T119DA, $18.

 

[Samuel Groner]

I don't quite understand the problem; phantom power is usually switchable and will not do any harm to your spekear if it is inadvertently switched on.

Samuel

 

[SSLtech]

yes. The 48V is between both signal pins and GROUND.

Since you don't connect the speaker to ground, there's no problem, and phantom won't hurt ANYTHING.

Even if the mic cable is wired with a short from pin 3 to ground, the speaker impedance (8Ω perhaps) forms a potential divider with the 6,800Ω resistor, so you get 56mV of DC... which is then 'killed' by the mic pre's input transformer or signal-coupling capacitors. (ALL ofthem have such things, apart from the one which Wayne (mediatechnology) is trying to devise, and hasn't yet built precisely because of the issues with mis-wired cables etc...)

So all in all you're worrying about a problem which doesn't exist.

Keith

 

[bitman]

Ok Thanks everyone.

I guess I shoulda payed better attention.
I hooked mine up using pin 2 and ground.

The mic is hooked to a console and I cannot turn off +48 to just that channel.
But all this is academic if I can use 2 and 3 and not gound.

I bought a Roadmaster woofer tube from Sprawlmart for 19.88.
http://www.walmart.com/catalog/product.do?product_id=5823396

While it's out of stock on the internet, I found some at a superspawlmart in Denver.
I cut in in half, made some rear baffles, loaded a bose 201 woofer in the other half. I'm gonna mount them on old drum stools.

:Ron

 

[SSLtech]

[quote author="bitman"]I hooked mine up using pin 2 and ground.[/quote]
That simply won't work with ANY transformer-coupled console that you plug it into. -And you're lucky it even works at all well with a differential, transformerless input. (unless it uses the 6.8k as a VERY weak signal circuit completion path... either way it's going to be awful compared to doing it right.)

Pins 2&3 will not only grant you immunity from phantom, it'll also give you more level... not that you probably need much of that with a speaker as a source... consider making a pad with a variable front-load impedance (down to a few ohms...) as this will allow you a LOT of control of LF resonance and the 'boominess' associated with these types of mic pickups.

Keith

 

[bitman]

Hey SSLTECH,

You are an angel.

Everyone said speaker mics are HOT and I'd need to pad mine.
I was proud of my soundcraft ultramic preamps cause I did not have
any overload issues using the woofer.

- Now I know why.

:Ron

 

[Guest]

You don't need to worry about a phantom power, put it between 2 and 3 pins, do not ground any end of a speaker; that's it.
I made my kick-drum mics from small globes putting drivers in them. No need for a transformer since output from the speaker is high already no impedance match is needed. However, with a transformer you can get much higher level, but have to worry about transformer's saturation on such low frequency.

 

[bitman]

Globes!

That's thinking way outside the box man.

I'll send pics of mine as soon as it's done (awaiting xlrs from ebay).

Let's see your globe-o-mics.

:Ron