Mic solution for a (very) small church

Jon Fairhurst · September 12th, 2009, 09:55 PM

Quote:

Originally Posted by Mike Demmers

So the question is - shall I start it or do you want to? (to avoid duplication)

Go for it. I've got too many minutes of picture to compose to over the next few days...

Jon Fairhurst · September 27th, 2009, 12:22 AM

Quote:

Originally Posted by Rick Reineke

...Maybe you could use this Rapco in-line variable pad w/mute, but then you would need a battery-powered lav with an XLR, and attach some kind of belt clip..

Rapco Variable Pad with Mute Audio Signal Conversion at Markertek.com

So, I've received the AT803, built the cables and have the Rapco CVPBLOX...

The good news is that when the Rapco is at full volume, you can pull/push the knob and mute with only a slight signal bounce. It's usable.

The bad news is that when the Rapco is at less than full volume, the signal bounce is loud - lots of boom and click.

The other bad news is that the potentiometer is noisy. I shouldn't be surprised, as it's on a mic with -40dB or so sensitivity. It's okay when untouched, but you can hear the pot sweep as you turn it. At least it's mostly hiss, rather than crackle.

The Rapco is better suited for a line-level signal than a mic signal, and might even be too noisy at line level.

We will try the mic out in the church tomorrow...

Mike Demmers · September 27th, 2009, 09:11 PM

Quote:

Originally Posted by Jon Fairhurst

The bad news is that when the Rapco is at less than full volume, the signal bounce is loud - lots of boom and click.

The other bad news is that the potentiometer is noisy. I shouldn't be surprised, as it's on a mic with -40dB or so sensitivity. It's okay when untouched, but you can hear the pot sweep as you turn it. At least it's mostly hiss, rather than crackle.

That is a phantom power mic, may I safely assume that you are not using that, and are using the battery instead? And if you are using the battery, I wonder if that mic could be putting some dc on its outputs.

It sounds like there is DC across the pot to me.

There are pots in mic preamps, they do not HAVE to be noisy.

Perhaps isolate both sides of the pot with caps and bleeder resistors. And a much higher value resistor right across the pot.

-Mike

Mike Demmers · September 27th, 2009, 09:47 PM

Buy a cheap mic splitter transformer. Normally these have a primary conncted to the mic, and two secondaries to go to two different mic preamps.

Connect the mic to the primary as normal. Connect your mic preamp to the first secondary as normal.

To the second secondary, connect a pot roughly equal to the imput impedance of your mic preamp (about 2400 Ohms) in series with a 300 Ohm or so resistor (to protect the mic output from what could be a virtual AC short). You could also put a switch across the pot for mute.

This would guarantee no DC across the pot, maintain the CMRR, and probably provide noiseless operation. The only danger might be the load on the mic output, I would check its rating and adjust the fixed resistor to protect it - the voltage and current levels are so very very low it is hard to imagine them blowing an output stage, but better safe than sorry. It probably does not have to allow the mic output to go completely to zero, which would be safer.

I have not tried this, try it at your own risk. Just another idea that is very inexpensive.

-Mike

Jon Fairhurst · September 28th, 2009, 11:08 AM

Thanks Mike,

Yes, I had phantom on during my test on my mixer. At the church, phantom was off, and it worked great. The potentiometer is still a bit dirty, but usable.

Previously, I had used a borrowed cardioid lav and had mounted it too high on the shirt. With the AT803 omni mounted a bit lower, it worked well even with the look-up-look-down while speaking from notes. Sure, it gets louder when she looks down, but her direct voice projects less, so things balance out.

I had to get a bit more aggressive on EQ cuts to nip all of the feedback, and in the end there was no resonance at all, and everything we clearly understandable, if not as flat as I'd like. My original plan was to buy components, including a 31-octave EQ. Instead, I got a great deal on a powered mixer with speakers and cables that I just couldn't pass up, but the EQ is only 7-band.

Anyway, thanks everybody for your help!

September 27th, 2009, 09:47 PM	#19
Mike Demmers Regular Crew Join Date: Jan 2009 Location: Portland OR Posts: 159	Here is another idea Buy a cheap mic splitter transformer. Normally these have a primary conncted to the mic, and two secondaries to go to two different mic preamps. Connect the mic to the primary as normal. Connect your mic preamp to the first secondary as normal. To the second secondary, connect a pot roughly equal to the imput impedance of your mic preamp (about 2400 Ohms) in series with a 300 Ohm or so resistor (to protect the mic output from what could be a virtual AC short). You could also put a switch across the pot for mute. This would guarantee no DC across the pot, maintain the CMRR, and probably provide noiseless operation. The only danger might be the load on the mic output, I would check its rating and adjust the fixed resistor to protect it - the voltage and current levels are so very very low it is hard to imagine them blowing an output stage, but better safe than sorry. It probably does not have to allow the mic output to go completely to zero, which would be safer. I have not tried this, try it at your own risk. Just another idea that is very inexpensive. -Mike

September 28th, 2009, 11:08 AM	#20
Jon Fairhurst Inner Circle Join Date: May 2006 Location: Camas, WA, USA Posts: 5,513	Thanks Mike, Yes, I had phantom on during my test on my mixer. At the church, phantom was off, and it worked great. The potentiometer is still a bit dirty, but usable. Previously, I had used a borrowed cardioid lav and had mounted it too high on the shirt. With the AT803 omni mounted a bit lower, it worked well even with the look-up-look-down while speaking from notes. Sure, it gets louder when she looks down, but her direct voice projects less, so things balance out. I had to get a bit more aggressive on EQ cuts to nip all of the feedback, and in the end there was no resonance at all, and everything we clearly understandable, if not as flat as I'd like. My original plan was to buy components, including a 31-octave EQ. Instead, I got a great deal on a powered mixer with speakers and cables that I just couldn't pass up, but the EQ is only 7-band. Anyway, thanks everybody for your help! __________________ Jon Fairhurst