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Mic pre-amp for music interruption?
Mic pre-amp for music interruption?
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Old 16th December 2017, 03:28 AM   #1
patterrr is offline patterrr  United States
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Default Mic pre-amp for music interruption?

I'm a newbie, been reading / searching these forums a lot for the last week but haven't yet found an answer so thought I'd post.


I've got a "portable" outdoor audio system for music that's much like what you'd find in a car - a 12V battery, a head unit, line level to amplifiers, and speakers. In addition to using this for music, we'd like to use it for PA. What I picture would be a mic pre-amp box that sits in the middle of the line level connection, so that when the microphone is used the music would be cut out. Something like this:


Head unit ----RCA Line Level----->Mic Pre-Amp Box---RCA Line Level--->Amp ----> Speakers

Most ideally would be the style of microphone used on a CB or HAM radio, where it's handheld and you push the button on the side of it to activate the microphone. Also, ideally the box would be powered by low voltage DC rather than line level.


I don't really know what to call it, but I've tried Googling everything I can think of, but can't find such a product. Any pointers?


This is my first post, so a little background: I'm an electrical engineer, I tinker with audio systems occasionally such as car audio and whole house audio, but know nothing about PA. I'm looking for a simple off-the-shelf solution rather than building something myself, if possible.
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Old 16th December 2017, 09:00 AM   #2
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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I would and have in the past, used an MC3340 and either drive it with a push switch or detect the audio from the microphone after the pre amp, rectify it and feed the DC to pin 2 of the MC3340.
When you speak, it will attenuate the music.
Obviously power will be required to supply the pre amp and MC3340.
Data sheet is here http://www.applelogic.org/files/MC3340.pdf
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Old 16th December 2017, 10:26 AM   #3
turk 182 is offline turk 182  Canada
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this might fit the requirements:ST-ACR1M ‐ Microphone Level Audio Controlled Relay - 0.5 to 5 s delay
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Old 17th December 2017, 02:52 PM   #4
patterrr is offline patterrr  United States
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Thanks for the responses. I'm leaning towards the MC3340 because it can be powered by our 12V system, while the ST-ACR1M would require a boost converter or inverter since it's 24V.


For either case, any suggestions for a 12V or lower voltage microphone pre-amp?
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Old 17th December 2017, 03:19 PM   #5
patterrr is offline patterrr  United States
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Another approach I could take is using a cross-fader, bit it would need to be a very simple knob (we don't have space for a mixer, and need it to be super user-friendly). Something like this: Amazon.com: PAC LC-1 Remote Amplifier Level Controller: Car Electronics


But instead of a volume control, it would be a cross-fader with two sets of RCA line level inputs (one coming from the music source, the other from the microphone pre-amp), and then RCA outputs to the amp. Any idea if such a product exists?
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Old 18th December 2017, 11:10 PM   #6
MAAC0 is offline MAAC0  Portugal
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Patterrr


Yes it exists and is called a simple mixer. A dual volume pot one wired backwards would do the trick. Put a resistor after the viper on each pot before the summing point. Try 10k for the pot and 1K for the resistors. RCA music goes to one pot, RCA mic to the other.


Passive Audio Mixer W/ Channel Volume Control: 6 Steps
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Old 18th December 2017, 11:19 PM   #7
patterrr is offline patterrr  United States
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Quote:
Originally Posted by MAAC0 View Post
Patterrr
A dual volume pot one wired backwards would do the trick.
Thanks for the advice and the link. From how I read your description, it sounds like you'd have one pot to fade out the music, and another to fade in the microphone, right? If possible I'd like one knob to do both. The article talks about "double-ganged" pots to do both left and right channels; is there such a thing as a "quad-ganged" pot so that I could get the cross-fade effect?


Any advice on a somewhat low-cost 12V or less microphone pre-amp?


Thanks!
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Old 18th December 2017, 11:30 PM   #8
patterrr is offline patterrr  United States
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Actually (after doing a simple Google search...) I think this is the exact 4-gang pot I want for a stereo cross-fade, right?PTD904-1020K-A103 Bourns | Mouser
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