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Passive Summing Mixer for Low / Medium Impedance Microphone
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Author:  dennismbird [ 28 May 2017, 20:22 ]
Post subject:  Passive Summing Mixer for Low / Medium Impedance Microphone

To expand on the topic statement;

I have 2, 600 ohm XLR microphones. I want to build a passive mixer. The mics both came with an XLR to 1/4 cable. I'd be using those cables to go into a battery operated PA for busking. The PA only has 2 1/4 inputs, So I'd like to make a summing box to merge my vocal & ambient instrument mics into one output, and use the remaining PA input for my piezo pickups for my guitar.

So mainly, what values of potentiometers & resistors would be best for the project. I'd like to have as little loss of signal as possible without detriment to sound quality.

My first thought was to google schematics, but most seem to be of 500k pots and 50k-ish ohm resistors. My initial thoughts while posting are to use 10k pots and <10k resistors. But I really dont know. I have a good quantity of different 1/4W resistors on hand of varied values to choose from, but I'd need to order the pots off amazon and am very unsure of the values to order, aside from knowing I want linear.

Thanks.

Author:  Geek [ 29 May 2017, 09:26 ]
Post subject:  Re: Passive Summing Mixer for Low / Medium Impedance Microph

Hi,

dennismbird wrote:
I have 2, 600 ohm XLR microphones. I want to build a passive mixer.....
.....
.....I'd like to have as little loss of signal as possible without detriment to sound quality.


That isn't happening :(

I used to tech for a local band and without some sort of active summing, you're losing a good deal of something.

Our solution was a little old Radio Shack battery mixer on the stage and it met the criteria. I'm sure there's plenty of options at your local Long & McQuade or the like.

In the tube mixer days with 1Meg input impedances, this was possible. But modern SS inputs have 10K input impedances for the XLR lines, which means using a 10K pot or so. Then you have the summing point which is another 10K. So right away you're losing a good 6dB each line at max volume.

If you have a "Parts-Express Special", it'll probably have a 2.2K or 4.7K input-Z, compounding the problem.

Make and model of your input board may be of help? Also, is phantom power needed?

Cheers!

Author:  dennismbird [ 29 May 2017, 09:36 ]
Post subject:  Re: Passive Summing Mixer for Low / Medium Impedance Microph

Geek wrote:
Hi,
That isn't happening :(

I used to tech for a local band and without some sort of active summing, you're losing a good deal of something.

Our solution was a little old Radio Shack battery mixer on the stage and it met the criteria. I'm sure there's plenty of options at your local Long & McQuade or the like.

In the tube mixer days with 1Meg input impedances, this was possible. But modern SS inputs have 10K input impedances for the XLR lines, which means using a 10K pot or so. Then you have the summing point which is another 10K. So right away you're losing a good 6dB each line at max volume.

If you have a "Parts-Express Special", it'll probably have a 2.2K or 4.7K input-Z, compounding the problem.

Make and model of your input board may be of help? Also, is phantom power needed?

Cheers!



I'm using Pyle Dynamic Mics, 600 ohm.
I'd be using a portable karaoke unit for busking in the streets. It's a Pyle as well It comes with a 600 ohm mic that I am not going to use as it is much cheaper than my cheap mics I already own.

Again, I will not be using an XLR connection / preamp and going straight to 1/4 jacks which expect to receive cheap karaoke mics.

This is just for street busking; so although as a musician sound quality is important; as a gear carrying human batteries and extra wires are a detriment. Being able to plug and go, trumps crystal clarity.

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