Want to build a simple microphone mixer

[MikeHolmes]

I'm new to diyAudio, so I'm not even sure I'm posting in the right forum. I've come up with an op amp-based design for a 4 or 6 input microphone mixer, and I'm looking for any tips on the design. I'm attaching a schematic.

The mic input stages are differential amps with 40 dB gain, and these are combined in a summing stage with unity gain per channel. For the microphone level output, I'm planning to use a Jensen transformer, the same one that's used in DI boxes.

I didn't use any caps in the design. Should there be a blocking cap before the summing stage, or maybe before the transformer?

Is the overall gain appropriate for a mixer with mic-level output? Any ideas will be appreciated.


Thanks!

 

[sreten]

Hi,

Your mixer or this :
Behringer Xenyx 502 Mixer at Gear4Music.com
What would you choose ?

or this :

or this for 4 balanced mic inputs :

rgds, sreten.

Yuor a lot better off buying and then modding if quality really matters.

 

[nigelwright7557]

I would put a capacitor after r9 to r12 otherwise you will be amplifying any dc offsets.

I don't know about the inputs, it depends if the mic's give out any dc offset.
I have always put coupling capacitors on the inputs and outputs of my mixers.

 

[counter culture]

Google 'differential amplifier'

 

[nigelwright7557]

Google 'differential amplifier'

Whoops sorry forgot to add about adding a resistor to make inputs differential.

 

[MikeHolmes]

Thanks Nigel. I see that I am missing the resistors from the non-inverting inputs to ground on the differential amps. I'll add those, and also appropriate capacitors to block the DC offsets.

 

[tkroeker]

optional

Could you take out the T1 and R15 to make it a "line" output mixer? also could this be hooked straight to a power amp?

 

[sreten]

Could you take out the T1 and R15 to make it a "line" output mixer?
also could this be hooked straight to a power amp?

Hi,

Yes, but there is still a lot missing from the schematic.

Buy and mod if needed is my attitude.

rgds, sreten.

 

[tkroeker]

Thanks. I am simply working on something for a drummer to hear guitars and vocals. Loud and close to the touch for adjusting while playing. Sound quality is just not that important lol.

 

[sreten]

Thanks. I am simply working on something for a drummer to hear
guitars and vocals. Loud and close to the touch for adjusting while
playing. Sound quality is just not that important lol.

Hi,

You will need to give a lot more salient and accurate information
before anyone can work out the best approach to your problem.

Foldback is not a new problem and there are lots of approaches.

rgds, sreten.