Quick help with TL082 based 4 Channel Mixer Schematic. (Issue: WAY TOO QUIET.)

[aeiou]

http://s13.postimage.org/lrquzmihh/4chmixer.jpg

I've put together this mixer and my issue is this: It is mixing the 4 signals together, but it's way too quiet, regardless of how many instruments are plugged into the inputs. I have my keyboard turned up way past the point where it would make my little practice amp run into overdrive. However, run into this mixer it sounds clean, but at an extremely low level.

I'm sure I've just made a silly mistake here - Can someone quickly point it out for me?

THANK YOU!

[aeiou]

http://www.me.umn.edu/labs/hmd/lab/electronics/images/lf412.jpg

Here's the pinout for the TL082.

Additionally -- It's not simply an error in my build from this schematic as its a transcription by me of my personal project.

[slacker]

You need a capacitor and resistor in series between each of the inputs and pin 2, and a resistor between pins 1 and 6. Try 100k for the resistors, that will make the output the same volume as the input.

[aeiou]

ah ok.. -- those are the only apparent issues?

what value capacitors do you recommend?

THANKS!

[Gurner]

ah ok.. -- those are the only apparent issues?

To my eyes no! You should take the output of the circuit from pin 1 to the cap rather than have pin 1 feeding the output cap via a 100k resistor (that 100k resistor is gonna act like a potential divider in conjunction with whatever follow on resistance there is ...end result, loss of signal magnitude).

A high value pull down resistor to ground wouldn't go amiss on the right hand side of the output cap either.

[aeiou]

http://s16.postimage.org/y7s4jk1kz/4chmixeredit.jpg

Very well -- here are the edits to my schematic based on your suggestions. i've not yet made these changes to the build on my desk.. does this look right?

[gritz]

A couple little things:

1) You've wired the output of the mixer amp to the output of the second amp, rather than to it's inverting input via a 100k resistor.

2) The 10n caps at the mixer inputs will cause a rolloff of the signal below 159Hz (the input impedance of an inverting opamp is equal to it's input resistor). 100n will take you down to 16Hz, so the audio band will be essentially flat. Even 47n would be ok if that's all you have.

Nearly there.  

[Gurner]

Personally, I'd disconnect everything presently connected to pin 6 & 7, then short pin 6 to pin 7. (& get rid of the 100k resistor that was feeding pin 6)

[aeiou]

http://s7.postimage.org/jycvqm2h5/4channelv11.jpg

OK - here are my edits at your suggestions. about to get thee to the desk and i'll report back.

[Gurner]

http://s7.postimage.org/jycvqm2h5/4channelv11.jpg

OK - here are my edits at your suggestions.

Not quite, here's what I suggested...

Personally, I'd disconnect everything presently connected to pin 6 & 7, then short pin 6 to pin 7. (& get rid of the 100k resistor that was feeding pin 6)

all you should have for pin 6  & pin 7 is them shorted together, with nothing else connected   .....but you keep persisting in wanting to connect the output of the first opamp (pin 1) to these pins!

[aeiou]

http://s9.postimage.org/oehoagpml/4chmixfin.jpg

MY BAD -- now I THINK that I geddit. -- Pardon the myopia, this is my first ever self (now group) designed schem.

[aeiou]

I've updated my build to the latest revision of that schematic and it still isn't working -- it's mixing, but still super quiet. any advice?

[Gurner]

I've updated my build to the latest revision of that schematic and it still isn't working -- it's mixing, but still super quiet. any advice?

At this point, I'd say to measure your DC voltages on all the opamp pins

[aeiou]

sorry to make such a huckadoo -- maybe someone can sort out a confirmed working schematic for me. I've tried a few i've uncovered online to little success. here's yet another I found --

http://lh5.ggpht.com/-ySuv8zhUr2M/TzxP-LngCAI/AAAAAAAABQw/ZC5-Dy2ZKGg/s1600-h/image%25255B2%25255D.png

[slacker]

That will work just fine. Ignoring the pots, if you'd made the changes to your original circuit that I suggested that's what you would have got.
If your last version doesn't work properly then there must be something wrong with how you've built it, like Gurner said post some voltages, that will help debug it.

[bluebunny]

+1

I've built a couple of small mixers using this schematic.  Works fine.