Dual Input to Mono Output

[Citadel231]

Hi there, I would like to ask some help from your brilliant minds. Im planning to have a project that consists of 2 inputs (Input 1- Piezoelectric, Input 2 - Electret condenser) Ive seen separate preamp schematics with the use of TL071, but i want to make them compact as much as posible due to the limited space i have. i am thinking to combine the circuit using dual opamp TL072 but my concern how to make those outputs a mono signal knowing that they have different input.

my application will used on my violin, id like to use piezo and electret simultaneously

Thank you so much guys.

[PRR]

Welcome.

[Citadel231]

WOOAH! I really apprecite your effort sir. This might be the solution of my problem hehe. ill work on this schematic later on. also, sorry for the demand, how and where can i put the balance knob (For piezo & electret) , main volume knob and Tone Knob? what values also? thank you so much

[PRR]

> the balance knob (For piezo & electret)

The plan I posted/hacked has separate level pots for each input.

I'm not able to sit at PC tonight. Maybe someone else can help with your feature list.

[Citadel231]

Hi Sir, good day! i already made the assembly using your circuit, the output is bit a problem, It cant play simultaneously, the results are playing EITHER of the output and From electret, bass were missing. can you please help me. thank you so much

[Citadel231]

By the way im using tl074 since tl071 and tl072 were out of stock. i leave the 6 unusable pins open.

[GibsonGM]

If you have unused opamp sections, you should take the output from each and connect it to "In - ".   Then tie "In +" to 1/2 supply voltage ("VRef")...this is where R1 and R2 meet.   Many circuits have a separate biasing network called "Vref" or "Vr" which does the job R1 and R2 are doing here.   For permanent construction, use a TL072.

This helps to stabilize the chip, preventing it from oscillating or picking up and amplifying noise.

So, pin 8 to pin 9, pin 10 to R1 R2 junction, and so on for unused '74 opamps.



First problem:

Are you using 10k B taper pots for each output, through the two 10k mixing resistors?   The pots should allow you to set each level independently...they are your balance controls.

[antonis]

It cant play simultaneously, the results are playing EITHER of the output and From electret, bass were missing. can you please help me.

Are all caps, pots & resistors values, posted by Paul, correct..??
(caps, except C3, toghether with resistors form HPFs - their values are critical for frequencies allowed to pass through..)

About TL074 unused op-amps, plz follow Sir Mike's suggestion (strongly recommended..!!) 
(alternatively, you may use one of them as Vref stabilizer (for voltage going to non-inverting inputs) and the other as final mixing buffer - but it should complicate the whole circuit a bit..)

[Citadel231]

Hi to all, thank you so much for your inputs, i really appreciated it.

anyways, ive attached photo for my revised circuit using TL074, i followed the components (pots, resistors, and caps) for sir paul. and i have not yet executed the Instructions of Sir GibsonM. I also used Taper pots, 10k each.

[Citadel231]

I followed the instruction of Sir GibsonM about how to handle unused pin for opamps and surprisingly there is an improvement for the sound quality alone, but for the main concern on mixing the output to mono still doesnt change the Piezo output will always prevail as to normal conditions (electret mic distance to the sound emitter around 10cm). I also tested and tried the Coil Microphone instead of electret, although sound quality increased but the mono output thing is still a problem