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How to make a RCA output for subwoofer on Reisong A10

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#21
rayma said:
No, the capacitors are only required due to the single supply. And there is no decoupling for the noninverting input.

See the circuit in post #8 for a proven dual supply circuit that will work, and work well.
I do not understand why you are looking for other circuits, when the circuit in post #8 is appropriate.
Click to expand...
Chris Hornbeck said:
This will work just fine if you increase the value of the mixing R's quite a lot, maybe starting with 1M Ohms each. Modern subwoofers will have an input impedance around 10K Ohms, so there is appreciable loss in the passive mixer. If 1M Ohms each does give enough signal, with the subwoofer's gain turned wide open (don't worry, it's just a gain control), reduce that value to 1/2M Ohm and try again.

Your design goal is to have the largest possible resistor value (to maintain channel isolation) with just enough summed signal to drive your sub. Ideally, you'd grab this from a lower impedance location, but your choice above will work fine and with minimal complication. Well worth trying first, at least.

All good fortune,
Chris
Click to expand...


Hello Thanks for the help.
For Rayma, I choose the second schematics on my link because I found it more simple to make for me.
For Chris Hornbeck: I will try to make my schematics and post it for validation please. but if it's not good I will try the link given by Rayma.

thanks
 
#22
This is what I made and regroup the tube preamp art with schematic from the link of Rayma.


complete schema.png

IS it ok please ? with resistor R1, R2 and R 4 will be 1Megaohms resistors Chris Hornbeck ?

I thank you
 
#23
With an opamp for the summing junction, R1 and R2 values don't have to be quite so big, but it doesn't really hurt anything. High frequency response isn't an issue feeding a subwoofer. But for stability, you'll want a small capacitor in parallel with R4. Maybe something like 1000pF to 10,000pF, and physically small enough to be mounted very close to the opamp pins. R4 can probably be a lower value, maybe as low as 100K (if R1 and R2 are 1M ).

All good fortune,
Chris
 
#30
Hello Chris Thanks for the reply. I made some modifications after searching technical informations, I found a book of Texas Instruments OP amp and I calculate the value of R3 resistor, this is my last file I will made it with JLCPCB so if you have time to verify please before I buy the pcb it will be great. I thank you
Note: the 9VDC is filtered outside of this circuit

final version.png
 
#32
Sorry , I'm not very shure to understand because I'm French So I must put the decoupling cap connected to VCC+ and GND ? a MKT capacitor ? but what is the value ? how can I calculate the good value please?
I put the R4 between output and the aop

Am I right ? Thanks

modiftest.png
 
#35
I would make R4 1000 Ohms and C1 330pF. Both Vcc+ and Vcc- need to be decoupled to ground, and they cannot just "float". They must be positive and negative with respect to ground, and their common "ground" connection needs to be brought to your board.

It's usual to tie off the unused opamp in the package, pin 7 grounded, pins 5 and 6 tied together.

You might benefit more from an opamp tutorial (in French) than my writings on a forum in the wrong language. I wish I had some French because I love Godard, Resnais, Rivette, Malle, etc. but it's too late in my life now.

All good fortune,
Chris
 
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#36
Bear in mind Your circuit is inverting the signal. (input on the inverting pin)
So invert the sub speaker leads or activate the phase switch if there is one.
Take a look at Behringer schematics FBQ1502 for example. They usually have a sub out
 
#37
Hello Thanks for the answer, I will make some modifications, and Yes my circuit is inverted because I connected the input signal on the IN negative pin 2 .
I must change it and connected the input audio signal on IN positive Pin 3.
 
#38
Opamps don't work that way. You really should study a tutorial first, before wandering about in the dark. Opamps are not complicated if approached from a position of basic knowledge, and the general principles of feedback are necessary to understand any linear electronics. Everyone on this forum needs to understand the principles of feedback, and opamp theory is a perfect way to learn.

All good fortune,
Chris

ps: either don't worry about polarity, or use the other half of the opamp as a unity gain inverter.
 
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