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herryawan 23rd May 2012 05:48 PM

mixer and!!!
1 Attachment(s)
please help me ...

I'm making a circuits audio but there is a problem with the circuit ..

so this story:
I'm making some of the mixer group. each of these mixers have no connection at all with the audio mixer other, only the power supply connections to connect all the mixer (+12 v, 0 v, -12 v) ..

each mixer is connected with some "pre amp + mic​​" and "power amplifier headset +" ..
I use the input-output Unbalanced and cable length between the pre amp with a mixer and mixer with power amplifier is more than 1 meter ....

My question is why there is a kind of crosstalk interference in the audio system?!?! audio on each mixer can be heard in another mixer ..
what is the solution to solve the problem?!?!

This attachment is a schematic of the audio system that I created

Speedskater 23rd May 2012 10:49 PM

Are these balanced or un-balanced inputs and outputs?
Each and every signal, power supply and ground wire has to be considered. There is a correct way to connect each of these wires and many incorrect ways.
A common power supply can also cause crosstalk problems.
Do you have more detailed drawings of the sub-sections?

Speedskater 23rd May 2012 10:56 PM

This paper is a good start on wiring.

ChristianThomas 25th May 2012 07:43 AM

Look to your grounds. I would guess that you have common paths back to the main ground. If it is from one mixer console to another, which is what it sounds like then the grounds from those two should meet only at the ground chosen from your power supply.

herryawan 25th May 2012 03:36 PM

2 Attachment(s)
I've tried doing a ground connection type star, but still there is crosstalk ..

This is a sub section of my circuit .. pre amplifiers and power amplifiers are located on one PCB and connected to the mixer with a cable length of more than 1 meter ... type of headset and mic that I use is a computer headset and mic ..

is there something wrong with the circuit?!?!

Moon Track 27th May 2012 08:48 AM

You can troubleshoot the channel with crosstalk by grounding signal path in safe for components points .
So far thereís unclear how your power amp and pre-amp switches are working.Switch can be closed by applied small positive current and opened by negative ,relatively to emitter, voltage . Filtering capacitor wouldnít hurt here at switch output too.
It was possible to transmit in two times higher level signal through cable if pre-ampís R12 and R16 resistors were placed at mixer board. At least you can use SMD to replace R16.

herryawan 27th May 2012 04:10 PM

sw_preamp and sw_pwramp connected to I / O microcontroller so that the headset and / or mic can be enabled or disabled by the microcontroller ..

I agree with Speedskater and ChristianThomas,, may be the cause of my problem is ground path from the common power supply ..

if i use a power supply for each set of audio, switching circuit can not work because the ground is connected to the other power supply ... should I separate the ground for circuit switching with audio ground?!?!

is there an additional circuit to eliminate crosstalk?
my Should alter or Unbalanced input and output into a balanced input and output?!?!

is there any advice?!?!

Moon Track 27th May 2012 08:05 PM

Preamp works in very small current modes, only two milli-amper ripples are here.
I canít help here with grounding. These things you have to check yourself. Ideally, mixer and phone amp boards should have decoupling capacitors.
Schematically, the weakest place is cable between mixer and preamp. For example, when trim resistor R12 is set in middle position your output resistance is 47kOm, in min and max position 22-24kOhm. Such connection will be very sensitive to any capacitive or inductive influences from other cables. In context of stable output resistance the decoupling capacitor at switch output becomes a must.

herryawan 30th May 2012 03:28 AM

What is your opinion if I add the 78xx and 79xx regulators on each mixer for grounding problem?!?! will be affected?!?!

Is the addition of regulator look like using the power supply to each mixer?

Moon Track 30th May 2012 07:11 AM

As far you don’t have a problem with power noise rejection, there would be enough of using the decoupling, film or ceramic, capacitors 0.25-1mkf,mounted right on the board.
I hope your power supply has enough of juice to hold the null potential.
If you have o-scope, you can connect power rails by two series capacitors, bypassed by resistors. Their central point will give you virtual “ideal” ground to check if there are noises in real ground.
The crosstalk from ground can came from grounded differential inputs in mixer and power amp section . Just short the signal path to the ground, at mixer input, and it will be clear is it preamp with its cable or ground problem.
By the way, boards, especially without strong decoupling capacitors, must be powered from star type connection too.

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