Solved: DIY Passive Monitor Controller: panorama off ???

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weiss

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Hey guys,

i built myself a passive monitor switcher with 3 possible sources and 3 outputs as well as 5 controls.
For the moment i only connected 1 channel (R+L) to test the circuit but i have a problem: the balance of the panorama is off by 30 degrees. I used bx_control and a mono signal to measure how much i need to turn until it is completely in the center again.
Apart from that all the controls work fine. I checked the wiring and the resistors to be sure i haven't overlooked anything. Also replaced the pot with a resistor and jumped the monitoring switch but nothing really helped solving this issue.. i just don't get how a simple circuit like this gives me such a problem ???

1. 4 pole 3 pos rotary selecting the signal source A / B / C
2. 4 pole 3 pos rotary selecting between -15dB dim / normal operation / mute
3. dual gang potentiometer 4k7 log scale to control the output volume (i am probably gonna replace this later on with a stepped attenuator)
4. 4 pole 3 pos rotary to switch between mono listening, stereo listening (normal) and sides only (wired as mono rev phase, schematic below)
5. 4 pole 3 pos rotary selecting the speaker A / B / C




Here is the wiring scheme i used:


I modified the attached version by some elements (mentioned above)
 

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weiss

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wiring scheme for the monitor rotary switch (only modified order)
 

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radardoug

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The mute switch as wired will not mute, only short everything out. The quality of the sections of your pot will affect the channel balance.
 

weiss

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radardoug said:
The mute switch as wired will not mute, only short everything out. The quality of the sections of your pot will affect the channel balance.

So you are saying, if i ground everything properly it would work out?
 

TwentyTrees

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Tolerance between gangs on your attenuator pot could easily cause stereo image wobbliness, especially as it’s a log pot where tolerance is that much harder to achieve. A rotary switch with closely matched resistors would give a great deal more L/R precision. I’d try breadboarding that section and see if that sorts out the issue.
 

ruffrecords

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To mute you need to connect each + and - together at the output. In a balanced system, ground is not ground it is a screen. It does not carry signal.

Check the total resistance of each half of the 4K7 pot. This probably accounts for the stereo offset.

Cheers

Ian
 

weiss

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ruffrecords said:
To mute you need to connect each + and - together at the output. In a balanced system, ground is not ground it is a screen. It does not carry signal.

Check the total resistance of each half of the 4K7 pot. This probably accounts for the stereo offset.

Cheers

Ian

Thanks for your ideas but I already replaced the pot with a 5k resistor and the problem persists.. ???
 

ruffrecords

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weiss said:
Thanks for your ideas but I already replaced the pot with a 5k resistor and the problem persists.. ???

So with all fixed resistors you still get the mono image shifted? Maybe you should check the values of the other resistors.

As you are driving L and R from a common source then if all the resistors are identical the image should be central.

Cheers

Ian
 

weiss

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ruffrecords said:
So with all fixed resistors you still get the mono image shifted? Maybe you should check the values of the other resistors.

As you are driving L and R from a common source then if all the resistors are identical the image should be central.

Cheers

Ian

yes i know, that's the weird thing. i already checked each of the 8 resistors, which are 1% btw.
also when i dim the signal it gets dimmed equally left and right which practically means that i didn't confuse anything by mistake there
 

ruffrecords

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weiss said:
yes i know, that's the weird thing. i already checked each of the 8 resistors, which are 1% btw.
also when i dim the signal it gets dimmed equally left and right which practically means that i didn't confuse anything by mistake there

OK so if you swap the L&R connectors at the output does it stay the same or change? - just wondering if the problem is in the receiver.

Cheers

Ian
 

moamps

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The simplest procedure for checking your controller is by using ohmmetar :)
Disconnect all inputs and outputs and measure resistances between input and output XLRs pins for each setting.
For example, between input L XLR pin 2 and output L XLR pin 2 should be 2k7 for -6dB,  10k for -15dB, and so on.
If everything is ok, and problem is still there, one of your interconnecting cables is most probably unbalanced.

 

weiss

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ruffrecords said:
OK so if you swap the L&R connectors at the output does it stay the same or change? - just wondering if the problem is in the receiver.

Cheers

Ian

it changes to the other side. i also connected the 4 xlr cables directly and the signal was okay again. it is definitely the switcher.

moamps said:
The simplest procedure for checking your controller is by using ohmmetar :)
Disconnect all inputs and outputs and measure resistances between input and output XLRs pins for each setting.
For example, between input L XLR pin 2 and output L XLR pin 2 should be 2k7 for -6dB,  10k for -15dB, and so on.
If everything is ok, and problem is still there, one of your interconnecting cables is most probably unbalanced.

i checked this, the resistance is okay and equals the position of the switch i set (2,7k or 10k). the other pin is always 5k on top (which equals the potentiometer)
 

ruffrecords

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weiss said:
it changes to the other side. i also connected the 4 xlr cables directly and the signal was okay again. it is definitely the switcher.

i checked this, the resistance is okay and equals the position of the switch i set (2,7k or 10k). the other pin is always 5k on top (which equals the potentiometer)

Since it changes side when you swap the output leads it is definitely not the monitor circuit but whatever you are feeding it into.

One problem you have is the the output source impedance of your monitor circuit is rather high so it may be affected by variations in the load you attach to it.

Cheers

Ian
 

weiss

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ruffrecords said:
Since it changes side when you swap the output leads it is definitely not the monitor circuit but whatever you are feeding it into.

One problem you have is the the output source impedance of your monitor circuit is rather high so it may be affected by variations in the load you attach to it.

Cheers

Ian

Ian you're right, my bad. of course it can't be the switcher then.... I am gonna do some variations with the wiring and see if i can find the cause. But shouldn't the impedance influence both channels?
 

weiss

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Okay this is strange.

i inserted some other analog hardware gear next to the monitor controller and as soon as i do that the stereo balance shifts to some other positions. it seems like additional gear does change the phase or something. what's also strange then, as soon as i turn the volume knob down the stereo balance goes completely to the left. it acts like a balance control... how is this possible... what am i missing?
i also tried disconnecting any other gear going out of my fireface and any other hardware like headphone amp and so on..

:eek: :eek: :eek:
 

ruffrecords

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weiss said:
Okay this is strange.

i inserted some other analog hardware gear next to the monitor controller and as soon as i do that the stereo balance shifts to some other positions. it seems like additional gear does change the phase or something. what's also strange then, as soon as i turn the volume knob down the stereo balance goes completely to the left. it acts like a balance control... how is this possible... what am i missing?
i also tried disconnecting any other gear going out of my fireface and any other hardware like headphone amp and so on..

:eek: :eek: :eek:

Sounds like a possible wiring error. Try shorting one input and testing the other channel in isolation.

Cheers

Ian
 

weiss

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ruffrecords said:
Sounds like a possible wiring error. Try shorting one input and testing the other channel in isolation.

Cheers

Ian
Thank you Ian!
At which position should i short the input?
Directly after the XLR?
 

ruffrecords

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weiss said:
Thank you Ian!
At which position should i short the input?
Directly after the XLR?

I always keep some XLRs plugs with pins 2 and 3 shorted for noise checks. If you make one of these you can easily use it to check either channel just by plugging it in to the input.

Cheers

Ian
 

weiss

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ruffrecords said:
I always keep some XLRs plugs with pins 2 and 3 shorted for noise checks. If you make one of these you can easily use it to check either channel just by plugging it in to the input.

Cheers

Ian

So i did as you recommended.

mono signal in the analyzer


when Left input shorted


when Right input shorted


When left is shorted, it seems the signal doesn't get completely mono and it has a weird spatial spectrogram
Something wrong with the right channel then?
 
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