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Benimur's Avatar
  • Answered by:Benimur
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Customer Question

Why is it possible to connect the left and right audio outputs of a Panasonic PV-D4744S DVD/VCR Player together through a Y adaptor, with no resistors in line, to the input of a 600 ohm Mackie CR1604-VLZ Mixer and actually get a mixed signal? (essentially each output driving into each other) Shouldn't this cause a catastrophe? But it works! What is the circuit analasyst that explains this? Thank you Ron XXXXXX@XXXXXX.XXX

 

Optional Information:
Make: Panasonic
Model: PV-D4744S

Submitted: 350 days and 22 hours ago.
Category: Consumer Electronics
Value: $58
Status: CLOSED
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Expert:  Silicon Savant replied 350 days and 21 hours ago.

Hi there happy to help.

 

By "Y" adapter are you referring to a cable like this........

 

http://www.amazon.com/Belkin-Audio-Cable-Splitter-1-Mini/dp/B00004Z5CP

 

Let me know,

 

 

Customer replied 350 days and 21 hours ago.

Yes, that would do. The red a white RCA connectors plug into the output from the DVD/VCR (essentially shorting the two outputs together) and the other (black) connector plugs into an adaptor that converts the RCA into a 1/4 Phono with a tip and sleeve which then plugs into the Mackie mixer's balanced 1/4 phone line input.

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Expert:  Silicon Savant replied 350 days and 21 hours ago.

Hi, understood. Here's what's going on. These cables aren't shorting the connections. The analog left and right signals still stay separate. They just plug into the Mackie using the different type single 3.5mm or whatever sized plug. If you look at this plug closely you will see black "rings". This is actually the separation of the signals.

 

I hope this makes sense. Its the same type of theory with a headphone connection. You still retain your left and right audio (stereo) sound, it just connects through the single physical plug.

 

 

Hope this helps,

 

 

Positive feedback/tips appreciated!

Have a great day

41018.8609023958

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Expert:  Silicon Savant replied 350 days and 21 hours ago.

Here's a diagram showing graphically what I explained above........the L/R signals are still electrically isolated, they just reside on the same plug.

 

graphic

 

Hope this helps,

 

 

Positive feedback/tips appreciated!

Have a great day

 

 

41018.8684144676

Customer replied 350 days and 21 hours ago.

I understand what you are saying but I misunderstood the connector that you showed me. This is not the case with the "Y" connector that I'm using. It does not have separating black lines. I've measured with an ohm meter and all three plugs(connecting points) are definitely shorted together. This is not the same as a head phone stereo plug. It is three points that are electrically tied together.

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Expert:  Silicon Savant replied 350 days and 20 hours ago.

Ok in this case you are simply combining the left and right audio signals to get a single analog mono signal. Not ideal but it is possible, you lose your stereo sound though.Please don't forget to accept and have a great evening.41018.9018329514

Customer replied 350 days and 19 hours ago.

You say "not ideal but is possible", but that is my original question - I know it is possible because it is happening. What I asked was HOW IS IT POSSIBLE? I asked for a circuit analasyst, not just an answer that says it is possible. How can one amplifier output look into another amplifier output, each having a very small output impedance (usually in the order of 10 ohms or less. It's practically like looking into an AC coupled short circuit to ground. Wouldn't this load be too demanding on each amp to drive a signal into? Could you drawer me a circuit equivalent of the set up that will allow me to see how the signals a split.

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Expert:  Silicon Savant replied 350 days and 18 hours ago.

The connection to the mixer is an INPUT not output. So you have two analog signals combining and being input to another device.

 

You actually said this in your poriginal question. Connecting to the INPUT of the Mackie mixer.

 

Hope this helps,

Positive feedback/tips appreciated!

 

 

 

 

 

 

 

41018.9778450231

Customer replied 350 days and 14 hours ago.

My question is not concerned about the input to the mixer, it is about the two outputs of the left and right amplifiers being tied together. Even if you remove the leg of the "Y" that goes to the mixer which would leave the two amplifiers looking into each other. It seems to me that you can't drive two amplifiers into each other and get a mixed analog signal without them overloading each other. I appreciate your attempts to help me but you don' t seem to be a circuit designer or analyzer.

I asked for a detailed circuit analysis explaining this to me. All you have done is restate the conditions that I have observed and said something like " yes, this is what you get in such a set up". Well that is not a detailed analysis. To get an answer I selected the answer with the highest details and you have given me no details.

I guess this means I should select the button that says " not satisfied with your expert?" but I wanted to reply first so you might understand. Sorry, I'm sure you are nice person.

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Expert:  Silicon Savant replied 350 days and 5 hours ago.

I am a circuit designer with over 10 years experience designing some of the largest mixed signal integrated circuits on the market today.

 

I am simply not clear as to what you are talking about here. I will opt out and let someone else help.

 

 

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Expert:  Benimur replied 350 days and 4 hours ago.

Hi and welcome to JustAnswer,

Thank you for the question and your patience. Should you still need assistance for information purposes only...

Initially, the OUT L & R AUDIO if joined together would not result to a cancellation of their respective outputs. Neither would it result to "overloading" each other.

Offhand, factors to consider:

  • • the left and right audio signals are not identical hence would result to a summation of signals; i.e. both audios L & R would be heard;
  • • the left and right are not out of phase of each other hence the L signals would not cancel the R signals;
  • • the typical output impedance of the L or the R jacks are less than 1KΩ;
  • • joined together it would at most go down to 500Ω which is pretty close to the 600Ω input impedance of the mixer;
  • • referencing the schematics as shown below from the Service Manual of the PV-D4744S, internally it has an inline 1KΩ resistor and a 10μF/16V capacitor in series to the audio output jack from the switching IC, IC4304;
  • • these in combination produces an isolation circuit of sort which prevents the L feeding to the R or the other way around or if combined would degrade one or the other or both;
  • • the audio output is produced by a (dual) OP AMP IC4303, a μPC4570G hence each output is driven separately.



Please post back should you need additional information.

Good luck and thank you for asking.
Benimur41019.5972523148

Customer replied 350 days and 3 hours ago.

I would like to opt out of this. I could not get the details I was asking for. Today I have a meeting with an engineer friend who will give me the details I'm asking for. Please allow me off the hook without complications. Thanks, XXXXX XXXXXDavid-Mod41019.6600302431

 
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