Balanced TRS to unbalanced RCA okay?

Discussion in 'A/V Interconnects, Cables & Power Conditioning' started by WxMan, Mar 18, 2012.

  1. WxMan Audioholic Intern

    WxMan
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    I need to know whether or not this mono 1/4" jack to RCA jack adapter can make a proper unbalanced connection when used in a balanced TRS jack? What I plan to do is use my existing premium quality audio cable interconnects (with male RCA jacks at each end) to connect my home audio AVR pre-outs to a pro audio active crossover having balanced TRS input and output jacks.

    Will the use of these adapters make it quick and easy to make those connections without introducing audible hum or hiss and still preserve the same audio quality that I already have in my system? That way I can get by without having to make or buy new cables with a male RCA jack at one end and a mono 1/4" jack at the other. TIA.
    Last edited: Mar 18, 2012
  2. BoredSysAdmin Audioholic Overlord

    BoredSysAdmin
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  3. TLS Guy Audioholic Overlord

    TLS Guy
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    Normally, putting a mono 1/4 jack in a balanced TRS jack will convert it to an unbalanced line. It should so state in the instructions with your mixer. Usually manuals are very precise about whether you can do this.

    Sometimes balanced inputs are very low impedance and you have to use an inline transformer, but that is mainly older gear. With more modern gear with solid state front ends using Op amps doing what you plan usually works.
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  4. WxMan Audioholic Intern

    WxMan
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    The Sound System Interconnection article is just what I needed to figure out the best way to make the connection. Unfortunately it doesn't recommend the connection I had in mind originally because my home audio interconnects are 1 conductor shielded cable. It seems from that article 2 conductor shield cable is used for what I had in mind (bridging the ring and sleeve).

    The closest adapter I can find that will serve as one of the recommended cable connections is this 1/4" TRS stereo to female RCA adapter.

    This one is represented by cable connection number 10. The above adapter will work as long as I use the right channel side which is on the tip. I can put a RCA plug cover on the left channel (ring) so I don't accidentally use that side. According to the article the ring is left unconnected when using 1 conductor shielded cable. That should do the trick. I expect it to work perfectly with my audio cables.

    Thanks guys for your suggestions.
  5. WxMan Audioholic Intern

    WxMan
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    I recently ordered a dbx 223s 2-way stereo active crossover which is still on backorder. I have already downloaded the manual. It says it can be connected to other equipment using unbalanced audio cables. However it didn't specifically state which type to use, 1 conductor shielded cable or 2 conductor shielded cable. My intuition tells me that the 2 conductor is probably better. However, I have 6 high quality 1 conductor shielded cables that are left over from with my old blu-ray player with multichannel analog outputs going to my AVR multichannel inputs. Since upgrading my blu-ray player and going HDMI, those cables are just stored away in a box. I'm glad I kept them. Hopefully they'll work with 1/4" TRS to female RCA adapters.
  6. TLS Guy Audioholic Overlord

    TLS Guy
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    [​IMG]

    Well, when you put the mono plug in the balanced TRS socket, then what would be the ring (3) becomes connected to the ground (1) and it becomes unbalanced. You never ever leave pins 1, 2 or 3 unconnected.

    Pin 1 (sleeve/screen) is always ground. Pin 2 (tip) is always the positive deflection. Pin 3 (ring) is the negative deflection, So if you ever reverse pins 2 and 3 you create an out of phase condition.


    Now the thing is that pins 2 & 3 in a balanced arrangement, never have a potential with respect to ground, just each other.

    So to unbalance a line you connect pins 1 and 3 together.

    The next question is where do you do it?

    Strict practice requires the line be left balanced at the output (source) and unbalanced at the input. This is called floating a line.

    Now I suspect you will have short runs. The only advantage of unbalancing at input rather than source is signal to noise and not sound quality per se.

    So I would go ahead and do it the way you intended. If there is no hum or buzz, then you are fine. If there is then you should formally float the line as I described.

    That is the way this works.
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  7. WxMan Audioholic Intern

    WxMan
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    That's one of the best explanations I got so far. Thanks.

    Just so we're clear. I am not using XLR inputs/outputs anywhere in my system, only balanced TRS. There is no XLR connection involved with my interconnects. Thus your diagram showing a balanced XLR connector at one end and a TRS at the other should instead show a balanced TRS jack, not an XLR. Correlating the XLR to TRS is easy but gets confusing since the TRS doesn't go by pins 1, 2, and 3.

    I will go with my original plan then. That's what I thought too just what you wrote in reply. However, the Sound System Interconnection article seemed to suggest otherwise. In unbalanced audio connections having one shielded conductor (red), the conductor lead is connected to the tip and the shield is connected to shield on a 1/4" TRS jack. The diagram in that article clearly shows in Cable Connection Diagram #10 that the ring is left unconnected. If that isn't kosher, I will stay away from it and just use the mono 1/4" TS jack instead.

    The leads will be short, about 0.75 meter in length. None of my audio sources is balanced. So floating the line at the source won't be possible except at the outputs of the active crossover.
  8. TLS Guy Audioholic Overlord

    TLS Guy
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    It makes no difference whether you have xlr of TRS, but you have to reference TRS to xlr, to understand the lead number one two and three.

    You must never leave a pin unconnected as you only have half the wave!

    I have absolutely told you the correct way to go from balanced to unbalanced.

    The negative deflection must be connected to ground. If you connected tip or pin 2 to ground you would have an out of phase condition.

    I do think you understand it now though.
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  9. WxMan Audioholic Intern

    WxMan
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    Yes, I understand it clearly.

    I'll need 6 of those RCA jack to 1/4" mono plug adapters as originally planned to turn my 1/4" TRS balanced connections to unbalanced RCA.

    Thanks again for your help. :)
  10. BennAV Audiophyte

    BennAV
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    I know I'm coming in late on this one, but other people might benefit. The statement that "all pins must be connected" is not true. It will depend on the equipment and whether you are connecting to an input or output. In many cases, it is a best practice to jumper + and - on an input when connecting an unbalanced signal to a balanced input. So, in this case, yes all pins would be connected.

    Now for a balanced output, you can simply connect the + and GND terminals and ignore the -. This does not result in a "half wave" as was stated. Balanced signals work by transmitting 2 versions of the signal (completely out of phase with each other). On a devices input, the out of phase signal is inverted and the signals are now in phase and sum together. This provides common mode rejection (CMR) which is all designed at removing interference and improving SNR primarily to allow greater cable runs and premium quality for sensitive environments. Search common mode rejection for further details. One Rane Note was mentioned earlier, but they have a ton more and some specifically on balanced signals and CMR.

    So, connecting only the + and GND terminals on an output will simply give you a standard unbalanced signal which consists of the AC signal and a "ground" signal reference. You can also use one of many format converters on the market if you'd like/need to. RDL (Radio Design Labs) has a bunch of great options.
  11. tom1454 Audiophyte

    tom1454
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    I need to come off my Behringer 6200 eq. with 1/4 inch balanced cable,but I have to plug into my marantz amp that only takes RCA into the inputs .So I need 4 1/4 inch balanced cable with 4 balanced RCA adapters to go into the amp. help ,tom
  12. jinjuku Moderator

    jinjuku
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    They have this stuff readily available at ZZounds, MusiciansFriend, Sweetwater, Guitar Center etc...

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