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1/4" Cables TS vs TRS, Using Mixer Inserts as Outs

Discussion in 'Accessories / Connections' started by natem345, Feb 9, 2009.

  1. natem345

    natem345 Guest

    I have a M-16DX digital mixer/interface I want to record with. It has 16 balanced line ins (4 with mic pres).
    I plan to buy a Nady PRA-8 to add some more mic pres, and an 8-pack of short 1/4" cables. I hear it does have balanced outs, but the distances are short anyway. Should I go TS or TRS 1/4" cables? I want to maximize flexibility of things I can connect with them.
    What will happen if say I plug unbalanced source thru TS cable into balanced mixer? Or vice-versa, unbalanced source thru TRS cable?
    What about a different mixer with unbalanced or even stereo ins, will it properly ignore the balanced part of the TRS signal?
    For guitar to direct box or Hi-Z in, will TRS work or must it be TS?

    Finally, I want to do some live recording of various gigs. I read I can either use the half-plug trick: plug cable (any type?) into the insert until just the first click. Or I can buy an adaptor such as this from RS for a better connection; will they work, are they worth it, and would it matter what type of cable with them?
    I'm even considering a patch bay, but don't think I want to get quite that serious yet.. plus I don't have a rack.

    Thank you very much for any enlightenment you can provide. I know I have a lot of questions! You can reply on top of the quote or whatever is easiest.
     
  2. dvdhawk

    dvdhawk Well-Known Member

    1: The Edirol specs don't indicate that it will take unbalanced 1/4", using a standard TS cable would cause levels to be mismatched and you're essentially shorting the R (out-of-phase) pre-amp to the shield.

    2: If you plug a TRS cable into your instrument that has a standard TS, you're likely to have problems.
    When you plug that into your TRS input on the mixer, the T is the normal in-phase signal, the R is out-phase. So you in that case, if the same signal is going into both the T and R, those signals will cancel each other out and you will hear nothing.

    3: If the mixer is equipped to accept both unbalanced & balanced 1/4" it can adapt to TS or TRS
    BUT the connector senses the third conductor and throws that signal to the appropriate op-amp. So, when you plug in a TRS it had better be a balanced signal. Otherwise, you're putting things out of phase and potentially cancelling the sound out.

    4: Can you do the half-plug trick with the M-16X?. I don't see any inserts on it or the Nady.

    5: Don't plug that RS adaptor into an insert jack.



    Moral of the story... just 'cause it fits in the hole - don't mean it's the right connector.

    Good luck.
     
  3. Boswell

    Boswell Moderator Distinguished Member

    The M-16DX has TRS balanced line inputs on channels 1-14. Use TRS cables for connecting your new pre-amps. You should also use TRS cables when feeding the M-16DX inputs from equipment that has unbalanced outputs.

    Avoid using standard TS cables from equipment that has balanced outputs, and don't feed balanced outputs into unbalanced inputs with either standard TS or TRS cables. For this job, you need specially-wired cables using TRS plugs but with the R left open-circuit at the sending end and the R grounded at the receiving end (or a TS plug).

    That RS stereo-mono jack adaptor could possibly work for extracting a signal out of an insert jack without breaking the signal chain. It depends on whether it has resistors inside to perform the stereo-mono summation or whether it simply shorts T and R together. It's the latter you would require for extracting a signal for recording from a mixer with no direct outs but equipped with inserts (the M-16DX has neither).
     
  4. natem345

    natem345 Guest

    I realize the M-16DX has no inserts or direct outs; it would just act as the DAW/interface in that situation. Its line inputs would be connected to another mixer with inserts, to send those signals to a laptop over USB for recording. Sorry for being unclear about that. So basically I can try the RS adapter, there's a chance it will work. @dvdhawk, why do you say it won't?

    It seems there is contradictory information here: one says use TRS cables to connect unbalanced out to balanced ins, another says only use TRS cables for equipment with balanced outs.
    Forgot this before, but I did actually hook up an iPod to the line ins with this cable. The level seemed a bit lower than when using the mixer's single stereo 1/8 in, but it did work.
    I also looked in the manual: "You can also connect standard (unbalanced) 1/4” plugs to these jacks."

    What if I use TRS cables where both ends are unbalanced: would the ring affect anything?

    Thank you for all the help!
     
  5. dvdhawk

    dvdhawk Well-Known Member

    Inserts are effects loop connections, providing BOTH the output (send) going to the effects unit usually via the T tip - and the input from the effects unit via the R ring. They share the shield S.

    If you plug that RadioShack stereo to mono 1/4" adaptor into an insert you will be shorting across the send and return contacts in the insert connector. It combines the T & R of the male to the t of the female.

    Boswell and I are in complete agreement. You can make or buy special TRS cables with the ring conductor cut - to ignore the ring, but I don't know why you go to the added expense of buying balanced 1/4" and disabling the balancing contact. Some TS jacks you would plug that custom cable into would be looking for the shield where you would have a disabled conductor.

    As a rule, if you want quality audio - Anytime you have the option use a balanced cable.
     
  6. natem345

    natem345 Guest

    "You should also use TRS cables when feeding the M-16DX inputs from equipment that has unbalanced outputs." vs "So, when you plug in a TRS it had better be a balanced signal."
    He did not say special cables. I just want to be able to use the same cables with balanced and unbalanced cables (perhaps with adapter) if possible. Fewer $ and fewer cables. Can I do so with TRS cables? He says I can, you previously said no.

    I am asking two separate questions here. The goal of the RS adapter is to send the output back into the mixer, so that the mixer is unaffected by the cable, then record that cable. To basically make the insert a direct out.
     
  7. dvdhawk

    dvdhawk Well-Known Member

    Hi Nate,

    I can see why that would be confusing and I'm not trying to bust anybodys chops. I'm just trying to keep you from wasting money on cheap cables and adaptors.

    I'm less concerned about whether it's possible to route the signal through every conceivable combination of TRS to TS under the sun. I'm telling you there will be impedance and input sensitivity differences between balanced and unbalanced inputs. If it wants a balanced signal, send it a balanced signal. If the input specifies it will take both balanced and unbalanced, you're golden. But you can't do both jobs with the same kind of cable TS<->TS or TRS<->TRS. (which is at the root of your original post)

    This would be recommended reading for you all the way through if you have time.

    http://www.soundonsound.com/sos/Jan02/articles/faq0102.asp#Anchor-41113

    These are the most important bits pasted over from that excellent resource.

    <Quoted from SoundonSound.com>

    Q What's the best way to connect unbalanced signal sources to balanced inputs?

    The traditional method is to use balanced cable and connect the cold to the screen at the unbalanced end. However, this can sometimes result in ground loop hum problems, so it is safer to connect the unbalanced end of the cable as follows.

    Connect the screen to the ground pin via a resistor of between 100(ohm) and 500(ohm) or leave it disconnected altogether. Connect the cold core of the cable to the connector pin normally used to connect the screen. Connect the hot core to the connector pin normally used to connect the hot conductor

    Q What's the best way to connect a balanced source to an unbalanced input?

    You'll need to check your equipment manual for this one, as the way you wire the cable depends on the design of the balanced output stage. In some cases you need to link the cold and screen pins at the balanced end (if the output stage is 'fully floating') while in others you must leave the cold pin disconnected. In situations that require the latter approach, you will probably find that the signal level is 6dB lower than when using the equipment balanced. This is because you're only using one half of the signal from the output stage.

    - end quoted material.



    Nate I have miles of cable here, 500+ connectors, and mad soldering skills. Can I build myself a custom cable that will let the electrons flow from just about any kind of connector to just about any other kind of connector? Yep. Will it be the right level and impedance when it gets to where it's going? Sometimes - it depends on what we're interconnecting. Can you get signal with any combination of adaptors, TRS cables, TS cables, etc? Probably. Will it be a good signal? Once in a while. Do you hate it when people ask you something and then answer the question themselves? Probably ... I know I do.

    You have to know your gear. What kind of signal they want delivered to the inputs matters, if you care at all about fidelity. There for a while the European manufacturers and the Japanese manufacturers couldn't even agree on how to wire an XLR connector. Ever wonder why it's called an XLR? The name is telling you it's wiring scheme. X being a symbol for shield. L stands for line and R is the reverse, or out-of-phase.

    Pin
    1 - X = Shield (referred to as the 'screen' by the SOS article)
    2 - L = Line (referred to as 'hot' by the SOS article)
    3 - R = Reverse (referred to as 'cold' by the SOS article)

    Anyway, as I see it using the Shack adaptor in an Insert will shunt the insert's send to it's return closing the loop. Tapping into that loop with a TS cable will result in an unbalanced send being split off (probably pre-eq/pre-fader). I suppose if you're going into some other unbalanced device you might get an ok signal. Give it a try. Without any resistors or transformers inline, I'd be concerned that there would be significant bleed from one devices to the other. (adjusting the gain on the first device will usually affect the level going to second device - that's normal even with direct outs) with nothing buffering them, adjusting the gain on the second device may also make unexpected changes to the first mixer. The combined impedance (load) of both mixers can now interact in ways you may not like. Not to mention opening yourself up to more potential grounding issues.

    The half-plug trick doesn't work on everything. Some manufacturers wire their inserts the opposite way.

    Using Inserts as Direct Outs, isn't foolproof either. It completely depends on the engineering. I've seen mixers designed in different ways, some would work - some wouldn't.

    Using a TRS cable to connect a guitar or keyboard might be ok with some equipment, some equipment I've run across would not handle that well at all.

    If it's just wiring schematics we're talking about, this is one of the most thorough free webpages with lots of diagrams of how to balance, unbalance, and wire cables to passively split and combine. Brought to us by the fine folks at Rane Audio.

    http://www.rane.com/note110.html

    But again: just 'cause it fits in the hole - don't mean it's the right connector. (or right impedance, or right sensitivity)

    Best of luck!
     
  8. Boswell

    Boswell Moderator Distinguished Member

    Nate - Two short follow-up points:

    (1) You can't use that RS jack adaptor for what you want to do.

    (2) TRS cables are often better than TS cables when driving from an unbalanced output to a balanced input because you still get some of the benefit of rejection of interference picked up in the cable. It does rely on the jack socket at the sending end correctly grounding the ring connection to the local ground. If this can't be guaranteed, use a TS cable.
     
  9. baze sax

    baze sax Active Member

    hi another question about inserts: can I plug outboard preamp in the mixers insert to bypass the mic/line preamp inputs? what about cables? is xlr- trs ok?
     
  10. dvdhawk

    dvdhawk Well-Known Member

    Hi,

    The insert jack is after the first pre-amp in the signal path. Inserting an outboard preamp into your mixer's insert jack may add some character of the outboard gear - but it doesn't bypass the mixer's pre.

    On most mixers the TRS is a bi-directional cable. When you plug the TRS jack into the insert, the Tip sends signal to the outboard device, and the Ring returns the signal from the device back into the channel - the send and return share a common Shield.

    So, if you plug a TRS to XLR cable into the insert the result won't be good. Neither gender of XLR will give you both the send and return. Unless your mixer has dedicated balanced direct outs on the channels, there's no way to use XLR-TRS cables in the way you're describing. If you DID have direct outs, you could go out of the channel from the DO, which you would then have to return into another empty channel.

    (Still not bypassing your mixer pre's - actually now going through two of them using that method)

    You're better off plugging directly into the outboard pre, then from the output of the pre - into a mixer channel. I'd try to keep the mixer's gain down and get as much flavor from the outboard pre as possible.

    Just my 2 cents.

    Good luck!
     
  11. Boswell

    Boswell Moderator Distinguished Member

    Are you still talking about the Edirol M-16DX? As far as I can tell from the scrappy documentation on their web site, it doesn't have inserts.

    You can plug external pre-amps into the line inputs on channels 5-14 using balanced cables. These should have a TRS plug on the mixer end and on the other end a mating connector for whatever your pre-amp is fitted with on its outputs (probably XLR or TRS). Since channels 5 - 14 on the M-16DX do not have XLR inputs, there are no microphone pre-amps to bypass.
     
  12. baze sax

    baze sax Active Member

    mixer insert

    sorry, I was not precise. I talk about live mixer (dynacord) which has single point insert. the tip is send and the ring is return. I would use return only, of course. as someone mentioned the xlr end (output) is unchanged and the tip of the trs is disconnected. is this correct?
     
  13. Boswell

    Boswell Moderator Distinguished Member

    Yes, in most cases. You need special wiring, or else use standard insert cables with just the return lead connected. The problem comes in taking an unbalanced signal (needed for the mixer insert return) from the balanced output of a pre-amp.

    Pre-amps outputs are one of:

    (1) separate amplifiers driving the + and - signals, or a transformer output centre-trapped to ground. You need to take the +ve signal only, leaving the -ve signal floating. On an XLR plug, this means taking pin 2 as signal to the TRS ring and XLR pin 1 as ground to the TRS sleeve. For a TRS output, take the tip to the insert return (ring) leaving the ring unconnected.

    (2) floating transformer: just plug the return TS plug on the insert lead into the TRS socket or (if XLR) wire as for (1) but additionally take pin 3 to pin 1.

    (3) electronic transformer: treat as for (2).
     
  14. bouldersound

    bouldersound Real guitars are for old people. Well-Known Member

    Actually, it doesn't matter which way they are wired as long as the loop isn't interrupted.
     
  15. dvdhawk

    dvdhawk Well-Known Member

    I see what you're saying bouldersound ( and don't disagree ), but I've come across a couple mixers over the years where the ring is normalled in such a way as it was strictly the return. Half-plugged was just not going to give up a signal out.

    Don't ask me what mixer(s), I see literally hundreds of mixers some years.
     
  16. bouldersound

    bouldersound Real guitars are for old people. Well-Known Member

    Hm. Perhaps the switching was done on the ring contact rather than the tip contact, in which case we're both right.

    To the OP: The best way to do an insert tap is to wire a cable with a TRS on the insert end with the tip and ring connected together and to the tip of the other end. That will replace the normalling in the jack and get signal out. If the "first click" method works an alternative is to make 1/4" long spacers out of 1/4" inside diameter fuel hose to put on TS cables so they can't be pushed in too far.
     
  17. Boswell

    Boswell Moderator Distinguished Member

    I would never recommend the "first-click" fudge for live sound use - it's simply not reliable enough to guarantee no interruption of the live channel, never mind the recording.

    If you don't want to make up the special wiring needed or don't want to use something like the Hosa DOC106 adaptors, you can use standard insert cables along with mono (TS) 2-1 jack adaptors. Plug both the send and the return plugs of the insert cable into the outputs of the dual adaptor and then plug the adaptor into your recording interface.
     

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