1. Register NOW and become part of this fantastic knowledge base forum! This message will go away once you have registered.

Wiring classic Shure 545 unidyne iii 4 pin amphenol to XLR

Discussion in 'Recording' started by MxWebb, Jan 19, 2012.

  1. MxWebb

    MxWebb Active Member

    Can anybody help me with the correct cable wiring for a shure 545 which has 4 pin amphenol connector (the type which changes impedance by changing the mic cable) very early I believe made in USA before Shure moved production to Mexico.
    I bought 2 of these for my son but need to try to sort cables for him
    I have seen an old thread by RemyRAD and others which seems to describe my problem (low output) so I think I have probably wired cable wrongly.
    Can anyone help a newbie please? Pin numberings would help

    Having read various posts around the Web I have currently wired the cable Amphenol to XLR like this but it is very quiet, have I reversed pins 2&3 in the XLR ...

    Amphenol
    MC4F------------XLR---------polarity?--------wire colour

    pin 4------------pin 3--------(+/hot)-----------white
    pin 3------------pin 2--------(-/cold)-----------black
    pin 1------------pin 1-------(g/chassis g)-------shield
    Pin 2 ---unused

    This is a post by "DX Studio?" that describes the issue I think ...
    A differential amplifier like ... M-Box works by inverting the cold signal and adding it to the hot. So if you have some signal "A" the hot will have +A, the cold will have -A. With a correctly wired cable the amplifier will produce -(-A) + (A) = 2A.
    If the hot and ground are swapped, the +A term will be zero, so you get -(-A) + (0) = A. This is half of the proper value, or 6dB down.

    The Shure 545 wiring for my son's Mics is here
    http://www.angelfire.com/music/harmonica/shure545.html#545fourpin
    Any guidance will be hugely appreciated. And if anyone has any Amphenol mc4m or mc4f connectors kicking about I'd be very interested.
     
  2. Boswell

    Boswell Moderator Distinguished Member

    What are you plugging this mic cable into? Is it an Mbox?

    The first part of the quote from DXStudio is correct. The second part is incorrect, as the two signal pins are floating with respect to ground.
     
  3. MxWebb

    MxWebb Active Member

  4. Boswell

    Boswell Moderator Distinguished Member

    I think your wiring is probably OK, but the Fast Track Pro has only 40dB of gain. This is enough for high-output condenser mics or close-miked vocals using a dynamic microphone like an SM58, but is not enough for low-output mics.

    You could consider getting either a different interface box that has a bit more gain or something like the Cloudlifter to put 20dB more gain in before the Fast Track Pro pre-amps. This latter solution would also suppress the noise problem that the Fast Track series are known for.

    By the way, don't confuse the M-Audio products with the Digidesign Mbox series. They both come under the Avid umbrella, but are quite separate.
     
  5. MxWebb

    MxWebb Active Member

    thumbTHANK YOU VERY MUCH -It's good to know that the cables are probbaly OK.

    One phenomenon that seemed odd to me (but might be normal) there is basically nothing from the Mic until the Input Gain is right up nearly at the maximum, then there is quite a change of input in say the last half a tick - so if the scale is up to 10 then at 9.5 there is a little input from the Mic which increases sharply so at 10 the Mic is distorting and the clipping light comes on. Is that normal for this situation?

    I have 2 more cables that I can solder up the opposite way on pins 2&3 of XLR to see if that might make any difference - should I bother or just do all the same?

    Just wondering (I really do know nothing!) if I was to wire the cables so the Mic becomes Unbalanced high impedence - is my understanding of the literature correct that it would make it Higher output? And is that worth a try or will it simply add lots of noise to the signal?
    Thanks again
     
  6. Boswell

    Boswell Moderator Distinguished Member

    The behaviour of the Fast Track Pro at the top end of its gain range is typical of that type of unit.

    Reversing 2 & 3 on the XLR will make no difference to the gain - it will just make the signals the wrong polarity.

    You could try using the high-impedance unbalanced output connection on the mcrophone and take this via a TS jack plug into the combo input of the Fast Track Pro. Switch the input to INST (not LINE). You may get more system gain using that method over the low-impedance/XLR input, but you would have an increased risk of interference due to using an unbalanced input.
     
  7. MxWebb

    MxWebb Active Member

    Son also has an Mbox Mini which since you mentioned it I looked up and see it has 54dB gain - is that likely to be enough (I'll give it try later - but just wondering what your thoughts are)
     
  8. Boswell

    Boswell Moderator Distinguished Member

    You could try plugging the mic with the XLR cable into the Mbox and see if it has more useful gain than the Fast Track Pro. If it isn't much better, something like the Cloudlifter or the FetHead would be a cheap-ish solution, or you should consider a better-specified interface unit.

    (Dead Link Removed)
     
  9. MxWebb

    MxWebb Active Member

    Thanks for that, sounds like a pre-amp is the way forward.
    As we happen to have two of the 545s I'm wondering about the M-audio dual pre-amp which is about the cheapest thing I can find. I don't think we're sophisticated enough to worry about and colouration or change to the sound and he hasn't used the 545s yet so won't be aware of any difference, think I'll risk taking a cheapskate approach (£75 for 2 pre-amps) unless anyone thinks it's terrible ...
    M-Audio Audio Buddy Audio Interface
     
  10. Boswell

    Boswell Moderator Distinguished Member

    The Audio Buddy is far from being the greatest in terms of audio quality. It's worth trying the high-impedance connection to the FTP before you go any further.
     
  11. RemyRAD

    RemyRAD Well-Known Member

    Your 545 series microphone is perfectly fine for miking guitar amplifiers, drums & loud vocalists i.e. rock 'n roll. This and its newer cousin the SM57/58's is the de facto, quintessential, rock 'n roll recording microphone. You really don't need much more than 50 DB of gain for rock 'n roll recording. The reason why the gain trim seems so touchy is because it is a linear taper type and not an audio taper type potentiometer a.k.a. volume control. This type is typically used for gain trim. The audio taper type is generally used for mixing faders than for gain trim. Proper gain setting experience comes from, well, experience in setting gain properly. You don't need additional front end preamps as suggested. They build these units with the same mindset as my above suggestions. So what you currently have is 100% adequate in the right hands or left. I almost never need to utilize more than 50 DB of pre-amplification from my 70 or is that 80 DB of available Neve pre-amplification. So if you are already seeing overload lights, what? You want to see more overload lights? Or you want more noise? Learn how to tweak your level trims and you'll have no problems. Perhaps if the unit has been sitting around too much, you might be suffering from some dirt from airborne particulate pollution in the trim control? For that, you can get a can of spray stuff to SHPRITZ into the level trim control. Otherwise, you're just not setting it correctly for the proper signal source. And an additional 4 DB of gain on your M-Box Mini ain't going to make much difference. 50 DB again is all you need for rock 'n roll.

    Pragmatically practical
    Mx. Remy Ann David
     
  12. MxWebb

    MxWebb Active Member

    Aha thumbligtbulb comes on. Thank you for explaining the linearity of the gain potentiometer - that clarifies things for me completely, being a self-confessed "helpful dad" I was only familiar with audio taper volume controls. The gain with the Mbox is 14DB more than the M-Audio but as you say - the 40 is enough as we get to the point of the clip light. Marvellous, we will keep experimenting as we are and i'll learn to fiddle with my knob properly.
     
  13. Boswell

    Boswell Moderator Distinguished Member

    I think you will find that the gain trim on those units is done with a "reverse log" characteristic potentiometer. The action probably departs from the accurate law at the top end because of the need to include a fixed series resistor that prevents the amplifier going open-loop. More sophisticated designs use a more complicated arrangement that makes the whole of the variable range usable without a difficult section at the end.

    That detail apart, it may turn out that the maximum gain is numerically enough in dB, but is unusably noisy. I would try the high-impedance connection at the microphone going into the DI input, and if that is not workable, try the Mbox Mini. You only get a single mic channel with the Mini, of course. If none of these work out, you can decide whether to spend money on the Fetheads or else a different interface.
     
  14. MxWebb

    MxWebb Active Member

    I'm delighted to report that it is indeed possible to get clean signal with the Mbox - gain up to about 95% and the Shure 545 seems great.
    Next weekend I will wire up a cable as High Impedence to try out and see if we notice any difference.
    Thanks again RemyRAD and Boswell - terrific to be able to get such knowledgeable help.
    Martin X Webb
     
  15. Derrick111

    Derrick111 Active Member

    This is wrong... The hot and cold are in reverse order here. It should be:

    Amphenol
    MC4F------------XLR---------polarity?--------wire colour

    pin 4------------pin 3--------(-/cold)-----------white
    pin 3------------pin 2--------(+/hot)-----------black
    pin 1------------pin 1-------(g/chassis g)-------shield
    Pin 2 ---unused


    The mic would still work, but anything tracked with this arrangement would be out of phase with the rest of the tracks (like flipping the phase switch on your mixing board) and cause you problems.
     
  16. MxWebb

    MxWebb Active Member

    Thanks for that info. I don't quite follow what the implication is - as all the pins and wire colours you suggest are the same - so I'm assuming that I won't notice any difference as I don't have a phase switch on the MBox Mini nor on the MAudio (at least not as far as I know). Thanks again. Martin
     
  17. Derrick111

    Derrick111 Active Member

    Hmmm, right... and I don't remember the 4 pin Amphenol wiring off the top of my head so check what pins from the Amphenol go to what pins of the XLR. I guess I just mean that on an XLR plug, pin 2 is hot or + and pin 3 is cold or -. So just make sure that you wire hot to hot and cold to cold when wiring from Amphenol to XLR or your phase will always be reversed in relation to everything else causing you sonic problems.
     

Share This Page