Budget recording woes

Discussion in 'Recording/Live Sound' started by DanR, Oct 12, 2004.


  1. DanR

    DanR Member

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    I'm trying to record an electric guitar track with my Boss BR-8. I'm mic'ing the amp, a Fender Vibo Champ, with a Shure SM57. As the Boss recorder does not have an XLR input, I'm using a XLR to 1/4" adapter, which also is an impedence matching transformer. My problem is the fact that no matter how low I set the input and trim levels, I get distortion. I'm only trying to record a clean guitar with the Champ's volume at about 4.

    I then dug out an old Yamaha mixer from their old Personal Studio series (MM30) and got the same distortion through that. I even selected line input and still got some distortion.

    Are SM57's known for being particularly hot? Would an inline pad, such as the Shure A15AS, solve my problem? The online description of the A15AS states that the device helps overloading when using a hot low-Z source to a low-Z input. I'm guessing that the BR-8 input may be hi-z as it uses a 1/4" input jack. By the way, I'm NOT using the hi-Z guitar input jack.

    Any ideas?

    DanR
     
  2. tedm

    tedm Gold Supporting Member

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    do you have the BR8 manual? Maybe the BR8 is expecting a TRS balanced (stereo style) 1/4" from the mic or vice versa. I'd try to get an external mic pre, even an art or behringer in between the mic and BR8.

     
  3. DanR

    DanR Member

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    Thanks tedm,

    Yes, I do have the manual (I bought the BR-8 new a couple of years ago). I will have to look at it as I admit, I haven't looked at the manual yet. But I also had the distortion problem with the old Yamaha mixer even when selecting line level for the input that the mic was plugged in to. I was going to take the line out from the Yamaha to the line in of the Boss, just to see if I could eliminate and isolate the source of the problem

    DanR
     
  4. tedm

    tedm Gold Supporting Member

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    What you'r going to try is good. If your cable connections, and line levels are all set right, and you can't get around the distortion, consider the mic or the BR8 unit.

    I've had mics/pres/mixers/recorders that on paper should have all worked perfect, but in reality didn't sound as good as other combinations.

     
  5. DanR

    DanR Member

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    I haven't checked the manual yet (I'm at work :eek ), but I found these specs on the net:

    Nominal Input Level (Variable)- GUITAR/BASS jack: -10 dBm
    MIC 1, 2 jack: -40 dBm
    LINE jack: -10 dBm

    Input Impedance- GUITAR/BASS jack: 1 M, MIC 1
    2 jack: 2.2 k(HOT-COLD),
    1.1 k(HOT-GND, COLD-GND), LINE jack: 50 k

    Connectors-
    MIC 1, 2 (1/4" TRS Balance)
    GUITAR/BASS (1/4" phone)


    Is the mic input considered low-z according to the specs? Is the use of the 1/4" adapter/impedance matching transformer appropriate? Again, I'm using the mic input. I'm assuming that the 1/4" plug on the adapter is TRS, but could I be wrong?

    DanR
     
  6. tedm

    tedm Gold Supporting Member

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    Dan,
    Just look at your 1/4" end of the cable to see if it's TRS balanced or just TS.

    Take a look here for a picture of a TRS:

    http://www.kellyindustries.com/articles/tip_ring_sleeve.html

    Ask Boss, or a user forum for that unit, what line adapter they recommend for the low Z sm57 mics for a) balanced use (TRS) and unbalanced use (TS) 1/4" cables. They'll probably have a specific Shure or Hosa P/N for you.


     
  7. enharmonic

    enharmonic Old Growth Gold Supporting Member

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    Good call tedm!

    As for the common 57, I wouldn't say that it's a particularly "hot" mic. You shouldn't be killing your recorder if you have the gain on the pre trimmed way down...so something is amiss in the signal chain....meaning...that if you have a clean tone coming from your amp, and even if you have the 57 right up on the grill or cone of your speaker...you should be good to go.
     
  8. DanR

    DanR Member

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    Thanks again tedm!

    After looking at the pictures you referenced, my adapter/matching transformer is unbalanced (TS). Since looking at the owner's manual for the BR-8, I found that the inputs accept either balanced or unbalanced jacks, although the impedance is doubled for the unbalanced usage. So, the input impedance of the BR-8 is 2.2k and the impedance of the Shure SM57 is 310 ohms. The transformer is 250-50k, so perhaps this mismatch is causing my distortion. I guess I have the option of buying a new cable or finding an adapter.

    Again, I appreciate your help.

    DanR
     
  9. tedm

    tedm Gold Supporting Member

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    A different line matching low to high adapter might work, as might an adapter to TRS balanced, which would also let you run longer cables, but I'd highly recommend trying to find out what is working well for other users, or get the Boss customer service guys to recommend what works well with a '57. Also, if using your external mixer/mic pre is an option, be sure to have those specs handy as well.

     
  10. GaryNattrass

    GaryNattrass Member

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    You dont need the matching transformer when plugging the SM57 into your unbalanced unit.

    The input impedance is high at 2.2k ohms and the mic is 300 ohms. It is OK to load a high impedance input with a low impedance mic. You do not need to match input impedance like you have to with loudspeaker loads where a lot more power is involved.

    You can plug the mic directly into the quarter inch jack using a 3pin xlr to jack lead.

    I do this with my fostex DMT8 recorder and it works fine you problem is that you are trying to match the input impedance and it is the transformer that is causing the distortion.

    Hope this helps.
     

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