When amps have mic inputs...

Discussion in 'Amp Tech Center' started by schmee, May 30, 2019.

  1. schmee

    schmee Poster Extraordinaire

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    I wonder what the input difference is? A harp playing friend has asked me to look at a SS guitar amp he uses that feeds back too much. Wondering if there's something simple I might do to tame the input better for a crude mic those guys use...
     
  2. Rockdog

    Rockdog Tele-Afflicted

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    Just a thought and maybe worth a try...

    My old Bandit as a High and Low input. When you put a plug in both, the output defaults to Low. A dummy plug in the instrument input may attenuate the mic input.
     
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  3. kennl

    kennl Tele-Afflicted

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    Suggest a different harp mic.
    Green Bullets feed back less than those Astatic mics, which behave like a microphonic Tele bridge pickup.
     
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  4. Bill Moore

    Bill Moore Tele-Afflicted Silver Supporter

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    I have been thinking of building a harp amp for my brother in law, and thought I might use a 600 to 10K ohm matching transformer on one input. (With an XLR).
     
  5. schmee

    schmee Poster Extraordinaire

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    He's using a Bullet. But I'm not sure he's just gotta learn some more tweaks, I sold him a SF Champ a while back and he "cant get it loud enough without feedback" he says.
     
  6. Dacious

    Dacious Poster Extraordinaire

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    Drop input gain if you can. I've built a couple of 5E3 and with a 12AY7 in the first slot they work very well with a cardioid mic.

    You can well and truly use a mic in one input and guitar in the other. Even when the guitar is starting to break up the mic sounds clear. Would be giggable with a quiet drummer and doghouse bass.
     
  7. Milspec

    Milspec Friend of Leo's

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    My old '49 Epiphone Century has 3 inputs (instrument, phono, mic). How that works in the circuit is outside of my depth to explain.
     
  8. schmee

    schmee Poster Extraordinaire

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    I need to get him over here and see what he's doing. He should be using input 2 I imagine.
     
  9. printer2

    printer2 Poster Extraordinaire

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  10. philosofriend

    philosofriend Tele-Holic

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    Look at where he is standing. Right in front of the amp is not good. If the amp is open backed, right behind it can be bad also. Get the mike away from the amp.

    Does he know how to experiment with the tone controls?

    Some amps with two inputs have different tones between the two, one might have less feedback problems. But don't count on it.

    If you adjust the mike by itself so it is right on the edge of feedback, it will squeal when the players hand are cupped around it.
     
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  11. Chunkocaster

    Chunkocaster Poster Extraordinaire

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    Make him a copper shielded fedora?
     
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  12. Old Deaf Roadie

    Old Deaf Roadie Tele-Holic

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    Might I suggest a graphic EQ pedal (or rack unit) between the mic & the amp to control the offending frequencies?
     
  13. schmee

    schmee Poster Extraordinaire

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    You know, that's a good idea, I have one he can try.
     
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  14. magicfingers99

    magicfingers99 Friend of Leo's

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    put a mixer in front of the amp so you can eq it.

    upload_2019-5-31_11-35-28.jpeg

    65$ on amazon
    they make smaller ones but this is good if he want to loop an fx pedal like reverb into his signal. can also record his sound so he has a mix of his performance using the appropriate routing to a recording device like an iphone or mp3 player etc.
     
  15. KyAnne

    KyAnne Tele-Afflicted

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    Instrument, old phono, and mic in 1949? Probably not a nickels worth of difference (impedance wise) in any of 'em.
     
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  16. Milspec

    Milspec Friend of Leo's

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    I suspect not
     
  17. FenderLover

    FenderLover Friend of Leo's

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    Maybe check out the Weber 5F2H Harp amp for ideas:
    https://www.tedweber.com/media/kits/5f2h_schem.jpg

    They use local NFB on the first stage. That will decrease gain and input impedance.
     
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  18. 24 track

    24 track Doctor of Teleocity Silver Supporter

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    I have a pair of these ( one of each) they are inexpensive used (20.00 for the one with out the meter , and 25.00 for the one with) I replaced the 12 AX7 immediately with something of better quaulity and these work great , they also work as great tube powered DI's

    12611991_800.jpg

    180581000000000-00-500x500.jpg
     
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  19. kbold

    kbold Tele-Holic Silver Supporter

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    The phase reversal switch will do the trick.
     
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  20. Paul in Colorado

    Paul in Colorado Telefied Ad Free Member

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    Get him a longer mic cable.

    But seriously, I believe the mic inputs were padded down a bit. I should ask a guy I know who works on old amps and especially likes ones from the '40's.

    I will report back!
     
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