Input mods for harp mics - required?

[axg20202]

Hi all,

I want to use some stomp boxes with my blues harp mic and it got me thinking about optimizing the input impedance of the pedals for this purpose. My preferred mic is a classic harp mic - a vintage Shure 520 'Green Bullet'. It's element has a DC resistance of about 1300 Ohms. Any thoughts on how (or if) I should modify a typical guitar stomp box input to improve performance with this kind of source? I know there are some boutique pedals available that have supposedly been optimized for use with harp mics - not sure what those optimizations are though, it could just be hype - but input impedance seems like a logical place to start.

BTW, I am aware of the need to have an amp with a suitable input too - harp amps are usually guitar amps with tweaks at the input stage. However, my tube amp works well using this mic direct and I don't want to modify the amp because it is primarily a guitar amp.

[wavley]

What's the stompbox? Unless the input impedance is miserably low you shouldn't need to mod it at all as far as impedance issues are concerned.  Looks like all the common harp amp mods are to get more/spongier/saggier distortion.  One that I just found was raising the 1 Meg input to ground to a 5 Meg, but high impedance mics work just fine into regular tube amps.

I might suggest just building a JFet booster to use with your harp mic, it will certainly have a high enough impedance and you can push the amp a little harder for some dirt and there are any number of nice ones you can build cheaply and easily.

[axg20202]

Well, I have a Rebote2 delay build that has been ready to box up for months and I figured it would lend itself well to use with blues harp. I do have a mosfet booster (AMZ boost/buffer) that I might try out. I guess I could try various things, was just wondering if anyone had some general tips on tweaks. I don't think I need to push the amp any harder - the mic output is hot already.

[petemoore]

  First we can look at theory as to how 'it' [what we're after here] was done.
   'It involves masses on springs moving sympathetically with some cancellational tendancies doing a kinetic back and forth dance.
  The varying speed of the reed and related motion of the cone make double wiggle loading, one from the front end, the other loading from the back end.
  Without the mass on a spring of speaker/air and cone/coil weight and suspension.
   This route to 'it' is probably the most direct, also is known as the one that actually goes there, suggestion being to study what makes those amps tick:
  Lighwieght duty or XLlightwieght 15watter speaker with 'right' voicing, old Fender/Celestion designs are examples.
  Then a little tube amp...that's about it if the front end is hit with hot enough signal and the output is loaded to create substantial non-linear tube behaviour.
  Otherwise that leaves mostly distortion, compression and Eq but mostly a set/fixed fixed parameters for starters, little of the speaker/reed/air what a reglar cranked sweet speaker amp does..
     
   
   
   

[Mike Burgundy]

I guess Wah is cool on harp, if used sparingly.
Basically, if it's good for guitar it's good for harp. Pickups have very high impedance (way, way over 1k3), so the 1300Ohms won't interfere much if at all (unless you're planning on using a fuzzface - no idea what that 'll do. If that isn't incentive for you to try it, I don't know what is ;P )
After building it's the same for harp as for guitar too - tweak to taste
(edit:spelling)

[andymac1962]

Hi
I made a preamp for the harp player in my band, who also uses a green bullet. I looked at what harp players use for an amplifier, such things as old fender bassman or low wattage fender amps, and swap 12AX7 tubes with lower gain 12AU7 types.
I used the ronn off groove princeton circuit, but wasnt happy with the first revision, so i made some small changes. This included running the unit from 12V instead of a 9V battery, which gave more headroom & more output. I had an old 12V wall wart (plug pack) power supply i use.
Now you can set it so when you blow hard you get a nice spongy growl, without having to overblow the harp & reduce the useful life of the harp. Our harp player loves it. Gets him that amplified growl of an overdriven tube amp, and he finds it easy, once the controls are set to his liking, to change his blow pressure to get clean / growl as he needs.
Easy to build.  With no input connected, adjust each trimpot for 6V on the drain of each fet.

Ive no idea how to insert or attach a file here, so email me & will send you the files
andymac1962   aaattt hotmail     dddooottt   com

[axg20202]

Thanks Andy. I'm not really looking to build a dedicated preamp for harp - it's something I would have done in years gone by but these days I simply don't have the time. I'm hoping to get a moments peace and quiet this weekend (which I will seek to distrupt!) and see what works well. I think I will start with my AMZ booster/buffer pedal and go from there....

Interesting idea re the FF. I have a Germanium FF that I could try. However, I have a suspicion that dirt is not something I need to add to the mix; plenty of pleasing tube distortion is already available. I am keen to try out some modulation effects. I have a Univibe clone and also a Meatball clone, which could be fun....but I'm prepared for the fact that only a pinch of delay and reverb, and perhaps chorus, might be the only things that are really much musical use with harp.....