Re: [Harp-L] Low Z mics - Transformers

[G <gigs@xxxxxxxxxxxxxxx>]

Date: Sat, 2 Apr 2005 12:27:57 EST
From: AV1901@xxxxxxx
Subject: [Harp-L] Low Z mics - Transformers 
To: harp-l@xxxxxxxxxx
 
>I've never had much luck using a low-Z mic through a "guitar" amp, in 
>part  I  think because of the cheap piece of #*$!?" no name low-Z to 
>Hi-Z 
> converter I  picked up in an electronics shop a few years back.
>Anyone have a good recommendation for a good quality piece of equipment  
>that will do the job right?
>Thanks.
> Andy Vincent

Hi Andy.  
  In general there is very little inside an impedance adapter.   
By their nature regular adapters can only add +25dB to the output of a low
impedance mic, which is rarely pushes the signal up to the levels high
impedance mics used by harp players.  

I have a couple of impedance adapters - one is a no name brand from a local
shop, modified with the 1/4" plug wired to the end of a very short lead, so
that entire the whole weight of the adapter isn't levering down on the
jacks of my equipment -  instead it hangs applying less force.  
  It also has a switch for bypassing the transformer, when using gear like
the Hohner Blues Blaster which has an XLR connector, but is unbalanced high
impdeance.

The other is one I received with a balanced low impedance GB. It's "Archer"
model number 274-016.  I cannot find them on the internet anywhere - but
I've found Radio Shack sells something that is a dead ringer with their own
brand name, and strangely enough model number 274-016.

I've used both with SM58 and SM57s into amps and such, and they don't
affect the tone, and sound just fine - the SM57 with an adapter can give an
awesome over driven tone.

The most basic adapters like my Archer, simply have a small transformer and
a some wires connecting it to the XLR jack and 1/4" plug - very simple,
very little to go wrong.

The two signals form XLR balanced connection go into the transformer, and
the XLR earth is wired to one of the transformer's output signal and of
course the output's shield.  The remaining transformer output goes to the
1/4" tip (signal).

Not much to go wrong.  Things that could be a problem:
* shoddy soldering 
* substandard construction
* weak transformer, producing less than +25dB
* XLR pin 1 & 1/4" sheild earth aren't wired to the XLR plug's nub - if
this is the case you can end up with major hum, especially when unplugged
from equipment - but this wouldn't be noticable in live settings once
everything's plugged in and being played.

If the Radio Shack 274-016 is the thing as the Archer 274-016, then I
recommend it.    Shure sell some expensive alternatives, one of which is
identical in spec and design (+25dB, XLR to 1/4" short cigar shape),  as
well as others with more versatility due to different screw on jacks and
plugs and the ability to use them either way.   I use both my adapters
regularly - theres no difference, but when appropriate  I use my other
modified adapter to reduce strain on my equipment's jacks.  

If you are wanting a higher output from your mics than the +25dB any
adapter gives you, then use a preamp in some shape or form.

Since he's very popular and well regarded here - Jason Ricci used a low
impedance SM57 straight into his Octave stomp pedal without any adapter
(just a XLR to 1/4" cable), the stomp pedal worked as a preamp driving the
signal up to drive his amp properly.   Although I understand he uses a
different mic and setup now.

Cheers,
-- G.