[Harp-L] re: Impedance Mismatch Issue

[Greg Heumann <greg@xxxxxxxxxxx>]

Hi, Nate

The Blues Blaster doesn't really "put out" 5Mohm. 5Mohm is the "load"  
it likes to see, AKA input impedance. 1M ohm is standard on guitar  
amps and is considered a high impedance input.  It IS possible to  
substitute a 5M resistor in place of the 1M resistor that connects  
your amp's input to the mic, but the difference between 1M and 5M  
will be minimal. If your friend's Blues Blaster is one of the later  
ones, it no longer has an Astatic crystal element, but instead has a  
very cheap Japanese crystal. These elements are even more sensitive  
to the amp's impedance but they'll simply never be great elements. If  
that's the element, it is more responsible for the problem than the  
amp is.

For the SM57, you SHOULD use an impedance matching transformer to get  
the best performance out of the system. Typically these are placed at  
the amp end of the cable - so it looks like:

mic-->XLR  XLR<--cable-->XLR XLR<--impedance matching transformer-- 
>1/4" male

/Greg

http://www.blowsmeaway.com
http://www.bluestateband.net


> From: "Nate (The Blues Room)" <thebluesroom@xxxxxxxxx>
> Date: August 4, 2008 5:49:25 PM PDT
> To: harp-l@xxxxxxxxxx
> Subject: [Harp-L] Impedance Mismatch Issue
>
>
> Kia ora - Hello all,
> I have a friend who asked me the following and so I thought I'd see if
> anyone here has advice for him.
>
> "I am currently trying to solve my impedance mismatch issue with my
> amplified setup. I found out my amp only handles up to 1M ohms  
> while the
> Hohner Blues Blaster I bought puts out 5M ohms... The sound is very  
> thin and
> weak right now.
>
> I also have a Shure SM57 which runs at 150 ohms and even that  
> sounds better
> than my blues blaster plugged into my amp at the moment. I don't  
> even have
> an impedance adapter of any kind for that.
>
> So what do I do? Is it a specific DI that I need to get or do I  
> actually
> have to buy something like a mic preamp or harmonica preamp?
>
> Would really like to know the most affordable solution."
>
> Cheers,
> Nate in New Zealand