purpose and use of matchbox

John Robel · Post by **John Robel** » 27 Jan 2003 2:19 pm

Well I'm sittin' here wonderin'will a matchbox hold my clothes? Seriously why is it called a matchbox? What does it match? How do you know when the match is made? If impedence is the issue, shouldn't a meter or some means of verification be used? I am not trying to belittle a good product of a good company, I am just in the dark. Or "I aint got no matches but I still got a long way to go!! Thanks John

John Robel · Post by **John Robel** » 27 Jan 2003 2:22 pm

Why isn't it just called a preamp?

Bill Terry · Post by **Bill Terry** » 29 Jan 2003 7:53 am

It matches impedances. The matchbox is essentially an op-amp buffer circuit that is designed to eliminate some undesirable tone and/or gain changes that can occur with mismatched impedances. It could be called a preamp, with unity gain. A typical buffer circuit and a preamp circuit are very similar.

If you want to learn more about op-amp circuit applcations and theory, here's a link to the National Semi web site with a lot of good stuff. Or do a web search, you'll find tons of info.
http://www.national.com/appinfo/amps/0,2175,967,00.html

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Erv Niehaus · Post by **Erv Niehaus** » 29 Jan 2003 10:19 am

Besides doing what Bill said, I like it because it has a volume and tone control on it. It's real handy when you can't reach your amp. I've also noticed that it even takes the noise out of your foot volume pedal when the pot starts to get scratchy.
Erv

Terry Downs · Post by **Terry Downs** » 29 Jan 2003 8:02 pm

John, That is a good question. It really doesn't "Match" anything. The impedance that loads a magnetic pickup output varies widely with position of volume control, and the amp input impedance (cables have some effect too). When the volume potentiometer is backed off from MAX, it inserts resistance in series with the signal. This, in conjunction the pickup impedance and input capacitance of the amp reduces high frequencies.

The Matchbox is simply a preamp with some moderate gain, and a high input impedance for the pickup to "see". It has a low output impedance that helps top drive the volume pedal and line to the amp. Depending on your pickup, volume pedal, cables, and amp, the effect will vary. Some folks get by just fine without a Matchbox. If you experience reduction of high end when volume is reduced from max to less than max, a Matchbox will virtually eliminate that effect.

Regards,
Terry

John Robel · Post by **John Robel** » 30 Jan 2003 10:42 am

THANK YOU!!! guy's (I need all the help I can get)It (my 7a) is well constructed and has no foul habits, but I am a mechanic by trade and the fine points of sound equipment is something regretably I am ignorant of. I can make some adjustments with a hammer though! Take care, John