4 ohm dummy load...easy to make?

Steven Welborn · Post by **Steven Welborn** » 20 Apr 2000 10:54 am

to be on the safe side, I'd rather have a propper load in main speaker-out while practicing from preamp-out to headphone. No one I've spoken to knows anything abouut it. Anyone know about fashioning your own? 4 ohm resistor, jack and...? thanks SW

Robert Parent · Post by **Robert Parent** » 20 Apr 2000 11:18 am

Radio Shack for many years sold (and likely still does sell)an 8 ohm resistor, 25 watts which could be used as a 'dummy' load. To get your 4 ohms place two 8 ohm resistors in parallel. This will also allow a 50 watt load as well. Beware as these will get hot when used.

Mark Amundson · Post by **Mark Amundson** » 20 Apr 2000 11:58 am

Parts Express has 200 watt, 4 0hm audio dummy loads that may solve your problem. I've bought four of them last year to create a 4 ohm, 800 watt load for testing PA amplifiers. They cost $33.50 each and are rather large (about 6" x 3" x 1") sandcast resistors with aluminum extrusion encasement. If you really gotta push the power amps, buy two 8 ohm versions and parallel them together.

I place them on piece of plywood with them elevated using one inch aluminum PCB standoffs. They will get very warm if you push them to the ratings limit.

Parts Express: www.partsexpress.com
1-800-338-0531

4 ohm, 200 watt load part number: 019-025

Terry Downs · Post by **Terry Downs** » 20 Apr 2000 9:02 pm

Any modern day amplifer should not require a load to be safe. This was a concern back in the days of the first solid state car radios and home radios (<1965) that had a feedback loop driving the speaker current.

No amp I know of that you would use on stage with a PA or instrument, or headphone driver requires a load. A headphone load is usually 600 ohms...which is a large impedance anyhow.

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Terry Downs
http://nightshift.net
terry@nightshift.net

Terry Downs · Post by **Terry Downs** » 20 Apr 2000 9:06 pm

I forgot to mention that the loads described by Mark Amundson are intended to test or burn-in an amplifier. Engineers and repair techs need a way to play a big signal into the amp wide open to see if it can survive. The "dummy" load appears to the amp as a speaker but makes no (almost no) sound.

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Terry Downs
http://nightshift.net
terry@nightshift.net

Dan Tyack · Post by **Dan Tyack** » 21 Apr 2000 6:42 am

There have been many of these on the market, the best sounding (doesn't change the tone much at all) is the THD Hotplate.

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www.tyacktunes.com

Rich Paton · Post by **Rich Paton** » 21 Apr 2000 8:23 pm

"All Electronics" has a nice selection of power resistors (cheap) that could easily be lashed together to make an 8 and/or 4 ohm test load.
A very good outfit to deal with, and they carry all manner of neat electronics tools and goodies to play with!

http://www.allelectronics.com/

Steve Feldman · Post by **Steve Feldman** » 22 Apr 2000 11:23 am

Mark A., and Rich P. -

I gotta thank you guys for the tip on the two sources for electronic equipment. I've been thinking about rigging up my rack case for weeks now, but I could never get everything I needed in one place - and when you throuw in a $50.00 minimum order at some places, it makes it tough. And not being a big electronic whiz, I've been getting lost looking through the Allied Electronic catalogue that I have. How many freakin kinds of power receptacles can there be?????

Hopefully, I'll get it done now.

Steve