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Old 16th January 2009, 09:54 AM   #1
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Default Build speakers with low sensitivity

I wonder if anyone has any suggestions about elements (not expensive) and box to build a speaker for guitar and bass amps... It wil be used for testing purposes, and i want to turn up the gain a lot for testing the amps without too much volume. My wife doesn“t like when i test things loud....
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Old 16th January 2009, 10:02 AM   #2
OzMikeH is offline OzMikeH  Australia
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This isn't exactly the right forum, musical instruments would be more appropriate.

But I will answer you question because it is quite simple.
Get a very big resistor of 8 ohms, something that can handle as much power as the amplifier. To save money you can use a load resistor which is rated for half of the rated amplifier power but only if you play music, not continuous tones.

then you get a small speaker for monitoring, put about 80 ohms in series with it and put these in parallel with the big load resistor. You can use even more resistance and use headphones if you want. be careful selecting the values because you can damage your hearing or headphones if you get it wrong.

If you have any further questions you should ask in Musical Instruments or Amplifiers threads.

You should first search for the words: dummy load amplifier.
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Old 16th January 2009, 10:08 AM   #3
AndrewT is offline AndrewT  Scotland
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just add a couple of resistors to the speaker.
Add one in series with the driver to make an effective 16ohm load.
Then bypass the driver with 2r2. This reduces the load back down ~10ohms. and attenuates the speaker by ~-15dB.
The series resistor will need to very high power to dissipate the heat,
the parallel resistor can be just high power.
Adjust the values to suit the amp and the speaker impedance and the desired attenuation.
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Old 16th January 2009, 03:18 PM   #4
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Old 16th January 2009, 04:02 PM   #5
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Perfect, thanks for moving the thread to right place..


The most important thing is to still have 4 ohms for tube amps... And a resistor in 4 ohms that can handle up to 3-400 watts is expensive..... That is the reason why i will have as low senitivity as possible...
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Old 16th January 2009, 04:26 PM   #6
AndrewT is offline AndrewT  Scotland
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build up a stack of 50r 5W radial resistors to make your 4r0 load.
120 off @ 20p gives 600W resistor for just £24.
Add a few more to make up a 1r0 parallel resistor.
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Old 16th January 2009, 07:52 PM   #7
mjf is offline mjf  Austria
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hello.
mount it on a heatsink and cool it with a fan.
or perhaps watercooled?
greetings..............
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Old 16th January 2009, 08:10 PM   #8
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Perfect idea, all of it. I think i will buy effect resistors and build two four ohms stacks, mounted on heatsinks i have in the basement since a long time (didn“t wanna throw them away, now i'm lucky for that..) Then i can run it in two, four or eight ohms.. Is it ok to use "wire resistors" (i don't know what to call it.....) It shold't be a problem i think.
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Old 16th January 2009, 08:22 PM   #9
mjf is offline mjf  Austria
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hello.
perhaps there is annother option:substituting some resistors for lightbulbs (100watt? or so).if anybody can help you with this,i have no schematic...........
greetings.....
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Old 16th January 2009, 08:40 PM   #10
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Originally posted by mjf
hello.
perhaps there is annother option:substituting some resistors for lightbulbs (100watt? or so).if anybody can help you with this,i have no schematic...........
greetings.....
Lightbulbs are a VERY bad idea, they aren't a fixed resistance, and are very low resistance when cold.

Wirewound resistors are fine for testing guitar amps, although HiFi purists wouldn't be seen dead using them
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