Instructables
Picture of Minty Amp Attenuator
This project shows you how to build an attenuator for your tube practice amplifier, so you can crank it up loud at night if you live in an apartment. It will work with single-ended amps like the tweed Fender Princeton, Epiphone Valve Junior etc. Make sure the speaker is rated at 8 ohms. It will not work with bigger guitar amps with an output of over 10 watts. The resistors will melt, and then the power transformer in your amp will explode.

So do this at your own risk.

You will need:

Jacks £1.79 x 2 = £3.58
   Matrix board £1.69
   7w resistor 0.59
   3w resistor 0.55
   Altoids tin 0.90
   Gym membership card - stolen
   Tools - already have some

£7.31 total, mostly from Maplin, easy to find stuff, that’s around 10 bucks. You could spend 100 dollars on something that does the same thing, but that’s no fun. It's a simple project, you'll make 10 solder joints, which isn’t too much work. Leaving out the chassis ground saves you 2 if you’re in a hurry.

The whole project took me a morning to build. Drilling was the slowest part for me, it helps if you have good tools. I had a small drill, a soldering iron, some wire, a multi-meter and a pair of pliers.

According to the attenuator calculator we need a 5.1 ohm 7w resistor in series with the speaker, and a 4.4 ohm 3w resistor in parallel for a 9db output cut to 8 ohm speakers. The values I ended up using were 5.6 and 4.7 ohms, the closest I could find at Malins. For a bigger amp, you’d need bigger resistors with the same vaules, a bigger tin and some way of getting rid of the heat. For a smaller amp, the extra beefy resistors won’t make a difference. A 5w amp like the Princeton will put out about a watt through this attenuator. If you're working with something like a Champ or an Orange AD5 find out the speaker impedance and do your own calculations.

 
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mikeasaurus3 years ago
You should enter this in the musical instrument challenge!