Tonight I started working on the Attenuation for Amp #2. My friend will want to practice at home and most likely play in some smaller venues. I'm building into the amp the ability to reduce the volume at the speaker, but hopefully not affect the quality of the sound too much. This will allow the amp to be cranked up to get the desired distortion, all the while enjoying a volume level at the speaker that is neighbor friendly. There is also the possible situation of playing in a smaller venue where a full 18 watts is way too much power. Besides having the ability to go to eleven this amp will also be able to go to a polite eleven.
I found this schematic along with an excel sheet that
calculates the values for the various levels of attenuation given a speaker impedance value.
(Link to the site with the excel sheet
http://www.wohlgemuth.de/board/bridged_att_calculation.xls)
Luckily I had some turret board material and some turrets on hand. This set allows for two levels of attenuation. These these values will produce 9db or about 2.3 watts of output. The other level is for at home use with 20db or about 0.2 watts of output. I'll be able to tweak these values just by changing the resistor values out.
There will be an Attenuation Switch on the back of the amp that will function like this:
- Up - 2.3 watts
- Middle - Off (Removes it from the circuit)
- Down - 0.2 watts
Mouser (
www.mouser.com) didn't stock a 15watt 30 Ohm resistor, so I went to the next higher wattage rating to obtain the needed Ohm value. I'll most likely fashion a metal screen to protect and hide these resitors but still allow them to radiate the 18+ watts of heat at full tilt. Mind you that since we are talking waves, that roughly only .7 of the 18 watts is required.
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