Just to revive this thread a little and give everyone an update:
After prolonged days of "square eyed" research, I have decided to go the reactive route with this project. The preservation of amp tone is excellent when a reactive component, in this case an actual silent speaker, is added to the design.
I have decided on a design for an attenuator that is safe to use on amps up to 30W and will include:
- a high quality wire-wound potentiometer (rheostat), with solid knob and pointer, for adjusting attenuation between zero and 100%1.
- a true bypass switch.
- a selector switch that the user will set to the same impedance of the amp used (2,4,8 or 16 ohms).
- a switch to add an extra 6dB of attenuation to the level dialled up on the knob.
- a selector switch to boost treble on the output2.
- an optional line-out jack with volume control3.
Notes:
1 When 100% attenuation is selected, the unit will act as a dummy load. This helps one not annoy oneself when faultfinding amplifiers that present problems at full crank!
2 This helps compensate for the rolloff in response at higher frequencies that is a characteristic of the attenuation circuit.
Boost levels of 3dB at 8kHz, or 6dB at 16kHz can be added to help equalise the response.
3 The line-out tap is taken
before the variable attenuation and treble boost is applied to the signal and enables one to record or distribute the amp's fully cranked raw tone.
Currently I'm deciding on an enclosure, engraved faceplate and switchgear. I will start putting together a prototype next week and will keep you up to date as I proceed.
