I had this idea for a while and I finally put it in a box. Had it built for a while, but it didn't feel safe, without a box. I'm using it with an Ironheart Studio, and it eliminated all the noise from the clean channel, makes it crankable, and warms up the gain tones. It sounds better than the built-in attenuator in the 6505MH, could be the schematic, the amp, or just the quality of resistors used... These are a mix of ceramic Visatons and some metal oxides. The schematic is a simple voltage divider with the amp seeing a 17 ohm load and the speaker wired between the last two ohms and ground. This divides the voltage by 8.5, which results in a volume reduction of 19dB. The amp has all of 150 milliwatts now. Any impedance speaker cab can be used, and the amp will be safe. It barely gets warm. In conclusion, if you've thought of building an attenuator, you probably should. With nice resistors.