Here's another "Brian May in a box" circuits, this time from Run Off Groove. The May Queen is a treble booster/overdrive that should get you pretty close to those classic Queen tones. The cap between 9v and the drain of Q3 in the layout below is optional. It's a high end filter, so the larger the values will cut more treble frequencies (2.2n is just a good starting point–adjust to taste). I've added polarity protection, power filtering, and a pull down resistor at the input. You might be able to cram it into a 1590a. For the schematic, transistor voltages, and sound samples, check out RunOffGroove.com.