BSIAB2 with 18 volts??

[nero1985]

Hey guys, i built the GGG BSIAB2 and it sounds pretty good, i have a dunlop dc brick and it has 9 and 18v so i was wondering if i could just use the 18v output without damaging it, what do you think?

[mhartington]

shouldnt be a problem, as long as all the capacitors can handle it which they should be able to. You'd just have to rebias after to about 9volts on the drain leg of q3 i think. it could be q4. a bit less distortion but it does sound better overall

[brett]

Hi
short answer: don't bother
long answer: re-biasing to a mid-point voltage on the drain of the output stage has several effects, the greatest of which are to change Id and the available headroom.  In general, and in this case, there are no advantages of changing Id and substantial disadvantages of increasing headroom (who wants less distortion in a distortion box?). 
Of course there is the VERY popular psycho-social advantage of bullsh*tting your friends: "my BSIAB2 runs at 18V and it is sooooo much better now".  Maybe put a big "18V" sticker on it? 
cheers