Some of you may know I own a quad 77 pre of venerable age..... For several years I 've been meaning to look under the hood, but what with all those chips running everything I decided there was little point. A couple of years back I even invested in the schematic from quad ....so it was with some suprise that whilst looking for something else I found it. I had a quick look and found to my horror that quad in there infinate wisdom had fitted muting transistors Q2 Q3 on the output to both the balance out and rca out. Why I'd never seen this I've no Idea.....but there they were the little sods bleeding away that precious signal to the analouge ground all these years. Out came the clipper off they came....... with trepidation I reconnected and switched on ....no big thump. So with no signal and the volume turned up I operated all the controls and switches ......and ......deadly silence. Now the real test, some music WTF.....sodding h*ll fast, clean. dynamic prat up to my armpits...imaging to die for whats going everyone knows the quad can't do it ! Whilst the hood was up I then changed the two 100ohm resistor in the signal path R170 R117 for dale vishays. Then replaced the two 1000uf 35v c16,c17 for two times three stacked 330uf 100v 105 degree jobies. Both mods were obvious but small beer compared to the muting transitors. So don't wait ten years plus like me ....get those clippers out!
