I am not suire if I match the transistors of my QSXM2 in the right conditions and specifications, espcecially I always facing so many weird issue about gain and noise.
Would P-A please state the ideal, or perfect way to match the BC550C/560C, such as:
1) Under how many mA of IC at how many hfe reading is minimum requirment?
2) Needed to match NPN with NPN only, or need to match NPN with PNP?
3) Other then hfe, any other parameter have to or even must to match?
I am thinking to re-built my QSXM2 again.
BTW, I found you seems busy recently, I am not hurry for your answer, so if you are busy, take your time, no need to answer me in rush, as you are offer free suppoprt, I and everybody no rights to push you anything.
By the way, I match NPN with NPN or PNP with PNP only, with 5mA of IC, matching hfe at least at 480, matching tolerance at around 2%, not sure if this is good enough.
There is no words but only THANK YOU I can say for all your supports, I hope someday we can met, at least let me offer you a drink to show all my thanks and respect.
1 400 uA, 5V collector-emitter voltage, min 300 hfe
2 Best both (nearly impossible).
Personally I think you could skip the matching since you have DC-servos but it's no harm to match if you want to.
The very best solution is to use super matched transistors like MAT02/03 or SSM2210/2220.
If you happen to be in Sweden, give me a call.