# Transistor pin voltage question

bigp7099
January 30th, 2012, 11:54 PM
I'm troubleshooting a ROG May Queen (http://runoffgroove.com/mayqueen.html), i can't get it right so i'm going to start again, but i'm confused by one thing. the C on Q1 and Q2 both have a 10k resistor between themselves and the +9v, but Q1 should read 7.1v and Q2 (and Q3 G i think) should read 1.37v (G is supposed to be a little higher?). now my understanding of electronics is pretty lousy but shouldn't Q1 and Q2 c be about the same if they both have a 10k resistor?

Montana_Dawg
January 31st, 2012, 02:47 AM
I'm troubleshooting a ROG May Queen (http://runoffgroove.com/mayqueen.html), i can't get it right so i'm going to start again, but i'm confused by one thing. the C on Q1 and Q2 both have a 10k resistor between themselves and the +9v, but Q1 should read 7.1v and Q2 (and Q3 G i think) should read 1.37v (G is supposed to be a little higher?). now my understanding of electronics is pretty lousy but shouldn't Q1 and Q2 c be about the same if they both have a 10k resistor?

No, because of the 10K-470K-47K voltage divider that provides the bias for Q1 C and B. The majority of the voltage will be dropped across the 470K resistor, which biases C. On Q2, the majority of the voltage is dropped across the 10K resistor, so the rest is the bias of Q2 C.

G's measurement is from Gate to Source, much like Q1 and Q2 Base to Emitter junction. The Source voltage is from the Source to ground, which is developed across 2.2K resistor from the 220K-2.2K voltage divider.

Montana_Dawg
January 31st, 2012, 02:49 AM
The main thing to consider is making sure the components are identical to the schematic. If they are substitutes, then they may have different pinouts. Check the datasheets to confirm. Also, make sure the voltage divider resistors are correct.

bigp7099
January 31st, 2012, 10:27 AM
Thanks, i thought the parts had to be in series to draw off voltage like that but my understanding of how electronics actually work is pretty lousy, so time to do some more reading.

the parts are all right but something is wrong the circuit is so simple it will be easier to just do it again rather than try to fix it anymore, i made it even more compact so it's just too hard work on. my only sub was a 100k + 47k resistor instead of the 150k, and i've tried every pin configuration possible with the transistors (unless one of the outside pins is actually the middle), it gives some boost but no distortion at all, and i can't get Q2 right even though i have added a 250k pot as a variable resistor.