I have to fine bias a GE transistor, and I need a trimmer because next stage is direct coupled.
Bias resistors are,
rc=10k,
re=2.5k gain pot
rb1=470k (vcc to base)
rb2=100k (base to gnd)
vc about 4.5v
I need to keep noise to a minimum using metal film resistors,
where is the best place to put the trimmer, at rc, rb1 or rb2? (ignore the emiter since there is a gain pot there)
I ask because I ignore how noisy trimmers are (compared to carbon and metal film resistors).
thanks.
mac
That bias is very stable. Build it no-trim. I predict the collector will sit at 3.5V (on 9.0V supply). If you want to set it higher, put a larger resistor in parallel with Rc. 10K||47K will put it at 4.5V. If you feel you need to set it lower, increase Rc to 12K, 11K, 13K, whatever.
The problem is that a small change makes a big difference in the next stages which are all direct coupled.
That's why I need the trimmer.
The question is where to put it to get the less amount of noise. This is for HiFi project.
mac
Put it in the collector. That's the least-sensitive point.
QuotePut it in the collector. That's the least-sensitive point.
Because any noise at the base would be amplified by the transistor?
mac