A pearl of mine suddely quit working - it is always turned on, and one day, the left channel was suddenly very, very low. Got out my voltmeter, and checked voltages. All looks good, except Q4 (ZTX450 that supplies 13.8 volt to the double JFET output) instead of 13.8 volt is reading 0.8 volt - supposedly eliminating the last gainstage of the pearl.
Beeing a engineer of trade (computer however
....LOL) - I keep spares lying around, just in case - soldered in a new 450 in a few minutes - same case
This is where I whished I chose EE insted of Computer Science - anybody of you sharp brains got some clues to what I should start checking??
Kind regards
Hans
Beeing a engineer of trade (computer however
....LOL) - I keep spares lying around, just in case - soldered in a new 450 in a few minutes - same case This is where I whished I chose EE insted of Computer Science - anybody of you sharp brains got some clues to what I should start checking??
Kind regards
Hans
You will note that the Pearl schematic shows about 9 volts across
R14, which means that 9 mA is going through the pair of JFETs.
This is not enough to damage the 2SK389's. However, if the Idss
of the FETs used is high, it will cause too much DC across R14 and
saturate of Q4, at which point the whole think collapses.
Rather than assume that the 2SK389 is bad, I suggest you try a
higher value for R25 and see what happens.
R14, which means that 9 mA is going through the pair of JFETs.
This is not enough to damage the 2SK389's. However, if the Idss
of the FETs used is high, it will cause too much DC across R14 and
saturate of Q4, at which point the whole think collapses.
Rather than assume that the 2SK389 is bad, I suggest you try a
higher value for R25 and see what happens.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.