So, I've been enjoying (immensely) my pearl for a couple of weeks now. Tonight I went to change the volume, and static jumped from my finger to the volume knob. At first I thought I lost the entire left channel, but now it's playing quietly, and using the volume control (50k noble pot) to "6" brings sound to a semi-listenable level. Normally I'm a "3 or 4" on by control.
I've done enough troubleshooting to know that it's definitely the pearl, and that it's just not playing as loud. Where do I go from here?
I've done enough troubleshooting to know that it's definitely the pearl, and that it's just not playing as loud. Where do I go from here?
You might have fried a transistor...
To find the problem, I think you should measure the voltages on your left channel compared to the right channel and waynes numbers. If some of the voltages are way off, you might have the problem in that area or in the circuitry connected.
To find the problem, I think you should measure the voltages on your left channel compared to the right channel and waynes numbers. If some of the voltages are way off, you might have the problem in that area or in the circuitry connected.
cviller said:You might have fried a transistor...
To find the problem, I think you should measure the voltages on your left channel compared to the right channel and waynes numbers. If some of the voltages are way off, you might have the problem in that area or in the circuitry connected.
I was hoping that wasn't it. Thanks though.
I'm not exactly sure where on Q6 I should measure. And from which side of R25? From the side of R25 opposite of Q6:
1 2 3 4
.794 .307 .308 .795
5 6 7
.758 .383 .758
If I measure from R25 on the "facing Q6", I would subtract .307 from each measurement.
The voltage across R14 is 28.07 V
1 2 3 4
.794 .307 .308 .795
5 6 7
.758 .383 .758
If I measure from R25 on the "facing Q6", I would subtract .307 from each measurement.
The voltage across R14 is 28.07 V
Q4 is reading ~0.78 V from gnd
On the base?
You should have something like:
28V -[R17] - 14V - [R20]- gnd
and the base of Q4 is connected between R17 and R20.
The leg on R25 "away" from Q6 is the gnd, The voltage drop across R25 is 0.307 V.
Seems ok...
Is R26 the additional resistor for cartridge loading? My cart is 47k, so I did not use R26.
I don't know why I wrote R26, I meant R25.
cviller said:
On the base?
You should have something like:
28V -[R17] - 14V - [R20]- gnd
For Q4
Where Wayne has it marked 13.4 V, I'm getting 0.78 V.
Where he has it marked 19.3 V I'm getting 0.75 V
Where it's marked 14 V I'm getting 1.55 V
However, I'm getting a 27 V drop across R17... which definitely doesnt seem right.
Doesn't sound good to me..
Do you have an extra 2sk389? It sound like it is conducting too much current somehow.
You can try to take it out and place a ~1.2k resistor between where the 2sk389 had its drain and source (between Q4 and R25). That way Q4 should be able to give you the 10mA and correct voltages.
Do you have an extra 2sk389? It sound like it is conducting too much current somehow.
You can try to take it out and place a ~1.2k resistor between where the 2sk389 had its drain and source (between Q4 and R25). That way Q4 should be able to give you the 10mA and correct voltages.
cviller said:Doesn't sound good to me..
Do you have an extra 2sk389?
That might be the funniest (or most depressing) thing I've heard in awhile.
I'll try your resistor suggestion, any idea on if an LSK389 is truly a plugandplay for 2sk389?
I'll try your resistor suggestion, any idea on if an LSK389 is truly a plugandplay for 2sk389?
It should be, but the footprint doesn't match at all... or you can take two matched 2sk170bl from your drawer.
Happened to me too!
Recently I had the same problem in both channels while swapping some interconnects. I turned out the whole output stage was fried.
Just measure the voltage across R14. If this amounts to +/- 30 Volts, this implies that the whole rail voltage is across the resistor and none across the bipolar and JFET.
I have soldered new transistors on the PCB and now it is working as before. Just swapping a new ZTX450 for the old one is of no use when the 2SK389 is also fried. The ZTX450 will be fried instantly due to the resulting high voltage across it ...
There was a guy in Germany (Analog Forum) with the same problem, so apparently this output stage problem of the Pearl is more common than we would like.
I have learned from all this that the Pearl should be handled very carefully and perhaps it is best to keep some spare ZTX450s and 2s389s close at hand.
I would appreciate however if someone perhaps could offer an explanation as to why the output stage is prone to malfunctioning.
All the best,
JP
Recently I had the same problem in both channels while swapping some interconnects. I turned out the whole output stage was fried.
Where Wayne has it marked 13.4 V, I'm getting 0.78 V.
Just measure the voltage across R14. If this amounts to +/- 30 Volts, this implies that the whole rail voltage is across the resistor and none across the bipolar and JFET.
I have soldered new transistors on the PCB and now it is working as before. Just swapping a new ZTX450 for the old one is of no use when the 2SK389 is also fried. The ZTX450 will be fried instantly due to the resulting high voltage across it ...
There was a guy in Germany (Analog Forum) with the same problem, so apparently this output stage problem of the Pearl is more common than we would like.
I have learned from all this that the Pearl should be handled very carefully and perhaps it is best to keep some spare ZTX450s and 2s389s close at hand.
I would appreciate however if someone perhaps could offer an explanation as to why the output stage is prone to malfunctioning.
All the best,
JP
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