I may be too quick to say that the voltage across the TL431 is stable. It is actually fluctuating at a range of about 30mV, whereas the other side is stable to at least 10mV (measurement limit). As to why it is so, I couldn't find out why. Measuring continuity between components , and checking visually, there seem to be nothing wrong. May be the TL431 is bad.
TL431 is not that costly replace it if you want. So the out put is stable ? If it below 10mv after it warms up run with it .
I replaced the TL431, but it doesn't help.
Since then I tried a lot of stuffs, and finally be able to narrow down the problem, which is at C1. Here are the gist.
- The reason that the DC fluctuation at output symptom is voltage across TL431 isn't as still as it can be.
- When I soldered a 220µF electrolytic capacitor at C1, the problem appears.
- Replacing the 220µF electrolytic capacitor does not solve the problem.
- Soldering a 47µF film cap largely solved the problem, but soldering 220µF electrolytic capacitor on it brings the problem back.
- If I connect the 220µF electrolytic capacitor through wire with alligator clips, the problem disappears.
- If I clip the leads of the 220µF electrolytic capacitor directly without the wire, the problem came back.
So I thought, may be I need the resirtance of the wire. So I tried adding a resistor (1Ω, 5Ω and 22Ω). If I clip the resistor leads directly, the problem remains. If I connect the resistor through wire with alligator clips, the problem disappear.
Why is it that the wire with alligator clips seems to posses magical property? Any ideas?
Since then I tried a lot of stuffs, and finally be able to narrow down the problem, which is at C1. Here are the gist.
- The reason that the DC fluctuation at output symptom is voltage across TL431 isn't as still as it can be.
- When I soldered a 220µF electrolytic capacitor at C1, the problem appears.
- Replacing the 220µF electrolytic capacitor does not solve the problem.
- Soldering a 47µF film cap largely solved the problem, but soldering 220µF electrolytic capacitor on it brings the problem back.
- If I connect the 220µF electrolytic capacitor through wire with alligator clips, the problem disappears.
- If I clip the leads of the 220µF electrolytic capacitor directly without the wire, the problem came back.
So I thought, may be I need the resirtance of the wire. So I tried adding a resistor (1Ω, 5Ω and 22Ω). If I clip the resistor leads directly, the problem remains. If I connect the resistor through wire with alligator clips, the problem disappear.
Why is it that the wire with alligator clips seems to posses magical property? Any ideas?
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I've built 4 chanel F4 on IRFP240/9240 and everything seem to all right exept one thing. Both sides of my F4 are playing relatively dry comparing to F3 or F5. So I recon timbre of music to be not so impressive I expected. Simlilary like "Navyblue" I changed 220uF caps for different Elna silmic from differente source (thought the first ones were fake) but that didn't cure the problem. I sounds exactly the same. Any idea how it can be or just it's just like that ?
buzzforb said:
I dunno... I had my F5 out yesterday and it's really quite nice.
You have to remember that although we, through building a bunch of these different Pass amps, are getting good, informed ideas on which we like best, you must remember that all of the Firstwatt series are so much better than most solid state amps... my least favorite Pass amp is still miles ahead of any other power amp I have.
Essentially we are having an argument about which Ferrari is the most Ferrari-ish. They are all Ferraris.
I used BA3 front but to quit from any coloration I tried B1 buffer and no preamp at all (literally). Still it sounds the same. A lot of space but tiny dry and sibilants. So now my list of preference is as follow:
The winner SIT amp (my version)
the second F3
the third F5 (trimed to second harmonic)
and last F4.
But no complaints just fun !!!
is it secret - which SIT's you're using ?
edit - never mind - I'm not that lazy ........
http://www.diyaudio.com/forums/pass-labs/233057-sit-variations.html#post3433887
edit - never mind - I'm not that lazy ........
http://www.diyaudio.com/forums/pass-labs/233057-sit-variations.html#post3433887