FJN3302R (NPN) to replace the KRC102M. I think...
FJN4302R (PNP) to replace the KRA105M. I think...
Will these work...😕
FJN4302R (PNP) to replace the KRA105M. I think...
Will these work...😕
One of the HK898's is dead silent turning on and the other has a bump when it turns on. DC offset is 13mv and 9mv on the amp with the bump. The other amp has 60mv dc offset 😱 but its dead quiet 🙄 Still T/S that problem. Both trans data sheets look close and I can get the FJN3302R and FJN4302R from mouser for next to nothing.
I'll draw a small schemi for that portion of the circuit to make sure.
I'll draw a small schemi for that portion of the circuit to make sure.
Did you confirm that the drive voltage for the muting transistors was transitioning as it should?
You can simulate a mute condition by shorting the collector and emitter of the muting transistor.
You can simulate a mute condition by shorting the collector and emitter of the muting transistor.
I have not confirmed the drive voltage but will check it. That is cool info about simulating a mute condition. Awesome knowledge, thanks Perry..
I replaced the diff input pairs and got the amp down to 3mv (Lt) and 10mv (Rt)... Dumb luck without matching them first 🙂. Now amp has turn-on/off bump noise. Still T/S. 😎
These semi's checked good, thanks Perry.
I found on both of these amps that the op-amps circled in red were causing the turn on noise. Now they are very quiet an DC Off-set on both amps is lower than 13mv. FINALLY!!!
These make very good sub amps, there cheep and can take a beating.
Attachments
Are those before or after the muting transistors? If before, the muting transistors should have prevented any turn on/off noise if the mute driver circuit was functioning properly.
As far as I could tell, they are after...
I haven't had time to draw a schematic....not fun.
OK one amp still has a turn on bump if I turn it off and then quickly (within a few seconds) turn it back on. If I leave it off for 30 seconds or more, it turns on fairly quiet.
I know it has some bad op-amps because I swapped them around and it turned on fairly quiet.
I've got to order some new ones and I'll get new muting transistors and replace them.
I replaced the 5 op-amps and the 2 muting semis with FJN3302R and FJN4302R.
Results.....
No turn on/off noise at all.
Dc offset; 8mv and 3mv, Lt & Rt.
😎
Results.....
No turn on/off noise at all.
Dc offset; 8mv and 3mv, Lt & Rt.
😎
In the future, you may want to replace one component at a time and re-check the operation of the amp. This can help you learn more about which one actually solved the problem.
Thanks Perry, your correct. The only reason I change all components was they were inexpensive, I now they are all new and I'm going to keep them for sub amps. Plus the honey do list limits my time 😀 ...
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