Hello, recently (like 2 days ago) my amp started emitting this hum noise (around 50-60hz) which rly drives me insane. The noise is there even if the amp is not connected to the input. It doesnt increase/decrease with volume, and only thing that affects it is tone control (bass/treble). Also there is a slight noise coming from transformator itself.
What this could be and how could i fix it ?
What this could be and how could i fix it ?
I also forgot to mention, when amp is powering off, the "pop sound" is at extreme level since it completely pushes speaker membrane inside.
I'm guessing you haven't a scope which would find the problem very quickly...
Best guesses on what you say are either an open circuit reservoir cap, and/or a leaky shorted rectifier or physical damage such as a crack in the pcb,
Best guesses on what you say are either an open circuit reservoir cap, and/or a leaky shorted rectifier or physical damage such as a crack in the pcb,
I take it both channels behave the same way. If so then I would try bridging the reservoir caps in turn (by adding another across what is there). Anything from 1000uf up and of the correct voltage would prove the point. Don't dab them across because it would spark badly, solder them across and test.
Yes, both channels behave the same, same goes for channel A, B, A+B (but the lower hum since its lower amplification)
Noob question, what are reservoir caps, the big ones next to trasformator ? And how can i measure too see which one is a goner ?
Last edited:
Yes the big ones 🙂
You measure using a scope to look at the value of ripple voltage. A meter on AC may or may not give useful readings because there is a DC voltage present. All meters will behave differently in that situation.
You measure using a scope to look at the value of ripple voltage. A meter on AC may or may not give useful readings because there is a DC voltage present. All meters will behave differently in that situation.
An externally hosted image should be here but it was not working when we last tested it.
I presume you are talking about big black ones 🙂
I'll check with my friend who has elec. knowledge and all the instruments too see whats what.
Thx again m8.
You can also try comparing the readings across each of those caps with the amp on using both AC and DC ranges on your meter. Keep the meter lead polarity the same when measuring across the caps to get consistent readings.
Its not guaranteed to be the caps but they are favourite. The other possibility is the bridge rectifier having failed. This is the sort of fault where a scope comes into its own. Without and its a lot of guesswork.
Its not guaranteed to be the caps but they are favourite. The other possibility is the bridge rectifier having failed. This is the sort of fault where a scope comes into its own. Without and its a lot of guesswork.
Yes, I did mean those but I also see two smaller grey ones next to the bridge. They could be for other power rails to other parts of the amp. Same applies to those with regard to testing.
Hey guys, soo yesterday i been to my wiz friend, and we fixed the dam thing 😀
We added 2 caps (10000uF) and that fixed the problem, and then we added 2 additional industrial grade super fast caps to the existing ones, for better release timing on outputs, works like a charm.
Thx Mooly for all your help.
We added 2 caps (10000uF) and that fixed the problem, and then we added 2 additional industrial grade super fast caps to the existing ones, for better release timing on outputs, works like a charm.
Thx Mooly for all your help.
Hope you removed the old capacitors, nothing more fun than having an old power supply cap explode and wreck your amplifier.
Nah, we left them, too much hassle, and they werent swolen, soo they dont cause trouble.
But i still cant belive how can a two small RIFA caps increase fidelty of a amp, its beyond magic 😀
Nah, we tested with original caps and resolider, then with new caps, and then we added those RAFA. With new ones we boosted output to 63w (original is 45w) and it was too loud, but when we added those small fast one, holy ****, what a revelation, bass is soo powerful, yet calm, precise, mid's are more dynamics and high's are more "pitchy". I cant rly explain with words, but improvement is epic !
Btw, those repairs are done by a man who made world most powerfull amplifer (in 80's) 2xMonoblocks each about 2.5KW 😀 They are about 0.5m long in big metal heatsink, 12 military transistors from Radar unit, 8 caps (10000uF) and a whole bunch of little thingys i dont know what they are, but magic is ensured 😀
Btw, those repairs are done by a man who made world most powerfull amplifer (in 80's) 2xMonoblocks each about 2.5KW 😀 They are about 0.5m long in big metal heatsink, 12 military transistors from Radar unit, 8 caps (10000uF) and a whole bunch of little thingys i dont know what they are, but magic is ensured 😀
Do you have any photos of the new caps, and their location? I recently came across a KA-3500 that also has a similar buzz. Thanks!
Hey man, nah, i didnt took pictures, but new caps are the same as the old one, just bigger (old ones are 6500uF, new ones are 10000uF)
We just "jamed" them behind old ones, not a lot of space back there... (and u want to avoid placing them next to heatsink and transformator).
The small, fast ones are these, dont know what values tho..
An externally hosted image should be here but it was not working when we last tested it.
- Status
- Not open for further replies.