Computer speakers - fixing hum

[pfrcom]

I've had these brand X speakers for >20 years - great sound, thought they were worth hanging onto

But they've been developing a bad hum, which has been getting worse, until now it overpowers the sound

Would replacing any or all of its six capacitors maybe fix the problem ?
- 4700uf 25v - two of
- 33uf 16v - two of
- 1uf 63v - two of

[Andrew F. Ali]

Re: Computer speakers - fixing hum

I would look at the Power Supply section and change-out the big e-caps.....Yes probably those 2 e-caps 4700uf 25V are the problem....

[stj]

Re: Computer speakers - fixing hum

change the lot.

[momaka]

Re: Computer speakers - fixing hum

Also check for bad solder joints on the input jacks.

I would look at the Power Supply section and change-out the big e-caps.....Yes probably those 2 e-caps 4700uf 25V are the problem....

+1

Though, you might as well change all of the other electrolytic caps then, as stj suggested. They won't be nearly as expensive as the two 4700 uF 25V units.

Another thing worth mentioning is that, depending on the output voltage of the transformer, you may use a linear regulator to feed the amplifier. When you do that, this should eliminate pretty much all of the hum. Something like a 7812, 7815, or 317 (adjustable) should be fine, so long as you put a proper heatsink on it and don't exceed its specs. But this suggestion is perhaps more fitting if you like playing with amps an audio gear.

[eccerr0r]

Re: Computer speakers - fixing hum

curious if there's hum when no signal is presented?

[jiroy]

Re: Computer speakers - fixing hum

Also check for bad solder joints on the input jacks.


+1

Though, you might as well change all of the other electrolytic caps then, as stj suggested. They won't be nearly as expensive as the two 4700 uF 25V units.

Another thing worth mentioning is that, depending on the output voltage of the transformer, you may use a linear regulator to feed the amplifier. When you do that, this should eliminate pretty much all of the hum. Something like a 7812, 7815, or 317 (adjustable) should be fine, so long as you put a proper heatsink on it and don't exceed its specs. But this suggestion is perhaps more fitting if you like playing with amps an audio gear.

+1 ..

Better also change wires , they may be rusty after long use .

[techman1025]

Re: Computer speakers - fixing hum

I would start with the connector ..the switch get stuck in side grounding out.
Techman1025

[goontron]

Re: Computer speakers - fixing hum

+1 ..

Better also change wires , they may be rusty after long use .

And that heatsink. Thats got to be more Oxide than Aluminium.... /s

[pfrcom]

Re: Computer speakers - fixing hum

curious if there's hum when no signal is presented?

Yes

[dick_barton]

Re: Computer speakers - fixing hum

I would scope the DC supply lines and see if your introducing hum via poor smoothing of the DC supply.

[pfrcom]

Re: Computer speakers - fixing hum

would scope the DC supply lines

Not an option for me, neither scope nor knowledge how to use

Waiting on caps from China - I know, I know - but RS Components pissed me off with their MOQ for 1uf 63v, and delivery charges rule out other top tier vendors

[budm]

Re: Computer speakers - fixing hum

The 1 uf cap sounds like for coupling cap, may be you can use 2.2, or 4.7uf just for testing for now, but if they are coupling caps then I doubt that it will fix the hum problem. since the highest rate Voltage cap is 25V then it does not have to be rated at 63V.

[pfrcom]

Re: Computer speakers - fixing hum

I replaced all six caps with:
- 4700uf 25v - Nichicon PW
- 33uf 16v - Rubycon YK
- 1uf 63v - Panasonic EB

I reckon they're all genuine, otherwise pretty convincing fakes - and all tested OK on Banggood kit Transistor Tester

FWIW, both old 4700uf & one 33uf tested as "No, Unknown or Damaged"

All the old ones were marked 85 - but no way did I buy those speakers in 1985, more like 1995

And the outcome - no more hum and clear as a bell

My thanks to everyone who contributed

[diif]

Re: Computer speakers - fixing hum

All the old ones were marked 85 - but no way did I buy those speakers in 1985, more like 1995

85 is the temperature rating in C.

Nice fix BTW.

[pfrcom]

Re: Computer speakers - fixing hum

All the old ones were marked 85 - but no way did I buy those speakers in 1985, more like 1995

85 is the temperature rating in C

Full disclosure:




I assumed 40/85 was a date, but maybe it's tolerance/temperature

[Per Hansson]

Re: Computer speakers - fixing hum

No it's temperature rating.
From -40°C to +85°C

CD11 is the datecode

[momaka]

Re: Computer speakers - fixing hum

FWIW, both old 4700uf & one 33uf tested as "No, Unknown or Damaged"

Wow, even the 4700 uF units tested open?!?!

Those are some seriously crappy caps then.

Nice job on the fix. Those Nichicon PW caps should not give you any trouble for at least the next 15 years (I'd say at least 25, though).