Help troubleshoot amplified speaker

[cvill]

Hello all!

Anybody willing to guide me in troubleshooting an amplified speaker? Its a bose knock-off named dibo and had a good bass when it was new. Its a 30W speaker with volume, balance, treble and bass knobs. As it aged, the bass became incosistent and makes some scratchy sound while fiddling with the bass knob. Sometimes I get the bass back but have to lower the treble as well. It got stored for a long while and now that I'm using it again, the left channel lost most of its signal. I can still hear some sound but very weak, probably from the tweeter only. I can do basic soldering and parts replacement but circuit analysis is not my cup of tea/coffee.

Give me your insights...

Thanks and more power!

 

[audioguru]

Cheap woofers were made with plastic foam instead of rubber for the cone surround. It rots away then the cone is not held properly and sound from the rear cancels sound from the front through the space where the surround used to be. Some people are able to replace the cone and surround all in one piece but most people just throw away the defective speaker.

Bose has poor quality. Yours is lower?

 

[cvill]

bose has poor quality? why the heck does it cost so much? well anyway, back to my problem, i think its more on the amp circuit. but i will check out the cone as well. will post a picture of it in case anyone can identify it.

 

[audioguru]

There are many "Bose Bashers" on the internet. Bose speakers are cheap. The woofer is too small so it BOOMs with no deep bass. The satellite speakers are cheap and are too small. There are many frequencies that are not played by the woofer and not played by the satellites. Not much power.
Bose makes money, not good sound systems.

There is an arena near me with a Bose PRO sound system. It sounds horrible and it was also very expensive.

 

[mneary]

Consider the Emperor's New Clothes. (By Hans Christian Andersen). If you charge enough, the buyer will insist that it is good.

No highs, no lows; must be................

 

[cvill]

back to the topic, i isolated the problem to the passive speaker. the cone looks fine and energizes when connected to another source. could the capacitor on the speaker be at fault? wasn't able to check it yet. its a 50V 3.3uf capacitor (pink color if that helps)

 

[audioguru]

I don't know what is a "passive speaker". Years ago they used an unpowered "drone cone" as a substitute for a port on a speaker system.

Since it has a 3.3uF capacitor in series with it then it is a tweeter for high frequencies.
If the capacitor is shorted then the tweeter is probably blown up.

 

[cvill]

i presumed that an active speaker is a speaker with built-in amplifier and a passive speaker is one that doesn't. but never mind that. my stuff is a usual two speaker system, one holds the amplifier and the other one just plugs in to it. well i plugged the un-amped speaker to another source and got the same result, no low frequency sound but the woofer is still making a weak sound. tweeter seem to work also.

 

[Menticol]

And what about changing the amplifier IC'?

Could be a TDA xxxx or something, it isn't?

 

[cvill]

i haven't gotten into the amplifier part yet. i'll get on it this weekend. can this tdaxxxx, if it is present, be responsible for the bass problem it exhibited before the other speaker went bad/weak? i'll post again by monday. thanks for all the inputs.
BTW, if bose is bad, which is best/good?

 

[Nigel Goodwin]

i presumed that an active speaker is a speaker with built-in amplifier and a passive speaker is one that doesn't. but never mind that. my stuff is a usual two speaker system, one holds the amplifier and the other one just plugs in to it. well i plugged the un-amped speaker to another source and got the same result, no low frequency sound but the woofer is still making a weak sound. tweeter seem to work also.

As it's just a 'passive' speaker, the only thing to go wrong are the drive units - your woofer is blown!.

 

[Hero999]

Have you tested the continuity of all the woofers and tweeters?

Is there any physical damage to the cones?

It's possible that your speekers are just junk and don't have any bass.

 

[cvill]

The cone doesn't seem to be damaged. No continuity test yet. Ohmmeter test only?
The woofer is about 3" dia with a big magnet. no markings unfortunately.
The amp ic is a tda1xxx, forgot the last 3 digits.
What makes me wonder is that how come only the left channel gave? the right channel is fine.

 

[Hero999]

A continuity test is the same as resistance. If you don't have a multimeter, then you could connect an LED in series with a 470hm: resisor and woofer to a 9V battery. If the woofer is good the LED will light and the woofer will emit a pop sound.

 

[audioguru]

The woofer is about 3" dia

Hee, hee, ho, ho, hee, hee!
Are you serious? The drivers in some headphones are 3" dia. Many fragile little tweeters are 3" dia. The speakers in most clock radios are 3" dia.

 

[Bob Scott]

I don't know what is a "passive speaker". Years ago they used an unpowered "drone cone" as a substitute for a port on a speaker system.

Audioguru! Some days you sound so cynical!

"Drone cone" is the old name for "passive radiator". I haven't heard the old name since 1966. You should know this stuff 'cause you are the expert. Passive radiators work just like a port except that they don't generate whooshing noises as the air shoots in and out of the port. The mass of the diaphragm is identical to the mass of the air in the tube of a comparable port, which can be larger than you think. A cubic foot of air weighs about 1.2 ounces. A cubic metre of air weighs more than 1 Kg.

 

[audioguru]

Audioguru! Some days you sound so cynical!

"Drone cone" is the old name for "passive radiator". I haven't heard the old name since 1966. You should know this stuff 'cause you are the expert. Passive radiators work just like a port except that they don't generate whooshing noises as the air shoots in and out of the port. The mass of the diaphragm is identical to the mass of the air in the tube of a comparable port, which can be larger than you think. A cubic foot of air weighs about 1.2 ounces. A cubic metre of air weighs more than 1 Kg.

Hi Bob,
Are you an old geezer like me?
I was raised in what is now called "Hongcouver". I moved to Toronto when the hippies in Toronto went to Vancouver.

 

[cvill]

Hee, hee, ho, ho, hee, hee!
Are you serious? The drivers in some headphones are 3" dia. Many fragile little tweeters are 3" dia. The speakers in most clock radios are 3" dia.

Well I didn't have a ruler so I just estimated. Also, i would like to ask you to please give constructive advice. I'm no expert so I probably call out some things incorrectly but you don't have to rub it in.

 

[cvill]

i presumed that an active speaker is a speaker with built-in amplifier and a passive speaker is one that doesn't. but never mind that. my stuff is a usual two speaker system, one holds the amplifier and the other one just plugs in to it. well i plugged the un-amped speaker to another source and got the same result, no low frequency sound but the woofer is still making a weak sound. tweeter seem to work also.

I was correct about the active and passive speaker. check out What is a passive speaker?? for the definition.

 

[Torben]

I was correct about the active and passive speaker. check out What is a passive speaker?? for the definition.

In hi-fi terms (i.e. consumer speech) I would agree, but in electronics speaking I believe it's more common to call the actual speaker the speaker, not the whole cabinet/driver/whatever. It helps prevent confusion.


Torben