I got ripped off but it works well and I am happy

[audioguru]

A local store had a Boxing Day sale for a "Special Buy" of a name-brand 2.1 Speaker system for only $24.99CAN.
It has a 5inch "sub-woofer" (it lights up with blue LEDs) and two satellite speakers each with two 1.5" mid-range speakers and what looks like a 1" soft-dome tweeter. It sounds great and goes very loud.

On the internet it got good reviews. It is rated at 150W. On the box and in its owner's manual it is rated at 75W RMS.

BUT ... its sensitivity is a little low so I took it apart to see if I can easily increase it gain.
1) Its amplifier is two 16 pins DIL ICs with a small piece of aluminum glued on top. 3W each?
2) Its little power transformer is labelled 9VAC/1.1A. That is 9.9W and only about 6W goes to all the speakers.
Maybe one 3W IC powers the sub-woofer and the other 3W IC powers the satellite speakers.
The advertised output is 150W or 75W RMS but the actual output to the speakers is only about 6W so the lie is 25 times or 12.5 times wrong.
3) The "soft dome tweeters" are actually ports for the satellite speakers with a passive soft dome covering the holes.
4) The 5" sub-woofer measures only 4.25" and its moving cone measures about 3".

It has bass and treble tone controls but has no transistors nor opamps to do it.

I measured the frequency response with my old ears and it works well from 40Hz to 18kHz.

I don't know which Chinese power amp ICs it uses. Since its actual power is much less than advertised then adding more gain might blow it up. I will not modify it.
It sounds great! It sounds great! It sounds great!

 

[RichTheDude]

If something sounds good to the ear I usually leave things as is .

I think the Chinese are prone to labelling any power output on amp/speaker set ups. I had a pair of PC speakers some time ago, rated at "400 Watts". The speakers was about 2 inches in diameter, and the mains transformer about the size of a 6VA, unfortunately these sounds really tinny

I am currently running a Trio KA-2000A with some Wharfedale Denton bookshelf speakers on my PC, got the amp for a few pounds and the speakers for a tenner I think .

 

[audioguru]

I think the Chinese are prone to labelling any power output on amp/speaker set ups.

Of course I know that cheap Chinese junk is labelled "150W" which is 150 Whats. 15 Watts?? The high power 5" sub-woofer is labelled 8W.
But the Name-Brand system I bought was advertised as 150W (Whats peak power?) and the box and owner's manual said 75 Watts RMS and I stupidly believed it. I guess the sub-woofer gets 3W and the satellite speakers get 1.5W each.

 

[Reloadron]

I figure it this way, you spent $25 CDN and got something you like. Hell if it sounds good, be happy.

Ron

 

[audioguru]

I figure it this way, you spent $25 CDN and got something you like. Hell if it sounds good, be happy.

I am VERY happy because it sounds good for the TV beside my PC. Its input is from my digital cable-TV box. FM radio and TV sound is excellent but far from maximum output since its gain is low. I tried my Sony Walkman radio as an input and the sound level was much higher (deafening). Since the cheap Chinese amplifier has almost no heatsink then I think a few of Watts output is safe.
It sounds much better than my son's and daughter's TV sound systems that costed 20 times more.

I am surprised that the "soft-dome tweeters" (which are just vents for the satellite speakers) are not just photos of tweeters.

 

[KeepItSimpleStupid]

I need a 4 volt two Watt light bulb/
For what?
No Two.

 

[Mr RB]

...
1) Its amplifier is two 16 pins DIL ICs with a small piece of aluminum glued on top. 3W each?
2) Its little power transformer is labelled 9VAC/1.1A. That is 9.9W and only about 6W goes to all the speakers.
Maybe one 3W IC powers the sub-woofer and the other 3W IC powers the satellite speakers.
...

Porbably two stero amp ICs about 1.5W each channel? They use one stereo IC for the left/right stereo speakers, and the other one bridged for the subwoofer.

...
It has bass and treble tone controls but has no transistors nor opamps to do it.
...[/quote ]

That's probably not so bad, some of those amp ICs have pins for tone controls and have the necessary internals to get decent tone controls without needing external ICs.

...
It sounds great! It sounds great! It sounds great!
...

It's easier to put up with the "Chinese honesty" (ie the mislabeled specs) when it works well and gives decent value for money.

I'm surprised you didn't put the sine and 'scope on it and get a power output figure into 8 ohms? I don't think I could have resisted after the "150W" advertising.

 

[audioguru]

I'm surprised you didn't put the sine and 'scope on it and get a power output figure into 8 ohms? I don't think I could have resisted after the "150W" advertising.

The transformer is 9VAC, the sub-woofer is 6 ohms and each satellite speaker is 4 ohms.
The DC supply will be 10.7V at full power.
Assuming a bridged amplifier for the sub-woofer then each amplifier in the bridge has a p-p output of about 6V for a total of 12Vp-p and an output into the 6 ohm sub-woofer of 4.2V RMS which is a power of 3.0W RMS.

Each satellite amplifier has an output of about 6Vp-p which is 2.1V RMS and the power into 4 ohms is 1.1W each or 2.2W total.

Actually, I think the little transformer has a much higher output voltage between power surges in the music and the main filter capacitor stores it so the dynamic "music power" is much more than my guesstimate.

The system is labelled SYLVANIA model SHTIB1044.

 

[transistor495]

I am surprised that the "soft-dome tweeters" (which are just vents for the satellite speakers) are not just photos of tweeters.

..

I still buy some Chinese items which I think worth trying it. Like there are some really genius toys they cheaply made but definitely gives fun and value for money!

I'm happy that now you have agreed that your 3W powered 3" 'subwoofer' can go well down to 40Hz

Recently I've also came to a conclusion that whatever system sounds interesting to us -that is the best one from our perspective -no debate on 'whats' and muscles.

 

[RichTheDude]

As long is it sounds good and is loud enough I would be happy .

I have a terrible habit of wanting to know about products though even if I am happy with them - taking them apart just to see how it's built etc or characterising them formally (in the sake of amplifiers etc).

 

[Veraxis]

I had something similar happen to me when I picked up a cheap pair of speakers for my computer. They were rated at 15W, but the power supply they run on is 12V 0.5A max, so I am not entirely sure how this is accurate. This does not bother me as much, however, as the fact that they become horribly distorted at anything above even a low volume, so I may just get rid of them.

Even so, that does not sound nearly as bad as a "150W" system which only has 6W of output. I have never heard of anything with specs that exaggerated... but perhaps I am just not looking hard enough? Either way, if you are happy with it, that is all that really matters.

 

[audioguru]

I have seen many powered computer speakers labelled 1000W and powered from a little 9V/300mA ( 2.7W) wall-wart AC/DC adapter. But they don't have a sub-woofer.