TDA1552Q based computer speakers

I got these speakers, a pair of OEM computer speakers.
They are 1996 era IBM speakers that were bundled with IBM Aptiva's.
Here is a small pic of a complete system with the speakers I'm talking about:
http://engine.cyber-cancer.com/wp-content/uploads/IBM-Aptiva-full-system-300x152.jpg

They were originally powered by the 12v wiring in the computer tower via a female socket in the back of the computer case and connected with an IBM male-male power cord which hooked into a typical female power plug in the back of the (right) speaker with the controlls and power button.

I use these with an ummmmm more modern computer so I power these with a 12v wall wart.

In my opinion they sound just fantastic. very powerful, clear and crisp. I can say that are "room filling". Well suited to play classical music in wav or flac format. On the back there is an output port for a subwoofer? Thats what it says. So am I correct in thinking that this was suposed to be an OEM IBM 2.1 sound system? I've never seen a boxy little subwoofer with white/blue old IBM colors.

Anyways, I cracked both units open and installed some of that rag like cloth
which wasn't in there to begin with. Resoldered the power connection as it got flaky. I looked at the chip attached to the heatsink and I found the datasheet on it. I always wondered but now I know why they sound so damn good, the chip was designed for car stereos! Interesting.
Says it puts out 20 watts per channel.

Anybody hear of other speakers which use this chip, or anybody who owns these old IBM's? Thoughts?
 
Last month I found a Sony stereo (mini component) I do not remember the model number but it had two of these TDA ic's and even they did not were powerful enough to blow a window, they sounded really good and loud.
There are many companies that use this kind of ic's. one that many people know is the Bose wave radio (Bose=crab) sorry ,but I had to get it out of my chest lol. :p
 

mt490

Member
2010-06-09 2:32 pm
I have used and tinkered with these extensively in the past and they are very good for what they are.

I never had a sub-woofer for any of my sets, so I don't know if IBM ever released one with it.

The chipamp really isn't a forte in what it does, it's more the fact that IBM packaged a computer speaker that had a long stroke midwoofer with a tweeter, whereas other manufacturers (and some still do) came with rancid full-range driver affairs.

Possible improvements to these speakers include:
Repackaging of the woofers into a better tuned box
Addition of a real tweeter-woofer crossover (instead of series cap only)
A sub
Upgrade the plugpack to 3A
upgrade to the preamplifier and amplifier sections

The TDA chip it comes with provides quite ample power to the woofer by itself, it can come quite close to full excursion with a strong supply.
 
I have used and tinkered with these extensively in the past and they are very good for what they are.

I never had a sub-woofer for any of my sets, so I don't know if IBM ever released one with it.

The chipamp really isn't a forte in what it does, it's more the fact that IBM packaged a computer speaker that had a long stroke midwoofer with a tweeter, whereas other manufacturers (and some still do) came with rancid full-range driver affairs.

Possible improvements to these speakers include:
Repackaging of the woofers into a better tuned box
Addition of a real tweeter-woofer crossover (instead of series cap only)
A sub
Upgrade the plugpack to 3A
upgrade to the preamplifier and amplifier sections

The TDA chip it comes with provides quite ample power to the woofer by itself, it can come quite close to full excursion with a strong supply.

Thanks for your input! They are good for what they are. Can't compete with the bigger brothers, but for bundled oem type speakers weee you really got something back in those days! Perhaps to balance out the primitive OS's of the time with sweet sounding speakers? Not like now, the plastic junk keyboards and printers you get bundled with a computer. I never bought any premade computers, as I build my own rigs. Just saying.

I read the chip (which is two amplifiers in one package) will handle from
6v to 18v typical for a maxof 18v. So I went out and bought a 15v wall wart. Plugged it in setting aside the 12v one. And I got strange signs.

The speakers are "off" the power button is "off" but there is amplified music
coming out of the left speaker. I can turn it down and up with the volume control on the right speaker. Swtch the power button "on" and everthing works fine, the sound quality is better I think. But I assume parts of the circuit are not designed for the extra volotage. Opened it up and all the caps I saw were rated for atleast 16v. Hmm. Not wanting to press my luck and overtaxing 15 year old components, I went back to 12v and threw the `15v wall wart in a drawer.

Yeah I noticed the cheap "crossover". How would I go about adding a more respectable one to them? I believe these are tuned to the speakers and the ohm rating of them? I am not sure how that works in the way of replacement. Is ther a "kit" I can buy or can this be made?
 
I have used and tinkered with these extensively in the past and they are very good for what they are.

I never had a sub-woofer for any of my sets, so I don't know if IBM ever released one with it.

The chipamp really isn't a forte in what it does, it's more the fact that IBM packaged a computer speaker that had a long stroke midwoofer with a tweeter, whereas other manufacturers (and some still do) came with rancid full-range driver affairs.

Possible improvements to these speakers include:
Repackaging of the woofers into a better tuned box
Addition of a real tweeter-woofer crossover (instead of series cap only)
A sub
Upgrade the plugpack to 3A
upgrade to the preamplifier and amplifier sections

The TDA chip it comes with provides quite ample power to the woofer by itself, it can come quite close to full excursion with a strong supply.

Good suggestions for improvement. I'd like to keep the original speaker cabinets, as they seem to be made of fairly robust plastic, and I like the vintage look.
Whats that about the plug pack? The wallwart I am using is a 12v DC 800 mA one. What did you say about the preamp/amp sections? Better capacitors might help? I hear this being done, replacing old electrolydics caps with new film caps.
You might know if it is worth it as you probably looked at the circuit design.

On a side note, I am thinking of drawing a scematic (reverse engineering)
the preamp and amp circuit boards and perhaps building a standalone box with nice aluminum knobs and jacks for a headphone amp. I like the sound and design,
It's proved itself to me, I'd like to save the exact same circuit.

But being I've never mapped out such a thing before its a lot of connections.
Anybody suggest a good circuit simulator or schamatic builder? I was thinking of just snappping both sides of both boards with a digital camera set to to high quality and big picture, and carefully drawing out the schematic with MS Paint.
I draw alot of stuff with that program. Aparently I'm told I'm very good technical drawer so says the old guru at the industrial electronics supply shop.
 
Well well, look what I found. Searching around my database in my HD, I found a crossover schematic. And I was the one who drew it!!!

It faded in my memory that I reverse engineered (for fun only) a crossover circuit from an a decaying pair of Zenith Allegro 300 speakers.

I uploaded a jpg version of my drawing. Excuse the crudity of my drawing please. Tried my best, never did reverse engineering of circuits before.
ImageShack® - Online Photo and Video Hosting

It is for just the arangement I need 1x woofer 1x tweeter. But Iconfess I am totally unfamilier with building the correct arangment for my speakers. Would anybody please
give me a hint on how this cicuit |I drew can be made to work again or point me in the direction of some good reading material so I can LEARN how this works please? Thanks!

I'drather learn then have it handed to me totally finished.
 
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Yes ,if I remember ,those bonsai garden speakers were made at different height ,which is a first no-no in projecting a system . Beyond the artistic value of the thing ,there are serious goals that have to be achieved in a system...which can be satisfied even by a TDA amp and budget speakers .
But ,going along the line , it is preferred to have a high power amplifier to handle whatever load and be distortion-proof in dynamic explosions . The speakers follow the same rule ,and they suffer from the same problems (heat,box-dimensions ,induced vibrations ). From an electrical and mechanical point of view ,it's even better to leave the crossover out of the box ,or have it super-damped with resin or glue ..
But having all the components integrated in one box it may have some advantages , like having short wires or needing only one transformer .;)
 
Back to Civic Protection's problems : at 12 volts and a 4 ohm load TDA 1552 has an output power of about 2x15 watts ( at 10% THD ; for 2x22 wats you need 14.4 volts according to the datasheet ) , if the speakers have 8 ohms impedance you get about half the power ( around 2x8 watts ) ;the wallwart you use might be seriously underpowered ( if it's 12 volts x 0.8 amps = 9.6 watts and you need a power supply capable of at least 40 watts - or 3.3 amps at 12 volts ). Changing the electrolytics is a good ideea ( they dry out over time and can cause serious problems if they fail )
 

mt490

Member
2010-06-09 2:32 pm
The impedance of the drivers is 4 ohms, but yes it can benefit from a 3 to 4A 12V plugpack or even a regulated supply.

The preamplifier section consists of a MC4558, some selector chip and a LM1036. the 1036 is quite the noisemaker, as well as not being a stellar Hi-Fi performer. Unfortunately upgrading it would require fitting a new tone control board which isn't a simple task because of the size constraints. Of course if you choose to go external then this isn't an issue at all.

Personally I wouldn't bother trying to mod the preamplifier section, too much effort for too little gain.

The circuits for the main ingredients are mostly datasheet circuits, so there's not a real need to draw any. Just trace the pins back from the chips and you'll see most of everything you need to know about.

As for the crossovers, I prefer active crossovers which could be possible if you were to get two active units and reroute the left channel to tweeter duties. I also don't see too much point in dropping in a passive crossover without looking into the design first. There's plenty of articles for crossover design all over the net.

To sum up basically, yes you could retain the original plastic housings but it would be the best in terms of flexibility to put all the electronic upgrades into an external box.