Creative Sound Blaster 16s with incorrectly capped TEA2025 amplifiers

[Logistics]

Re: Creative Sound Blaster 16s with incorrectly capped TEA2025 amplifiers

Just real quick, because I'm out eating pho, I think you interpreted what the data sheet wrong. It doesn't say that NP caps should be used only on the inputs, it says that the capacitors used on the inputs should only be NP. This says nothing of the caps elsewhere on the board.

Edit: I'm interested in your observations of the effects of that 0.15uF cap. Why does changing the capacitor type yield such an effect? And since the data sheet cautions against using a smaller value, I wonder what effect a larger value has besides stability.

[gustinmi]

Re: Creative Sound Blaster 16s with incorrectly capped TEA2025 amplifiers

First of all, the datasheet for tea2025b stated, that NP caps should be used only on input (allowing source to be referenced to ground). So there you need 0.22uF NP cap.

I noticed that the cap that changes everyting is the small serial capacitors that goes from ground into PIN 2 (OUT-1), 0.15 uF.

If I used ceramic or polyester capacitor, the chip started to draw 4 AMPS of current (max should be 1.5), and the distortion was huge.

It only worked when I used small ceramic cap (104) or polarized cap. The last one worked the best, and chip consumption was 0.9 AMPS.

Go figure!

BTW, according to Make: Electronics book, you can make your own bipolar caps with joining 2 electrolyte together. They should be double in capacitance. Minus poles are joined. It works well for input capacitor I mentioned in beginning.

[Logistics]

Re: Creative Sound Blaster 16s with incorrectly capped TEA2025 amplifiers

For whatever reason, I never noticed this thread, and I even made a thread of my own, dedicated to refreshing the SB16. Obviously, I took things a step farther, in some ways, with a refreshed motherboard and PSU to stiffen the power delivery and increaae stability of the system in general.

But I wanted to address some minor things, which were commented on in the thread:

One user commented that you must use passive speakers with the SB16's output. However, as with most amplifiers, this is not entirely true. You may also use headphones, but you do need to be wary of your volume-levels as the output-power is quite high on the Speaker-Out. As far as impedance is concerned, the data sheet only scales to 16-Ohm IIRC, but I have used 24-Ohm headphones on my refreshed SB16, and I can barely turn the volume up within Windows when running directly off the card. (Maybe the low-impedance caps)

There seems to be confusion as to why one would use bipolar capacitors in the signal-path--this is because audio signals exhibit A/C-like characteristics which are better reflected through bipolars.

The way I understand it, larger you in value you go in capacitor, the farther down you generally bring the ceiling as concerns frequency handling. On inputs, often a careful combination of capacitors are used, one bypassing another--the combination often consisting of 1.0uF and 0.1uF, and sometimes the addition of an even smaller capacitor. But placement must be sequential or you will defeat the purpose of one or more.

Matthew

[Dans2530]

Re: Creative Sound Blaster 16s with incorrectly capped TEA2025 amplifiers

So what you are telling me is that Doom would have sounded MORE awesome!? I had a 486 running this card through a maranz amp with some beefy speakers and it sounded good then.
Good on you for fixing something a massive company thought was "good enough" or couldn't be f'ed fixing it. If I still had that gear I would do your mods and test again.
Top work mate!

[mockingbird]

Re: Creative Sound Blaster 16s with incorrectly capped TEA2025 amplifiers

Yup. Please do take some pics, I'm interested in seeing yours. Are you considering re-capping with the "mods" (More like circuit corrections) posted here?

[Th3_uN1Qu3]

Re: Creative Sound Blaster 16s with incorrectly capped TEA2025 amplifiers

Is that a SB16? I have one too round here, and i believe i've some pics of it somewhere... If not, i'll just take a couple more. I also have an AWE64 ISA, that one has the TEA1517 amplifier on it.

[mockingbird]

Re: Creative Sound Blaster 16s with incorrectly capped TEA2025 amplifiers

Just thought I'd show you my card, and point out that there are subtle differences between them, your having a later datecode. They're both CT2230, but different revisions it seems.



(See attachment for higher-res version)

[chozo4]

Re: Creative Sound Blaster 16s with incorrectly capped TEA2025 amplifiers

I don't see why bipolar output caps would help. I really don't think the output of a TEA2025 can ever go negative. I don't even know how close to 0V it can get.

Thinking it's more so because of the AC going through it being attenuated more in one direction than the other.

[lti]

Re: Creative Sound Blaster 16s with incorrectly capped TEA2025 amplifiers

I don't see why bipolar output caps would help. I really don't think the output of a TEA2025 can ever go negative. I don't even know how close to 0V it can get.

[UraBahn]

Re: Creative Sound Blaster 16s with incorrectly capped TEA2025 amplifiers

I've replaced the bootstraps with 100uf bi-polars, as the datasheet's diagrams (see 'Stereo Audio Circuit' in the ST TEA2025B datasheet) specifies to use bi-polars there. Haven't heard a lot of difference though. (I surmise the bi-polar application is to prevent distortions at some point.)

Considerable improvement in the treble range for both amplified and direct line-out, however, comes from replacing the small 1.0uf caps near the CT1745 chip with 1.0uF metalized polypropylene-film caps (requires some ingenuity to fit them due to their much larger size though!) Replacing all the 4.7uf and 10uf caps near the chip helps too, though you'll probably have to use regular electrolytics there since you're not likely to come across film caps of those values that will fit.

Afterward you'll begin hearing the flaws in Windows 95's startup sound much better, revealing it as the hissy 8-bit sample that it is. You'll also hear Sierra's Police Quest VGA kick out some serious bass: https://www.dropbox.com/s/9olev2ykbj...0CT2230%29.ogg

[chozo4]

Re: Creative Sound Blaster 16s with incorrectly capped TEA2025 amplifiers

So out of curiosity, what kind of results did you get with recapping the bootstrap capacitors? Have you given raising their capacitance a try to see the potential differences? I only ask as I noticed a marked increase in clarity when replacing them with 16v/100uf Chemicon PXA polymers and curious if an increase in capacitance is worth looking into on them at some point.

[UraBahn]

Re: Creative Sound Blaster 16s with incorrectly capped TEA2025 amplifiers

OK, sorry for resurrecting this old thread, but I've made a few further discoveries here: ST (repeat, NOT NatSemi... :P) specified .22uf non-polarized caps on the TEA2025's inputs, so what I did is I replaced the 1 uf film caps I was using with .22 uf film caps. The end result was a very noticeable increase in treble, allowing my CT1770 to finally almost match my modded CT2230 in the high-range. The bass did decrease slightly, but this was offset by the improvements made elsewhere (eg. the 47uf feedbacks being replaced with 100ufs proper) and I still get a very decent bass output.

Also I've installed 470uf bi-polars for the output decouplers, and yes, there was a noticeable improvement in sound quality, though nothing too dramatic. A quick look at the recorded waveform in Audacity, though, reveals that the negative swing on the output waveforms is now much less distorted looking. (I do understand that polarized caps, when given a negative charge, react in a non-linear way...)

So yeah I'm on the way to a better sounding SB16, just still have a few adjustments to do here and there. A few sound cards were maimed in the process (such is the nature of 'science') but all is for a good cause.

[UraBahn]

Re: Creative Sound Blaster 16s with incorrectly capped TEA2025 amplifiers

National Semiconductor (now part of Texas Instruments) never made the TEA2025.

Oh yeah, derp. ST made the TEA2025, my bad. (Typed all that whilst under the weather.... glowry be pertussis, with hints of pneumonia and fever!) I'm a little bit better today (thank goodness for azithromycin), so now I can think somewhat clearly.

That's pretty interesting.
I wonder how the card sounded when the original caps where brand new though...

Perhaps they have degraded allot through the years?

Oh, the cheap ELGEN and Wincap capacitors degraded over the years for sure, making most Sound Blasters sound even worse as they age. Of particular importance is the SVR (ripple reject) cap and the two feedback capacitors connected to the TEA. Creative LOVES to pinch pennies on the feedback caps, using 47ufs where the datasheet specifies 100uf. They usually don't under-size the 100uf SVR cap but replacing it with a 220uf anyway gives audibly better results. (The new breed of 220ufs occupy the same space as the old 100uf cap does, so replacing it is a cinch.)

My headphone amp actually has polarized 10uF caps there, and the voltage across them is only around 10mV. For some reason, those caps have to be perfectly matched or one channel will have less bass. That could be caused by the tone control circuit. It's a really weird circuit, and the caps might not be the actual cause of the lack of bass.

It's true that caps alone aren't the entire story behind a circuit's sound, the design of the circuit as a whole affects the total sound quality. That sounds like a very strange sound circuit you've got there, obviously one with razor-thin tolerance margins. It'd be interesting to hear what would happen if one were to use bi-polar 10ufs there. (Hopefully not magic smoke?)

[lti]

Re: Creative Sound Blaster 16s with incorrectly capped TEA2025 amplifiers

National Semiconductor (now part of Texas Instruments) never made the TEA2025.

I don't think the caps on the input are needed unless there is some DC offset on the input signal. The increase in treble caused by replacing those caps is interesting.

My headphone amp actually has polarized 10uF caps there, and the voltage across them is only around 10mV. For some reason, those caps have to be perfectly matched or one channel will have less bass. That could be caused by the tone control circuit. It's a really weird circuit, and the caps might not be the actual cause of the lack of bass.

[stj]

Re: Creative Sound Blaster 16s with incorrectly capped TEA2025 amplifiers

i had most of the sb16 variants btw, but they are long gone.

i do have a pci 5.1 card - if i find it, i'll look at the caps.

[lexwalker]

Re: Creative Sound Blaster 16s with incorrectly capped TEA2025 amplifiers

Still have one of these soundcards, and in working condition also. Never bothered to modify it, and didn't bother about that TEA2025 anyway (which requires passive speakers) as I've always used the Line Out instead (using active/amplified speakers)...

[Th3_uN1Qu3]

Re: Creative Sound Blaster 16s with incorrectly capped TEA2025 amplifiers

I'm quite sure it sounded about as cheap. Penny-pinching on coupling caps (especially when you make them smaller than they should) always results in loss of bass.

[Per Hansson]

Re: Creative Sound Blaster 16s with incorrectly capped TEA2025 amplifiers

That's pretty interesting.
I wonder how the card sounded when the original caps where brand new though...

Perhaps they have degraded allot through the years?

[UraBahn]

Re: Creative Sound Blaster 16s with incorrectly capped TEA2025 amplifiers

"i dont think the pedophiles - sorry, audiophiles would give a damn, they would start with a turtle-beach or some other stupidly expensive card."
Well, this article is for the rest of us who went the SoundBlaster route back in the 90s. With the exception of the SILMIC (which were purely out of morbid curiousity than any kind of audio-phoolery BS) everything I am recommending here is just typical, plain-jane stuff you can order from digi-key or, in the case you are really fortunate to have a GOOD one nearby, ratshack. (I was stunned to see mine had a pair of 1.0uf metal-film caps in stock...)

"btw, good luck finding a 470uf bi-polar - they dont exist. atleast not unless they look like a coke-can!"
What's wrong with coke can caps? Besides Nichicon makes some 470uf's that are 10mm in diameter and a whopping 22mm tall - a little big *ahem*, but not too bad really. So it's more like a MagLite flashlight. Later Sb16's give just enough room for 10mm caps there for the output decouplers anyway. (The Silmics were 12.5mm, a bit too big...)
http://www.digikey.com/product-detai...081-ND/2539563

UTC made TEA2025Bs are cheap clones of the NatSemi TEA2025B. (Though better than a few no-name Chinese knockoffs I've encountered, *shudder* CD2025) I noticed differences in the sound quality between clones and the real, genuine NatSemi TEA2025B articles. Yes their scanning of the document could have been better, but if I look closely I definitely see how some caps were indicated as being NON-polar. (I think the cloners were just too cheap to care when they marked their schematics...)

In any case the proof is in the sound files. I did not turn up the treble or bass on any of the cards, all of them are using the default, middle settings for treble and bass in Windows 9x.

[R_J]

Re: Creative Sound Blaster 16s with incorrectly capped TEA2025 amplifiers

Here is utc's data sheet..., I also checked a few audio amp schematics nad, H-K, bose etc. they all use polarized caps in the audio path.
looks like that copy from ST was faxed across the country a dozen times