Just got my ALS100 (non plus), I'm going to test it thoroughly.
AmoRetro says it has 1:1 clone of the OPL3 (LS262), we shall see.
Also, I'm going to test self-noise, SBPro, and SB16 behavior and all their aspects.

EDIT:
My card is dead on arrival, so there will be no testing. 😵
Sorry.

Oh well, that's a pity. Sorry to hear. 🙁
Anyway, thank you very much for your reply!
If I can test one or two games for you, just tell me. 😀

When i searching about GUS clones i found archived website of ASOUND / ASONIC. They started under name DnB and produced GUS clones but from 1995 switched to ALS chipset and sold six different cards with different ALS chips:
http://web.archive.org/web/19970412114603/htt … 0/catalogs.html
(German Tango 100 card with Crystal Dream wavetable is same as ASOUND)

Nice writeup Jo22. I got no ALS ISA cards myself, but I got an ALS4000 card which compares to the ALS120/100 in many ways: SB16 compatibility, nice FM synth and noise (it's the noisiest PCI sound card I got). It also works nice with later SiS and VIA AGP chipsets in DDMA mode.

Hi, all.
Sorry to bump a very old thread. I would like to share my experience regarding ALS120 based soundcards noise suppression.
There's a lot to tell about, but I will try to keep it as brief as possible. So here it goes:

I've got 3 different revisions of an AS9708 PCB and one of them had been with defective IC, until I replaced the chip.
I used the defective one as a reference, desoldered all components, took high-res pcb scans, measured values and redrew a replica card in Sprint Layout.
Then I ordered new old-stock IC's to repair the defective card and take this chance to examine it.
After some consideration, I also decided to design a 4-layer pcb pc/104 soundcard based on this chip to compare the noise and other things (see pics below)

To record the noise for spectrum analysis I used a battery powered hi-fi headphone amp connected to a soundcard line-out and a battery powered WAV sound recorder with a line-in input.
Only the minimum amount of components were soldered during tests. mic\line-in\gameport\cdrom\amp components were removed and the soundcard itself was powered directly via 5V battery, no PC connection.

Here are the brief results I got:
1) PSRR voltage regulation will have little effect. I hooked the (removed from PC) card directly to a 5v battery. The noise is still there even without initialization or any connection to PC. Card initialization in DOS and mixer will only add a small portion of noise to it.
2) This noise is a "1/f" noise in nature (pink noise or flicker noise) and is insanely similar to "by the book pink noise generator" (see the spectrum of the noise below), which makes me think it's a design flaw rather than silicon\grounding etc
3) Ground loop isolation transformer will have no effect (unsurprisingly), but the impedance mismatch causes the noise to be reduced. Sound volume also suffers greatly, but if amplified again by the speakers, you can get somewhat decent volume and quality (by ear). I suppose this also can be done with resistors, but not worth doing anyway.
4) My 4 layer design PCB did not perform any better noise-wise (I'll do some spectrum comparisons later). But all PC "thinking" noises are gone. I used (analogSIG\power<>ground<>digitalSIG\power<>digitalSIG) PCB layers layout. The traces layout is completely different. Only DAC filter values are the same. The idle noise is absolutely similar to #1
5) VREF1 and VREF2 IC outputs measure about 20mV peak noise (I'm sorry, but I could not make any pics, you'll have to take my word for it there). I cannot tell the spectrum either, all of my oscilloscopes are useless when it comes to audible band FFT
6) Disconnecting ALS120 VREF outputs and hooking the filter circuits directly to a LM4040 2V voltage reference did not improve things very much either (by ear). Interestingly, disconnecting VREF1\2 completely has no drastic effect either 0_o.
7) Bipolar electrolytic 10uF vs 10uF Y5R MLCC as coupling line-out caps perform absolutely identical
8) Shunting floating inputs via 10K to ground - no effect

I may add some additional tests later (e.g. -0.3v digital to analog voltage rail diff, ground pin lifting, etc ), but I'm not sure there's any point.

UPD: additional tests will be added there:
8) 5V analog side ON \ 5V digital OFF = NOISE ; 5v analog side OFF \ 5v digital ON = silent (which is logical, since I disabled the mixer section completely)
9) Lower digital voltage below analog voltage level and vise versa = no effect. Lowering analog voltage decreases useful signal levels.
10) Lifting GND pins, so only one pin of each plane is connected and far apart= no effect + pc thinking noises return
11) Dry ice freezing (just for giggles and in the name of science). No effect, but I think I overhead some silicon cursing and threatening to be back.

My conclusions (please, take #2 with a grain af salt, It's only my theory):
As much as it pains me (the soundcards itself are not that bad at all.Good compatibility and OPL), I'm afraid there's not much that can be done in terms of supressing the noise.

1) Bad PCB grounding, EMI or amplifiers are not the culprit. I could not find anything out of the ordinary there. Amplifier capacitors, which are out of spec are simply either buffer ones or gain. But of course, they contribute their small part too.
2) Based on a sketchy datasheet info and my experience, I'm considering the culprit to be the internal IC's reference voltage source. It is the only thing I found drastically different between ALS100 and noisy ALS100+\ALS120 (apart from integrated OPL on ALS120, but ALS100+ also has similar noise with external OPL chip). At some point, when probing VREF outputs, I somehow managed to internally shunt it. It muted the sound effects completely, leaving the music playing with much less noise. Here's the brief spec:
ALS100 - 100uA 2.25v VREF (very much like some opamp based reference)
ALS100+\ALS120 - 1.5mA 2v VREF (1.5mA makes me think of some cheap-clASS zener reference)
Zeners are prone to noise and ARE actually used as a source for 1/f noise generator circuits.
Next thing I assume, that for a cheap IC, resistor ladder was probably used as a simple DAC. vref noise there may get attenuated to form a 3db point.
In noise generators, resistor ladder is used to filter and attenuate the curve of the noise spectrum.
Of course, you cannot exclude bad op-amps/DAC, but I have not yet found such absurdly noisy ones (on the other hand, maybe I have just found one).
UPD: Poor dynamic range and output gain contributes to the noise problem.

Any additional input, criticism, ideas are highly appreciated!
I've got a lot of files, which need sorting first, then I'm planning to add them there such as:
ALS120 replica gerbers or sources, high-res pcb scans, component values and maybe I'll draw a schematic also, because the datasheet is missing one.

P.S.
Some noise reduction points, not much, but nevertheless:
You can only reduce it to some reference level. Below is the picture of the similar soundcard, where I pointed out the most affecting modifications:
1) A place to solder 7805 regulator, TO-92 package.
1a) Ferrite choke, which connects motherboard's +5v to the soundcard analog power rail. Should be removed when soldering 7805 to avoid shorting their voltages.
2) Ferrite choke, which connects analog and digital grounds to a single connecting point.
3) vREF bypass\buffer capacitors
4) This capacitor will significantly reduce whistling\thinking noises. Many cards miss it. (Monkey Island 2 for instance, make astounding high-pitch whistling without this cap)
5) Digital +5v ferrite choke and bypass caps
6) When crystal is not used\soldered, 100 ohm resistor is soldered there instead to carry signal from motherboard. The crystal itself uses 1.8M resistor in parallel in addition to caps.

P.P.S.
Link to the scans and sprint layout file
https://drive.google.com/file/d/1xrRGQaRi8glw … iew?usp=sharing

Kudos, excellent work! 😎👍

Your contribution is wholeheartedly welcome, thank you very much! 🙂

Very nice effort ! Thänk you ~

One thing that may help is forcing your own VREF from a clean source into the VREF pin(s) and particular voltage can make a significant difference too.

Thank you for researching this so thoroughly.

Excessive noise is the main reason I stopped using my ALS100. Good to know the full story behind it.

Thanks everyone, I do really hope there may be a redemption for it yet )

One more interesting thing, new chip fails to be detected by Avance Logic Drivers 0_o.
Unisound works flawlessly. Maybe there's some ROM info missing. IDK

Tiido wrote on 2022-10-05, 06:53:

Very nice effort ! Thänk you ~

One thing that may help is forcing your own VREF from a clean source into the VREF pin(s) and particular voltage can make a significant difference too.

Thanks for the suggestion!
I've also thought of that, but at the time I was worried that reverse voltage would damage the circuitry. And if it's a shunt based ref - it would just be regulated back with no effect.
Now that I have some IC's to spare and a prototype pcb, I may try it. I have jumper pins there, so it should be easy to test.

UPD:
Here's the result. recorded WAV file, software amplified
First 10 sec - idle card with both vref intact.
10-20sec - just attached the wire to vref 1 pin (some wire jiggling noise) to the output of the powered off power supply. Noise reduced already. If I put the wire out of the powered-off power supply - the noise get louder again.
20-30sec - forcing 0.8 volt on the pin, futher noise reduction
30sec and further - switching between 1.5v and 1.6 volts. Above 1.6v the noise becomes louder.
At exactly 2.4v on VREF1 pin the great portion of the noise is reduced. IDK how healthy it is, though.
The datasheet is sketchy - it points out 2.0V in one place and 2.5v in the other
Forcing voltage to vref2 has little effect. Forcing the voltage to both vref1 and vref2 adds buzzing, maybe ground loop

All I have to do now is to replace LM4040 2V on my prototype PCB with another ref chip and hope I will not fry something
Also, I think I'll replace the stock values of the low-pass output filter from 820 ohm\10nf to 200 ohm\40nf to reduce impedance on the output

Interesting, I need to build some reference bench, because I've already lost track how exactly things get better or worse compared to stock card or others.
The noiuse is still there, but some of it gets reduced.

UPD2. I've added the link to the Sprint Layout files and scan of the PCB to my first post

I don't know if it might help? But I was able to extract the reference card schematics for the various ALS100 cards a couple of months ago: Re: Sound Blaster 16 Clones
Maybe they show some variation from the production cards that would give some indication of the cause.

What you've found so far is great though, I'll have to try out a couple of these modifications on my ALS100+ (or was it ALS200?) card that was extremely noisy.

Thermalwrong wrote on 2022-10-05, 16:32:

I don't know if it might help? But I was able to extract the reference card schematics for the various ALS100 cards a couple of months ago: Re: Sound Blaster 16 Clones
Maybe they show some variation from the production cards that would give some indication of the cause.

Yes, I've downloaded them already, great work by the way!

Thermalwrong wrote on 2022-10-05, 16:32:

What you've found so far is great though, I'll have to try out a couple of these modifications on my ALS100+ (or was it ALS200?) card that was extremely noisy.

I would rather say it's just adding the missing components which were meant to be there in the first place. Nothing of a breakthrough really, it keeps being noisy.

Anyway, I've recorded two 1-minute long samples of idle noise. Default mixer settings
My prototype pc/104 PCB and a reference card with most of the components in place, excluding 7805 regulator.
The reference card appears to be more silent than mine, but also has some harmonics, which the regulator should suppress a little.
Extra point goes for split A/D grounds vs my lousy solid plane prototyping 😀

UPD: Uploaded a sample to compare the results. First 5 sec defaults, another 5 sec - VREF connected to external power supply output (outputs have bypass capacitors, but connecting capacitor to vref does nothing, IDK yet what helps to suppress the noise, maybe impedance\voltage drop caused by the long wires. it's just the voltage drop to 0.7v caused by power supply) and then after that - forced 2.4v across vref and some sound\music samples. ALS120 produces whistling sound at around 2680Hz when playing sound samples, which may be due to DAC sampling noise. Line-out is amplified by battery powered headphone amp, but the dynamic and volume is still rather poor.

Well, "overdiving" VREF1 voltage to 2.4V did help reduce the noise to some extent.
Now, it's "once more unto the breach", before I consider my options depleted : evaluate filter circuits (Nyquist freq, etc)

But I have some trouble figuring them out. (pls, see the pics below)
Any help or suggestions are highly appreciated.
I tried to draw the schematic more legible, than it is on actual pcb.

Without the IC's internal schematic it's a bit tricky for me to figure out what exactly the circuit does.
I've also drawn an assumption, how the anti-alias filter may be connected, although I don't quite get the purpose of 1nF caps, just a bypass?
Also, the type of the low-pass filters is a bit cryptic to me also.

Some of the resistors values seem a bit extreme to me.

UPD:
Filter circuits do not appear to be the cause of the noise.
To sum it up: driving 2.4v directly to VREF1 pin definitely helps, but a portion of that idle noise remains and it's definitely the mixer section.
To test this further and call it a day, I'll need to design another board with a separate adjustable voltage regulator for each AVDD\VDD pins and separate jumpers for grounds, probably a "star connection" too.