mbandalauk wrote on 2025-08-30, 13:45:

Hello again, […]
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Hello again,

Now that I’m back, I can share my findings using the PCM-3370 on the backplane. In short — it works flawlessly!

I mounted the PCM-3370 on a PCA-104-ISA REV.A1 sourced from AliExpress. The SBC can be powered directly from the ISA connector, and everything seems to run fine. Both Windows 98 and MS-DOS detect the onboard ESS sound chip without issues. The audio is a little noisy, but nothing that really bothers me.

My only nitpick was with the PSU connector: mine has a 24-pin plug, and as you can see in the second picture, a capacitor is in the way. Because of that, the connector doesn’t fully seat. Fortunately, since it’s actually a 20-pin + 4-pin design, I was able to detach the extra 4 pins without any problem. (It might be worth considering a small layout adjustment in a future revision — if that capacitor were just 2 mm farther from the edge, the connector would fit properly.)

Performance-wise, the SBC is excellent. With its Celeron 400, it boots Windows 98 in under 10 seconds. Since it’s an Intel processor, your PC/104+ adapter should work fine with it, right? If you tried your PCM-3353 with the Chinese PCA-104-ISA, would you get the same results?

Best,
Manuel

Awesome! Thx for the IDSEL numbers!

After assembly, I did notice the 24-pin ATX didn't fit. It did fit on a previous version, but after I moved those caps it no longer did. This didn't bother me, though as the 24-pin ATX was unnecessary to the design, and most current ATX supplies can detach the extra 4 pins as you mentioned. Moving those caps again isn't out of the question on a revised board.

Glad to hear it's all working. You mention a noisy sound output? In my testing, there was some slight background hiss coming from the ESS chip. However, it seemed to be no worse than my genuine ESS sound cards, so I considered that a reasonable compromise. During the design work, I really wanted an ISA sound chip with a built-in digital out, that way I could have implemented a simple DAC, and the outputs would have been truly noise free. The options were super limited, and nothing would have fit into that small footprint on the board.

I did add a simple RC filter to help reduce the noise. My schematic shows 1k over 8nf, but I believe I went with 1k over 10nf or slightly higher. So, 8nf ≈ 19khz F3, and 10nf ≈ 15khz F3. (R25 + C90) and (R88 + C89). Unfortunately, the chip itself is the source of the noise. But, if you were so inclined, you could increase the capacitor values. I was mostly testing with a battery-powered JBL until and was satisfied with the results. Definitely not audiophile grade, but reasonable when I compared it to my genuine ESS cards.

As for my PC104+ boards... I fear the limitation is in the AMD Geode CPU at this point, and it would perform just as poorly with a PC104 ISA adaptor. So, I'm keeping my eyes out for a better PC104+ board, or something like an older 486. I don't consider the PCM modules to be a bad purchase as I needed a real PC104+ board to test the socket fit. I'm happy with the results so far.

Please feel free to offer more feedback on the backplane. Of the few that have sold, I'm curious about how you plan to use it, and I might be able to offer help.

PS. If you were interested in one of these adaptor cards mbandalauk, let me know!

Also, I see in your pic that you have the ISA adaptor card in the ISA slot? In case you weren't aware, you can also use that ISA card in the SBC slots. Just FYI. 😎 Although with the ISA only adaptor, having the back slots for ISA cards is probably more reasonable.

Tevian wrote on Yesterday, 05:58:

Awesome! Thx for the IDSEL numbers! […]
Show full quote

mbandalauk wrote on 2025-08-30, 13:45:

Hello again, […]
Show full quote

Hello again,

Now that I’m back, I can share my findings using the PCM-3370 on the backplane. In short — it works flawlessly!

I mounted the PCM-3370 on a PCA-104-ISA REV.A1 sourced from AliExpress. The SBC can be powered directly from the ISA connector, and everything seems to run fine. Both Windows 98 and MS-DOS detect the onboard ESS sound chip without issues. The audio is a little noisy, but nothing that really bothers me.

My only nitpick was with the PSU connector: mine has a 24-pin plug, and as you can see in the second picture, a capacitor is in the way. Because of that, the connector doesn’t fully seat. Fortunately, since it’s actually a 20-pin + 4-pin design, I was able to detach the extra 4 pins without any problem. (It might be worth considering a small layout adjustment in a future revision — if that capacitor were just 2 mm farther from the edge, the connector would fit properly.)

Performance-wise, the SBC is excellent. With its Celeron 400, it boots Windows 98 in under 10 seconds. Since it’s an Intel processor, your PC/104+ adapter should work fine with it, right? If you tried your PCM-3353 with the Chinese PCA-104-ISA, would you get the same results?

Best,
Manuel

Awesome! Thx for the IDSEL numbers!

After assembly, I did notice the 24-pin ATX didn't fit. It did fit on a previous version, but after I moved those caps it no longer did. This didn't bother me, though as the 24-pin ATX was unnecessary to the design, and most current ATX supplies can detach the extra 4 pins as you mentioned. Moving those caps again isn't out of the question on a revised board.

Glad to hear it's all working. You mention a noisy sound output? In my testing, there was some slight background hiss coming from the ESS chip. However, it seemed to be no worse than my genuine ESS sound cards, so I considered that a reasonable compromise. During the design work, I really wanted an ISA sound chip with a built-in digital out, that way I could have implemented a simple DAC, and the outputs would have been truly noise free. The options were super limited, and nothing would have fit into that small footprint on the board.

I did add a simple RC filter to help reduce the noise. My schematic shows 1k over 8nf, but I believe I went with 1k over 10nf or slightly higher. So, 8nf ≈ 19khz F3, and 10nf ≈ 15khz F3. (R25 + C90) and (R88 + C89). Unfortunately, the chip itself is the source of the noise. But, if you were so inclined, you could increase the capacitor values. I was mostly testing with a battery-powered JBL until and was satisfied with the results. Definitely not audiophile grade, but reasonable when I compared it to my genuine ESS cards.

The attachment schematic.jpg is no longer available

As for my PC104+ boards... I fear the limitation is in the AMD Geode CPU at this point, and it would perform just as poorly with a PC104 ISA adaptor. So, I'm keeping my eyes out for a better PC104+ board, or something like an older 486. I don't consider the PCM modules to be a bad purchase as I needed a real PC104+ board to test the socket fit. I'm happy with the results so far.

Please feel free to offer more feedback on the backplane. Of the few that have sold, I'm curious about how you plan to use it, and I might be able to offer help.

PS. If you were interested in one of these adaptor cards mbandalauk, let me know!

Hi – yes, the sound is a bit hissy. I’m no audiophile either, but as a reference I’ve been comparing it with my WeeCee mini PC, which uses a CS4237 sound chip. That one sounds a bit cleaner, especially under Windows 98. Still, the hiss is barely noticeable once you’re actually using the SBC, so it’s not really an issue for me.

I might replace those capacitors at some point, but for now I’m happy with the backplane. I did know about using the EISA slots—I just forgot to mention it in my previous post. My SBC worked fine in both EISA slots, and it detected the sound chip without any problems. However, I preferred using the ISA slot since I wanted the SBC to be powered directly from the slot, which felt safer.

Honestly, I just wanted a backplane like yours for fun. The PCM-3370 works great, but I also plan to try another SBC I have: the IEI PCISA-3716EV-R4 VER 4.1. I’m just waiting on a P3-S 1400 Tualatin processor for it. If everything works as expected, I’ll be very happy!