Very naiss ! (The card I modded isn't mine, it belongs to a friend 🤣)

Hopefully many more cards will get de-CQM'ed ~

Thanks! I hope more CQM cards get de-CQM'ed myself. It's a terrible shame Creative had to afflict so many otherwise semi-decent sound cards with the CQM virus.

Thanks to your other thread on it, I de-CQM'd my CT2950 & CT3620 cards the other day 😀

Outstanding work!

And today I repaired a non-functional CT2940 and de-CQM'ed + re-amped it. The fault was the CT2502-SDQ ViBRA 16 chip and an LS245, the latter of which quite visibly bought the farm (had a scorch mark in the center). The CT2502 was getting really hot, so hot it was burning the dust that accumulated underneath it. After replacing the busted LS245, stripping a working CT2502-SDQ off a CQM-only CT2980 and transplanting it, the board came fully to life. I then replaced the miserable TL064's with TL074's and dealt with the CQM tumor chip.

Still a little noisy (the TL074's are pretty noisy op-amps) but certainly much better than before I had started. Later when I get some lower-noise op-amps I'll replace the TL074's.

I have 3 CT3600 and would love to do this, is there a guide or something to follow?

Excelent work!

No guides yet for the non-CT3990 cards yet unfortunately, but I hope to some day transcribe my actions a bit better. I generally hunt the interwebs for pictures of cards with the YMF289s already fitted, resolution permitting, and try to replicate similar resistor placement and values when possible.

I do know though that, barring the CT3600 and maybe a few other cards which use clock chips, the crystal/resonator the YMF289 needs is 33.868 MHz, and it needs 15pF filtering caps on the outputs and inputs. Also there are usually a number of 100nF caps involved with the swap that must be added, as well as a few 47K resistors. Where all these parts go OTOH, is something I need to find out for all models of SoundBlaster 16/ViBRA 16 that is afflicted with CT1978 CQMitis.

Taking a closer look at the CT3600, I see you have to add an 18 ohm resistor to R13, as well as a 10 ohm resistor to R17, and what I presume to be 100~180nF caps to C50, C52, C45, C46 and maybe C48. I'm sure there's something else you need to add too, but at the moment I can't recall which exactly off the top of my head. (I was following Tiido's pictures of the CT3600 he also de-CQM'ed.)

Thanks! I guess I can make some experiments in one off the older CT3600 I have.

I can put together a picture like I did for the CT3990 and CT3620, if that would help?

Chalk up another de-CQM'ed CT2940. This time I had to order the YAC516-E from China, fortunately the very first one I tried from the batch was good. Haven't tried the others yet (I need to now get more YMF289Bs). Accidentally lifted a few pads for the YAC516, but fortunately they were no-connect pads anyway, and once the chip is fitted you'd have to look REALLY hard and close to notice.

Next time though I'm definitely using lower temperature.

Great work Sir!
Could I kindly ask to OP a simple detailed guide for the sake of the community to this mod?
like:
-Remove Rxx;
-Replace Cxx with yy uf
-Solder Cxx

etc etc
Thanks in advance,
Jorge

I think I just purchased this exact modded CT3600 on ebay, in the details of the sale they noted some of the details to the mod which could be of use to someone out there.

"
I've replaced the original CT1978 CQM synthesis chip and its related DAC with a genuine Yamaha YMF289B OPL3 FM synthesis chip and companion YAC516-E DAC, and did a number of modifications to the FM/AWE filtering, op-amps and capacitors used to improve overall sound quality. Card works great and sounds great.

Note that this modified card has somewhat heavier filtering on the FM and AWE output than usual for these cards. As the Yamaha YMF289B can generate some pretty gnarly treble, I lowered the low-pass filter cut-off frequency to 16kHz to bring the FM output more in line with that of the SoundBlaster Pro 2. (This does not affect SoundBlaster DAC playback, only FM synthesis and AWE synthesis.)

I also lowered the FM/AWE mixing gain somewhat to fix clipping problems with the original setup when loud songs were being played. (I took great care to not lower it too much, so that FM and PCM sound do not become excessively unbalanced.) The FM and AWE outputs are both filtered by the same op-amp stage, so both outputs are filtered at 16kHz first-order, effectively.

The resistors that control the gain are R27 and R36, while the caps that control the filtering for this stage are C55 and C65.

The current gain resistors are 20K, the caps for filtering approximately 470pF. I personally prefer this more bass-heavy filtering as it makes for a nicer listening experience, but if you want to 'open it up' you can replace the caps at C55 and C65 with 180pF units for a 44.2kHz first-order filter instead.

The card originally had very poor quality MC3403 op-amps that were very noisy. I replaced them with higher quality units: I used an MC33079 for the FM/AWE mixing, and an MC34074, a TL974 and a TL074 elsewhere. I also replaced the larger-valued electrolytic caps, including two slightly oversized Nichicon 1000uF output caps for the TDA1517 outputs (which match its datasheet recommendations).

The card had its 30-pin SIMM sockets replaced by the previous owner. While they did a good job on the replacement overall, I reinforced some of the solder points just for good measure. (Notice the slight bit of solder goober on the one pin on the back - that is a ground pin, so that extra solder goober on that pin is harmless.) I fitted the card with 4MB of RAM, which should be big enough to play most average-sized AWE32 soundfonts.
"

Wow, you bought my card. 😁
How's it working out for you?

Thermalwrong wrote on 2019-04-27, 15:42:

Thanks to your other thread on it, I de-CQM'd my CT2950 & CT3620 cards the other day 😀

I received CT3620 form eBay! guy made those changes already. I don't do that stuff, at least yet, but at least now I understand how it works!
Thanks for the pictures!