Audio problem with MegaFlashRom SCC+ and a Sanyo Wavy-70FD

I have wavy phc70 fd2 (with 2 drives) and I have the same problem with playsoniq SCC, volume is WAY too low.

I think the reason is that playsoniq and the newer megaflashrom scc+'s are FPGA SCCs (as in not original SCC chips). I have yet to buy a megaflashrom scc+sd so I cant verify if I have this problem as well but I am pretty sure the sound would also be softer. Although it was discussed a long time ago in another topic, some ppl do have reasonably normal volume balance, so maybe there have been differences between batches of the sanyos. If anyone wanna borrow me a mfrscc+ I can test it.

Placing in a resistor and capacitor will not magically fix audio problems related to bad mixing or too low volumes. To fix these kind of problems you can either change the attenuation level of the HW itself which is not easily done or do a active amplification between the HW and the MSX.

However, if the problem for the phc70 is the same as for the NMS8250 a more complex fix is required.

I am confused, you state that the audio level is lower than the PSG, so why are you putting a resistor and a condensator in the cartridge ?
You dont want to lower the volume of the cartridge but increase it ? right ?

Hi @roadfighter and thanks for your reply.

I'm not an expert on this, but I do agree it's a bit strange.

The fact is that with unmodified megaflashrom scc+ the SCC audio level is quite lower than the PSG level (in fact, I'd say I can't hear the SCC at all). I tried the same audio track with the openmsx without scc (I have a disk with all the scc tracks on it) to check whether it was the PSG or SCC and the test gave me the same audio than the wavy+megaflashrom scc+ (that is, just PSG).

Manuel (@Guillian) suggested placing a capacitor (100nF) and a resistance (1,2kohm) in the cartridge, that made the SCC audio level to be closer to the PSG audio levels (but not enough). It would appear that lowering the resistance was also making a the SCC audio level to raise a bit (but also not enough).

Reviewing the problem the 8280 has (that is, the PSG level is lower than the SCC level, instead the problem I'm havinig) I do agree I don't understand why that fix would work with the wavy and the megaflashrom, because is PSG which is way louder than the SCC generated by the cartridge. However, I can confirm that it has some impact.

I'm not an expert on this and I have to say I'm a bit lost right now. Any idea would be appreciated. I can provide photos of the wavy if that helps.

Thank you @Daemos,

I don't have the schematics, but I can provide you with photos of the motherboard. I can also measure components values' with a tester if needed.