STE SOUND DAC CRACKLE & POP FIX - Discussion thread

[exxos]

First test completed, i cut the 5v pins and soldered 2x 42.2ohm resistors on the chips. Unfortunately this did not solve the crackling sound issue on my Mega STE. Will try a higher value later, how high can we go, max 100ohm or something?

One thing I forgot in all this is that the IC should have a 100nF on its power pins (after the resistor). I'm sort of surprised it worked in the STE without them added.

[complicated]

First test completed, i cut the 5v pins and soldered 2x 42.2ohm resistors on the chips. Unfortunately this did not solve the crackling sound issue on my Mega STE. Will try a higher value later, how high can we go, max 100ohm or something?

One thing I forgot in all this is that the IC should have a 100nF on its power pins (after the resistor). I'm sort of surprised it worked in the STE without them added.

Do you have any picture or drawing how to install this 100nF capacitor together with the resistor?

[exxos]

Do you have any picture or drawing how to install this 100nF capacitor together with the resistor?

You just put it across the supply rail pins on the chip.. 5V and 0V. Keeping the leads as short as possible.

[complicated]

Do you have any picture or drawing how to install this 100nF capacitor together with the resistor?

You just put it across the supply rail pins on the chip.. 5V and 0V. Keeping the leads as short as possible.

The 5v supply rail is where i soldered the resistor right? But which pins on the ICs are 0v?

[exxos]

The 5v supply rail is where i soldered the resistor right?

yes

But which pins on the ICs are 0v?

Capture.JPG

[Maximilian]

That should be from GND (pin 10) to VCC (pin 20)
They both are at the far corners of the chip.

[complicated]

Adding 100nF capacitors to 5v did not fix the crackling noise on my Mega STE either.

Will do one or two more tests with 75ohm and perhaps 100ohm resistors, doubt it will fix the issue though but worth a shot.

[exxos]

Adding 100nF capacitors to 5v did not fix the crackling noise on my Mega STE either.

Will do one or two more tests with 75ohm and perhaps 100ohm resistors, doubt it will fix the issue though but worth a shot.

Indeed. All worthwhile experiments to do.

If you have a scope then it could help as well.

[complicated]

Adding 100nF capacitors to 5v did not fix the crackling noise on my Mega STE either.

Will do one or two more tests with 75ohm and perhaps 100ohm resistors, doubt it will fix the issue though but worth a shot.

Indeed. All worthwhile experiments to do.

If you have a scope then it could help as well.

Sorry i dont have a scope.

I did one more test with 75ohm resistors and then i did not get any DMA sound at all. So my guess is the chips stops to work around 3.5-3.7v.

So this mod doesn`t seem to work on Mega STE, atleast not on mine. I think my motherboards is an older revision, like 4.1 or something. That stupid revision where you have to cut a resistor on the back to get the FPU working and add a patch cable to use HD floppy...

One last thing i noticed when testing, the sound seems to get a little better when running the CPU @ 16mhz.

[complicated]

Hello again,

A little update on my Mega STE crackling DMA audio.

I have tested Exxos resistor fix lowering the 5v with different resistors and it did not work. Already reported this i think.

Also tried Exxos ground cable fix on different GND places on the motherboard, it did not work.

Did also remove the 74F chips and put sockets in and tried different types of 74LS chips. It did not work at all, got no sound at all just some strange noise from the speakers. Seems like my Mega STE is not compatible with 74LS chips which is very strange cause they work in my STE.

After this i gave up and ofc got a little angry, i`m not a tech guy with tons of skills and equipment to measure things up.

Anyway since i got alot of 74F chips lying around i thought i would give it a last go. So i soldered 8x 33pF capacitors (one on each dataline) on a 74F chip and put it in my U601 socket and guess what? IT F-CKING WORKS! No more crackle and popping, beautiful perfect DMA sound on my lovely Mega STE!

OS62lNp.jpeg