Reversing the Disney Sound Source

[matze79]

yes when software activates dss (Wolfenstein 3D running) and plays no sound, there is also no noise at all. Sound is clear.
only if dss is uninitialsed there is buzzing noise from it.

Looks like something is in a undefined state.

[matze79]

https://www.youtube.com/watch?v=_037Fkx ... e=youtu.be

Ah i rechecked and this is cleary 50Hz buzz..
As you can see it goes away when the DSS is initialised.
Its not the NE555.

But somehow it pickups those nasty frequency..
the DSS behaves like a antenna.

Also with R2R Network there is a light buzz..

It comes also when i power both units from Battery so its not powersource..

[matze79]

I will add some filtering to the circuit, 50hz cut off..

Keep listen

reducing cable length did some light improvment..

EDIT:
Also added few capacitors to the dss.
Getting better now.

We will getting a Rev2 PCB for sure..

[Paralel]

It makes sense to cut off anything below 50-60Hz. Its hard to make anything below current cycle rate sound decent when dealing with simple circuits.

[matze79]

so using a 25kOhm Resistor and a 100nf for a simple high pass would suffice ?
This should cut off anything below 60hz right ?

Code: Select all

Audio in >---C----> Audio Out
                        |
                        R
                        |
                       GND



[Jepael]

so using a 25kOhm Resistor and a 100nf for a simple high pass would suffice ?
This should cut off anything below 60hz right ?

Code: Select all

Audio in >---C----> Audio Out
                        |
                        R
                        |
                       GND



It does not really cut off that much at 60Hz.

With those component values, the cutoff frequency is about 64 Hz. And at cutoff frequency, signal power is halved, and signal voltage is 0.707 times the original.
So at 32Hz, you still get 0.5 times the signal voltage, 0.25 times the power.

Maybe the problem is something else than powerline frequency coupling, if it is silent when initialized?
Like if the fifo is empty and the clock is still clocking data out? Should it be stopped/gated when fifo is empty so no more data is popped out?

[matze79]

I will add a preamp with proper filtering when i have some time.
The recording i posted before on the other thread has some stutter on the CHIP DAC.
i realisied this is releated to battery drain

I added some Powerfiltering to the DSS and it improved behavior.

Also shortend cable, i think a PCB Redesign will help also.
A Big Groundplane on Top and Bottom.

I can now get it silent by moving it around..
if proper arranged its quiet also.
(After reducing Antenna Size... (Cable) )

[shock__]

It's definitely D0 and D7 which are noisey, which appear to pick up some interference somewhere. D1-D6 are fine.

[shock__]

Maybe the problem is something else than powerline frequency coupling, if it is silent when initialized?
Like if the fifo is empty and the clock is still clocking data out? Should it be stopped/gated when fifo is empty so no more data is popped out?

I tried that the other day ... tying the clock to the FIFO's empty/full signals (CLK NAND FULL, CLK NAND !EMPTY, CLK NAND EMPTY), which only lead to the DSS having issues being detected. As of now it's constantly clocking out data when activated.

[matze79]

What about using a Latch on the Output and trigger it when data is coming in ?

[shock__]

Might be worth a shot ... permanently enabled bus driver (configured as output only) certainly does not help.

EDIT: 74HCT573 (CLK connected to FULL) added to the data lines between DSS emulator and covox didn't help either.
Trying different PSUs only made things worse.
I suspect a ground loop somewhere by now.

EDIT2: Remaining "local" (DSS -Emulator > COVOX -> ARGUS Line In -> ARGUS Line Out -> Headphones - all in one machine) seems to have fixed things. I still get the usual interference from my system (HDD accesses mostly) but the sound itself is clear.

[matze79]

EDIT: 74HCT573 (CLK connected to FULL) added to the data lines between DSS emulator and covox didn't help either.
Trying different PSUs only made things worse.
I suspect a ground loop somewhere by now.

Thats why i tried running the stuff from battery.
Also did not help.

Opto Isolated LPT Port ?

[shock__]

No idea ... and at this point I'll leave that for others

[Paralel]

Anyone have a 'scope to see what the structure and exact frequency of the noise is?

[shock__]

Sadly not at hand ... but I might get one on loan on monday - good idea actually.
Funnily enough, the noise can easily be heard and appears in recordings - yet no matter what level I zoom in, it can't be seen in the signal.

[shock__]

Amplifying the noise helped ... 72Hz seems to be the frequency of the noise I'm getting (7524 based DAC)

[Paralel]

Amplifying the noise helped ... 72Hz seems to be the frequency of the noise I'm getting (7524 based DAC)

Ok, can anyone think of any common source of a similar frequency, or a harmonic of one, perhaps a fractional harmonic even?

[matze79]

from Amp Output, also happens without Amp (only when DSS is not active)

[dreamblaster]

Thanks Matze79 for sending me the DSS converter PCB.
I soldered an usb connector on it (for 5V supply through PS/2 -> USB adapter).
Then plugged a CVX4 as the DAC, and this works well.
It is detected as a DSS by Wolf3d, the sound effects work great :
See this demo : https://youtu.be/5d0PH-WSzAg
(recorded through line in of my Zoom Q4 camera)

[Jepael]

2017-12-09 (1).png

from Amp Output, also happens without Amp (only when DSS is not active)

Op-amps can be tricky sometimes. Can you post schematics, so I can take a look at what parts you have used and how you have connected them, and with which voltages?
There might be an issue that's not obvious.