VOGONS


Reversing the Disney Sound Source

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Reply 80 of 139, by matze79

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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.

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Reply 81 of 139, by matze79

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https://www.youtube.com/watch?v=_037Fkx09A8&feature=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..

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Reply 82 of 139, by matze79

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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..

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Reply 84 of 139, by matze79

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

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

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Reply 85 of 139, by Jepael

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matze79 wrote:
so using a 25kOhm Resistor and a 100nf for a simple high pass would suffice ? :) This should cut off anything below 60hz right ? […]
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so using a 25kOhm Resistor and a 100nf for a simple high pass would suffice ? 😀
This should cut off anything below 60hz right ?

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?

Reply 86 of 139, by matze79

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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) 😁)

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Reply 87 of 139, by shock__

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

Current Project: new GUS PnP compatible soundcard

[Z?]

Reply 88 of 139, by shock__

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Jepael wrote:

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.

Current Project: new GUS PnP compatible soundcard

[Z?]

Reply 89 of 139, by matze79

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

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Reply 90 of 139, by shock__

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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.

Current Project: new GUS PnP compatible soundcard

[Z?]

Reply 91 of 139, by matze79

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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 ? 😉

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Reply 94 of 139, by shock__

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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.

Current Project: new GUS PnP compatible soundcard

[Z?]

Reply 95 of 139, by shock__

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

Current Project: new GUS PnP compatible soundcard

[Z?]

Reply 96 of 139, by Paralel

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shock__ wrote:

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?

Reply 97 of 139, by matze79

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

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Reply 98 of 139, by dreamblaster

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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)

Visit http://www.serdashop.com for retro sound cards, video converters, ...
OPL2LPT, OPL3LPT, X2, S2, S2P, MCE2VGA, ... many projects !
Special vogons LPT bundle : https://www.serdashop.com/Parallel-port-retro-sound-bundle
Thanks for your support !

Reply 99 of 139, by Jepael

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matze79 wrote:
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.