Saturn audio hissing

[Gummi]

I got my SCART cables in just over a week ago, and didn’t play much on my Saturn until now. I immediately noticed an extremely loud hissing noise whenever there is any sound output from it. Just in the console menu for example, flipping between the buttons, it produces a very loud hiss whenever it makes the button sound, but a second later it stops. If there is constant sound, there is a constant audio hiss.

White video does not increase this noise, just to make it clear that’s not what’s happening here. I feel pretty confident that the OSSC itself is the cause of this issue. If I use the AV1 audio passthrough straight to my receiver, there is no hiss. I also tried the SCART connector on my Panasonic TX-P50GT60Y plasma, and connected straight to that there is no hiss audible either. There is also no hiss when using the composite cable connected to the TV, although there is an audible hum through that.

I tried switching the audio downsampling to off, but doing so produces no sound.
I have a Japanese model 1 Saturn and I’m using a Retro gaming cables packapunch sync on luma cable.

The hiss is almost the same level as other sound that the Saturn makes, so it is very loud. My other consoles sound crystal clear, although I have only tested a Super Famicom and a GameCube.
Anybody experience this or knows what might be wrong?

Thanks!

[BuckoA51]

Drawing a blank here, my Saturn sounds great via the OSSC.

[mistahsnart]

This is crazy, but I’m having the EXACT same problem with only ONE of my three Saturn consoles through the OSSC.

I’ve had both of my model 2 Saturn units hooked up for a while through my OSSC. No issues at all.

Today: I hooked up my US model 1 (to get a game save off it), and noticed the hissing sound. Just like Gummi said, it only shows up when the Saturn is playing a sound. I connected my Saturn audio *directly* to my receiver and the hiss went away. Connected through the Framemeister, my CRT, directly to a headphone amp… no hiss. As soon as I run it through the OSSC, I get the hissing sound.

I’ve used 3 different SCART cables and 2 different sets of HD Retrovision component cables. So I can confirm that it’s not a cable issue.

It’s the craziest thing.

[BuckoA51]

Can I get the serial number of the unit with the hissing?

[mistahsnart]

Absolutely.

USA ‘model 1’ (oval buttons)
Serial AE62022839
Manufacture date: March 1996

[Gummi]

Thanks for posting mistahsnart.
I’m glad I’m not alone with this problem, though I’m sorry you have this issue too.

I was gonna try to make a good recording of the hissing to better illustrate it, would that be of any use Matt?

My Saturn is a Japanese model 1 , as previously mentioned.
Serial number is B52 198292.

Thanks.

[BuckoA51]

According to that both of your motherboards are VA2, I wonder if that’s anything to go by. I don’t have a VA2 here to test though.

[prof_abrasive]

I get the same behaviour with my VA7 (Japanese s/n A67014671). Booting without a drive the noise is constant in the CD Multiplayer.

edit: using an RGC sync on luma cable

[prof_abrasive]

Looking at the audio output from the Saturn itself, I see a good 250mVp-p of noise on both channels. It looks like it’s all north of 50kHz.

There’s no antialiasing filter in the OSSC, so those inaudible frequencies get folded back into the audible band by the sampling process in the ADC.

I wonder why some Saturns do this and not others?

[SirRockALot]

That’s really interesting, I would’ve expected that any decent ADC is bandlimiting the signal prior to sampling. I guess there was little motivation for the older consoles to eliminate that noise since it would’ve never been directly audible on speakers / headphones.

[prof_abrasive]

I think even by ’90s standards these Saturns are pretty bad! And ultrasonic content can still cause audible problems in analog singal chains (intermodulation).

The datasheet for the ADC used in the OSSC basically says that you shouldn’t need an AA filter unless there is a lot of out-of-band noise. It doesn’t specify what counts as a lot!

My VA7 Saturn uses as a DAC a Burr-Brown PCM1710U. Looking at the VA13 schematics they’d switched to a PCM1717E. Both are designated IC22. Both seem to have the same skimpy low-pass filter. Perhaps the (newer) PCM1717E has better integrated filtering?

[marqs]

Maybe some Saturn units have different audio circuitry. One service manual I could find shows TDA1386 DAC driving line output which should already provide a well filtered signal. There’s some strange circuit connected to final output before connector (maybe for bias?) that might affect sound quality, though.

[prof_abrasive]

The PNP and 2x NPNs? That’s on the VA7 and VA13 also. I think that’s a startup muting circuit. Shouldn’t affect sound in my reading.

The PCM1710U datasheet seems to suggest a 3rd order active lowpass on the output. The VA13 schematics show a single pole at 140kHz instead!

[BuckoA51]

Great to have you hear on our forums btw, Prof 😀 I hope we can work together on Satiator.

Is the VA7 console the only one you have there, or the only one that’s got the hissing issue?

[prof_abrasive]

I’ve only got a VA7 – it’s my faithful (and well-thrashed) dev unit.

I wondered if the DAC output amp bypass caps had gone dry, but tacking in another 10µF in parallel on one channel didn’t seem to make a difference.

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