Hissing and whistling in the STe audio output

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JezC
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Re: Hissing and whistling in the STe audio output

Post by JezC »

@exxos I'm not trying to compare his expertise to yours...just that he has a bit more spare time than you do (oh, OK, a lot more free time) & so he might be able to help me when bringing up the first prototype board...
exxos wrote: Sun Jul 19, 2020 10:25 pm Yep, working on it in the background. 8 DAC channels to play protracker music without needing much CPU time..
Sounds great - sounds like a similar capability to the Falcon.
What's that being based on (if it's not a big secret at this time)? FPGA/CPLD or another micro or a mix of those?
Interested for a variety or reasons, some relating to our custom test kit at work & others to music & retro-hobby activities...
Paulo P
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Re: Hissing and whistling in the STe audio output

Post by Paulo P »

OMG, guys. I can't believe how professional and extensive discussion on this topic started here! At the beginning it was just my innocent question about whistling in the STe audio output and now things are being solved here that I no longer understand at all. Unfortunately, I'm not an electrician. But it's definitely very interesting. Thanks to all the contributors who deal with this! I see that you have gone really so far in research. So, the solution of this problem is not simple at all and practically impossible to do if I understand it correctly? Is there any simple explanation? Or is it not over yet?
Thanks very much once again!
One more interesting thing, I remember that my friend had the Amiga back in the day and there was the same issue - it whistled in audio output too. I remember it as if it was today. :) He connected it to a HiFi amplifier and I heard whistling during silence.
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Re: Hissing and whistling in the STe audio output

Post by exxos »

Paulo P wrote: Mon Jul 20, 2020 7:43 pm So, the solution of this problem is not simple at all and practically impossible to do if I understand it correctly? Is there any simple explanation? Or is it not over yet?
Unfortunately there is no simple solution to this. Noise is introduced on the power rails on various parts of the motherboard. It is in particular been noticed that when RAM is being accessed, it generates all sorts of additional noise... Multiply that by every trace on the PCB... But because a lot of this board is running in the megahertz range, noise simply gets transmitted and coupled to other traces which compounds the problem which all ultimately ends up in the audio system.

As I said in a previous post, the entire DAC & audio system would have to be designed on a better PCB. Maybe even run on its own power rail. And would likely need to be screened in a container to stop the RF pickup as well.

The DAC fix PCBs I did for people to test, this did solve some problems, but as far as simple fixes go, I don't believe there is anything else which can be done other than rebuilding the whole circuit.

Really,we have to accept that these computers ( like many others) were built to a price. They not going to invest months of research in ironing out all these little issues. But back in the days of TVs, maybe was just not simply noticeable, or the TV amplification was just so bad it never reproduced the noise anyway. But again, these are low-cost computers and built to a price,. Works yes, works good, not so much :)

So it is over until someone takes on the challenge of rebuilding the circuit and continuing the investigation. Though I think no one will really have the time interest or motivation to do such work. This thread is already over two years old now :)
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Re: Hissing and whistling in the STe audio output

Post by exxos »

I may see if I can find my STE with the DAC fix boards in place while I'm looking at audio faults. But I'm not sure I'll find anything new. But never know.. It will help a lot to see what's going where now we have a STE board layout.
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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Re: Hissing and whistling in the STe audio output

Post by exxos »

Right I see what's been throwing me. The STE for some odd reason keeps muting the audio. When I play a tracker tune, and reduce the volume, it mutes when it gets down to about 30 (80 full) but it's also doing it with @fenarinarsa second test program.

So is there something which will keep the audio "on" so I can hear the noise as its hard to diagnose because the "whine" keeps turning off and on.

Edit:
Oddly might be the TV muting, :roll: doesn't seem to mute on headphones though.. Feking TVs.,, :roll:

The noise still seems to be generated on the DAC. I need to find my STE with the DAC fixes as I think it will solve it anyway .
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Re: Hissing and whistling in the STe audio output

Post by exxos »

The DAC fix boards reduce the whine no end. Though it seems to be originating from the 32Mhz clock. But oddly pressing down on the board in various places seems to reduce it a bit as well.

IMG_0255.JPG
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EDIT:

I think what the remaining noise is, screening and grounding of the outer ground on the motherboard and metal shielding. The more I push on the edges of the board, the better contact it has and the less the whine is there. The more points I push down, the less it gets. So I assume with the DAC fix boards and proper shielding contact (assume upper shielding will also help) That it stands the best chance of eliminating the noise.
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Re: Hissing and whistling in the STe audio output

Post by exxos »

I have redesigned the board and made it smaller with 0603 parts. As I was having to assemble them myself before, I was using 0805 parts which made the board larger than it really needed to be.

I'm looking to get a lot of these built up and hope they will be back in my store over the next few weeks. Hopefully there will be more interest in them this time around.

Capture.JPG
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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Re: Hissing and whistling in the STe audio output

Post by stween »

:thanksyellow:
nokturnal
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Re: Hissing and whistling in the STe audio output

Post by nokturnal »

@exxos any news about new DAC fixes?
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Re: Hissing and whistling in the STe audio output

Post by exxos »

nokturnal wrote: Mon May 09, 2022 12:16 pm @exxos any news about new DAC fixes?
Forgot all about it.

I think the problem was I could not get JLC to actually cut the boards as they needed to be done.

While currently dealing with two other PCB assembly companies. They would like cost a lot to get them built up. I could get the PCBs done, but people would have to obtain parts and assemble them themselves.

EDIT:

The original PCB is free for personal use anyway https://www.exxosforum.co.uk/forum/viewt ... =74&t=3021
https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
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