Hissing and whistling in the STe audio output

Various tweaks and fixes from video ghosting to audio fixes etc.
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sandord
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Re: Hissing and whistling in the STe audio output

Post by sandord » Sun Oct 14, 2018 1:04 am

I am happy with it as it is though. The improvement is vast already.

Of course I'll be interested in future improvements.

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Re: Hissing and whistling in the STe audio output

Post by exxos » Sun Oct 14, 2018 1:27 am

sandord wrote:
Sun Oct 14, 2018 1:04 am
Of course I'll be interested in future improvements.
I think one of the next steps I suggested was a while ago in this thread, basically start by changing all the electrolytic caps in the DAC circuit to ceramic versions. Electrolytics cause hiss in audio circuits, don't know why, but bet they are not helping. Possible they are more suseptable to RF noise generated mostly by the PSU and RAM aceses etc.
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

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Re: Hissing and whistling in the STe audio output

Post by sandord » Sun Oct 14, 2018 1:35 am

exxos wrote:
Sun Oct 14, 2018 1:27 am
I think one of the next steps I suggested was a while ago in this thread, basically start by changing all the electrolytic caps in the DAC circuit to ceramic versions. Electrolytics cause hiss in audio circuits, don't know why, but bet they are not helping. Possible they are more suseptable to RF noise generated mostly by the PSU and RAM aceses etc.
Oh no, more capacitor browsing :shock:

Seriously, that sounds like an interesting thing to do. Will cause headaches due to the caps being axial, I think though...

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Re: Hissing and whistling in the STe audio output

Post by exxos » Sun Oct 14, 2018 11:45 am

sandord wrote:
Sun Oct 14, 2018 1:35 am
Oh no, more capacitor browsing :shock:
Welcome to my world ;)
sandord wrote:
Sun Oct 14, 2018 1:35 am
Seriously, that sounds like an interesting thing to do. Will cause headaches due to the caps being axial, I think though...
Yeah, though you may find some which physically fit by the pin pitch.. You probably don't need the full value either.. Looks like there is 47uF for the coupling caps, so even 1uF may work... There are some larger SMT caps like 2220 size which can go up to 100uF.. bodge some wires on those... actually as it looks like I will have to send you a new simm, I have some 33uF ones coming for my PSUs, so I could just send you 4 of those caps as well to try.

It would help if you could scope out the audio path from start to end, and see if any section has the 2600hz spike more than another section...
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

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Re: Hissing and whistling in the STe audio output

Post by sandord » Sun Oct 14, 2018 11:57 am

exxos wrote:
Sun Oct 14, 2018 11:45 am
Yeah, though you may find some which physically fit by the pin pitch.. You probably don't need the full value either.. Looks like there is 47uF for the coupling caps, so even 1uF may work... There are some larger SMT caps like 2220 size which can go up to 100uF.. bodge some wires on those... actually as it looks like I will have to send you a new simm, I have some 33uF ones coming for my PSUs, so I could just send you 4 of those caps as well to try.

It would help if you could scope out the audio path from start to end, and see if any section has the 2600hz spike more than another section...
Ah, another learning journey awaits ;-)
Let's do it. I mean, the scoping part and trying those caps to see if they help. The other stuff, bodging wires etc. is still a little beyond me, in terms of coming up with stuff like that.

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Re: Hissing and whistling in the STe audio output

Post by exxos » Sun Oct 14, 2018 12:02 pm

sandord wrote:
Sun Oct 14, 2018 11:57 am
Ah, another learning journey awaits ;-)
Let's do it. I mean, the scoping part and trying those caps to see if they help. The other stuff, bodging wires etc. is still a little beyond me, in terms of coming up with stuff like that.
If you can scope before and after the cap changes, then we have all the info documented then. The noise may only be on one section, or all, or get amplified across sections.. nobody knows yet.

There is a negative -5V rail there somewhere.. noise could even be on that rail.

Capture.JPG
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4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

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Re: Hissing and whistling in the STe audio output

Post by sandord » Sat Oct 20, 2018 2:55 pm

exxos wrote:
Sun Oct 14, 2018 12:02 pm
If you can scope before and after the cap changes, then we have all the info documented then. The noise may only be on one section, or all, or get amplified across sections.. nobody knows yet.

There is a negative -5V rail there somewhere.. noise could even be on that rail.
I can't get the scope to display the typical 2600 Hz spike. I'm afraid my scope isn't very useful in this regard (no scale display) OR my knowledge of electronics is simply lacking.

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Re: Hissing and whistling in the STe audio output

Post by exxos » Sat Oct 20, 2018 6:45 pm

I forgot about this again, need to send you some caps..

can you try with your audio software and measure the points I highlighted in this post viewtopic.php?f=17&t=643&start=40#p5634
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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Re: Hissing and whistling in the STe audio output

Post by sandord » Sat Oct 20, 2018 7:49 pm

exxos wrote:
Sat Oct 20, 2018 6:45 pm
can you try with your audio software and measure the points I highlighted in this post viewtopic.php?f=17&t=643&start=40#p5634
I just did some measurements. Your picture shows circles around two-sided components so I still had to pick a side. You can see which exact points I measured in the picture below. The read arrows point to the exact points. I hope I got them right :)

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Re: Hissing and whistling in the STe audio output

Post by sandord » Sat Oct 20, 2018 8:04 pm

sandord wrote:
Sat Oct 20, 2018 7:49 pm
I just did some measurements. Your picture shows circles around two-sided components so I still had to pick a side. You can see which exact points I measured in the picture below. The read arrows point to the exact points. I hope I got them right :)
By the way, I used the cinch ground when measuring.

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