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 » Mon Nov 12, 2018 6:29 pm

sandord wrote:
Mon Nov 12, 2018 6:12 pm
Good thing you mention that because I was about to do it in my other STE.
I thought it'd be good to get measurements of the effects of the caps in comparison to a stock STE but things are usually not that simple, are they?
I'm putting the caps in my DAC-fixed STE now so don't worry :lol:

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Re: Hissing and whistling in the STe audio output

Post by exxos » Mon Nov 12, 2018 6:36 pm

sandord wrote:
Mon Nov 12, 2018 6:29 pm
I'm putting the caps in my DAC-fixed STE now so don't worry :lol:
:dualthumbup:
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
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Re: Hissing and whistling in the STe audio output

Post by sandord » Mon Nov 12, 2018 9:38 pm

So, here's C567 and C520 replaced with ceramic caps:

IMG_20181112_221502.jpg
IMG_20181112_221502.jpg (156.11 KiB) Viewed 487 times

In the spectrum diagrams below, purple is before, green is after recap.
Note that no monitor is connected because the monitor cable being connected (even with monitor of) influences the result.
Of course the right channel doesn't show any significant change because I only recapped the left channel.

Disconnected (cable noise):

disconnected l+r cinch.png
disconnected l+r cinch.png (27.55 KiB) Viewed 487 times

Left channel only:

after-no-mon-L-only-merged.png
after-no-mon-L-only-merged.png (81.92 KiB) Viewed 487 times

Right channel only:

after-no-mon-R-only-merged.png
after-no-mon-R-only-merged.png (32.82 KiB) Viewed 487 times

Both channels:

after-no-mon-LR-merged.png
after-no-mon-LR-merged.png (38.95 KiB) Viewed 487 times

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Re: Hissing and whistling in the STe audio output

Post by exxos » Mon Nov 12, 2018 9:44 pm

No real change then :( If anything looks worse ? Though that could be as the caps are "high up" on the board...

I think it would be interesting to cover the channel with foil ( insulated with paper first of course ;) ) connected to gnd to screen the audio and see if its picking up interference via RF.. or if its just down to pcb noise...

Looks like big noise spike at 15.2Khz also...
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
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Re: Hissing and whistling in the STe audio output

Post by sandord » Mon Nov 12, 2018 9:59 pm

exxos wrote:
Mon Nov 12, 2018 9:44 pm
No real change then :( If anything looks worse ? Though that could be as the caps are "high up" on the board...

I think it would be interesting to cover the channel with foil ( insulated with paper first of course ;) ) connected to gnd to screen the audio and see if its picking up interference via RF.. or if its just down to pcb noise...

Looks like big noise spike at 15.2Khz also...
First, I see that there's something wrong in my recording path because when I connect the right channel plug to the left channel connector, I get kind of the same result as a disconnected cable.

So I have to measure the right channel again using the left channel cable.

I'm now trying to measure at the DAC, to see if there is any difference between L and R over there.

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Re: Hissing and whistling in the STe audio output

Post by sandord » Mon Nov 12, 2018 11:07 pm

I decided to measure the audio path from begin to end like the last time.

Here are results, for the right channel only this time (as I recapped the right channel only, per the schematics in this thread).

= [R] DAC: U503 pin 4 ======================================================================

Before and after are the same because the caps sit later in the audio path.

dacr.png
dacr.png (33.13 KiB) Viewed 472 times

= [R] U504 pin 14 ======================================================================

Before recap:

before-r-u504-p14.png
before-r-u504-p14.png (26.92 KiB) Viewed 472 times

After recap:

after-r-u504-p14.png
after-r-u504-p14.png (27.46 KiB) Viewed 472 times

= [R] U506 pin 5 ======================================================================

Before recap:

before-r-u506-p5.png
before-r-u506-p5.png (28.15 KiB) Viewed 472 times

After recap:

after-r-u506-p5.png
after-r-u506-p5.png (25.22 KiB) Viewed 472 times

= [R] U507 pin 7 ======================================================================

Before recap:

before-r-u507-p7.png
before-r-u507-p7.png (28.52 KiB) Viewed 472 times

After recap:

after-r-u507-p7.png
after-r-u507-p7.png (28.32 KiB) Viewed 472 times
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before-r-cinch.png
before-r-cinch.png (30.03 KiB) Viewed 472 times
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after-r-cinch.png (35.06 KiB) Viewed 472 times

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Re: Hissing and whistling in the STe audio output

Post by sandord » Mon Nov 12, 2018 11:09 pm

Wow, if you look at the diagrams it almost looks like I swapped before and after... but that may be wishful thinking, right? :(

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Re: Hissing and whistling in the STe audio output

Post by exxos » Mon Nov 12, 2018 11:11 pm

wow, the crappy electrolytics seems to be actually filtering out some of the noise...

What do you actually get on the DAC output ( pin 2 & 4 ) ?
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 » Mon Nov 12, 2018 11:12 pm

exxos wrote:
Mon Nov 12, 2018 11:11 pm
wow, the crappy electrolytics seems to be actually filtering out some of the noise...

What do you actually get on the DAC output ( pin 2 & 4 ) ?
That's the first picture...

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Re: Hissing and whistling in the STe audio output

Post by exxos » Mon Nov 12, 2018 11:16 pm

sandord wrote:
Mon Nov 12, 2018 11:12 pm
That's the first picture...
ah ok...

have you measured the power rails on each chip to see if anything spiky there ?

Also, hold down the reset button (it will stop the machine from running) so that would be interesting to test...
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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