I'm sorry, I can't do any more measuring anymore any time soon. I have a lot of stuff to do and will be out for a long weekend. Gotta get some sleep now!
Hissing and whistling in the STe audio output
Re: Hissing and whistling in the STe audio output
Re: Hissing and whistling in the STe audio output
I forgot about some left channel measurements I also made, they might be interesting to compare to the right channel measurements.
NOTE: these are all AFTER recap so some filtering might be missing. I can't make measurements of this setup BEFORE recap now because I don't have time.
= DAC ============================================================================================
[L]
[R]
= U504 ============================================================================================
[L]
[R]
= U505 ============================================================================================
[L]
[R] (U506, the R requivalent of U505)
= U507 ============================================================================================
[L]
[R]
NOTE: these are all AFTER recap so some filtering might be missing. I can't make measurements of this setup BEFORE recap now because I don't have time.
= DAC ============================================================================================
[L]
[R]
= U504 ============================================================================================
[L]
[R]
= U505 ============================================================================================
[L]
[R] (U506, the R requivalent of U505)
= U507 ============================================================================================
[L]
[R]
Re: Hissing and whistling in the STe audio output
It looks like the problems start right after the first op-amp ?
In that case, it would have to be getting some frequency from somewhere, looks like it starts off at about 1.3KHz, also at 15.6KHz.
I would have to assume the noise is being introduced by the power rails to the op-amp.
That wouldn't be exactly simple to fix... Really it needs its own little regulated PSU, looks like 8.2V and -5V ?! odd, but I would be tempted to lift up those 2 10R resistors....
... and use a PP3 battery for the 8.2V (would be about that for a rechargeable one) then have another in series with a 7905 regulator to get the -5V rail.... or 3x AA batteries in series instead...
Noise can still get into the op-amps via bad grounding on the MB.. but if that ruled out some noise, then at least we have a proper starting point to what is going on...
In that case, it would have to be getting some frequency from somewhere, looks like it starts off at about 1.3KHz, also at 15.6KHz.
I would have to assume the noise is being introduced by the power rails to the op-amp.
That wouldn't be exactly simple to fix... Really it needs its own little regulated PSU, looks like 8.2V and -5V ?! odd, but I would be tempted to lift up those 2 10R resistors....
... and use a PP3 battery for the 8.2V (would be about that for a rechargeable one) then have another in series with a 7905 regulator to get the -5V rail.... or 3x AA batteries in series instead...
Noise can still get into the op-amps via bad grounding on the MB.. but if that ruled out some noise, then at least we have a proper starting point to what is going on...
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.
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.
Re: Hissing and whistling in the STe audio output
Just a question about the -5 supply to op amp were is coming from some of those setups are antenna
Tom
Tom
Re: Hissing and whistling in the STe audio output
The whole PCB & parts is an antenna and the audio circuit has bad grounding in the mix. The only likely solution would be to rebuild the whole audio circuit on a new PCB and enclosed in a metal case. I suggested such but nobody is willing to build and try it
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.
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.
Re: Hissing and whistling in the STe audio output
@Tomswork i deleted your post as the photo gave away your location
Maybe post it again but edit the photo?
Maybe post it again but edit the photo?
If it ain't broke, test it to Destruction.
Re: Hissing and whistling in the STe audio output
Thank you I did not see that I'm more than halfway to tunnel vision
Tom
Tom
Re: Hissing and whistling in the STe audio output
This little amp is small and could bi pass the problem
uxcell® Super Mini PAM8403
Tom
uxcell® Super Mini PAM8403
Tom
Re: Hissing and whistling in the STe audio output
I didn't have an STE when you first posted this...things change
Now I have 2 working STE's & would be interested to do this...just the two usual constraints lack of time & lack of money...
I have a colleague at work who is very into his audio & analogue designs (including audio amps) so I might manage to 'volunteer' at least some of his expertise to assist.
Anyway, probably one for the back-burner but definitely one of real interest at some point (and IIRC @exxos you mentioned possibly adding in some upgraded sound system onto a future STF platform...?)
Re: Hissing and whistling in the STe audio output
I am a audio repair and design engineer , built and repaired amps for 30 years, hobby and work. I mostly did digital amps towards the end, before I got swamped with all things Atari related. I still need to finish my power amp one day
Yep, working on it in the background. 8 DAC channels to play protracker music without needing much CPU time..
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.
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.