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lfantoniosi / tn_vdp

Tang Nano 9K TMS 9118A VDP
BSD 3-Clause "New" or "Revised" License
120 stars 23 forks source link

low, noisy audio v2 #16

Open dantaipan opened 1 year ago

dantaipan commented 1 year ago

I have dropped v2 in the SG-1000 console which is effectively the same as an SC-3000 computer. Things are working well for the most part. For audio, this machine has a sn76489. When i jumper to pin 7 which is audio out the signal is very noisy and low. I saw some other comments for this console that suggested putting a cap between pin 7 and ground. That was for standard RCA jack modification. Any thoughts on how I might approach fixing sound for the TN-VPD v2?

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lfantoniosi commented 1 year ago

Look my latest v3 board (Tang 20K only). There I added a trimpot for voltage divider and also a 10uF cap in series. Sorry I moved into Tang 20K and I don't want to make new 9K boards. You can try adding this mod. Other thing to help would be connecting the audio straight to the board instead of the socket and removing the pin on the header to avoid creating an antenna and using a shielded cable to pull the audio from the system. You can just start modding by adding a 10uF in series, see what you get but the voltage divider really helps.

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dantaipan commented 1 year ago

Hmm. I was trying something similar to your last suggestion with a fixed 3k3 resistor like so but still very noisy. I can try something variable or keep playing around with it. Thanks. image

lfantoniosi commented 1 year ago

Put the capacitors close to the ADC not on the source

On Mon, Aug 28, 2023 at 8:55 AM dantaipan @.***> wrote:

Hmm. I was trying something similar to your last suggestion with a fixed 3k3 resistor like so but still very noisy. I can try something variable or keep playing around with it. Thanks. [image: image] https://user-images.githubusercontent.com/642598/263755738-4d5c5326-6621-4189-9ddd-278836f11683.png

— Reply to this email directly, view it on GitHub https://github.com/lfantoniosi/tn_vdp/issues/16#issuecomment-1695941101, or unsubscribe https://github.com/notifications/unsubscribe-auth/ACCJWUZOAQRUGYZGRJQZGR3XXS5PRANCNFSM6AAAAAA4BOHAMI . You are receiving this because you commented.Message ID: @.***>

lfantoniosi commented 1 year ago

And should be a voltage dividee not a resistor in series

On Mon, Aug 28, 2023 at 8:55 AM dantaipan @.***> wrote:

Hmm. I was trying something similar to your last suggestion with a fixed 3k3 resistor like so but still very noisy. I can try something variable or keep playing around with it. Thanks. [image: image] https://user-images.githubusercontent.com/642598/263755738-4d5c5326-6621-4189-9ddd-278836f11683.png

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dantaipan commented 1 year ago

Thanks, I think I get it.

dantaipan commented 1 year ago

Like so?

tn-vdp audio

lfantoniosi commented 1 year ago

Yes

On Mon, Aug 28, 2023 at 9:59 AM dantaipan @.***> wrote:

Like so?

[image: tn-vdp audio] https://user-images.githubusercontent.com/642598/263770055-a557d10d-e445-4336-bcc6-8abc208d59dc.png

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dantaipan commented 1 year ago

It is not pretty but this did significantly approve the audio. Still a certain amount of hiss even when tuned but it did remove a lot and helped with volume. Thanks for your help. Feel free to close this issue.

image