TURBO-R poor audio quality ...Why????

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By robivy

Supporter (8)

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25-01-2015, 06:39

Thanks! Check out my overall review of the Turbo R

https://www.youtube.com/watch?v=CE-XoXHaoVY

By Colemu

Champion (478)

Colemu's picture

10-01-2017, 22:12

very interesting thread,

I always wondered why the FM sound on my Turbo R ST was 'muffled' compared to the audio from my old Sony + FM Pak. Earlier in the thread sd_snatcher mentioned that this was due to incorrect capacitor values in the low pass filter. Has anyone with access to a schematic ever figured out which capacitors to change to either correct, or improve the issue??

Seems a shame that such a wonderful computer is let down by this small design fault... Sad

BTW: nice video robivy

By hamlet

Hero (569)

hamlet's picture

12-01-2017, 02:54

I like your videos! Thank you, man!

By Colemu

Champion (478)

Colemu's picture

29-01-2017, 14:13

After trying different solutions with varying results, here's what I found to be the best (easiest) solution to the FM 'soft/flat' sound.

Replace R23 with 27k resistor (to increase volume of FM sound)
Replace C159 with 150pF capacitor (to increase the frequency of the FM sound)

Optional: Replace both NP capacitors C40 & C19 with 1uF tantalum capacitors (it seems to cut down some of the high frequency background noise)

Thats it Wink

Try it, you won't look back. The difference is like night and day Running Naked in a Field of Flowers

By roadfighter

Champion (306)

roadfighter's picture

20-05-2017, 08:08

Hi there, I did my fare share of research and came to the conclusion the sound of a Turbo-r is not that terrible after all. It's more how you experience it then "bad".
I did do some modifications to make it "better". One of the things i found that makes the "noise" on the audio output drop dramatically was the removal of the RF-Unit. At least the disconnection of the unit. The 15kHz. from the RF generator is very "aggressive" and you can hear it back in the whole machine's audio. So just disconnect the 3 pins to the motherboard and most of the noise is gone.
Then i did some of the mods Colemu suggested:
1e - Replace R23 with 27k resistor (to increase volume of FM sound) = a good step for the volume indeed.

2nd - Replace C159 with 150pF capacitor (to increase the frequency of the FM sound) did do some thing but my hearing must be of a bit because i find it not enough noticeable.

3rd - Optional: Replace both NP capacitors C40 & C19 with 1uF tantalum capacitors (it seems to cut down some of the high frequency background noise) = did not do it, tried it thou but no difference was heard.

After doing this research i came to MY conclusion that the audio is not that terrible. Let us be reminded the machine was made in 1992 when we all watched our movies on VHS or Betamax and did listen to a Cassette recorder for our favorite music.

And i must say, i am going to replace all the Capacitors in the machine.
Because the ones i did check and tested, I also have replaced and that is noticeable.
Also the video caps are replaced and the picture is more stable/brighter.
So thats the next step to do my completed turbo-r and other computers oO

Emil

By Meits

Prophet (4096)

Meits's picture

20-05-2017, 12:46

At least the complete audio level should be amplified before noise gets added. I'm far from an electrotechician, but I guess that should be possible. Once noise is added and you amplify it, you amplify the noise as well. The first batches of the ST suffer this low volume thing. It seems that the later batches had an audio update or so I read here somewhere.

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