Hello!!

I have a GT and a 8280 (and in the early years a F700 and a Sony HB-20P). The question is that I cannot obtain a "pure-clear" sound from my MSXs (but I don't remember If the 8280 did that cos I have it in the armchair lost with lot of old consoles and I'm lazy to test it, but the problem is that I use more the GT).

Well, so the sound that I obtain both from different TVs I have had and from the internal output of the F700 (and something rare I have made with the turbo R that I have no idea on how to explain it in a correct english)is: "RRRRRRRRRRRRRRRRRRRRRRRRRRRRR" and... more intense when the white color is displayed on the screen!!

God! How terrible english I have!! :'( Gotta practise more... but, anyone has understood what I've said??

thanks!

I had something like that once... I think putting a cap between GND and the sound output more or less solved it. Don't quite remember the value tho, was it something around 47uF? Dunno, if you have a couple of caps lying around, just test to see if there's a difference... Putting a resistor on the output line(s) can also help reduce the noise a little. And unless you were talking about the weather in Guadalajara I guess I did indeed understand your English

What you hear as disturbing hiss and rumble etc can be caused by:
1. weak power supply filtering in the audio circuits parts of the computer
2. crosstalk from the video lines to the audio lines in the wires between the PC and the monitor.

What you describe sounds like problem 2, since the disturbance is influenced by the video.

Problem 1 is often caused by the load floppy drives impose on the powerlines. It takes some difficult to implement measures such as a better power supply or adding filters to the powerlines. Often the audio circuits are given power by 'dirty' powerlines and you hear that. A wellknown problem if old floppy drives, using +12V, are replaced by modern drives that take power from the +5V line (+12V is connected but not used).
The NMS8280 is better here than other MSX machines like the NMS8250 or turboR.

Problem 2 is easier to handle: separate immediately as close to the source as possible video from audio. The least is doing this at the connector on the MSX.

A capacitor of this value, 47 UF, between sound and ground is an effective short, so you wont hear sound nor disturbing noise!
I can imagine a much lower value will help a bit by attenuating high-frequency video crosstalk. I would suggest pF values.

A resistor helps a bit by attenuating the signal, because a resistor has an inductance too for higher frequencies.

Quote:

A capacitor of this value, 47 UF, between sound and ground is an effective short, so you wont hear sound nor disturbing noise!

Might have been 0.47uF, I really don't remember. Like I said, experiment a little. I do remember it did to the trick tho. The noise coming from my ST was considerably less after this 'fix'. I remember using both a resistor and a cap, tho I don't remember the values...

thanks to all!

0.47 is a good short for high freqs for low impedance outputs like for earphone amps, but you also will reduce sound high freqs.

maybe something like a cap of 0.47 plus a resistor of 27 ohms in serie..... to ground will help. But you never will get reduction of noice to 0 without lose signal.