Fixing STE microwire "mixer" error

Petari · 21-01-2015, 08:56:04

Some people observed problems with unbalanced audio volumes of PSG and DMA by STE, Mega STE years ago . There should be possible to set PSG volume -12db with microwire in SW, but it never worked - I talk about serious sources like Atari ProfiBuch.
I looked schematic of microwire in STE, and there is something very wrong.

Correction took some 15 minutes:

How to perform fix: no need to desolder anything - just cut pin of resistor R531 which leads to 2 capacitors connected to GND. Solder there, to resistor new 10K resistor, and other pin of it to point where R531 was soldered. Add shortcut from common point of 2 resistors to pin 5 of IC. That's all.
This divides PSG auidio level to 18%, what is aprox. -12db . With different resistor value may change that ratio.

And proper setting of microwire mixer is not %01 for this, but %10

I wonder how this went this way in Atari . Seems that communication between SW and HW crews was bad.
Anyway, this correction is very useful. For instance, now sound quality in modded Xenon 2 is better, because PSG volume settings remain same, 4-bit, while I needed to lower them down, so used less bits, what made not so good volume changes by sound effects. And will help in other cases where DMA and PSG audio works simultaneously in STE.

Anemos · 22-01-2015, 21:45:50

Applies and for the STE any models?

Petari · 23-01-2015, 08:42:53

I'm sure that yes. Hardly that anything is changed in that circuit part in later STE revisions. It is same in Mega STE too.
And should be same in TTs too, according to some people - same problem is present, that PSG is much louder.
Checked TT schematic - 100% same circuit, with useless muted inputs.
Only by Falcon it is balanced.

Anemos · 24-01-2015, 16:36:37

If i found free time i will do this mod, (i think my STE need inside cleaning also,so is time to opening..)
thanks petari.

Anemos · 24-01-2015, 19:33:42

Before mod 1040 STE motherboard By Anemos

..wrong...

Anemos · 25-01-2015, 09:37:48

No.. is wrong.. lol i make new the right.. (i think)

Anemos · 25-01-2015, 09:43:18

....

Anemos · 25-01-2015, 10:33:20

Sorry for the trolling.. i have Headache from yesterday..

This is must be the right..

Petari · 25-01-2015, 11:11:20

Yes, that will be fine. No need for kilometers of wire

And when done, run with RUNICDM.TOS , or RUNACSIM.TOS. So far, supported only in modded Xenon 2.

Anemos · 25-01-2015, 12:47:01

Thanks petari.
Mod is rdy.. test in next seconds..

Anemos · 25-01-2015, 13:00:40

Oh yaa....! sound and music is perfect! stereo and clear.
Good work petari.

qq1975b · 25-01-2015, 21:45:19

Can you post a picture of your motherboard with the fix done?

On the last picture...the resistor on the bottom is the one that the STE motherboard already has and the upper one the new 10K resistor, right?

thank you!

Anemos · 25-01-2015, 22:50:55

Yes here is the final.
Ps.Careful later must be do not touching the solder to metal shield of PSU.
Cover the solderings with electrical tape or something.

qq1975b · 26-01-2015, 08:30:31

Thank you! Nice work there. I have ordered some 10K resistors

Anemos · 22-02-2015, 14:09:27

If im right this mod help the: STE background audio Player v0.9 ?
quality seems to hear better now?