RCA audio out mod on standard ST/STFM's

[Gunstar]

I just completed a very simple mod on my 1040STF tonight that I highly recommend. I attached a single, RCA audio jack to my ST. I drilled a hole(in the case right where the hole already is in the metal shielding that the RF jack normally goes, so if you have RF, you'll need to drill a hole through the sheilding too, or run a wire out and not use a mounting RCA Jack) to fit the mounting RCA jack I had (can be picked up at radio shack for small change), and connected the inner part (of the RCA jack) to pin 1 on the (inside) of the monitor port, and the outer (ground) to the metal shielding inside the ST. Pin one is the top, left most pin if looking at the monitor jack from the inside, top, rightmost pin if looking at the jack from the outside on the back of the ST. It's a standard audio signal, so it's a VERY simple mod. I then connected a "y" RCA cable to the jack and plugged that into a pair of PC speakers (self amplified)I have that have standard RCA inputs (normally connect to a PC via a headphone jack to RCA cable that came with the PC speakers. These speakers have simulated surround sound too, so the sound quality is SUPERB for a mono ST audio signal through them! It sounds 100 times better than the SC1224 monitor speaker! Very good base and no more "tinny" sounding audio! It took me 20 minutes to do the mod. Great stuff! No resisters or anything else needed, just two bits of wire, and RCA jack (preferably a mounting one), soldering iron, solder and a drill...and screwdriver to open up the ST. of course you wouldn't even need to solder if you just used some small alligator clip wires!

[Paolo]

You know, I've had an ST for a long time, then I bought an STE. I was so used to the 'standard' sound of my ST that I didn't bother to use the STEREO RCA plugs on the back of my ste. Then I found a demo showing the stereo capabilities of my ste, so I HAD to connect it via the RCA plugs.

WHAM! a whole new world (not mentioning the stereo feature).

Since then I used extensively those RCA plugs.

But I never thought of creating an RCA out for my 1040.

Good job, Gunstar!

Paolo

[Gunstar]

Yeah, wish I had an STE...

But I have disliked the sound coming from the sc1224 since I got My ST, I put in a bid for a "Tweety Board" stereo upgrade kit for the 1040ST, but lost, so pissed and with some resolve, I searched the net for mods I could do myself. This one was VERY simple and I had the couple parts needed at hand. It may not be TRUE stereo, but the difference the added base sound and simulated surround that my PC speakers have make a WORLD of difference. I don't even care about stereo anymore, this sounds VERY good. Thanks for the praise!

[krupkaj]

In my old STFM I had modiffication wich I was build myself. First chanel from Yamaha comes to left, second to right and third was mixed to both left and right. What about your mod? Is it similar?

[Gunstar]

No, just a monophonic jack like I stated above, but it still sounds fantastic compared to the SC1224 speaker's "tinny" sound. Plus, I have Simulated surround speakers, which turn the monophonic signal into simulated stereo. But, your mod sounds very cool, I think I will do it too, if I can find the pin-outs for the YM processor...and have both for any type of ST sound/music.

[krupkaj]

I have found pinout for Yamaha soundchip on my harddrive. So here it is. Unfortunetely the scheme of stereo sound modification I cannot find. But I know that it was very simple just some capacitors and resistors.

[Ayreon]

Yeah thats a great mod, worthy of opening your ST again

Keep in mind that this mod can mess up the sound quality when playing sampled sounds/music (at least my bro's ST had that problem, weird noise). So make it in such way that you can switch it back to mono.

[+rdemming]

Hereby the schematics for the Stereo upgrade for an Atari ST. These were published in the Dutch S.A.G. Atari Magazine December 1988. The circuit was designed byRob van der Haar.

 

The 'double' toggle switch is to switch between mono-and stereo mode. You have to cut pins 3, 4, and 38 of the soundchip loose from the motherboard and fed them into this circuit. The 'monitor audio' goes back to the motherboard at one of the pins you cut loose. The left and right audio signals goes to a standard audio connector.

You can adjust the potentiometers to adjust the signal between the chanels.

 

Robert

[+rdemming]

O, yes, the switch is necessary to switch back to mono sound while playing digital samples. This because samples sound not as intended in stereo (a lot of noise). Samples are played on an ST by adding the volume levels of the three sound channels. If you separate the channels, the volumes will not be added and the sound will be distorted.

 

Robert

[Gunstar]

So, I take it those four 2k5's are potentiameters? I'm glad you mentioned that, poor schematics not to show those as adjustable resisters, in fact, all those resisters should look like; ///, not rectangles, but that's no problem. Also, is the "double switch" a single pole, double throw, or double pole, double throw? I'll have to redo this schematic properly and post it so others will have an easier time (include the rca jacks, proper electronic part symbols, and show the best possible places for ground, etc. on the motherboard). I assume the rest are standard resisters? I think I'll build this circuit myself, just for fun, instead of buying the "tweaty board" from B&C like I had planned (since I didn't feel like figuring out the circuit myself), now that I have this schematic. Thanks!

[Ayreon]

LOL.. there's nothing wrong with this schematic.

It's european standard and complies with the NEN rules as far i can see. Although the potentiameters might be drawn wrongly. I always learned to draw the arrow skewed through the resistor "/ " . //// looks too much like the symbol of a coil so i guess thats why we use rectangles for resistors.

My english sure lacks here.. we never learned anything like single throw switches..erh but i think it's a single throw (both latches switching at the same time to the same point), double pole (since it switches YM38 and YM4 with YM3 to combine the 3 channels for mono)

 

. . YM3. . . . . YM3

. . .| . . . . . . . |

. . ----------

. . | . . . . . . . |

. . YM4 . . . . . YM38

 

OR

. . . . . . . . . . . YM3

. . . . . . . . . . . .|__

. . . . . . . . . . . .|. . |

. . . . . . . . . . . .---

. . . . . . . . . . . . |. .|

. . . . . . . . . . YM4 . YM38

 

Phew i hope these ascii pics work

Aaarghh it did not, I had to use a load of dots as this forum doesn't allow more than one space between characters. It doesn't make my drawing any clearer

 

 

I think it's a good idea to convert it into the overseas standard and add more detail of where to connect what.

Maybe a short guide of whats the best place to drill the whole for the RCA connectors, where to place the new circuit, etc is handy too.

[+rdemming]

So, I take it those four 2k5's are potentiameters? I'm glad you mentioned that, poor schematics not to show those as adjustable resisters, in fact, all those resisters should look like; ///, not rectangles, but that's no problem.

 

This is indeed the European notation. See http://www.tcars.org.uk/tcars/electronic_symbols.htm.

If it isn't American, it doesn't mean it is wrong

 

Maybe I should have drawn a big dot at the intersection of the ym4 and monitor audio since these are connected. You might get the impression that it is a crossing and not a connection.

 

Also, is the "double switch" a single pole, double throw, or double pole, double throw?

 

I'm not that familiar with the English terms but in Dutch we call it a "dubbel polige schakelaar" so a double pole switch. (two switches in a single housing that are operated together).

 

Regards,

 

Robert

[Gunstar]

Thanks! problem is, those rectangles could be mistaken for parallel circuit traces (however unlikely), our coils don't look anythin like our resister's, so we don't have a problem confusing them, I can't show you the schematic for coils in ascii though, but it it looks like a stretched "slinky" spring with two parallel lines next to it, so much different than a resister=//// (remember that this resister drawing is also in ascii which isn't too good)

[Ayreon]

ah well for a coil we use the slinky without the extra lines.. We only use 1 line inbetweem 2 slinkies if we draw a transformator (duh is that good english?) When drawning quickly one could draw them trianglar like or the triangle thingy slinky like. Anyhow i don't know what the creators thought when they designed this standard. They didn't think the same as their overseas counterparts for sure wich doesn't make things any easier. We need world standards.. so if you change to the metric system we will take your electronics symbol system

[Gunstar]

You are speaking of an inductor coil, right? Transformer is the spelling you're looking for, and it sounds like transformers are drawn the same way for both of us. As far as the metric system goes...they tried switching over a couple decades ago (I had to learn it growing up in school), and I think they still teach it in grammer school, but Hell will probably freeze over before we drop our American standard system (we do use both), so I guess you'll be sticking to your electronics system (or use both).

But as long as we're a world power, and have proud ego-maniacs in charge, the U.S. will try to bend the rest of the world to it's will, not the other way around.