A1000 Audio Lowpass filter bypass ===================================================== Ok... here's the deal: if you're an A1000 owner and would like to get the same high fidelity sound that can be achieved in other amigas by turning off their lowpass filter, this file documents how you can do it. Just a word of warning.. if you're not comfortable opening up your computer and removing boards, etc., I would rather recommend some computer technician (or hacker friend) to do it for you. I won't say anything about voiding warranties (at least I didnt get a 6 yr. manufacturer's warranty on MY A1000 :) ) If you have one of those refurbished models which still have valid warranties... consult your amiga dealer! The newer amigas (500, 2000, 3000, 3000T?) have the same audio chip and surrounding circuitry as our A1000s, except that theirs provides for a software-selectable audio filter bypass, which can be toggled at will. The fix I present here is permanent (see below), but I doubt that you will ever want to switch the filter back on! Now... on with the instructions: Instructions: ===================================== +---------------------------------------------------------------------+ | DISCLAIMER::: Ok, I hold no responsability for damaged computer | | components or project-related fatalities. This, after | | all, is a hack, and although I am quite sure it will | | work for you the way it has for me, accidents do | | happen, words are misspelled/misread, etc. | | Although this is a fairly simple modification (it only| | involves soldering two wires), beware: | | ***MODIFY YOUR COMPUTER AT YOUR OWN RISK!*** | +---------------------------------------------------------------------+ First, before you go prying your computer open, here's a list of what you'll need: Philips Screwdriver 22 Gauge Wire (or 20) Wire cutter or wire stripper Small Pliers Soldering Iron (20-25 Watts) Some solder (For PC board work) Ok.. now after removing all pheripheral connections, 256k memory expander (you DO have one, don't you?), bus devices and power connections, flip the computer over and remove all the screws that hold the case together. I suggest you find some place to put and organize all the screws since there are lots of them, and they're easy to confuse and maybe even have some left after closing the case (trust me.) Ok, now carefully put the computer face up again. Now remove the top cover by prying each corner open, first the ones on the back, and then the front ones. A small flat screwdriver often helps in this procedure, just be careful and don't force the cover off. Now that you have the top cover in your hands, look at the inside portion. See all the signatures? Neat, huh? :) Now remove the RF shield by first using your pliers to straighten the metal tabs that hold it and then removing the screws around it. You should now see the motherboard, kickstart daughterboard, floppy drive and power supply. We shall now concentrate on the daughterboard. The daughterboard is a small board that stands about an inch above the main motherboard, components facing down. This board is connected to the main board by several gold posts located at each end. Since the audio buffer/filter chip is below this board, we must first remove it. First, make sure you ground yourself to avoid zapping any components with static electricity. If any of the floppy connectors are in your way, push them to the side, or remove them carefully, noting their orientation so you can put them back in correctly. To remove the daughterboard, first remove the screws that hold it in place, and then pull up on each corner of it just a bit at a time, making sure that the gold posts aren't being bent by keeping the board as level as possible. Take your time-- it'll come off eventually. When you finally pull the board off, set it aside on a clean static-free surface. Now, look for the audio buffer chip. It is located at position U5G, right below the main power supply connector on the motherboard (refer to the diagram in the IFF file.) Now, for the fun part... Cut 2 lengths of wire, strip the ends of each one. Don't tin the ends of the wires, just twist them... it'll be easier to afix them this way. One of the wires connects pins 14 and 3 on the chip, and the other one connects pins 5 and 8. Wrap each end to the appropiate pin on the chip, and after making sure that the wire doesn't touch any other pins, solder it in place, aplying only the necessary heat. The chip may be damaged if you place too much heat on the pins. Also make sure that the solder doesnt touch any oother pins, either. If it does, remove it with solder wick or a vacuum bulb, and try again. (Refer to diagram for pin numbers and jumper location.) That's it! Now, we must put the daughterboard back in place. Do so by aliging each of the red connectors on the daughterboard with the gold posts from the motherboard, and then gently pushing down on each corner, a bit at a time, following the same precautions we took when removing it. Keep pushing down until the plastic parts from the gold posts and the connectors on the daughterboard come together completely. Replace the board's screws. Also, if you removed any of the floppy connectors, replace them, being sure they're correctly connected. At this point, connect the monitor and power cable to the computer, and power it up. If the kickstart 'hand' picture doesn't appear on the screen, then you didn't mount the kickstart board correctly. Power off and check that it is seated correctly. Load kickstart and then any sound demo of your choice (game, program, etc.) to test the computer's sound. There should be a noticable change in audio quality. When you're ready, power back down and remove all cables. Screw the RF shield back in, and twist the metal tabs to secure its ground connection. Replace the top cover, flip the computer over, and replace the remaining screws. Now you can re-connect all your peripherals and power cord. Now you're ready to Rock and Roll! And now...... ===================== There it is. Simple, isn't it? And its worth the trouble... my A1000 has had the modification for about 1 1/2 years now, and there have been no problems. One thing I did put in was a switch- just in case I wanted to get the old sound back; but I've never used it once! But if you want to get your old sound back, just place a DPDT switch between the jumper cables. One drawback to this method is that there's a bit more noise due to the longer wires, but not much. I would rather have you NOT put a switch in-- maybe a defective switch could ruin some components, etc. (I wouldn't know WHY someone would even care to go back to having lesser audio fidelity...) I guess some of you who aren't too techinaclly inclined have their doubts or maybe some of the instructions aren't very clear to you... so here are my addresses (electronic and real-world) just in case you want to ask me something, or just to chat! Alejandro Garza González pa250225@mtevc2.mty.itesm Rio Rhin 514 pte. @131.178.1.5 Colonia Del Valle (Internet address) Garza García, N.L. 66220 MEXICO JanusMan@IRC (phone 38-46-86) (Internet Relay Chat) Before I sign off, I'd very much like to thank Howard Bassem, who did the original article back in '88 on Amazing Computing Magazine V3.4 about bypassing the audio filter. Thanks, Howard! Also, thanks to everyone at +Amiga! (IRC) for all the tech support, Teijo Kinnuen (for MED) and Psyke-nose-is! If you ever come to Mexico, gimme a call! Glad to show any amiga pal around! (Of course, if you're from around here, don't bother 8^) ) --------------------------------------------------------------------25/Oct/91 ============================================================================ | Alejandro Garza González/38-46-86/Monterrey, Mexico:: ^^^^^» | | JanusMan@IRC::pa250225@mtecv2.mty.itesm.mx :: (..) » (the hell?)| | :: /_ » o | | // Only amiga, folks! :: |_- _» ·° | | \X/ "What the hell is THAT, boy??" :: == J'91! | ============================================================================