rebuild arcade sound in LTSpice - Page 1
Forum section: electronics / beginners

author: beta-tester
author_rank: Contributor
timestamp: August 13, 2020, 02:34:09 pm
content: hello, its the very first time, i am writing a post here and hope you can help me.i am trying to rebuild some sounds from an old arcade machine "borderline", because the sound files available on internet do not realy sound like that, what i mean to remember me from my childhood where i spend more time in the video game hall than in school. (until is was forbidden for kids under 18)because i do not have the parts of the schematic (its made of NE555, LM324 - shame on me), i can not rebuild it in real hardware on breadboard.so i came up to try to rebuild the schematic in LTSpice.but something i make totally wrong... i don't get anything useful out of what i rebuild.and my knowledge is not good enough to figure out what i should get out of it.the schematic is from this PDF:Borderline_-_1981_-_Sega.pdfon page 28 at A/8 starting with EMAR_TRG i rebuild the schematig as good as i could.i assume IC4 (MB4391) is a kind of analog audio mixer, where the CON pin controls the loudness of the IN pin.and i assume the IC33 (LS123) gives a pulse of about 13.356 ms (i think that value is not critical)so those both components i did not rebuild... instead i used a PULS voltage source.but the rest of that EMAR_TRG path i rebuilded.see attached the zip file with my LTSpice files...when i start the simulation i get nothing on V(emar-sound) that would make a sound.can somebody tell me, what i made wrong?BTW: in the schematic it looks like the capacitors are in µF (handwritten) but in the partlist those values are written as MF (typed)...is it because old mechanical type machines did not have a µ character to type or did i used everywhere wrong values?

author: beta-tester
author_rank: Contributor
timestamp: August 14, 2020, 10:10:01 pm
content: is it possible, that all these transistors in the schematic for that part are drawn in the wrong orientation (base and collector are swapped by mistake)?i found a example schematic of a voltage controlled oscillator cirquit, that looks similar to parts of the sound path (except of the NE555) and there the transistor is connected the other way round.when i swap base and collector in my LTSpice rebuild, i get a wave as output, but it is only a ramp/zigzag that is generated near IC6.but i am missing the change in frequency... both IC14/IC15 (NE555) should influence the output signal in one or another way, but it doesn't.

author: Ian.M
author_rank: Super Contributor
timestamp: August 14, 2020, 11:24:34 pm
content: Yes, your supposition that the transistors are drawn wrong is almost certainly correct. Nothing else makes sense. In some of the OPAMP/555 pairs you could argue that there is a missing dot so the combined Discharge pin and transistor collector is meant to pull down a signal it crosses, but TR14 & TR4's collector circuits on the original don't cross any other signals, so that idea is a bust.Why it doesn't work?Well your sim is railing the OPAMPs during the pre-run operating point analysis during which the 555 chips cant toggle and you aren't running it long enough for it to recover. Try.tran 1 startupand you'll find it much better behaved. Also your C36 should be 0.022u as a 22 milifarad capacitor would have been very large back in the early 80's, maybe the size of half a beer can! Anyway its called out in the BOM asQuotewhich is obviouly a 22nF film cap.Why the BOM was typed up with 'MF' for microfarad instead of the more common substitution 'uF', we'll never know. Perhaps it was prepared on a computer that couldn't do lower case!HTHIan.

author: beta-tester
author_rank: Contributor
timestamp: August 15, 2020, 08:53:21 am
content: hi Ian.M,thank you very much... yes, the 0.022µ capacitor i totally overlooked.now that sound is working and i could export it to wav file.it was alittle bit tricky for me to get the wave form to the range of (+1V .. -1V),now it is time to rebuild the other sounds...PS.: the errors in the schematics were they made by intention, to prevents noobs like me to rebuild?or is that schematic from a cheap rebuild/bootleg

author: beta-tester
author_rank: Contributor
timestamp: August 15, 2020, 07:19:33 pm
content: unfortunately i got stuck again...at ANIMAL-TRG page 28 at D/8 there is a part i don't get anything useful of it.i assume it sholud oscillate and should trigger the transistor TR16 to pull down the input of the second part of IC54(LS123).the first part of IC54(LS123) will generate a pulse of around 1224ms duration when it got triggered, the second part will generate a pulse of around 13ms, when the transistor TR16 opend during the duration of 1224ms.so i expect TR16 will multiple times open with a period bewteen the 1224ms and 13ms.but the part i rebuild isn't even making one single shot...does somebody see what is worng here this time?

author: beta-tester
author_rank: Contributor
timestamp: August 16, 2020, 11:13:46 pm
content: ok, i have skipped that part i couldn't get to work and substituted it synthetic voltage souces.now i have all sounds from that board.but it seems i made it for nothing...see here:https://github.com/mamedev/mame/issues/7091

author: james_s
author_rank: Super Contributor
timestamp: August 17, 2020, 12:06:37 am
content: I will be curious to see what sort of sounds the simulated circuit produces. Some of those old analog sound generation circuits rely on characteristics of some of the components that would normally be considered deficiencies. They may not work quite the same with ideal simulated components.I've long been fascinated by sound generating circuits. I've recreated a number of different digital arcade and pinball sound boards with FPGAs.

author: beta-tester
author_rank: Contributor
timestamp: August 17, 2020, 05:16:53 am
content: yes, the simulated sounds sounds a little bit harsh - maybe it needs some filtering at each stage of wave form generating.also noise, big tolerances and temperatur drift (i guess back in these days every electric device was driven way warmer/hotter than these days i think)but it is what it is as long there is no original arcade machine available, or at least real rebuild in hardware, that is better than nothing.i think these sounds are now closer to the original real ones than any fantasy sounds out of a collection of random sounds fom other arcade machines.maybe someone who has the components laying around can rebuild the sounds on breadboard (with these days components)and tell how close or far the simulation is from reality...PS.: and there are also the special components for that there are no documentation exist on interenet...like MB4391... its characteristics is unknown to me. does it mix sound linear or logarithmic, does it distort/filter the input in an other way...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 17, 2020, 05:51:47 am
content: Mind that the sound recorded from outside the speaker and cabinet will be affected considerably by them. A combination of bandpassing (speaker limitations), peaks and troughs (speaker and cabinet resonances), and delays/reverb (cabinet and ambient echos).I like this random recording I made some years ago,https://www.seventransistorlabs.com/Solfeggettio.mp3it is the familiar tune, played by a single square wave channel (on a platform that lacked enough memory to hold the full song heh), recorded in a dorm room, so the reverb is quite short and strong. And, well, I don't have a raw electronic recording of it to compare directly, but, well, you know how brash an unfiltered square wave sounds!Entirely possible that onboard filtering is there, too. (I guess I should, y'know, actually read the schematic at this point)(Heh, bonus clip: I later ported the 4MHz chiptune code to a platform at 8MHz. I forgot to regenerate the song data for the new clock rate. So it ended up overclocked...https://www.seventransistorlabs.com/Solfeg_Fast.mp3I also hadn't implemented the "rest" note yet, which used the lowest accessible note as a special case. That note happens to be 122Hz, so the end of the song sounds more like, well...)Tim