Sound experts...

modessitt

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Today I looked at a System 1 cab that had been converted to Smash TV. I was originally told they thought the speakers were blown because the sound is all distorted and vibrating, kind of like it is passing through wax paper.

Well, I get there and find that the speakers seem to be just fine.

So, what is causing the problem? I figure it is one of three things:

a) Incompatible speakers - these are 4" 4 ohm speakers. Is it possible that the JAMMA Smash TV needs 8 ohm speakers or something? Do they make a 4" 8 ohm speaker?

b) Problem with the sound board - either a voltage issue, amp problem, etc.

c) Problem with the wiring or volume pot - it has an external volume pot like older Williams games. The volume goes up and down smoothly, with the same distortion at low levels as at high levels.


What do y'all think?
 
Personally I would guess B. I think the fact that the distortion is still there at low levels as well as high likely rules out the pot. I guess there could still be a wiring issue but since sound is getting there it's got connectivity. I know it's not advisable to run 4ohm speakers on an 8ohm system or the opposite but I've done it before with no issues. I doubt there would be issues considering the volume levels these boards output. I guess over time the wrong ohm speakers could damage the amp causing distortion. I still lean toward B. Although I'm not an expert.
 
I would lean towards agreeing with p1899m. One thing you can try is just to run the speakers in series off one of the channels. The two speakers in series would give you the approx. 8ohms. If you still get distortion, you probably have a sound board problem. Bob Roberts sells 4x4 5watt and 15watt 8ohm speakers.
 
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Just because they look fine doesn't mean they are fine, if you can hook up another board just to check for a difference in sound i would try that first, if it still doesn't work right i'd then move on to checking the wires and making sure they aren't picking up interference from other wires, if those check out then i would think of trying any 8ohm automotive speaker (just because they're super common and easy to find local/free/in a corner in the garage). Last i would buy a speaker and that would most likely tell me if the soundboard was bad/there was some other hidden issue.


And regardless of that

http://www.arcade-museum.com/manuals-videogames/S/SmashTV.pdf

is a link to the pdf manual, page 2-2 says it came with a 4"tweeter and 6" round speaker, 8ohm flavor :D
 
I have the kit manual and it doesn't say anything but "connect to speaker". Page 2-2 is a parts list for the audio board.

I've got some 8-ohm speakers here I'll take next time I go out...
 
I have the kit manual and it doesn't say anything but "connect to speaker". Page 2-2 is a parts list for the audio board.

I've got some 8-ohm speakers here I'll take next time I go out...

page 2-2 on the pdf i linked, your manual is most likely different.

page 3-20 shows how the original speakers were wired also if you need that.
 
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http://www.arcade-museum.com/manuals-videogames/S/SmashTV.pdf

is a link to the pdf manual, page 2-2 says it came with a 4"tweeter and 6" round speaker, 8ohm flavor :D

A couple of things....

Yes, it appears that dedicated SmashTV did have a 6" 8ohm speaker. However, if you scroll on down to p52 of that PDF, you'll see that it was wired in parallel with the other speaker (a 4" piezo). If the 2nd speaker is also 8ohms, the net impedence seen by the amp is 4 ohms.

No matter though. The amps used by Williams here (according to 2-5, same doucment) were TDA2002 (the same amp Atari used in the ARII boards). The TDA2002 datasheet says it'll happily drive loads down to 1.6 ohm. The pair are operated together for a single output in a push-pull (bridge) mode here, so that's 3.2ohms in our case. So, they should be fine connected to a (net) 4 ohm load, or a (net) 8 ohm load, but of course less loud with the 8 ohms.

Now, regarding the speakers... System I was (from what I can tell) a stereo system, and had two independant channels and seperate speaker wiring. SmashTV has only a single audio channel. There's no telling how the speakers were wired when the conversion was made... series? parallel? only connect one? In any case, so long as the net impedence ended up 3.2 ohms or more, it would have been within the specs of the audio amps. The only scenerio I can see that would cause a problem is if there were two 4 ohm speakers wired in parallel, giving a net of 2 ohms; combined with the volume being turned up pretty high.

Getting back to the OP... I'd guess it's more likely that something on the audio board is hosed. If it were just mis-matched speakers, I'd expect it to be OK at low volume levels.
 
yup pg52 must be p3-20 i'm going by the numbers on the page scanned in. and your completely right, the manual doesn't say what resistance the piezo is tho. i just think that if you have an 8ohm spare speaker around try that first as it will be super easy to do.
 
Now, regarding the speakers... System I was (from what I can tell) a stereo system, and had two independant channels and seperate speaker wiring. SmashTV has only a single audio channel. There's no telling how the speakers were wired when the conversion was made... series? parallel? only connect one? In any case, so long as the net impedence ended up 3.2 ohms or more, it would have been within the specs of the audio amps. The only scenerio I can see that would cause a problem is if there were two 4 ohm speakers wired in parallel, giving a net of 2 ohms; combined with the volume being turned up pretty high.\.

ya know, It might have both in parallel. The kit just has two speaker wires coming out of the board/volume control, and those two wires go to both speakers. I guess I should check to see if they are daisy-chained or not...
 
8 ohm speakers made no difference.

When I go out next week, I'm going to pick it up and bring the entire game into the shop so I can use my audio probe to track down where the sound is going wonky....
 
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