Mar Show full post »
bakersnarkMDW
I’m adding to Marc’s log the transcript regarding the “repairs” done to fix excessive volume from his R-Type board when installed in his MK2 cab.
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22/6/19

Mar: I think I'm going to put R-Type in my MK2 cab. But that's going to be an adventure... Not sure I'm up for that tonight

dennydevito: @Mar you have had more than enough beer to give it a go

Mar: haha

dennydevito: *will not be held responsible for damage resulting from terrible advice

Mar: Anyone got any tips on how to make speakers less loud, outside of any volume pots or controls?

bennbanasik: Earmuffs?

dennydevito: Unscrew speaker, add rag + tape

BakersnarkMDW: Tape coasters over them. 😋🍺

Mar: The best suggestions...

dennydevito: I like the coaster idea better

Mar: The good news was that R-Type worked perfect in the MK2 cab. The bad news was that the MK2 cab is so loud I couldn't play it. It's fine with MK2 because you can turn the sound down in the settings. Not so much R-Type
Stupid arcade games. I quit this hobby!

bennbanasik: You shouldnt need to turn it down
Everyone should hear shooting aliens right in face

Mar: Tell that to my neighbours!
Haha
Might have to pull those speakers out and put in some shitty ones
Anyway, I've gotten no where tonight, and I've played no games. Sounds like a classic night in the arcade!

BakersnarkMDW: Tape the coasters on and punch holes in them to turn the volume up.
Alternatively, punch holes in the speaker cones, then tape over them to turn the volume up!

Mar:
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bennbanasik: Its a sound plan
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23/6/19
Evn: get a little amplifier from strathfield car radios
something like that: https://www.highway.net.au/arcade-parts/other/arcade-sound-amplifier/11658-1.html

Hwaygo: Does the board just output 3.5mm jack?

BakersnarkMDW: @Mar As I’m not arcade cab familiar I may be way off base, but looking at your R-Type board at top left near the large capacitors: Is that a potentiometer I see before me, it’s shaft toward my hand?
Couldn’t be a manual volume control could it?

dennydevito: Yeah generally most boards have volume control. It was so obvious I didn't think to mention it, also I don't know much about capcom boards

BakersnarkMDW: I know nothing, so I had the confidence to say!
By the power of looking...

Mar: Yes it has a volume pot, which I knew about. That’s not the issue at hand. The issue is the speakers are too loud regardless what volume the game is set at. MK2 as an example at lowest possible volume is too loud. Which I was asking is there tips on how to reduce the loudness independent of the board in it

BakersnarkMDW: What Ohm Rating are the speakers? 4 Ω, 8 Ω...?

Mar: Have no idea. Maybe I’ll have to look in the manual

bennbanasik: Does the Jamma go straight to the speakers or is there something between?

Mar: Thinking I’ll do the coaster trick!
Straight to the speakers as far as I can tell

BakersnarkMDW : Is it easy to get to back of speakers?

bennbanasik: Hmm you should put something between to regulate the sound

Mar: It might be easy. I’ll take a squiz later today. Won’t be in the game room for a bit. Yeah if there was some volume control I could do in between, that would be ideal

Evn: Capcom CPS boards have volume
Might be u have the wrong speakers in the cab

Mar: It’s possible. Though midway cabinets are usually bloody loud. They liked to make a presence

Evn: Most boards are built to drive speakers directly so if your speakers are expecting attenuated signal from an amp it will be too loud
Forget the terminology, line level and mic level or something like that

BakersnarkMDW: I was thinking you might have 4Ω and it’s made to drive 8 Ω. Rating should be clearly marked on back of speakers.
@evn Line level is pre-amplified level - as comes out of a CD player’s RCAs to connect to amp.

Evn: right so yeah, arcade boards I believe output already amplified audio
so superguns usually have a circuit to attenuate it to line level

BakersnarkMDW: Do you know if there’s a usual impedance rating on the speakers? Are they wired for actual stereo at all, or is it just parallel mono?

Mar: That little amp from strathfield car radios is interesting. Though it requires 12v power so it might be a hassle to get up and running in the cab. Worth thinking about though. I believe the MK2 cab has 12v. Or at least the PSU should output that

Evn: yeah Im not sure u want an amp
u need an amp for stuff like naomi
because it outputs line level

sneak:
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BakersnarkMDW: But you want it quieter, not louder. To use an amp with amplified sound you need to bring it back to line level to then amplify it again. You just need volume control or even impedance matching (as I’m enquiring about).

sneak: hmmm capcom q sound......

Mar: This is from the manual. I'm assuming it's all factory
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Evn: Q-sound it line level too right?
but the jamma sound is amplified

Mar: https://www.gamesdatabase.org/Media/SYSTEM/Arcade/Manual/formated/Mortal_Kombat_II_-_1993_-_Midway_Games.pdf

sneak: Not sure its one of those things where its been sitting around for years for me to do science on and never got around to it :/

Evn: Well I guess if the audio in that cab is too loud for all games then the problem is the cabinet

Mar: Yeah, and as far as I can tell the jamma goes straight to the speakers

BakersnarkMDW: So they’re 4 Ω. If R-Type is wired expecting 8 Ω speakers it may explain excessive volume.

Mar: But MK2 is too loud too

Evn: Yep

BakersnarkMDW: Two speakers right? Wired independently?

Evn: Check the speakers to see if they are right

Mar: Too loud for me. I'm guessing they are right for what they were trying to do. At lowest volume it's kind of acceptable

Evn: If it's 2 wired in parallel could be why
Disconnect 1 of them

Mar: LOUD FOR MAXIMUM PROFITS
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But yes I need to check if they are factory speakers
And perhaps disconnecting one is worth trying too

BakersnarkMDW: Looked at your info above again. Like pinnies they are actually wired to cover different ranges (one is a tweeter with a capacitor to filter low frequencies out [high pass]) making life a little more difficult. Be great to have a pic of the back of the speakers.

Mar
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I understood the part about taking a picture...

bennbanasik: F806E978-D37B-49EF-A950-E35E8398854A.gif 

BakersnarkMDW: Good, that’s the first part you need to do. 🙂
You could potentially wire the speakers in series making them function as a single 8 Ω speaker, cutting volume significantly. Very straightforward particularly if the speaker wires are are just slide on terminal connectors.

Mar: Ohh I like that idea

BakersnarkMDW: I still think holes in the speaker cones was the winner! 😄
But if you must have something slightly less destructive.

Mar: Thanks for all the tips dudes. I'll muck around with it later today. And provide some pictures
Excited to be able to play it without the whole neighbourhood hearing it

bennbanasik: Moving your head away from the speaker also might help

BakersnarkMDW: @Mar Do you have alligator clip leads? They might make things easier when the time comes.

Evn: For what an R-Type PCB costs, the whole neighbourhood should hear it

Mar: hah

BakersnarkMDW: R-type cab was equipped with 8Ω speaker (according to manual). Cooking with gas!

Mar: Finally in the arcade
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Evn:
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BakersnarkMDW: Up to armpits in pinnie. Look on return journey.
Banana Flipper!
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Mar: The fuck
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Evn:3A744785-21A7-49BD-BE1D-BF8078287FC6.gif   

bennbanasik: So 4 ohm speakers. How many is in there?

(Pinball repair interlude)

BakersnarkMDW: @Mar Just the 2 speakers from different angles?
Limited time so have to be quick. Listen very carefully, I will say this only once!

(13 min gap)

BSS: Highly anticipating this @bakersnarkMDW comment

BakersnarkMDW: Remove the Brown/Blue patch wire that goes between the two speakers but keep handy.
Move the Brown/Blue from the large speaker and attach to small speaker where Brown/Blue patch used to be.
Remove Red/Blue from small speaker. Connect the bare main lug on the big to bare main lug on the small with the patch. Done!
You might want to send pic when done.

BSS: So the cap isn't in the circuit anymore?

BakersnarkMDW: @BSS It’s a high pass filter for the tweeter. Tops might be a little dirty but should be no issue.
...
@BSS so, no - cap not in. Should be a simple circuit through both speakers in series adding their impedances. 4+4=8

BSS: if still too loud i wonder if you can swap the terminals on the small speaker to run it out of phase
analogue noise cancelling

BakersnarkMDW: @BSS They’re ‘now’ in series so they have to be in phase.

BSS: oh right

Mar: @bakersnarkMDW @BSS thanks for the tips. Unfortunately I got caught up speedrunning Ghouls again so I didn't end up going back to the speaker
Never enough time to do all these things.... I'll give that a bash next weekend though
@bakersnarkMDW I've copied the text and pasted in my notes. So I remember! I don't usually remember things

BakersnarkMDW: After all that! I was assuming you’d be enjoying a nice quiet game of R-Type by now. I plan to add all this palaver to the forum (your repair thread if that’s OK), which is where it belongs for future & searchable reference.
Of course, no proof it works yet.

Mar: Sure thing


28/6/19

Mar: The arcade is on. Like something something Donkey Kong
Now, do I have enough motivation to play with these speakers...

@bakersnarkMDW is this what you suggested?
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3A744785-21A7-49BD-BE1D-BF8078287FC6.gif 
3A744785-21A7-49BD-BE1D-BF8078287FC6.gif 

This is what it looked like originally
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And this was your instructions
“Remove the Brown/Blue patch wire that goes between the two speakers but keep handy.
Move the Brown/Blue from the large speaker and attach to small speaker where Brown/Blue patch used to be.
Remove Red/Blue from small speaker. Connect the bare main lug on the big to bare main lug on the small with the patch. Done!
You might want to send pic when done.”

BakersnarkMDW: That looks about right From in the cab the red wire goes to the big speaker, the brown to the little and the patch cable joins the two speakers together. The disconnected wire is the one with the capacitor on it.
As I said to @BSS at the time:
so, no - cap not in. Should be a simple circuit through both speakers in series adding their impedances. 4+4=8

Mar: Awesome. I'll be back in 10 to turn it on and watch the fireworks

BakersnarkMDW: Make sure the video’s running on the tripod - twitch it maybe! 🔥🚒

BSS: convince me again that the polarity doesn't matter?

BakersnarkMDW: That original arrangement had 2 4ohm speakers in parallel which theoretically makes for a load of 2ohms! The cap may have mitigated that but would still have been running the amp pretty hot. Just keep an ear on the little speaker as it may distort a little with the low frequencies not being removed by the cap but shouldn’t be a problem at the volumes you’re likely to use.

BSS: oh
silly ohm's law
or whatever law

Mar: Ok, I'm turning it on...

BakersnarkMDW: @BSS Thinking on it further I was probably a little hasty to dismiss your polarity point simply because they’re in series. The way I’ve described should have them in phase. Swapping the wires would likely put them out of phase but probably not cause much volume reduction because I’m not sure how much the sound waves from each speaker would overlap and interact - you notice that sort of cancellation more if the speakers face each other.

Mar: Wow, so much quieter!
I can play the game!

BSS: does it sound correctish?

BakersnarkMDW: @Mar So I got something right? 🙂 Might need to turn it up!

Mar: I think it sounds correctish. It's hard to tell, because it's at a normal volume for the first time ever
I mean, it doesn't sound as bassy
bass-y?
But that's going to happen with a lower volume I would have thought
Both speakers are emitting sound
So that's something

BakersnarkMDW: Have you got the speaker panel back in place or is it out of the cab? The cabinet itself will give some bass resonance, but you also do need to drive the speakers at a high enough level to get proper bass response from the larger one.

Mar: The speakers are accessed from having the marquee off. And I haven't put it back on just yet. Also, it's at the lowest possible system volume, so yeah I can try turning that up and see what explodes, or doesn't

BakersnarkMDW: You would have been much closer to an explosion before, overdriving an 8ohm setup with a 4 (or even 2) ohm load!
Random item from my Tabletop Games Collection
[image] 
See it & the rest here:
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