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Don't forget to add a voltage divider to attenuate the audio or you'll likely blow the speaker.
Ok, taking you up on this offer.
What is the best circuit I could build to attenuate audio for that speaker?
 

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@acblunden2 I think the way to go is with a pi pad attenuator. Both the amplifier and speaker are impedance matched but it's likely that the latter expects a line level output rather than, erm, speaker level. Yes, I understand that the speaker is a speaker but it's also a tiny speaker. You are likely to flood it and get a lot of distortion.
This tutorial will explain it better than I will. Remember that you'll have to recalculate the k factor for the impedances you have.
 
@ic3b4ll, cool. Question concerning ground for these circuits. Can we consider JAMMA pin L (Speaker-) as ground? Or does this circuit need to be tied to actual ground?
 
@ic3b4ll, cool. Question concerning ground for these circuits. Can we consider JAMMA pin L (Speaker-) as ground? Or does this circuit need to be tied to actual ground?
Actual ground. Replace in/out in the circuit for positive/negative and it will all make sense.
You can try it on a breadboard so you can tune it before committing to a design, that way you'll know what works best for the speaker and 'average' board, so to speak.
 
So I think I have the values for the resistors needed. Thanks so much for that pi attenuation circuit because as I understand it, it would be an unbalanced circuit with JAMMA audio being 4ohms output impedance and the speaker is 8ohms. So......

Given:
  • JAMMA audio output is (typically) 8watts @4ohms
And the speaker I am planning to use is:
  • 1mW @ 8ohms
I should be looking at attenuating a decibel drop of 19.031 according to this calculator (watts to decibels). Now I have my output impedance value of 4ohms from JAMMA. Input impedance of 8ohms to the speaker. So I just need to plug those values into here. And this is what I get:
  • R1= 4.6232ohms
  • R2= 24.9823ohms
  • R3= 11.3461 ohms
Am I flip-flopping my input impedance with output impedance? If I am understanding it correctly, the input impedance is 'Speaker (+)' signal from the edge harness which is at 4ohms.
AttenuationCalculator.PNG
 
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I'll have to check your calculations to give you a definite answer but you got the wrong calculator. That's for the unbalanced pi pad attenuator version... The balanced one has a connection to ground. It shouldn't actually matter that much, mind.
 
Unbalanced isn't correct? JAMMA audio is 4ohms and my speaker is 8ohms. Shouldn't it correctly be calculated for unbalanced impedance?
 
Ugh... I was really tired when I wrote that. It *shouldn't* matter much actually. If it was a cable then you should balance it, but the traces are short and you're unlikely to pick up noise.
Do note as @pacoarcade was probably going to add, your common or garden variety 1/4watt resistors won't cut it in order to dissipate the power being output by the amplifier.
You need something like 15 watt resistors. Yes, they exist. You want ones with an aluminium sleeve. Also, it will get hot, so start thinking about copper planes and an heatsinks :D
Make sure the resistor you choose on the JAMMA side is above 4 Ohm to avoid shorting the amplifier.
 
I suggested a circuit to convert unbalanced to balanced audio using an isolation transformer (TY-250P is great), but it doesn't fit in this circuit and you are using a speaker.
 
I suggested a circuit to convert unbalanced to balanced audio using an isolation transformer (TY-250P is great), but it doesn't fit in this circuit and you are using a speaker.
That's a good suggestion! Next time just edit the response, we can't use that in this PCB but it may be useful in the future :)
 
Thanks @pacoarcade & @ic3b4ll. I think I will just use a different speaker. I'll start another thread on this subject and page you guys there.

I am derailing my own thread. So let's get back to fixing the S16b audio.
 
if you want to convert from a potentially BTL speaker signal, to a line-level then you can get cheap adapters intended for fitting between car stereo's and booster-amps
 
if you want to convert from a potentially BTL speaker signal, to a line-level then you can get cheap adapters intended for fitting between car stereo's and booster-amps
I started another thread for the test bench PCB. Keep this one on topic of fixing the S16b audio.
 
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