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Everten Taito F3 IO Board (Stereo Audio + CPS2 kick)

I tested an attenuation circuit with some good results. I’d like to get the levels down further if possible. Any suggestions on getting the levels closer to line level? I tried with 820 ohm & 220 Ohm and then with 10k and 1k. There was almost no difference in levels.


I recorded the stereo output from the F3 at true line level, attenuated level, and speaker level. I used a Focusrite Scarlett 18i20 3rd Gen into Reason with the input level at about 3/10. See the picture for level differences.

The F3 puts out some nice sound. I was pleasantly surprised. The Blast City speakers don’t do it any justice.

5DEDB7E6-4DB4-4BC8-9761-996BF888B744.jpeg


I’ll try to post some audio samples when I have time.
 
You probably know this, but will point it out just in case.

Whats the rms output of the onboard amp per channel and speaker ohms?

Use this formula:
V≈√P×R

Ex..
10watt rms into 8ohm speaker
√10×8 = 8.94Vpp
So you would use a 10:1 divider to bring that down to 0.894Vpp for consumer grade line levels
So 10k/1k ohm should work. You could use a 12:1 ratio to bring levels further down, etc...
or you could use a trim pot to let the end user adjust levels, etc..

Hope it helps man.
 
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That's the same circuit I sent Everten, however with different resistor values. The Konami circuit is reducing the signal by 50% whereas my circuit reduces it by 80%, and reportedly that's still not enough.

Maybe as the F3 has digital volume control an analogue pot would be best, @everten? This way users can dial in an approriate value and you won't need to mess around with resistor values.
 
Back in the days I added a stereo jack to my F3 pulling signals from the input section of the amp. I drilled a hole in the plastic frame where I mounted the jack.

The Konami solution requires that the volume is reduced a bit :)
 
If you want to go with a simple voltage divider circuit you can use this to calculate appropriate values:
https://ohmslawcalculator.com/voltage-divider-calculator

I believe for line level the end goal should be peaking under 1V to prevent clipping.
Then the addition of a simple cap for DC blocking.

This is the best "cheap"/"simple" way to go but I've personally always felt that when you're getting into pre-amp audio you also need to consider balanced outputs at which case you're talking the inclusion of inductors... a really indepth look at that can be found here: https://sound-au.com/articles/balanced-2.htm
 
Thanks for all the help everyone. It's entirely possible I'm not doing something wrong here. As Frank said, the digital volume control is automatically set to 50% when booting the F3. This might account for the difference between the line level pulled directly from the board and the attenuated circuit level.

Here is the circuit I have wired up at the moment. Excuse my amateur attempt at drawing this up... Let me know if this is correct.

circuit.PNG


Maybe it's not necessary to take the level down any further, but it seemed like it might not be a bad idea.

I'll see if I can find the voltage coming from the amp and use the calculator suggested.
 
How in the hell did this slip under my radar?
Put me on the interest list.
 
everten said:
Thanks for all the help everyone. It's entirely possible I'm not doing something wrong here. As Frank said, the digital volume control is automatically set to 50% when booting the F3. This might account for the difference between the line level pulled directly from the board and the attenuated circuit level.

Here is the circuit I have wired up at the moment. Excuse my amateur attempt at drawing this up... Let me know if this is correct.

circuit.PNG


Maybe it's not necessary to take the level down any further, but it seemed like it might not be a bad idea.

I'll see if I can find the voltage coming from the amp and use the calculator suggested.
Click to expand...
Put the capacitor before the resistors, I'm not an expert on analog but you probably don't want an RC circuit..
The output impedance should in this case be 820+a little, which is a tad high but nobody will notice.

I read somewhere that 'line-level' is supposed to be 600, but lower (stronger) is normal.

And what @rtw said, the sleeve of RCA connectors will be GND on the other end of the cable..
 
Ok, will try this. The heat sink I plan on mounting the board to is grounded so I assume it will be ok to pull from there if needed.
 
everten said:
Ok, will try this. The heat sink I plan on mounting the board to is grounded so I assume it will be ok to pull from there if needed.
Click to expand...
Like @invzim suggested you need to get audio ground from the source/amp. Did you look at the datasheet for this amp?

It looks to me its outputting a balanced (phased) output to each speaker, if so, you can probably leave the - output signal floating (not connected) or you can tie it to gnd via a resistor and do some impedance matching with the + output.

Added the datasheet - hope its the correct one :)
 

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Derick2k said:
or you can tie it to gnd via a resistor and do some impedance matching with the + output.
Click to expand...
I would strongly advice against this, the amplifier will just try to drive the signal through the resistor causing a strain on the amp and possible early failure.

If you have GND on the heatsink use that and leave both amplifier L- and R- outputs floating
 
rtw said:
I would strongly advice against this, the amplifier will just try to drive the signal through the resistor causing a strain on the amp and possible early failure.
Click to expand...
Derick2k said:
It looks to me its outputting a balanced (phased) output to each speaker, if so, you can probably leave the - output signal floating (not connected)
Click to expand...
:P :D
 
Derick2k said:
Added the datasheet - hope its the correct one
Click to expand...
Looks like the correct datasheet.

rtw said:
If you have GND on the heatsink use that and leave both amplifier L- and R- outputs floating
Click to expand...
Pins 5, 13 and 14 on the amp are ground and I have continuity with the heat sink on these pins (I'm assuming TAB is the screw mount for heat sink?). Is the audio ground same as ground on the F3? Doesn't appear to be different, but I'm no expert.

TA8221AH.PNG
 
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