Hi all,
Just a quick write-up/guide for the Sub Gain mods for the EF-1208i AMP which comes with the BF Liberties.
This is heavily based on this.
So, to summarise it quickly, the EF-1208i is very similar to the 1080i, but has a slightly different layout, power circuitry and input/output connectors. So please do not use that site for the pinouts as they are different.
Anyway, for today's task the changes are the same.
R519 controls the negative feedback, so it's a fairly task of updating this resistor value.
Skill Level : Medium
Effort: Minimal
Street Cred.: High
Benefit: High
Time: About 1hr
You will need;
-10mm socket
-phillips head screwdriver
-Multi-meter
-Soldering Iron
For the adjustable resistor mod you will need;
-1x 6.8kOhm resistor (or 10kOhm for a wagon)
-1x 50kOhm Linear Trim-pot + cap
-A length of 2 core shielded wire
-1x100nF cap
Or you can pick a fixed resistor to put in place, but why would you do that ;p
So firstly you will need to remove the amp from the vehicle. Move the passengers seat forward all the way and you should just be able to undo to the TWO 10mm nuts on either side.
Then remove the input/output connectors on either side and gently pry the amp out. You can now remove the plastic kick shield. It should be 5 small screws.
Remove the 'security' tape from the bottom and undo the screws which hold the silver bottom plate onto the amp. It should be 2 screws ontop, 5 on the bottom and 2 on each of the 3 sides. Don't remove any of the screws towards the inside as they attach the MOSFETs to the cooling plates. The cover should now slide off revealing the fun stuff.
Next up, locate the R519 resistor. Again, with the EF-1208i, there is slight update compared to the 1080i. The resistor used for the Sedan is 6.8k (not 4.7k). I'll assume the wagon is still 10k, but it may have also changed. The main thing to know is that this will be the minimum value for the circuit which will replace the resistor. The board is nicely labelled so should be quite easy to locate.
Once you have found it, you can carefully de-solder it. Now construct the replacement circuit with trim-pot. If you are experienced with electronics it's quite easy. Put the 6.8k resistor to pin 1 (or 3) of the trim pot. Then attach 1 of each of the cores to the end of the resistor and pin 2 of the Pot.
So it goes; Wire -> 6.8k resistor -> Trimpot (pin 1) -> Trimpot ( pin 2) -> Wire.
Most important is to test the circuit to make sure the resistance values are what you want.
At the '0' position; (6.8k)
At about 50%; (6.8k +50% of 50k, so ~32k)
At 100%; (6.8k+ 50k, ~55k)
Once you have confirmed that it's working as intended, solder each core to either side where the original resistor used to sit. Also solder the shield of the cores to the 100nF capacitor and then connect that to ground. This is just to prevent any ground noise from the trim-pot.
Closer look at the solder points
Now place some tape down over the wire to hold it in place and drill a hole into the cover and re-assemble.
And that's it, amp modified.
Now replace the amp in the vehicle connect it all back up and crank up the gain. Make sure you start with '0' and work you way up.
So, was it worth it.
HELL YES.
I have the trim-pot sitting at ~30% and it makes such a difference to the MM840 sub. It's definitely getting driven properly now ;p
Getting decent thump and rubble with deep base notes.
Headunit is set at +2/+3 Base.
Any questions, just shoot.