[How-To] McIntosh EF-1208I Sub Gain Mod

Detailed descriptions of how to do things to your Liberty.

[How-To] McIntosh EF-1208I Sub Gain Mod

Postby Viper » Fri Dec 21, 2012 3:15 pm

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.

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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.
Image

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.
Image

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.
Image

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)
Image

At about 50%; (6.8k +50% of 50k, so ~32k)
Image

At 100%; (6.8k+ 50k, ~55k)
Image

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.
Image

Closer look at the solder points
Image


Now place some tape down over the wire to hold it in place and drill a hole into the cover and re-assemble.
Image

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.
Image

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.
Last edited by Viper on Tue Jan 13, 2015 7:23 am, edited 1 time in total.
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby cvas » Fri Dec 21, 2012 7:58 pm

Very nice mate ill give this a shot next year
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby Surge » Wed Jan 23, 2013 5:41 pm

Great guide, I'm also going to follow this in the near future!
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby iSpecB » Tue Jan 29, 2013 7:26 pm

I just did this mod on my MY08 3RB.

R519 is actually 10kohm (103) in mine. Did the same rig and hooked it up to the car. Funny enough, no matter how much I vary the potentiometer, the bass level remains the same, no change to the amp response.

Haven't really troubleshooted this but the first possibility that came to my mind was the wire ends that ive soldered on the R519 SMD pads. Those pads are so damn small...and the cablesmight have come loose when I put the cover back. Having said that, without the actual schematic, it's hard to know as that would mean the original connection on R519 has been broken off and the amp is still functioning as normal.

OP: do you know what R519 is for? It seems to be connected in parallel with the capacitor next to it provoding some kind of charge/discharge function? Thanks.
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby Ric » Tue Feb 19, 2013 1:33 pm

iSpecB wrote:...
OP: do you know what R519 is for? It seems to be connected in parallel with the capacitor next to it provoding some kind of charge/discharge function? Thanks.

As stated in the first post, that resistor provides the negative feedback, which controls the gain of the amplifier.
It is common to have a small capacitor in parallel with that to limit gain at very high frequencies. That protects the amplifier from supersonic oscillations.
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby Surge » Fri Jun 21, 2013 12:52 pm

I've just picked up a Polk db840, I think I will need to do this mod, however I would like just a fixed resistor. Can you recommend the resister I should use?
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby tony_m » Wed Aug 21, 2013 6:28 pm

Appreciate the write up. Easy enough for me to understand- and I know 2/10ths of f-all! Bought the components from jaycar today. Just have to get my hands on a soldering iron.

Only have one question - the shielding from the cable, which is grounded through the capacitor, what about the other end? Does not matter?
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[How-To] McIntosh EF-1208I Sub Gain Mod

Postby tony_m » Mon Aug 26, 2013 8:36 am

So after reading the original original write up, and a few other electrical pages it seems like I connect the ground on the pot (pin 1 or 3) to the shielding of the cable, which passes through the cap at the other end, then to ground. Yes?

Edit: To clarify, as it's not stated in any of the versions of this mod- If you used pin 1 on the pot for the resistor, connect the shielding of the cable to pin 3, and then ground the other end of the shielding through the 100nF cap.
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby Monkey » Thu Oct 17, 2013 8:15 pm

This is awesome! I was wondering if anyone had done something similar.
I love the McIntosh system (as far as a stock system goes) but the volume is too quiet. I sometimes turn it up to vol 30-32 with the windows open (but maybe I'm deaf from too many years of DJing?!)
Can this be used to increase the speaker volume too, or is the amp a single channel (sub) only?
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby tony_m » Thu Oct 17, 2013 9:27 pm

Monkey wrote:This is awesome! I was wondering if anyone had done something similar.
I love the McIntosh system (as far as a stock system goes) but the volume is too quiet. I sometimes turn it up to vol 30-32 with the windows open (but maybe I'm deaf from too many years of DJing?!)
Can this be used to increase the speaker volume too, or is the amp a single channel (sub) only?


Depends on the input... If I remember correctly CD is fine under 30, AUX/iPhone etc is about 27-34ish, depending on the mp3 volume level. This particular mod will only increase the power going to the Sub, the rest of the speakers remain the same. There might be a way to increase the other speaker's power, but I'd guess that it'd damage the smaller speakers!
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby Monkey » Thu Oct 17, 2013 10:16 pm

Cheers for your reply. Any idea whether you can piggyback another small amp to add some power to the speakers?
Or is there another decently-priced (ie. around $200) amp which is a direct replacement for the McIntosh amp without having to rewire everything? (I know this has probably been answered in another thread, but couldn't find it).
I'm also planning on upgrading the sub to the Polk DB/MM840.
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby tony_m » Fri Oct 18, 2013 8:49 am

From what I've read, it's a bit of a nightmare. I think its hard to find an amp which takes balanced inputs, and our ones also have a strange number of channels due to the amount of speakers.

Definitely recommend the sub upgrade. I've done it (used a Kenwood 800F), and paired with this walkthrough, it goes hard. 100x better, without a doubt! Now I don't want to rip it all out and spend several thousand on a new system. I'm happy. I had to use a box, rather than keep stock location in parcel shelf, due to pretty bad vibrations.
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby Robbks » Fri Oct 18, 2013 10:23 am

If you want a bunch of extra grunt, but keep teh whole thing simple here's my thoughts
Keep all the mac gear in place as it is.
then use the speaker outs into 1x 4ch amp (obviously one with speaker level inputs) for the 4 main channels.
And do the same with a mono amp (or bridged 2ch) for the sub.

The McIntosh amp is only a 5ch amp regardless of how many speakers Subaru sales brochure says it has.
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby Monkey » Fri Oct 18, 2013 5:36 pm

Thanks guys - appreciate the responses.

I'm now thinking the most cost-effective way of improving sound is as follows:

1. Dynamat doors and parcel shelf (~$150?)
2. install my Kicker 460w monoblock from prev car (has high level inputs with an adapter)
3. Change Clarion sub to Polk Audio MM840 svc (~$150?)

As I already have the amp, fuse, and all wiring this is probably the most cost-effective solution. Should be able to do in 1-2 days and for about $300 - depending on Dynamat cost. Obviously this won't necessarily make the mid/highs louder, but from experience in previous cars, adding/upgrading a sub typically results in listening to music at lower volume levels.

However, I'm unsure whether to put the amp under driver's seat or underneath parcel shelf. The latter is easier (don't need to remove the seat) but 460w RMS going into a 250w Polk sub is likely to shake the $hit out of the parcel shelf and the amp. But maybe both will be fine with Dynamat? Never used the stuff...

So maybe I'll do a custom box install in the side cavity (rear quarter) in the boot with a grille like this:
http://i1135.photobucket.com/albums/m63 ... G_2625.jpg
This would be good but I'm wondering if a 8" will be a bit muffled/quiet in a sealed boot cavity? So I'd probably want to put in a 10"

Would appreciate any thoughts / advice.
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby tony_m » Fri Oct 18, 2013 8:07 pm

I'd go with the box, personally. I spent countless hours, days actually, trying to stop all the vibrating noises until I realised that it was just the shelf reverberating, making anything in, near or attached to it vibrate. Seatbelt mech's, torsion bars, cabling- you name it. You could hear it over the music at any volume. I've got the 8" in a box, just a home made, and its not muffled at all. You won't be disappointed. I reckon save yourself the headache and frustration and go for the box straight off the bat. I wish I had. I know its nice to keep OEM location as its a good clean spot, out of the way. I wasn't keen on a box initially... However the one you are looking at is nice & tidy, will be hard to calculate the volume tho! I just made a long box as it was the easiest lol

Just my .2c!

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