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

Detailed descriptions of how to do things to your Liberty.

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

Postby tom_kauf » Mon Nov 24, 2014 9:50 pm

wastegate wrote:I managed this mod on the weekend.

Amp is a EF-1208l out of a '06 SpecRB Wagon, the R519 resistor is a 6.8K. I used a 10k resistor base with the trim pot anyway. Even with just the 10k there is noticeable gain increase. Don't want to go too high as it's still only the stock sub.


Awesome! Good to hear it worked :).
I still haven't managed to get around to doing it. But I will soon.
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby Monkey » Mon Feb 16, 2015 4:00 pm

Hi all, I'm just attempting this today, but after 3hrs feeling pretty stuck. I have no soldering / electronics experience.

I've removed the amp from the car and opened it. I have the EF-12591 the same as Tom.
I obtained all the parts listed from Jaycar and I've located R519, however I have a few issues:

1. R519 is too close to C508 to possibly de/solder (about 0.5mm - maybe less!). I assume I could cut the original resistor instead of desoldering(?), but I don't know how I can possibly solder the right pin without fusing it to C508. The gap between the two appears to be about 1/4 of that in the previous pictures with the EF-1208 amp. The original R519 resistor appears to have "E01" printed on it in size 1 microscopic font.

board.jpg
board.jpg (194.58 KiB) Viewed 2602 times


------ PICTURE IS ABOUT 2.5 TIMES BIGGER THAN ACTUAL SIZE -----

2. I understand that the 100nF capacitor has one pin soldered to a ground point (big solder blobs) but what does the other end attach to? Viper said "solder the shield of the cores to the 100nF capacitor and then connect that to ground", but not sure what the first part means as "shield" to me means non-conductive plastic wire coating(?). I'm also confused because the corresponding picture has a black wire to the capacitor and then a grey one off that. It appears the black wire goes into the grey, but not sure what it connects to at the other end?
In Tom-Kauf's picture, his capacitor appears to be in a different ground spot, but again not sure what the other pin attaches to. He says "only connected one end of the shield" but again I don't know what "shield" means in thie context.

Batman87 posted the following which seemed much simpler:

Amp – red wire – resistor – trimpot right pin
Amp – white wire – trimport middle pin
Amp ground – 100nf cap – shieldwire

But it still doesn't explan what the capacitor is connected to with the other pin. Does this go back to the vacant (left) pin on the trimpot? And is this using a separate piece of cable, cut down, and using only one of the two wires inside with its shield intact, and then taped to the other bit of wire?

Considering just replacing the resistor and leaving out the variable mods. Just want more bass, and I can control bass levels from the head unit so won't likely use the gain anyway.
Has anyone done this in a sedan and what ohms did you use? I'm assuming 33-50k based on the previous write up would be OK for a sedan?

Alternately, is there anyone in Melbourne who might be able to assist with the wiring / soldering today, tonight or tomorrow?
Or even if someone could put up a wiring diagram that would be great?
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby Monkey » Mon Feb 16, 2015 6:55 pm

OK, so ended up attempting this myself just now and probably made a mess of it.

I put in a 33k resistor on R519. Now it appears the sub isn't working at all.
However, it feels like there is more bass coming out of the door speakers. I don't know if this is my imagination.
The main thing is that I have sound. However, I'd still like to get it fixed sometime.

I suspect my solder bled into C508 and that this is probably a crossover for the speakers?
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby bigBADbenny » Mon Feb 16, 2015 7:20 pm

If you click through to the nz link there's a much simpler example using just a resistor and no pot.

"Identifying R519...

Replace this resistor with a higher value to increase the gain.
Don’t leave it out of the circuit or it may overdrive the sub and do damage.
If you short it you will mute the sub entirely."

"You might want to use a potentiometer instead so you can adjust the sub gain as you please.
If you do this, I suggest a 50k linear (type B) pot in series with a 10k resistor.
Make sure you use shielded cable and keep the cable very short to help prevent any instability in the amp.
Connect the cable shield to a suitable ground point in the amp and (ideally) a 100nF or similar capacitor between the cable shield and the pot casing to prevent possible ground loops."

Image
from: http://jeremy.geek.nz/2010/04/19/subaru ... ofer-hack/

And from Tom's how to, the capacitor can be seen soldered between a ground and the shield for the pot wires.
Image

Perhaps you need a smaller soldering iron tip?
And maybe a solder sucker to cleanup the progress so far?

Also check you have the polarity of the pot set correctly, iirc the first page shows how-to with a multimeter.
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby tom_kauf » Mon Feb 16, 2015 11:52 pm

Yeah, what BBB said. I'm often amazed how people can solder with the fat tips that come with some soldering irons. I have a tip less than 1mm at the end. I congratulate you for having a go, but this is an expensive thing to practice soldering on. Hopefully you can find someone who can help - both with the process of soldering and the technical know-how.

The 'shield' is made up of strands of wire that surround the inner cables from electronic noise. So you might not have the right cable if it doesn't have a shield. Your local Jaycar will have them - ask for twin core shielded cable. That should explain me only connecting one end of the shield.

And definitely don't leave the resistor disconnected. Since you mention you're happy to do some Bass adjustment on the headunit, I'd suggest putting in a fixed Resistor value like BBB suggesed. It saves you doing all this work with the adjustable resistor. You'll get the same result, it just won't be adjustable at the amp end.
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby tom_kauf » Tue Feb 17, 2015 9:24 am

And Monkey, I have to add that soldering tiny Surface mount components such as these is tricky even for me (who's been soldering since I was a kid, decades ago). Like anything, most people need lots of practice to get good at soldering. But normal through-hole components are 1cm+ in size, and obviously much easier because of their size. But the amp has a lot of tiny surface mount components, which makes it hard.
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby Flat6Estate » Thu Feb 19, 2015 1:23 pm

https://www.youtube.com/watch?v=nvjRB9CA4ls

The above is a quick youtube how to solder surface mount.

I used to use a 0.5mm tip on my work iron. It's not hard, but you nedd to be careful.

Notice the addition of heat (about a second or 2) before adding solder to the first pad (tinning).
This allows the solder to flow when you add it. You don't need much. remember the pad is small, and the component is small as well.

DO NOT apply heat for too long. I you lift the pad off the circuit board, it can be goodbye board and probably amp as well.

Then heat the tinned pad while adding the component with tweezers or fine pointy nose pliers. I found it best to hold the iron at around 45 degrees to each surface to spread the heat evenly.
The very tip of the iron needs to be touching the pad and the resistor end to get the heat into both - so the solder attaches properly, otherwise you get a dry joint.
You also need to hold the resistor very still while the solder sets, otherwise you get a dry joint also.
The finished joints should be a bit shiny. If they look dull or crystally, its probably a dry joint.

The other end is the same. heat both the pad and the component end, add solder.

If you add too much solder, a roll of copper wick can be handy to "soak up" the excess.
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby bigBADbenny » Thu Feb 19, 2015 9:11 pm

Thanks for the heads up :)
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby Monkey » Fri Feb 20, 2015 10:01 am

bigBADbenny wrote:If you click through to the nz link there's a much simpler example using just a resistor and no pot.


Yep, this is what I did instead of the one with the trim pot / gain control.
However, it seems I butchered it as I've now lost my sub signal. Viper (Ben) had a look at it and confirmed the same (thanks very much Ben for your work!)
At least the rest of it still works and sounds fine. Will be on the lookout for a replacement amp as I wan't my Polk MM working properly
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby Flat6Estate » Fri Feb 20, 2015 10:48 am

bigBADbenny wrote:If you short it you will mute the sub entirely."

Perhaps you need a smaller soldering iron tip?
And maybe a solder sucker to cleanup the progress so far?

Also check you have the polarity of the pot set correctly, iirc the first page shows how-to with a multimeter.


As BBB said before, have you checked the above???

Post a photo of the damage (both side on and from the top) and someone might be able to advise on how to proceed...
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Re: [How-To] McIntosh EF-1208I Sub Gain Mod

Postby tom_kauf » Sat Dec 03, 2016 5:57 pm

kane2785 wrote:I have come up with an additional Mod. for the factory McIntosh amps also.

According to this site http://jeremy.geek.nz/2010/06/17/mcintosh-ef-1080i-information/, and my own observations, the amps are based on ST TDA729* series amplifiers. These can do up to 60W music power (for the TDA7296). However this does depend on the voltage available to the amplifier.
McIntosh has set the internal supply rails to +/-26V. This is on the safe side of the amplifiers, and as the maximum is +/-35V (TDA7296).
I have increased the voltage to the amplifiers, to 29.5V. This allows more 'Swing' on the output before clipping, and allows additional power output.
The mod is very simple. A 50k ohm resistorhttp://www.altronics.com.au/p/r7599-51k-0.25w-metal-film-resistor-pk-10/ between pins 1&7 of IC601 as found in this service manual:https://nzlamb.files.wordpress.com/2010/06/ef-1080i-c.pdf
I used 2 100k resistors in parallel. A 47K resistor will be ~30V, 51K ~ 29V
I don't think the power supply will be able to do much more than +/-30V with a battery voltage below 13V. The OEM configuration could not maintain +/-26V below 12.5V input.
Bench testing on PSU duty cycle doesn't change much from the original.

The increased voltage available to the amplifiers will mean that they dissipate more power. Power= Heat=Bad. So if you want to run the amplifier with this mod continuously, buy a bigger after market one. However if your music has a large dynamic range, and you were clipping in the louder sections, this might mean you will not risk destroying the speakers due to clipping.


Hi Kane,
If you're stil around, can you tell me if this mod increases the overall loudness, or just reduces clipping?

I was going to tackle this mod today, but then I read your description again, and I'm not sure it'll do what I want it to. I often find that the overall volume of the sound system is pretty low compared to all other cars I've driven (especially on the Aux input). It's ok with the windows closed, but even during city driving at max volume it's hard to hear it - and I'm not that deaf lol :lol:

I've never had issues with clipping, I just find the overall volume pretty quiet.
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