Here’s a quickie on adjusting the gain of the OEM-supplied McIntosh subwoofer in many BE and BH series (MY 1998-2003) Subaru Legacy’s. The subwoofer gain and crossover frequency is non-adjustable, at least until now. : ) If you have such a car and want to get a little more punch from the sub, read on!
The amplifier is bolted to the floor under the drivers seat and has two connectors on the end closest to the door. Disconnect and unbolt the amplifier and take it apart. Make a careful note of where each screw goes as they are not interchangeable; you can permanently damage the amp by shorting things out of you replace the screws incorrectly.
Find R519 on the underside of the PCB near the power and speaker connector. In station wagons this is rated at 10k and in sedans 4.7k, labeled as either 103 or 472 respectively. This resistor sets the negative feedback in the final stage of the subwoofer crossover.
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.
After some experimenting I feel 33k delivers quite a nice bit of punch in a station wagon, which should boost the sub by about 5.2dB. Feel free to choose any value you want between 10-100k. Be careful using high values as it becomes quite easy to inadvertently overdrive the sub.
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.
quick question, how do you get at the amp? Seems to be i can’t even get my hands under there let alone unbolt anything. Sounds like a cool mod tho keen to give it a shot. On a related question, my drivers door speaker seems to have blown (vibrates badly as soon as volume is turned up) – do i need to replace with 8ohm speaker only?
Move the seat as far forward as it will go and you can undo the nut on each end off the amp under a little flap in the carpet. You will also need to unplug both connectors. It might be easier to take the drivers seat out entirely; it’s only four bolts plus a few wires to disconnect.
Regarding the speaker, I had the same problem and replaced the surround with a butyl rubber one that I carefully removed from a cheap replacement speaker. It cost less than $20 plus some decent plastic glue and about half an hour of time. It’s been.going strong for two years now.
You can use 4 Ohm speakers fine but they are louder and therefore you should replace all of them and tweak the sub gain to compensate for the lost balance.
thanks. Fixed the speaker issue and removed the amp successfully but then chickened out with the upgrade as it looked a major to even get inside the amp and then I’d have to break out a soldering iron. Got the resistor from Surplustronics tho for 10c so no money lost. Maybe another day when I’m feeling braver – currently it sounds pretty good since i have fixed the speakers
did the sub boost…sweet!used slightly higher value than recommended (46.2k) the bassline is oustanding, when i dont want too much sub i just reduce the bass and i am good…thanks nzlamb… u have any more subaru legacy tips; b4 rsk 2001?
Hi NZ Lamb, thanks for all your info. Are you based in Auckland? I have a McIntosh Amp that I would love this hack to be performed on. Thanks
I don’t live in AUckland, but see the email I sent you. 🙂
Hi there Nz Lamb i would love to boost my amp if you would be willing to do this for me i would pay for your time and shipping.i live in Blenheim i also have a rattle in my sub sounds like it is blown can you please tell me what i can replace it with(after market 10″or 8″ Could you possibly reply with a cell or work num so i can call you directly?
I’ve recently purchased a 2002 legacy with the mcintosh system and I’ve pretty much read all your posts on here and clubsub. Really appreciate the time it must take you to detail the instructions and have found it interesting and helpful. One thing I’m wanting to do is get AUX in working via the clarion TV tuner. Your other method you outlined on clubsub won’t work on my unit (as mine has the MD player), but I notice you mentioned on your satnav/air con tutorial about another way to do it via the TV tuner. Could you share any further details?
It’s easy – there is a proprietary aux input jack on the TV tuner. Just desolder the jack and feed audio into the respective pins. I can’t remember which ones they are but I’ll try to dig up a photo. It’s pretty easy to spot them anyway – just look for two similar adjacent PCB traces that feed into identical decoupling capacitors on the board.
Thanks for the response. I pulled the tuner apart last night and got most of the way – just still stuck on removing the current proprietary jack. When you say feed audio into the pins, I’ve seen from your photo on clubsub that you’ve connected two wires (I’m assuming these are L and R), what have you done with the ground?
I see you’re not located in Auckland, but from your message above – do you know an AV pro based in Auckland happy to help? (I just imagine I might struggle getting the proprietary connector off and then may struggle to wire up a stereo input properly…)
Just thanking you again for your help.
I was able to get the AUX in working via the TV tuner – works great, only minor hassle is having to switch to it while stopped/in park.
Latest issue is replacing the rear speakers – will probably end up getting 4Ohm speakers to go along with the 4Ohm set I’ve got in the front. I’ve seen you mention that this shouldn’t be too much of a load on the amp unless it’s run at full volume. This will however unbalance the overall sound as the SUB would be quieter (previously half the impedance of the speakers).
Any ideas for managing this? I haven’t done your hack above – too precise for my soldering skills…
I bought a Anycar link interface (for Clarion) for my 2002 Subaru Legacy, and just plugged it into the tv tuner – works perfectly with no hassle.
Hi mate, this is excellent! Just a quick question though. Is any wattage rated resistor ok or should I use a 1w?
Cheers again mate
Any wattage will work fine. Smaller is better simply because it will be easier to solder into the amp and there isn’t a lot of clearance between the PCB and the base cover.
How do you take out the subwoofer in a 2009 Subaru Legacy 2.5 GT spec B sedan? I seem to have broken the subwoofer cover 😦 can’t seem to take back cover off to get to the subwoofer 😦
I thank you in advance for your feedback?
Thanks heaps for the guide, did mine with a 20k and a 50k potentiometer, drilled a small hole in the casing and now I have an adjustable bass level ! Your guide saved me a heap of time to find the resistor responsible so cheers.