Boss - LMB-2 Bass Limiter  [schematic]

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Boss - LMB-2 Bass Limiter

Postby umutgokcen » 26 Feb 2010, 04:38

Hi there,

I recently picked up this bass limiter even though I'm a guitar player. It sounds surprisingly transparent and noise-free compared to many other compressor/limiters I've tried, so don't pass it up if you see one (they are kinda rare).

And now I immediately want to mod it of course :D I think the release is a bit too long, for a limiter I'd expect it to recover quicker. Maybe it's tuned for bass frequencies or something. Has anyone messed around with this pedal? Any tips for modding it? Being able to change the attack time would be a nice feature as well. I checked the usual places for the schematic but nothing came up. I'd really appreciate it if someone here could post it if they happen to have it.

Thanks!
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Re: Boss LM-2B Bass Limiter - Looking for schematic, mods...

Postby mozwell » 26 Feb 2010, 05:02


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Re: Boss LM-2B Bass Limiter - Looking for schematic, mods...

Postby mozwell » 26 Feb 2010, 06:00

Its only the LM2, not the LM2B.
I think the LM2B has an added enhancer (gain stage ?) to compensate for hte slight volume drop when the LM2 is "activated"
Hope this helps, i couldnt find anything else
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Re: Boss LM-2B Bass Limiter - Looking for schematic, mods...

Postby umutgokcen » 26 Feb 2010, 07:17

Thanks a lot Mozwell :) It's not the same pedal but I'll try to work around it.

The real difficulty is locating the "release" resistor on the LM-2B. If I knew which one it is I'd replace it with trimpot and tune it by ear. Unlike the LM-2, the LM-2B has no release knob, so I'm not sure where to start tracing. Any suggestions?
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Re: Boss LM-2B Bass Limiter - Looking for schematic, mods...  [schematic]

Postby umutgokcen » 11 Mar 2010, 21:10

I bought the service notes for the LM-2B from someone on ebay and thought it would be appropriate to contribute to the archive here. There seems to be quite a few changes from the previous model (the one that's posted above). I'm not great at reading schematics but I think I was able to locate the "release" resistor. I believe it's R32. Can someone who's more experienced with compressors/limiters confirm this? I am planning to replace it with a trimpot so that I can have a release control.

Thanks a lot!!!
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Re: Boss LM-2B Bass Limiter - Looking for schematic, mods...

Postby umutgokcen » 13 Mar 2010, 03:14

Anyone? I promise I will post samples afterwards :mrgreen:
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Re: Boss LM-2B Bass Limiter - Looking for schematic, mods...

Postby analogguru » 13 Mar 2010, 03:55

umutgokcen wrote:I'm not great at reading schematics but I think I was able to locate the "release" resistor. I believe it's R32. Can someone who's more experienced with compressors/limiters confirm this?

yes, it is R032.
I am planning to replace it with a trimpot so that I can have a release control.

Place a 22k (- 100k) resistor in series with the trimmer to make adjustment easier.

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Re: Boss LM-2B Bass Limiter - Looking for schematic, mods...

Postby umutgokcen » 14 Mar 2010, 10:40

Thanks for the help. I tried what you suggested - 22K in series with a 1M trim - but I found myself turning the trim almost all the way down to get it to sound good. So, in the end I decided to take out the resistor and just put in a 200K trim. I set it less than a quarters up and the pedal sounds nice and snappy now. Basically I set it as short as I could go without getting distortion. With a long release you get a ducking and a swelling effect which I am trying to avoid.

I am really impressed with this pedal now :shock: . It sounds nothing like the CS-2 or the CS-3. It's very quiet and transparent. It really brings out the unique tonal characteristics of your guitars. And with the "release mod" you get that in-your-face sound. Unity gain is when the volume knob is at 12 o'clock so you can even use it as a boost :applause:

I'll record some clips and post some samples tomorrow, check back!
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Re: Boss LM-2B Bass Limiter - Looking for schematic, mods...

Postby umutgokcen » 15 Mar 2010, 09:20

Ok, here are the promised sound clips.

"Always on" setting http://www.sendspace.com/file/gpzypq : I call this "always on" because there's only a tiny bit of limiting going on and it's set at unity gain. It's all very subtle and not like an effect, hence you could always keep it on. Just makes everything a bit more alive and steady. I am running it into a tube screamer which then goes straight into the computer. I turn the pedal on and off a couple of times during the clip.

"Boost" setting http://www.sendspace.com/file/6l67w8 : More limiting and volume boost, with a bit of the "enhance" dialed in. The tube screamer is set the same as before and to get more drive and sustain I step on the limiter. I like that much better than turning up the drive on the tube screamer. Notice also how the pick attacks get more pronounced when the limiter is active.

Now I wonder what the other boss limiters sound like.. :wink:
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Re: Boss LM-2B Bass Limiter - Looking for schematic, mods...

Postby pedalgrinder » 27 Jun 2012, 12:23

ok i know this hasn't been touched this post for a while but i would take a different approach to modding this. I would remove c017 and replace it with a 2.2uf capacitor then get a 2meg to 5 meg potentiometer of evilbay leave ro32 where it is and put the potentiometer to earth as a proper release. then you have a decent release control. Thats my thoughts :thumbsup
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