SWR Aural Enhancer Bypass

Discussion in 'Amps and Cabs [BG]' started by duff2, Mar 29, 2010.

  1. Zecchinus


    Apr 21, 2011
    Exactly, the bigger red one wich is perpendicular to the other ones goes where the blue one is
  2. ThrashMaster


    Jul 7, 2010
    Boston, MA
    Bringing my amp in this week to my amp guy, who owes me some work, since I'm his guitar guy :)

    Anybody know any mods that will put 'subsonic' filtering into these amps? Basically, most amps block all content below 20hz or so, but the SWRs dont, which is partially responsible for their 'under powered' reputation, but also a wee bit dangerous to speakers.
  3. Don't know of a mod for 'subsonic' filtering, but Fdeck's HPF Pre does the job! I'm finally loving my sm400s after this AE mod and hooking up the HPF Pre in my EFX loop.
  4. LeonD

    LeonD Supporting Member

    I recently picked up a Baby Blue II. I noticed the aural enhancer did sound like the aural enhancer on all my other SWR gear. I'm guessing someone along the way had the mod done to the amp.

    I'd like to, at the least, have it put back to stock if not have it switchable.

    ThrashMaster, who's you're amp guy if you don't mind sharing. One of the reasons I haven't done this yet is because I don't know of anyone I confidant in doing this mod.

  5. the V

    the V

    Jun 8, 2011
    Hi to all,
    hope the thread is not too old to update.

    I don't own the discussed head but I might get one in the future, and I'm constantly interested in modding electronics.
    It's apparent from the response that this is indeed a consistent and appreciated mod, thanks for posting/trying it! :hyper:

    Here I upload a simple drawing (I admit I stole the stylized pot from another site...) of how to connect a push-pull DPDT pot to accomplish the mod and retain the option of instantly reverting to the standard circuit.
    It is indeed trivial yet some have asked for it/might find it useful.


    • You LEAVE the smaller .001 μF cap where it is (almost, read on).
    • The orange .1 μF cap is removed from the PCB and soldered across the center pins on the switch (orange "wires")
    • The black wires from one "throw" of the switch are soldered to the PCB in place of the removed cap.
    • The blue wires from the other throw of the switch are soldered to the blue .001 μF cap leads; it might be useful to desolder it and actually alter slightly its position to uncover a couple of mm of its leads, if possible, or make an equivalent connection.

    After the job, in the "pulled" position the circuit is exactly as from factory.
    In the pushed position, the .1 μF cap is disconnected and reconnected in parallel to the .001 one, implementing the mod.
    There's actually an 1% discrepancy (the summed nominal capacitance becomes .101 μF) but if we consider tolerances it's irrelevant.

    Of course you can swap the front and rear wires to change the default preference.

    Concerning the room for the push-pull pot, it might be needed to bend the DPDT pins to the outside to expose them, and move the eventual "in the way" resistors (visible in the close-up pics right behind the AE pot) to the opposite side of the PCB.
    Oh and beware of shorts with the switch casing or exposed traces, use insulating tape if needed.

    If you find mistakes in the above, feel free to point them out. :)
  6. the V

    the V

    Jun 8, 2011
    I guess at the very entrance of the power stages there must be coupling capacitors, whose value could be lowered to raise the bottom frequency limit.
    We should examine the schematics.
  7. parsons


    Feb 22, 2008
    Just finished up this mod and put my SM400 back in my rack. HOLY CRAP. This is how their amps should come from the factory. The old voicing is garbage in comparison. So crisp and clear, there also seems to be more gain at an earlier stage from the tube. Everything seems quieter as well, the amp didnt hiss alot before but now it sounds dead quiet.

    I have to say to anyone thinking about doing this mod- do it. You wont regret it. Total time was about 90 minutes but I had some issues with the red cap having to share one connection with a resistor that was already there. That resistor doesnt seem to be in some of the other models according to the pics posted in this thread. I had to make the hole in the board slightly larger with a 1/16th precision drill bit to fit the existing resistor and the caps leads. Two drops of solder later and it was done.
  8. juel


    Dec 17, 2007
    @parsons: Did you use the mod, using a push pull DPDT, as shown in post #105?
  9. Saw this thread last night and did the mod today, pretty easy, except the board was a bit tight getting out.

    I've always had a love/hate for my old SWR 350 redface, I've been using it for years and always loved the reliability, quality, and the 2 ohm capability. As you all know, SWR's can be tough at times to get a good, tight, low end sound. But its worked for me for the most part.... NOW, I can NOT believe how different this thing sounds after the mod, it sounds like a normal amp, someone here said similar to a GK 800rb, which sounds about right, very tight lows and the notes jump out of the cab!

    Its going to take some re-EQing and retraining of my ears after all these years, it does sound like the AE is now boosting the 200-250k range? so I'm going to leave it cut or off.

    Anyone have any new EQ suggestions to get started? I don't have another gig for a few weeks, but I found myself (at home) boosting the lows, adding a touch of 200k in the low mids, and a touch of highs as well to get a fat sound for funk, with a Jazz bass of course!

    Attached Files:

  10. parsons


    Feb 22, 2008
    No. I would never want to go back to how it sounded stock. Stock = garbage in comparison.
  11. +1 this is exactly what I have been doing with a inline FMOD 30hz and it works well.
    A 18db electronic high pass would be better for sure as I do notice a very slight bass loss but it still sounds way better than without and I just boost the bass a little.
    I don't know why some amp manufactures don't address this problem.
  12. father of fires

    father of fires Commercial User

    Nov 29, 2006
    Chief of Medicine at Damnation Audio
    OK. So I finally got off of my lazy ass and did the AE bypass mod. I hesitated doing it for a while because I actually like the Fender mid scoop sound. I finally realized that the SWR AE is not the same thing as the Fender scoop. I played an Orange AD200 today that has a Fender style tone stack and that head sounded like a 200 watt Dual Showman (I was in love)! I came home and played my SWR and the scooped sound was no where close to the Fender stack that I love.

    My first impression is that it removed the "clankyness" that I had always attributed to my strings and technique. My Roto 77 flats sound exactly how I've always wanted them to and I can dig in without any harsh notes. I'm very happy that I did this mod. Now I'm going to search out a Fender style pre to run with the head when I'm looking for that tone.

    Thanks Duff. You have been a life(gear) saver.
  13. Mo' Bass 00

    Mo' Bass 00

    Aug 15, 2006
    Could anyone tell me if the newer amps are effected by this cap placement?
  14. father of fires

    father of fires Commercial User

    Nov 29, 2006
    Chief of Medicine at Damnation Audio
    Which amp are you referring to?
  15. father of fires

    father of fires Commercial User

    Nov 29, 2006
    Chief of Medicine at Damnation Audio
    I posted this in another thread but I thought I should mention it here as well:

    I just had practice with my modded SWR, my G&L SB-1 w/ Roto 77 flats, and a borrowed Ampeg fridge. It f'n killed. I also put a new preamp tube in my amp when I modded it and now it gets some righteous grit when I crank it. I like my little SWR better than the SVT in my practice space. Even my band thought it sounded better than the SVT! But nothing replaces an 810. I don't know why I bother looking at other cabs.

    I haven't been this pleased with a rig/tone in a long while. I may borrow that 810 indefinitely. Until me and the other bassist have a gig on the same night.
  16. So, finally got to try out my moded SWR 350 at a gig last night... wow, the notes have so much more focus and clarity! Had to turn up the highs for sure, but man what a different amp, great for funk and R&B stuff were doing.

    Tonight I'm using my small SWR WM 12 combo, wondering if the mod is applicable with this combo? I like the sound for the most part with the WM, but I wouldnt mind trying it out...
  17. Shinbone

    Shinbone Supporting Member

    Dec 21, 2006
    Fleming Island, FL
    Anybody know if the AE bypass can be easily done on a WM 2004 head? If so, got any diagrams?
  18. ihixulu

    ihixulu Supporting Member

    Mar 31, 2000
    South Shore MA
    Hi All,

    Completed the mod on my trusty SM400. In order to get the preamp board out, I did have to get the front power module out of the way, but apart from that minor nuisance, it was quite a simple process. I did order replacement caps as the lead on the .1mf did not line up well with the 1kpf mounting holes.

    As others have noted, the tone change due to this mod is quite significant. The amp is definitely louder (which isn't a surprise when one considers the changes to the FR curve) and it loses the characteristic SWR mojo. In terms of how it sounds, I think others here have described it quite accurately.

    One thing that did surprise me a bit is that becasue of the increase of lower frequency content in the signal, the gain structure of the amp is quite different. I am a touch leery of the AE knob now becasue I feel that it's new effect is to chew up a lot of the clean headroom in the pre - something that I do like about the stock 400 topology. Again, very subjective.

    The EQ is much more responsive though so I imagine with judicious cutting (yay! no more wasting band 2 on boosting 250 up the wazoo!) I will be able to find a happy balance between the added girth (very welcomed) and a seemingly reduced headroom.

    I know that I want to be able to switch between the mod and stock tones - they are different characters which apply to different gigs I have. While the push-pull knob option is very attractive, once I looked at the circuit board real estate I think it's more work than I am willing to commit to. Instead I think I am going to mount a switch on the front panel, wired up according to the V's diagram above. Since I have no intention of ever selling the amp I don't care about poking a new hole in it.

    Very worthwhile mod. Once I get the switch in, it will be perfect for me.
  19. bobcruz


    Mar 10, 2004
    I suspect the mod is applicable and I've considered modding my WM12, but I can always bypass the preamp and plug directly into the effects return, which with my active bass provides enough signal to drive the power amp to full volume (although I have to turn up the master to 3:00 or beyond to get there). When I bypass the preamp I still have three bands of EQ on my bass so that's plenty of tone shaping for me. In some rooms like at my church, the cut at 250 Hz is useful so I guess I'll leave it as is.
  20. DeadPoet


    Jun 4, 2003
    Thanks for the info. This makes me sure of my decision not to mod my SM400s. The thing I totally love about this amp is its endless headroom. It has power enough for me (GoliathIII 410 or Ampeg 210AV) and I love it's clean-but-with-some-tube-in-it sound. I couldn't live without the headroom it has - in fact that's my fear that once this amp is gone I won't find something else/current that has the headroom I like in an amp.

  21. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

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