SWR Aural Enhancer Bypass

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


  1. duff2

    duff2 Guest

    Dec 16, 2007
    The mod should be applicable to all SWR amps other than the newly designed headlite and Marcus Miller Preamp. Both of these products have a preamp curve bypass option already built in.

    Cheers,
    Duff2
     
  2. duff2

    duff2 Guest

    Dec 16, 2007
    +1

    I have always preferred Eden over SWR amps for that very same reason. On a live stage, you cut through the guitars and drum toms SO much better without that mid scoop. Once those frequencies have been 'tapped of to ground' so to speak, you don't totally get them back with the active EQ. This is especially obvious when using a passive Jazz bass with both pickups full on through an SWR amp IMO.

    That being said, everytime my strings start to get a little old or if I am using flatwounds, I always end up wishing my Eden amp had a little more top end harmonic coloration.

    I am hoping that this modification will finally give me what I like about both amps.

    Cheers,
    Duff2
     
  3. jb63

    jb63

    Jan 3, 2002
    Cleveland, Ohio
    Yep, and I'll bet that EQ will be more effective after the mod. If it works out for you I'll probably do the same.
     
  4. wave rider

    wave rider

    Jan 5, 2005
    Would the Baby Blue II benefit from this modification? It already has a push/pull pot which toggles the EQ on and off but keeps the aural enhancer on...

    Fascinating stuff, thanks to all for the insights!

    =wr=
     
    Robert briglio likes this.
  5. duff2

    duff2 Guest

    Dec 16, 2007
    This amp would probably benefit most of all. After the mod, you could now use the push/pull pot to switch between 'true flat' and your chosen EQ setting.

    Cheers,
    Duff2
     
  6. wave rider

    wave rider

    Jan 5, 2005
    Thanks Duff2!

    Now to screw up my courage...

    Currently running the enhance pot 9-10 o'clock.

    =wr=
     
  7. baddarryl

    baddarryl

    Oct 26, 2008
    Cape Fear!
    Hey Duff2, thanks for all your info. As I have never even cracked a case on an amp could I do this myself? Freshmen electrical knowledge. If not what do you think an amp tech might charge? Any idea? That WorkingPro 400 btw. Thank you........Darryl

    Another thought, with out doing this mod, what is the least scooped setting for the AE? Thanks again.
     
  8. David1234

    David1234

    Jun 1, 2004
    Sydney, Australia
    Endorsing Artist: SWR Amplifiers
    The scoop is the same on all AE's from zero to about 5 where the notch starts to come in. I've tested three amps and the notch kicks in about 5 on two of them and 7 on the other.

    I'd recommend having an amp tech even if it's $100 rather than screw it up yourself if you're not a great solderer. Certainly that's what I'll do if ever I get the mod done.
     
  9. David1234

    David1234

    Jun 1, 2004
    Sydney, Australia
    Endorsing Artist: SWR Amplifiers
    By the way, most of you who want to hear the amp 'flat' should consider plugging straight into the effects return and listening that way for a while.

    You lose the EQ but that's what your starting tone will be: dull and not very "SWR." This gives you a chance to hear what you're planning to do before you do it.

    Most electric basses aren't flattered by a flat amplifier response nearly as much as by the AE's curve. Still - I'm grateful for this thread and watching with interest to see how the mods turn out. One of the reasons I don't own a spellbinder is that when stock, the EQ gets bypassed when the enhancer does, which is bad for my EUB sound. Maybe this will be my ticket...
     
  10. duff2

    duff2 Guest

    Dec 16, 2007
    Yes, but that's because you will be entirely bypassing the 12AX7 tube where all of those wonderful harmonics are added to your bass tone. The mod I have been describing will not do this.

    Cheers,
    Duff2
     
  11. David1234

    David1234

    Jun 1, 2004
    Sydney, Australia
    Endorsing Artist: SWR Amplifiers
    All true, but several posters here are focusing on the voicing curve and trying to get rid of it!

    Certainly, the valve makes a difference, or the workingman's heads wouldn't sound any different to the pro series.
     
  12. duff2

    duff2 Guest

    Dec 16, 2007
    The voicing curve dictates the levels (dB) of which frequencies (Hz) get through to the EQ section and on to the power amp. It does not affect the harmonic content (ie fundamental + added overtones) of the signal leaving the plate of the 12AX7.

    Case in point, if I EQ my Eden amp to match the preamp response curve of the SWR, they will not sound the same.

    If you want to hear the difference that the first half of the 12AX7 contributes to the tone of an SWR amp, compare the difference between using the active (bypasses the first half of the 12AX7) and passive inputs.

    Cheers,
    Duff2
     
  13. will33

    will33

    May 22, 2006
    austin,tx
    Thank you guys so much for posting this. I have an SM400S and I do like it but I use a 250 boost on almost anything I plug into it, it "un-SWR's" the sound. Thanks also for confirming what my ears have been telling me with the aural enhancer also. I always have mine set a bit above off as off sounds weak, like it's sucking power away, your graphs confirm that a bit of it boosts gain really and not so much alters the response until you get a ways up the dial.

    Switching parts that are already in the amp is a simple soldering job for me. Once again, I have saved a good bit of $ and learned something along the way just by reading TB.
     
  14. David1234

    David1234

    Jun 1, 2004
    Sydney, Australia
    Endorsing Artist: SWR Amplifiers
    Thanks again! Now you've explained why I never liked the Active input nearly as much as the Passive side.
     
  15. duff2

    duff2 Guest

    Dec 16, 2007
    This stuff drove me nuts for years. I always wondered why I liked certain amps over others, why some sounded better in the music store but not on stage with a full band and why some basses sounded incredible with one amp and like crap through another.

    I wish I could remember the names of all the people who answered these questions for me on this and other forums so I could thank them individually.

    Cheers,
    Duff2
     
  16. aBoMoFo

    aBoMoFo

    Jun 16, 2008
    Houston, TX
    Well Duff, more thanks are owed to you for getting curious enough to pursue exactly what this circuit does and how to get it to stop doing some of it's evil ways.

    Enjoy a beer and the sound of the "new" amp!
     
  17. duff2

    duff2 Guest

    Dec 16, 2007
    You're welcome and Thanks!

    Just spoke to my tech. He's backlogged with repairs right now. Amp may be ready by next Wednesday. Can't wait!

    Cheers,
    Duff2
     
  18. I decided to tackle the mod today. Not terribly difficult once I sussed out which caps to mess with- thank you Duff for the schematics- very helpful. But enough info is contained in his 'before/after' schematic clips to figure it out. Just follow from the 50k pot labeled 'aural enhancer' and you'll find your way once you remember or look up resistor color codes(I did). Took maybe 2 hrs. You do have to totally remove the preamp board(s) to do it, as you must have access to both sides. That, and reassembly, took most of the time. You have to remove every knob(21 of them), every pot bushing nut(15), push the LED's out of the faceplate(5), remove all the input jacks, etc. Then you have to put it all back. Fun stuff, not that bad, just time consuming.

    I must say, as you would expect from the graphs posted by Duff, this mod COMPLETELY CHANGES the overall character of the amp. If you like the sound of your amp now, this mod may not be for you. It is fatter, darker, and 'louder.' Noticeably darker sounding, to me. The SWR 'shimmer+boom' is notably absent. Previously the amp made a 'think' or 'thank' sound when popping a string; now it's more of a 'thonk'. It's much less 'Hi-Fi' sounding to me now, which, frankly, I think I like. I find myself turning the Treble control up, to maybe 1 or 2 o'clock, where previously I almost always ran it flat or reduced it slightly. The low end seems tighter and cleaner, which I like a lot. Better note definition IMO. Of course, I am going from memory as I don't have a way to record it, but I know I'm not far off- I've been using mostly this amp since 1992. And I did play the amp for awhile immediately before doing the mod, and then immediately after. But hey, grain of salt. My first listen sometimes differs from the next, when separated by a couple of hours. Anyway:

    Interestingly, the graphs indicate we'll get more sound mostly at around 200hz but to my ears it's a much more noticeable gain at 500-600hz. To get some of the 'SWR Sound' back, I am finding I need to cut in that range. Odd but true, at least to my ears.

    EQ set flat, the amp absolutely roars where before it simply purred very loudly. The amp does really sound a lot 'louder,' which is understandable.

    The Aural Enhancer now acts sort of in reverse from it's original state. Increasing it increases gain, harmonics, and upper midrange- a bit like the Character knob on a VTbass pedal but much more subtle.

    Oddly, selecting both EQ channels together(even when both are set flat) now noticeably increases gain, where previously this was not the case.

    I am thinking the amp now sounds a bit like my 800RB, which I like a lot, but with more 'tone,' and deeper low-end extension. I only played it for about a half hour or so, but I think I like it. More after I gig it.

    Here's some pics. Remember, this is an SM900- I'm not sure how other amps are laid out. I also have an original Baby Blue(R.I.P:crying:) and the layout is different.

    1st pic: the caps are in the upper-left, between the tube socket and the Aural Enhancer pot. A red one and a blue one.
    DSC01059-1.jpg

    Next pic: see the large red one directly behind the Aural Enhancer(middle) pot? That's the .1 cap. The blue one to the upper right, sandwiched against another red cap, is the .001 cap.

    Before:
    DSC01182.jpg

    And after:
    DSC01184.jpg


    Note: The .1 cap is physically longer that the .001 cap and so the leads are further apart. Fortunately, at least in my case, SWR included holes in the board to accommodate both spacings, presumably for R&D. If you are fortunate, your board is like mine. If so, nothing to it. If not, you'll have to make wire leads and then RTV the cap to the board- no big deal really.
    :bassist:
     
    orange joe likes this.
  19. Bonus find: my amp used to pick up and play local FM broadcasts rather loudly, with a bass connected. Now, utter silence. Same bass/cables/room/orientation etc. Another odd but definitely real result.
    Edit: after leaving the amp ON for several hours, the radio stations return. But definitely not as loudly. Still a good result.
    :bassist:
     
  20. duff2

    duff2 Guest

    Dec 16, 2007
    Dmusic148,

    Less 'shimmer and boom' and 'more bark' is exactly what I have always wanted from my SM-500. After the mod, it will also be nice to use the EQ section for something other than trying to flatten out the amp's response.

    Thanks a lot for taking the plunge and posting the results here. I can't wait to get my amp back from the shop!!!! :hyper:

    Cheers,
    Duff2
     
  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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