SWR Aural Enhancer Bypass

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

  1. IvanMike

    IvanMike TTRPG enthusiast, Happy, Joyous, & Free. Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    now that's a mod you should post here as well! maybe we need an amplifier modifications thread in the FAQ sticky (note to self)

    now come on who will answer my questions on the last page??:D
  2. duff2

    duff2 Guest

    Dec 16, 2007
    I have also previously owned a Thunderfunk TFB420 and I presently own an Eden WT-400. The mod does not make the SWR sound like either of these amps. Even after the mod, the SWR retains that harmonic coloration that the amps are known for, especially with the aural enhancer cranked up.

  3. Illinimax


    Oct 11, 2008
    Went ahead and did this mod to my old Redhead and as expected it does change the sound of the amp in a direction I like. Lots more beef and heft. My bass and my daughter's keyboard sound much more natural now.

    Hope to experiment a bit with cap values and report back.
  4. I've read through all these posts and got facinated, this simple little mod seems to be SO worth doing. I own a Bass 350, and my idea is to do it with a DPDT switch so its possible to switch back and forth to the "standard/original" vs. "modded" settings. One might call it "shape" vs. "flat" switch...
    So I opened the amp and found the two capasitors, but there's a "problem"...
    The second (original) capasitor that's supposed to be 0,001uF has a got a stamped label that reads 1000/100!?
    Take a look at the attached picture. It's the blue capasitor.
    Question : Is that 1000/100 reading supposed to mean 1000pF/100V or 1000uF/100V (u = micro). I suppose it's 1000pF, otherwise I've got a different value on that blue capasitor than anyone else here... :)
  5. 12bass


    Jan 2, 2003
    Victoria, Canada
    1000 pF = 1 nF = 0.001 μF

    It's 1000 pF. 1000 μF would be a much larger electrolytic.
  6. BassmanPaul

    BassmanPaul Inactive

    Yes it can with a simple 2 pole switch and an additional 100n cap. one pole switches the original 100N cap out while pole 2 switches a second 100N cap in across the 1n cap.

  7. lowfreqgeek


    Mar 15, 2010
    Tijeras, NM
    The only thing I'd add to that is that it's best to use shielded wire (shield connected to ground). If you notice most of the other cabling in the 350 (and others, I assume), it's shielded. I had made some mods (AE bypass) using non-shielded wire and got a horrific 60hz hum. Rewired with shielded wire and it's dead quiet again.

    I've got more mods to add, but may need a 3-way switch for that.

    My old schematics for my studio 220 gave me a lot of inspiration to finish my EE degree instead of dropping out to play music. I'll always have a place in my heart for *modified* SWR gear for that reason...
  8. David1234


    Jun 1, 2004
    Sydney, Australia
    Endorsing Artist: SWR Amplifiers
    Okay so now, who's got the mod to retune the M2 preamp back to the "classic" voicing curve?

  9. BassmanPaul

    BassmanPaul Inactive

    I consider that as a given. All wiring carrying an audio signal should be shielded.

  10. Well that's what I thought too, I just had to get it "confirmed" :)

    I did the mod by using a DPDT switch so the moded sound can easily be compared to the "original", and it does make it a bit more "heftier". Not as much as I expected, but noticable.
    I also did a simple trick to lessen the terrible noise from the fan, it used to sound like a powerplant in there when the fan kicked up revs... so I lowered the voltage from 24V to 15V by connecting a voltage regulator (7815) between the poweramp and the fan. Quite an approvement, and the fan still moves enough air to keep things "cool" enough...
  11. Alex1984


    Jan 16, 2010
    Anyone got any sound clips yet?
  12. Alex1984


    Jan 16, 2010
    Wow, that graph looks so flat and perfect it kind of makes me think that perhaps they stumbled upon the "SWR sound" by accidentally mixing up the caps. Does anyone know what the AE knob now does to the frequency response?
  13. FYI, you can get a 50k linear, DPDT Push/Pull pot for $2.65 at Small Bear:


    I'm still not sure if you need an audio or linear taper on it... the schemo doesn't seem to say. You can also buy the caps you'd need from there. It's a good little online store that I've used in the past.
  14. AndyMan

    AndyMan Commercial User

    Jun 17, 2000
    Columbus, Ohio
    I've got an Grand Prix I bought here with the mod. Superb! Tonally, it reminds me of the old Acoustic line of amps.
  15. Gaaaaaa. I didn't know it was possible to get more excited about this mod. Need to solder .... . . now.... ..
  16. After some inspecting last night, it appears as if it's a linear pot... a 50k B.

    FYI, mod accomplished, but sooner or later I'll bother to get a push/pull pot to switch between swr and flat.
  17. Southpaw5


    Jul 18, 2009
    Any recordings of the amp post mod?
  18. greenbass5


    Sep 16, 2007
    Oklahoma City
    Wow. I will open my SM400 non fan model and look at it today. Interesting Andy......I should just go ahead and build a viva Analog 360+ and get it over with....
  19. David1234


    Jun 1, 2004
    Sydney, Australia
    Endorsing Artist: SWR Amplifiers
    Next question: Is anybody here able to specify a mod for the SWR M2 to make it sound like "vintage" SWR instead of the Marcus tone? Ideally on a switch. On my Headlite all I use it the 200Hz setting, and on the M2 I feel it's too "cool" sounding a lot of the time.
  20. I gather the TL 072's can be improved upon. Anybody done this?

    and has anyone got a fix for the power on and DI whine and pop problems?
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