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anyone make a rack-mount B-15 preamp?

Discussion in 'Amps and Cabs [BG]' started by PB+J, Jan 23, 2005.


  1. PB+J

    PB+J

    Mar 9, 2000
    arlington va
    My favorite bass amp is the ampeg B-15--that's the tone I want. But as everyone knows, it's only 30 watts. There are lots of fancy preamps based on fender circuits (demeter, kerm, alembic) and ampeg makes versions of the SVT preamp, butI don't wnat the SVT--I want the old school B15 preamp--6SL7 tubes, 5AR4 rectifier, baxandall tone stack

    Soes anyone make a beast like that? I'm really surprised no one does. But I can't find it anywhere
     
  2. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    Don't know of one... someone could certainly do it. There are only three potentiometers, twelve resistors, six capacitors and one 6SL7 tube in the preamp circuit of a B-15-N. Of course one would also need a powersupply for the plate circuit and the heater circuit, but the audio signal path is pretty simple.

    Have you tried a flip-top model in a POD or similar with a power amp and cabinets to determine if you like the sound using it as a stand-alone preamp with your poweramp and cabinet(s)?

    I think that it would only have an effect on the whole amp as the demands of the poweramp on the power supply are what cause the plate voltage to sag.
     
  3. PB+J

    PB+J

    Mar 9, 2000
    arlington va
    good point about the recto tube--but it does seem like a b15 preamp would be aeasy to do.
     
  4. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    Here's the schematic, without power supply. I suspect that a rackmount stand-alone version would need some sort of outut buffer circuit to present a low impedance output to the poweramp and scale the output voltage to match the power amp's input sensitivity.
     
  5. J.Wolf

    J.Wolf Supporting Member

    Apr 29, 2003
    Asheville, NC
    did you ever figure this out? I may have a good resource for you
     
  6. jasonbraatz

    jasonbraatz

    Oct 18, 2000
    Oakland, CA
    I would definitely be interested in something like this. :)
     
  7. J.Wolf

    J.Wolf Supporting Member

    Apr 29, 2003
    Asheville, NC
    I've got a custom made baxandall tone stack in a rackmount box that is great. Its essentially the front end of a B15 with high grade parts AFAIK. The guy who made it is making them in half rackspace boxes now, and they sound awesome.
    I'll see if he's got any for sale
     
  8. jasonbraatz

    jasonbraatz

    Oct 18, 2000
    Oakland, CA
    OH MAN! Half rackspace?!
     
  9. J.Wolf

    J.Wolf Supporting Member

    Apr 29, 2003
    Asheville, NC
    the only thing I've noticed is that the output is too hot to run into the input on a head. Its line level 1/4" so, you'd have to run it into the 728 directly, and that....would be..... really nice!
     
  10. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    Doesn't the ouput section of the B-15 play a significant part in its sound?
     
  11. PB+J

    PB+J

    Mar 9, 2000
    arlington va
    Sounds interesting to me--sure, the output section has an effect on the tone, no doubt. I'd still like to check out a preamp like that
     
  12. im confused, the baxandall tone stack isnt exactly the most complex circuit...
     
  13. jasonbraatz

    jasonbraatz

    Oct 18, 2000
    Oakland, CA
    I'm not planning on changing out the DB680 in my rig, but I've been jonesing for some more old-school gear lately and having a B15ish preamp I could use when recording and stuff would be pretty cool. :)

    Who knows, maybe it would be cool as the front end for an IP cab too?
     
  14. J.Wolf

    J.Wolf Supporting Member

    Apr 29, 2003
    Asheville, NC
    yep- so does the speaker and the enclosure. These preamps aren't going to sound exactly like a B-15, there's too many variables to guarantee that. If you plug it in to Goliath 410, it aint gonna sound like a B15 thats for sure!!

    So I just got off the phone with Don, apparently they also have a mosfet section, so really they are a modified B15 circuit. He and I agreed though, that they are definitely within the ballpark of a B15, soundwise. He also said that the halfrack units have a large external power supply, so I think the rackable ones are better. Its just hard to come by enclosures to use, and buying a new one costs about 120 bucks, just for the box to house everything!!

    I will say that it sounds wonderful, very rich and tubey, yet super articulate, through my rig. I'e AB'd it against my Glockenklang preamp, and its sweeter sounding, and more airy and buttery down low, but its not as quick, and not as tight in the bass region (class a solid-state, big surprise there). I am surprised how swee and detailed the mids sound with this preamp though, it really sounds natural and buttery.

    He said that he'd make a couple, but it would be about a 6 month wait, and he's not sure of the price, but it would be reasonable (as far as preamps go).
     
  15. J.Wolf

    J.Wolf Supporting Member

    Apr 29, 2003
    Asheville, NC
    I have an AB switcher box that I can switch between preamps during gigs. Old school tone.... click. Modern tone....click. Easy!

    I would LOVE to hear it into an IP!!
     
  16. barroso

    barroso

    Aug 16, 2000
    Italia
    would be really interested in this potential unit too.
    I am having good results by the way with my SVP-CL
     
  17. James Hart

    James Hart

    Feb 1, 2002
    toms_river.nj.us
    Endorsing Artist: see profile
  18. J.Wolf

    J.Wolf Supporting Member

    Apr 29, 2003
    Asheville, NC
    I just got a production unit of the modified baxendall tone stack preamp, and its fantastic, PM me for more info and availability.
     
  19. A9X

    A9X

    Dec 27, 2003
    Sinny, Oztraya
    I've had the schem for the ROG design saved for ages, but never built it as I wasn't too sure of the tone; not generally a pedal fan. Must throw one together now. Cheers.
     
  20. main_sale

    main_sale

    Apr 26, 2004
    Cape Cod
    Barber Electronics makes a pedal called the Linden which is the preamp section of a B-15-N. I've never heard it so that's all I can say about it.