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18v preamp/buffer recommendations

Discussion in 'Pickups & Electronics [BG]' started by Maple, Feb 25, 2016.


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  1. Maple

    Maple Supporting Member

    Feb 25, 2016
    San Francisco Bay Area
    Hi,

    One of my basses has a custom 18v (only) preamp that Bill Bartolini made for me in the early 90's. I'm not sure if it was ever a production unit.
    The other bass has an off-the-shelf Bartolini 9v/18v preamp he gave me. At lower frequencies, differences in sound between them are huge. I'd like to find something current that can equal the custom preamp.
    I also have a custom Jim Williams onboard preamp in an EUB that I'd love to find a replacement for - it sounds great but is a real battery eater and a liability!

    Here's what I need in the preamp:
    true +V/-V rail design
    no DC blocking capacitor in output path -- can pump DC directly to amp!

    I sent a request to the Bartolini company and am waiting for a reply but it's been at least 20 years since I looked for preamps so I would expect there to be other options out there.
     
  2. wcriley

    wcriley

    Apr 5, 2010
    Western PA
    Why?
     
  3. Maple

    Maple Supporting Member

    Feb 25, 2016
    San Francisco Bay Area
    Because the capacitor introduces a low frequency rolloff that is noticeable on the low B string
     
  4. wcriley

    wcriley

    Apr 5, 2010
    Western PA
    Just needs to be a large enough value, then.
    Don't amps have a cap in the input stage to block DC leakage from pedals, etc. anyway?
     
  5. Maple

    Maple Supporting Member

    Feb 25, 2016
    San Francisco Bay Area
    I have an old SWR head (Steve Rabe era) but I figure it's similar to any other modern swr/eden style amp. With the custom preamp, if I grab the strings and push pull them slowly, the speaker cones move in/out to match. Not that I play like that, but it is a fun trick and does show that there's no rolloff in the signal. regardless, there's a huge difference in sound between this and the off the shelf 9v/18v preamp that doesn't have this architecture.
     
  6. BassLife77

    BassLife77

    Nov 13, 2009
    San Diego
    can you post pics of the Bartolini custom preamp. Is the Jim Williams preamp the one with the 5532 opamp?
     
  7. wcriley

    wcriley

    Apr 5, 2010
    Western PA
    Interesting that the amp has no low pass filtering. Sounds like a good way to destroy drivers.
     
  8. Maple

    Maple Supporting Member

    Feb 25, 2016
    San Francisco Bay Area
    Sorry for the delay, I must not have my alerts set correctly. Here's a picture of the spaghetti under the cover.

    There are 3 boxes
    a module labelled
    "NTMB_18" (not the 9/18 module they sell now)
    another module hand etched into the side:
    "NTMB3 use w/NTMB18"
    And a custom J-fet switch that lets a stereo jack turn the two batteries on/off
    "SW29V BARTOLINI" hand etched into the side

    I used to tour quite a bit with this bass and never had any equipment failure.
    bartolini preamps.
     
  9. JustForSport

    JustForSport

    Nov 17, 2011
    That may be similar to the 'ThunderGuts' setup with the main NTMB module, a TC mid module and the third one.
    If you can get a Pedula ThunderGuts schematic to follow the wiring... I may have one somewhere- will have to dig.

    Edit: A couple attachments. I don't see the Pedula or yellow wired ThunderGuts module, but it looks like you have the NTMB and TC modules along with another one.

    PedullaModThunderBassNTBT_Thunderguts. bart_Pedulla_Thunderguts2.
     

    Attached Files:

    Last edited: Feb 27, 2016
  10. Maple

    Maple Supporting Member

    Feb 25, 2016
    San Francisco Bay Area
    Here's a picture of the Jim Williams preamp. It uses a Texas Instruments TLE2092

    JimWilliams.
     
  11. BassLife77

    BassLife77

    Nov 13, 2009
    San Diego
    Since the Bartolini was custom I thought it would be open face but its sealed in epoxy so you can't see the components. you wouldn't want to de-goop it so you can make a clone for the other bass. The TLE2072 is a good opamp but it draws 4mA which kills batteries quick. I use them in effects pedals and they sound great. can't use them in onboards because of the current draw. you can try a LT1352 that only draws 250uA for each amp and can run at 18 volts. You can get 2 free samples from Linear Tech with free shipping LT1352 - Dual and Quad 250uA, 3MHz, 200V/us Operational Amplifier - Linear Technology
     
  12. Maple

    Maple Supporting Member

    Feb 25, 2016
    San Francisco Bay Area
    As far as I could tell, Bill always potted his creations. I have a handful of black modules from him all potted and with letter codes etched on the sides.
    Thanks for the idea on the opamp. that's the main thing that always frustrated me with the Jim Williams preamp. that and that it has to be powered by a toggle switch. So forget to turn it off on night and its dead by the next.
     
  13. I usually design stuff with low end roll off (high pass filter). this is in the interests of speaker driver longevity and efficiency plus clarity of tone. this is usually within the preamp and is not associated with the input and/or output coupling caps.

    I have certainly designed preamps with direct output (and fwiw, input) coupling. as mentioned, virtually all modern amps, di boxes, effects etc have input coupling caps anyway so it seems a little ott unless you do a lot of studio work with nice high end gear etc.

    but hey if you want direct coupling, then it's pretty simple to design/bias circuits this way. a nice bonus of an opamp circuit designed like this is that you can switch the batteries virtually silently. I have a couple of basses that have tilt switches on the battery wire so they turn off when you put them in a guitar stand.

    I guess that's why the old bart circuit has the fet switch. if you're bass has a front mounted jack or a plate mounted side jack, it's easy to get a jack with a separate switch. but for a barrel jack, yeah you'd need a little fet circuit or similar.

    if you have a circuit in mind I may be able to show you how to bias it this way, but really I'm guessing the lack of sub bass you hear (feel?... see?..) in your other pre probably had nothing to do with that output cap, and is actually a hpf designed into the pre.

    as for your eub, yeah swapping the opamp should be easy since it's mounted in an ic socket. but choose wisely. if your eub, like mine, has a piezo pickup, you should check to see if the pre has a separate input buffer (often a single fet voltage follower stage). if not, then the opamp will need fet inputs for a nice high input z. the datasheet I found quoted current at 1.6mA per opamp. this is a dual opamp. how many are on the board? 3.2 mA is not too bad really with modern batteries, but 6.4 is starting to get up there for an onboard pre. if there's just one of these dual opamps and no other chips or transistors and you are going through a lot of batteries, I'd be checking the jack, then the operation of the circuit itself.
     
    Last edited: Feb 29, 2016
  14. Maple

    Maple Supporting Member

    Feb 25, 2016
    San Francisco Bay Area
    I was asked for details on the SW29V module by someone else who has one too. This was a custom J-fet switch that was probably OEM for a few builders but not part of the catalog. It allowed for the traditional behavior of inserting cable into stereo jack to switch power on. But it differs in that it accommodates an 18v setup with true "floating ground" (+9,G,-9)


    Bartolini SW29V.
     
  15. Mr_O'B

    Mr_O'B

    Feb 22, 2015
    Does Mr. Bartolini no longer offer custom builds to the general public?
     
    Last edited: Nov 1, 2016
  16. Maple

    Maple Supporting Member

    Feb 25, 2016
    San Francisco Bay Area
    He retired a couple years ago. Bartolini-the-company still offers custom builds but you have to order in quantity to get them. Which is fine for a boutique builder and not reasonable for the average player.
     
  17. Mr_O'B

    Mr_O'B

    Feb 22, 2015
    That's too bad!
     
  18. thisthread is back... so you are still looking for an 18v pre with no coupling caps?

    are you just after a simple buffer pre? or do you need treble and bass filters etc as well?

    what sort of jack does your bass have?

    you do realise that your amp will almost certainly have dc blocking on its input or between stages, right? not to mention pedals, (active) DIs, recording interfaces etc...
     
  19. Maple

    Maple Supporting Member

    Feb 25, 2016
    San Francisco Bay Area
    Thanks, actually no im not right now. Another TBer asked me for help wiring up that switch - they have one but didn't know how to hook it up.

    I changed my gear since that post. My old SWR rig didn't have a low frequency roll off but my new Demeter head appears to. Also I'm playing a Zon now with a simpler 9v preamp and it has no lack of low frequencies!

    I'm starting a couple more bass builds this year so the pre amp pursuit will start again when those are ready.
     
  20. Old_Rover

    Old_Rover

    Dec 14, 2009
    Moscow, Russia
    And thanks a lot for giving that help! At least now I can be sure that I assembled it properly :)
     

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