Fernandes FAB-170 pre-amp knowledge/schematics

Discussion in 'Pickups & Electronics [BG]' started by Mike Mora, Jan 27, 2022.

  1. Mike Mora

    Mike Mora

    Oct 6, 2021
    Missouri
    Hey all, I purchased a Fernandes FAB-170 recently and I've had in 2 different shops near me (respected luthiers and repair). The first said he absolutely didn't want to tackle the job and the second has had it for 8 weeks now. Hoping to find anyone with knowledge or schematics or magic smoke to bring this puppy back to life would be greatly appreciated. I emailed Fernandes and as you can expect I got nothing.

    Problem: both pickups work beautifully in passive mode. Neither switch in either filter position makes no sound.

    In lieu of fixing it, what would be some recommended electronics to get this bass sounding as close to the Alembic sound as it looks and plays. Pickups and preamp.
     
  2. adje

    adje

    Feb 3, 2004
    If those switches are Q switches like on an Alembic, then don't expect a difference like a bass or treble EQ boost. The Q boost puts an accent on the start of the note, and the accent falls on the cut-off frequency of the filter. So if the filter is wide open, and the Q switch is in the boost position, there is a short spike in the higher frequencies, and with the filter closed the spike is more in the mid range. With the Q boost off, there is still a mild boost at the cut-off frequency, because that's what a low-pass filter does.
     
  3. adje

    adje

    Feb 3, 2004
    Another thing to try is to let a note ring out, and turn the filter knob as the note sustains. This should give you a mild wah effect, and with the Q boost engaged the wah effect should be a little stronger.
     
  4. JW56789

    JW56789 Guest

    Feb 18, 2017
    It may be cheaper to buy a real one.

    I owned a pair of Alembic fives, and over my years most everything else at one time or another. You might approach that sound with some neutral sounding Barts, but after it's all said and done, nothing else is as brutally, unforgivingly clear as Alembic pickups coupled to their tone networks.
     
    Last edited: Jan 27, 2022
    adje likes this.
  5. Obese Chess

    Obese Chess Spicy Big Dad Supporting Member

    Sep 4, 2005
    Portland, OR
    Mike Mora likes this.
  6. mikedeeez

    mikedeeez

    Sep 10, 2020
    Mike, do you have a photo of the interior of the controls cavity? It's possible that someone in the past already replaced some (or all) of the electronics, and now the switches no longer do what they originally did.
     
  7. Mike Mora

    Mike Mora

    Oct 6, 2021
    Missouri
    I am going to get down to the shop and see about getting some proper photos, pretty sure I can build a schematic from that and if I can I’ll share.
     
  8. Mike Mora

    Mike Mora

    Oct 6, 2021
    Missouri
    Yeah, here’s a really good video of the bass in action from a fellow from BJD.
     
  9. Mike Mora

    Mike Mora

    Oct 6, 2021
    Missouri
    Here’s some detailed pictures of the board. I’m seriously suspect of the switch. Anyone know the color coding by chance? I have no clue how this is wired, so I’d be seriously grateful. It appears during the run thru at the shop 2 of the 5 wire ribbon cable has dislodged and neither of us can figure out where they went. The switch is DP 2 common 4 load rotary, MX204. I can buy a new switch but it doesn’t solve the wiring issue. Still working on it today, then I’ll have to put her away for a week or so.
     

    Attached Files:

  10. Mike Mora

    Mike Mora

    Oct 6, 2021
    Missouri
    Currently I m seeing Red/White as common, Yellow/White on pin 3 and tied to pin 4, White on the 2nd common, pins 1, 2, 5 & 8 are tied together, 6 and 7 are tied together. Working up the schematic.
     
  11. Mike Mora

    Mike Mora

    Oct 6, 2021
    Missouri
    Well it looks like I have things wired at the switch, albeit what I think to be correct. I get sound now but it a screaming howl more than anything else.

    anyone know how the “hum cancelling” center “pickup” operates? It has a pair of wires running to the board just like a regular pickup.

    I really think this is due for new electronics and probably pickups. I’ll check out the Passwind stuff.
     
  12. Mike Mora

    Mike Mora

    Oct 6, 2021
    Missouri
    Ok, it's only been a short journey but this baby is too sweet not to be playing. I purchased 2 of the JTEX Filter preamp with the 3 position Q switch (one for each pickup) and ordered a pair of nice Bartolinis. Chances are this is exactly what I was looking for. I haven't decided how I want to wire in the end. The stereo plug is a bit annoying but could open up if I decide to expand or maybe even some recording opportunities I haven't considered yet. Considering leaving the 1/4" but making it mono and making the 5 pin connector a stereo option (I'd have to make a custom cable to do so).

    I haven't given up on the original setup. I will re-home this for some work to be done later. Updates will follow.

    I am still very clueless about the center hum cancelling "pickup". It has wires attached to the board. I will most likely bypass it leaving it in place for aesthetics right now. Anyone know what if does and how it does that?
     
    Obese Chess likes this.
  13. Obese Chess

    Obese Chess Spicy Big Dad Supporting Member

    Sep 4, 2005
    Portland, OR
    I'm completely out of my depth here but following along just to learn more.
     
  14. mikedeeez

    mikedeeez

    Sep 10, 2020
    Hi Mike,
    Interesting - unfortunately I think the big challenge is that to my knowledge, there isn't a schematic of the electronics available anywhere on the internet. These FAB (and Masterhand) basses are pretty rare instruments, and their controls are complex enough that it would be a bit of a task to establish what the "standard" circuit looks like. Although if you do, I'd love to see it!
    I don't own one, but I've tried finding a circuit diagram myself in the past because it's a cool filter-based preamp, and it's either an exact copy or a close copy of the Alembic Series 1 circuit (which I have also never seen a complete schematic of).

    Your approach to just replace it with Bartolinis and JTEX Distillers is probably what I would do too, if I couldn't figure it out. I have a Distiller myself; I don't know how "exactly" it copies an Alembic Series 1 filter, but it's supposed to be basically the same. If you have 1 for each pickup, and then actively mix the 2 together, you essentially have the original controls. That is, except for the humcancelling middle "pickup" (*).

    If you're still interested in fixing the original controls, best I can think of is to check out photos of other people's FAB-170 / FAB-180 / Masterhand bass electronics online, and visually see if everything matches yours. I know that's tough, and only helps if it's visually obvious what the problem is. But here are a few decent photos:
    - 2x attached
    - 2 links:
    Fernandes FAB-170 Bass Guitar 1979 | KOIZJAPAN | Reverb
    SOLD - RARE - Fernandes FAB-180 ((Alembic Series 1 Clone))

    And/or, you might consider replacing the 3 opamp chips. They're the ones labeled "AN6552". Fortunately the AN6552 had a very "standard" pin configuration, and could probably be easily replaced with something like a TL072 - cheap and easy to find. If that doesn't work, you could then try replacing the transistors. Beyond that, I can't think of anything else that would typically go "bad" that would affect both pickups equally, unless someone deliberately disconnected the Q switches for some unknown reason.

    (*) I believe the humcanceller pickup (aka a "dummy coil" or "air coil") works like this: It picks up the same amount of electrical NOISE as the regular pickups, but doesn't pick up the STRINGS at all. Then, the active electronics basically take that noise that the humcanceller is seeing, reverse the phase, and then add it to the signal from the regular pickups.
    What that does is cancel out the noise, but leaves the signal from the strings (i.e. the actual sound that you want) untouched.
    It's the same principle behind a regular humbucker pickup, but it (mostly) preserves the clearer single-coil sound. Some Music Man basses have dummy coils, for example, they're just hidden under the pickguard.
    But if the Bartolinis you're going to use are humbuckers already, then I think it's completely redundant. I would recommend just leaving it there, but disconnect the wires.

    Good luck!
    Mike
     

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    Last edited: Feb 7, 2022