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How to rewire a Hofner violin bass control panel for more tones

Discussion in 'Pickups & Electronics [BG]' started by fermata, Dec 4, 2017.


  1. fermata

    fermata

    Nov 10, 2015
    Preface:
    My favorite bass--and my #1--is my Hofner 500/1 Contemporary violin bass. However, that doesn't mean it's perfect; in particular, the arcane control panel wiring is somewhat limiting. I thought I'd share the rewiring scheme I've experimented with, in case any one else wants to make their violin (or Club) bass more flexible. (I've posted about this in other threads, but this gathers it all in one place and brings the circuit up to date.)

    Stock Wiring:
    The stock switch functions are as follows: Rhythm puts two resistors in series with the output signal, reducing the volume to 70% of full; Bass On puts a .1 uF treble cut capacitor in series with an 8.2K Ohm resistor parallel to the neck pickup (the resistor in series prevents the tone from being 'turned down all the way,' which reduces or eliminates the resonant peak and leaves a little more treble intact) and also switches the bridge pickup out of the circuit; Treble On puts a .01 uF capacitor in series with the bridge pickup (a capacitor wired in series cuts bass) and also switches the neck pickup out of the circuit. Everything up ('off') is bypass (no capacitors affecting the pickups). Because of the 'equal and opposite reaction' switch wiring, pickup blending is only possible with the pickups bypassing the capacitors, which is one of the biggest limitations. And the volume reducing Rhythm setting doesn't seem particularly useful.

    The Solution:
    So last year I set about keeping the existing control panel but rewiring it for more flexibility. In particular, I wanted to be able to use treble cut capacitors to affect both pickups, and I wanted to use the bridge pickup's bass cut cap to improve pickup blending.

    I went through several iterations and a quite a few capacitor values before settling on a simple yet versatile circuit (thanks to several folks on Talk Bass and Hofner Hounds for their help along the way):

    HOfner.jpeg

    What we have here is basically a Volume-Volume-Tone-Tone circuit; each pickup has its own volume and tone controls. (The diagram is missing the resistors I've wired in series with the two caps on the Bass On switch; more on that below.)

    Variations on the Theme:
    For a while, I had it wired more like a Jazz bass (red wire connected to to yellow and green on the Volume 2 pot and no treble cut cap on the Treble On switch), so the Bass On treble cut caps affected both pickups. Sounded good, but the pickups blend much better with the tone controls connected to the volume pot wipers. (In particular, the bridge pickup tone got pretty strangled with both a bass cut cap and a treble cut affecting it at the same time, making its volume pot act more like an on-off switch.)

    And for about a year, I had three tone caps (plus bypass) on the Bass On switch (run another jumper from the Solo switch to the unused side of the Bass On switch and add a cap). In the end, all that switching was too fiddly, as I didn't need three caps plus bypass in the real world. I also tried a slew of treble cut cap values along the way: .0068 uF imparted a woody, somewhat P-bass-ish tone; .01 uF, .015 uF, and .022 uF created rather harsh and honky resonant peaks, .033 uF sounded really good--fairly dark but with strong mids, .047 uF was dark and punchy, .068 uF and .1 uF were dark and dubby. The original .1 uF cap with the 8.2K Ohm resistor sounded good, too. Here's what I settled on in my final iteration of the circuit (the diagram above):

    How It Works:
    The Solo/Rhythm switch bypasses or engages the neck pickup's treble cut capacitors.

    From there, Bass On lets me choose between two treble cut caps: .015 uF with an 8.2K Ohm resistor in series for a moderate treble cut (without the honky sound the cap had on its own); .047 uF with an 8.2K Ohm resistor for a deeper cut and a really smooth tone (by comparison, I found the stock .1 uF/8.2K Ohm combo a little dull sounding).

    On the bridge pickup side of things, Treble On lets me switch the stock .01 uF bass cut capacitor in and out. This setting doesn't sound particularly great soloed (great for tic-tac tones, though!); where it comes to life is in blending the two pickups. The bass cut cap removes the comb filtering and phase interactions between the pickups, allowing the bridge pickup to be used a treble boost of sorts--switch in a dark sound on the neck pickup and then dial in the bridge pickup to taste for more bite and clarity, while still maintaining a really rich, full tone.

    And in the up position, the switch takes out the bass cut cap and puts a .033 uF treble cut cap in parallel with the bridge pickup for a tight, punchy tone that actually sounds good soloed (and also with some neck pickup dialed in); without any treble cut, the soloed bridge pickup is just too bright and nasal sounding for my taste.

    Together, these mods offer a lot more tonal flexibility and control than the stock wiring, while still being simple to use (which I find particularly important for playing live). The improvement in pickup blending is dramatic, thanks to the tone controls connected to the pot wipers and the switchable bass cut cap.

    Addendum:
    Note 1: The pickups blend best when the dominant pickup is dialed back to about 80% and the secondary pickup is dialed in to taste; there's less subtle blending control if one of the pickups is turned up all the way.

    Note 2: The capacitor values are very much according to personal taste; I settled on the ones that sounded best to my ear and for my playing situations. And there's a simple way to audition treble cut caps without even opening up the bass: unscrew the end of the instrument cable that plugs into the bass, attach an alligator clip lead to ground and another alligator clip lead to hot, and then put various caps between them (the switches need to be set to bypass [off/no caps] for this to work).

    Note 3: When putting a resistor in series with a capacitor to smooth out the resonant peak, the value isn't critical--anything between around 5 and 10K Ohms will smooth out the sound. If you like the resonant peak, skip the resistor, or lower its value. (A trim pot could be an interesting option...)

    Note 4: One could also put just one capacitor on the Bass On switch and use the Rhythm/Solo switch to select how deep the treble cut from that cap is, using something like a 150K Ohm resistor on one side of the switch and and a smaller resistor (6 or 8K Ohm) on the other side. The bigger resistor would be like turning down a tone knob part of the way, the smaller resistor would be like turning it down most of the way. (Or no resistor on one side would be like turning the tone down all the way, with the resulting resonant peak.)

    Note 5: Alternatively, if one were to have only one treble cut cap on the Bass On switch (so there's still a bypass setting), the Rhythm/Solo switch could be turned into a kill switch.

    Note 6: Another option in place of the .01 uF bass cut capacitor is a smaller value, like .0047 uF, a la Rickenbacker. The idea would be to let only highs through the bridge pickup and only lows through the neck pickup; the particular bass cut and treble cut capacitor values will determine the crossover frequency.

    Note 7: If one were to leave the stock .1 uF cap/8.2K Ohm resistor as a Bass On setting and if one were to omit the bridge pickup treble cut cap (leave off the cap and the yellow wire running from the Treble On switch to the Volume 1 wiper), the bass would offer all the original stock tones, just with more flexibility. (In fact, one could even leave the stock Rhythm/Solo switch; the Bass On switch would select between cap or no cap [bypass]. In this case, the only change from stock would be eliminating the 'equal and opposite reaction' from the Bass On and Treble On switches for improved pickup blending.)
     
    Last edited: Dec 6, 2017
    BigAndyA, Dr Gero, Jefenator and 10 others like this.
  2. ctmullins

    ctmullins fueled by beer and coconut Gold Supporting Member

    Apr 18, 2008
    MS Gulf Coast
    I'm highly opinionated and extremely self-assured
    Wow, nice work, I appreciate your comprehensive documentation, and your diligence and persistence with experimenting to find the right combination of components. :thumbsup:
     
  3. sikamikanico

    sikamikanico

    Mar 17, 2004
    I'm not particularly good at reading wiring diagrams with switches, but I wonder if you meant here the cap is in parallel with the bridge pickup? Or is it more like a third treble cut cap for the neck pickup?
     
  4. fermata

    fermata

    Nov 10, 2015
    Good catch--thought I'd finally nabbed all the typos! Fixed now.
     
    Glockburg likes this.
  5. DavesnothereCA

    DavesnothereCA

    Aug 21, 2017
    Canada
    ~
    Having owned a Ric 4001 from new in 1975 or so (and eventually wiring my bridge pickup directly, after for a while adding a switch to insert the bass cut cap or not, and more switches for other stuff), I immediately recognized in their schematics that Hofner seemed to have a similar thing going on, intermeshed with their other tonal tricks.

    I was pleased to notice that you too had noticed this Ric similarity in Hofner basses, as well as your efforts to improve the Hofner bass CP in general. :)

    And if I get a Hofner bass (would be a club, which I understand to be wired the same as the violin), I as well have plans to rewire its control panel to my own liking, as IMNSHO the illogic of their original schematic was either the consequence of a bad joke, or of a designer abusing psychogenic substances, and in either instance, it has persisted thru the decades.
    ~
     
    Last edited: Jan 31, 2018
    Stefan Verbeeck and fermata like this.
  6. fermata

    fermata

    Nov 10, 2015
    Yep, it really is time for an update! The thing is, the aesthetics can even remain--the switches should just do more useful things!

    While I'm posting--another correction to the above. Rhythm/Solo puts resistors in parallel with the output (not in series). The effect is still to drop the output in the Rhythm setting (which also cuts the treble slightly), and there's a resistor still in play in the Solo setting. Completely removing them (as I did) does make the pickups sound brighter when there's no treble cut cap involved. Simply turning down the volume resolves the issue (and the pickups are hot enough that the volume can be turned down quite a bit before the output is lowered.)

    And several months into using the wiring scheme I outlined above, I'm still loving it; after all the experimentation, this will stick. It's easy to use and offers a nice range of excellent sounds. I've also been playing with the volumes turned down quite a bit; pickup blending is particularly good when the dominant pickup is dialed back to between 50 and 75% and the secondary pickup is blended in to taste. And there's a good 'upright simulator' with the bridge pickup (.033 uF cap engaged) blended with some (no cap) neck pickup.

    And in case anyone is interested, here's the 'Jazz bass' wiring scheme, where both pickups share the same treble cut cap. (You can also see how one would go about having three tone caps + bypass, rather than the two shown above.) I think the wiring above is more versatile and overall better, but there are some merits to this approach, too.

    Hofner wiring.jpeg
     
    Last edited: Feb 13, 2018
  7. Killed_by_Death

    Killed_by_Death Snaggletooth Inactive

    If I was required to revamp a Hofner I'd completely remove the controls plate (leaving the components on it) & find another piece of plastic to fit that spot which I'd put V/V/T controls in.
     
  8. fermata

    fermata

    Nov 10, 2015
    I considered this option, but I'm happy with how mine has turned out, with the bonus of preserving the original look. But yeah, V/V/T (perhaps with a push-pull bridge volume to allow the bass cut cap to be switched in or out) probably would be the tidiest/most sensible option. One wonders why Hofner doesn't do this to start with (they do on the Green Line, and the no-control-plate look is pretty sharp).

    UPDATE: Well, in the end, I've landed not too far from that. See below for details.
     
    Last edited: Aug 20, 2018
  9. DavesnothereCA

    DavesnothereCA

    Aug 21, 2017
    Canada
    ~
    Like the Epiphone Violin bass seems to have, and of course the stock passive Fender Jazz.
    ~
     
  10. DavesnothereCA

    DavesnothereCA

    Aug 21, 2017
    Canada
    ~
    Even Rickenbacker eventually put in a switch to allow the bass cut cap to be engaged or not.

    I'm trying to recall the value of that cap, as my Franken-4001 has had it removed since 1985 or earlier.

    I have a feeling that it might have been half of the one which you now are using, IOW, 4.7 nf or .0047 uf, which I always felt notched out too much of the mids on a stock 4001 with both original pickups engaged and at similar volume settings.

    Your value for that cap (or even a bit larger) seems to make better sense, and indeed I might have tried such a cap at some point, back in the day.

    But my memory fades, as I had tried MANY circuitry and pickup mods during my first 10 or so years of ownership.
    ~
     
    Last edited: Aug 1, 2018
    fermata likes this.
  11. fermata

    fermata

    Nov 10, 2015
    The downside, compared to what I've wired up, is that the pickups share the tone control, and I've found the pickups to blend better when they don't. There's something about the dark neck pickup blended with the bright bridge pickup that really works.
     
    DavesnothereCA likes this.
  12. DavesnothereCA

    DavesnothereCA

    Aug 21, 2017
    Canada
    ~
    Coincidentally (or not) that is the same general concept which Rickenbacker embraced in their 4001/4003 series.

    However, all that my Franken-Ric has had since 1985 is two EMGs a la Steinberger, each preamped internally as the legacy EMGs are, the original 4001 pickup switch, one EMG 25K volume pot, no tone pot, no caps, no stereo, and my neck pickup is deliberately positioned lower, away from the strings, so that when I use it alone for mellower slow songs, I automatically lose a bit of volume compared to running both pups together for most uptempo louder ones.

    Also, my pups are located roughly where a Jazz bass would have them along the strings, so it sounds, if anything, more like a Jazz than any other common bass - except for one major difference - NO HUM. :thumbsup:

    I wonder whether anyone has tried EMGs on a Hofner bass ? - There would be less NEED to, as its original pups are humbucking anyway though.

    If Ric 4001 basses had not come with single coil pups, I might never have tried all of my mods, and would not have experienced first-hand a whole bunch of stuff about tone circuits, instead only reading about it in the theory books.

    And I might still be using mine wired stock.

    Still, I am curious to again wire in a bass-cut cap, and a switch to include or bypass it, and make no other changes from what I have now.

    However, with the lower impedance EMG electronics, the cap would prob'ly need to be around 10x the value of that in a Ric, to achieve the same rolloff characteristic for the back pickup, as it would be loaded by a 25K pot rather than (IIRC) a 250K pot.
    ~
     
    Last edited: Aug 2, 2018
    Stefan Verbeeck and fermata like this.
  13. fermata

    fermata

    Nov 10, 2015
    I finally came up with an even simpler switching scheme. In practice, the multiple caps per pickup aren't necessary, making the first switch (to engage or disengage the neck pickup tone caps) redundant.

    I don't know why I didn't hit on this sooner (maybe because three switches for two pickups is counter-intuitive), but what I've finally landed on is (I think) a rather clever and very simple V-V-T-T setup.

    Now, the first switch allows me to solo the neck pickup (more accurately, it removes the bridge pickup from the circuit, which gives the soloed neck pickup a pleasing extra bit of clarity). The middle switch is the treble cut switch; down (Bass On) switches in a .047 uF cap + 8.2K Ohm resistor for the neck pickup; up selects a treble cut for the bridge pickup (also a .047 uF cap + 8.2K Ohm resistor). The third switch (next to the bridge volume control), still allows me to put the .01 uF bass cut cap in series with the bridge pickup, which can have a positive effect on blending.

    Hofner wiring.jpeg

    The different pickup blends offer some really good tones: dark neck/bright bridge, bright neck/dark bridge, or, if I turn the volumes up all the way, which causes either tone cap to interact with both pickups, two variations on dark/dark. I can also solo either pickup with a bright or dark setting. The only blend that's now impossible is bright/bright, but that was always my least favorite sound, so that's not a loss.

    Since more typical V-V-T-T circuits can sum the values of the two capacitors, this 'reversible' circuit prevents that by switching in only one at a time. And it adheres to the main principal I discovered in all this rewiring: the pickups blend best when they don't share a tone control. The corollary is that the nicest blends occur when one pickup is set to bright and the other is set to dark.

    Revamping the Hofner control panel has been an iterative process over about two years. I've learned quite a bit about passive tone circuits and what does and doesn't sound good. And while there's all kinds of stuff one can do with passive wiring, when it comes to actually being useful in a musical context, less is more. (I'd rather play the bass than operate the bass.) It's probably not surprising that I've ended up where I did: there's a reason V-V-T and V-V-T-T are standard circuits; there's a reason .047 uF is a standard tone cap value. One can try to reinvent the wheel, but in the end, a round shape works best. ;)

    One more note (this isn't shown in the diagrams above): I've given some thought to the role of the resistors on the stock Solo/Rhythm switch, and in the solo position, they put 370K Ohms in parallel with the output, which helps tame a rather spikey high end. (It's surprising how bright Hofner pickups are.) So one could keep that switch stock, or put a 300-400K Ohm resistor in parallel with the output to make the tone plummier.
     
    Last edited: Sep 2, 2018
    mikewalker and DavesnothereCA like this.
  14. DavesnothereCA

    DavesnothereCA

    Aug 21, 2017
    Canada
    ~
    Bear in mind, we also need to consider that with passive pickup arrangements such as these, that the independence between tone caps and/or controls on individual pickups only holds true if neither pickup has volume turned to max, because if you do max one out (and I often would, on a two volume arrangement), then the tone circuits can 'crosstalk', and if either tone is changed, it directly affects BOTH pickups at the same time, or at least the tone circuit of the maxxed out pickup affects both, because it becomes like having a master tone instead of individuals.

    NOW, I bet I have muddied the waters ! :smug:
    ~
     
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  15. fermata

    fermata

    Nov 10, 2015
    Right, that's the inherent weakness with two tone controls in a passive circuit. But because the Hofner has hot pickups and 500K Ohm linear taper volume pots, one can easily dial back to about 7 or 8 before the volume drops, which gives the tone controls enough independence from each other. And the 'reversible' tone caps help with this, too, since they can't both be on at the same time (so cranking one of the volumes basically turns it into a V-V-T circuit, which works well, too).
     
    Last edited: Aug 28, 2018
    PawleeP and DavesnothereCA like this.
  16. HI Fermata. I'm gonna rewire my Ignition panel using your schematic. Thanks for spending all that time designing it :) is there a newer design? or is the last one you shared on Talkbass your most current?
     
  17. fermata

    fermata

    Nov 10, 2015
    Since this thread has gotten a bump, I'll give an update: I put the wiring back to stock.

    The various wiring schemes I tried were quite educational...so much so, in fact, that I ended up understanding the stock wiring well enough to prefer it!

    Getting rid of the resistors on the Rhythm/Solo switch changes the pickup loading (and eliminates some treble bleed-off), so the treble starts to get pretty spiky and bright. (That extra clarity seemed positive when I was using a dark amp; when I switched to a brighter amp, it wasn't nice, almost like a straight-to-output jack harshness.)

    And even the weird switching, where Bass On removes the bridge pickup from the circuit and Treble On removed the neck pickup from the circuit, has a logic: whether a pickup is in or out of the circuit affects loading--and therefore tone--too.

    So from a tonal perspective, the stock design is very good, even if the controls are unorthodox. And in the end, tone is what matters, right?

    Speaking of tone, I found my various capacitor switching schemes of limited use when playing with others. For one thing, I wanted to play, not mess with knobs and switches (which I spent far too much time doing at home); for another, the tonal differences were simply not that profound in a group setting. To which I might add, a Hofner has a pretty strong baked-in sound. My rewiring did change change the shade, so to speak, but it never changed the color. (Meaning, if a Hofner sounds green, one can rewire it to be a yellower or bluer shade of green, but one isn't going to make it red.)

    So with the band, I'd turn the neck pickup partway, dial in some bridge pickup for a bit of definition, and then I'd play for the night.

    And if one wants more tonal options, the stock wiring is actually quite flexible. Here are the various tone settings, from darkest to brightest.

    Neck pickup:

    --Bass On (dark tone)

    --Bass Off, Treble Off, neck pickup turned up to 10, bridge pickup turned down to 0 (brighter neck pickup tone)

    Both pickups (blending is best when neither is turned up all the way):

    --Bass Off, Treble Off, neck pickup turned to about 7, bridge pickup dialed in to taste (neck pickup plus extra definition)

    --Bass Off, Treble Off, bridge pickup turned to about 7, neck pickup dialed in to taste (bridge pickup plus extra depth)

    Bridge pickup:

    --Bass Off, Treble Off, bridge pickup turned up to 10, neck pickup turned down to 0 (burpy bridge tone)

    --Treble On (tic-tac tone)

    In addition, the Rhythm/Solo switch also serves as a secondary tone switch of sorts: because Rhythm bleeds off even more highs and cuts the volume a bit, the pickups don't play as hot, imparting a more acoustic vibe. Solo opens things up for a more electric feel/sound.

    Well, it's almost lunchtime. I think my hat is on the menu. Maybe with a side of crow.
     
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  18. onestring

    onestring

    Aug 25, 2009
    Richmond, CA
    Just wanted to thank you for a great read fermata (I had missed this post the first time around).

    I appreciate that you went back to stock. When I started reading your initial post, I got excited because I love tinkering with wiring projects and the weirdness of the Hofner wiring has always seemed to me like a problem that needed to be "addressed" someday.

    I backed away from the iron though because you are right, there's really nothing to fix. The Hofner wiring is bizarre (and my Club Contemporary looks like it was assembled/soldered by mice), but the sound it makes (to me) is the perfect bass tone. The variety of tones available is pretty outrageous considering it's just two passive pickups.
     
    fermata likes this.

  19. Wow thanks buddy. I tried all your suggested settings, and nice, there are a lot of different tones available on my Hofner, I just need to know how to find them. Thanks for your wisdom :) Greatly appreciated. I need to spend more time on the Hofner and learn.
     
    fermata likes this.
  20. fermata

    fermata

    Nov 10, 2015
    Yeah, no question Hofners are quirky! Part of their charm, but also a reason some people get frustrated by them.
     
    DavesnothereCA likes this.
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