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KK Baby Basses; Hot Rodding The Pickups

Discussion in 'Electric Upright Basses (EUB's) [DB]' started by Bruce Johnson, Nov 10, 2014.


  1. Bruce Johnson

    Bruce Johnson Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    I'm a Luthier in the Los Angeles area. Some of you know me from my specialty, which is the Ampeg-style horizontal Scroll Basses. I also do some limited work on Ampeg, Zorko, and Azola Baby Basses, mostly neck repairs. I only work on the originals, not the inexpensive copies.

    Recently, I've expanded my expertise to include the KK Baby Basses. These are the instruments built by Kris Kedzior in the UK, available here in the US directly from KK (http://baby-bass.com/). I've been in contact with Kris, and have been helping with some small repairs on his instruments that customers have here in the California area. I'm not a dealer or a paid rep or anything like that. I like his basses. They are very well made, and a bargain for the price. In particular, they are built strong. This is a Baby Bass that you can really take out on the road. I highly recommend them.

    However, one weakness that the KK Baby Basses have is in the pickup system. All of them (about 6?) that I've had here in my shop have been weak and thin sounding. The overall output level was low, and they didn't have the same booming bottom end that you'd expect from an Ampeg or an Azola.

    The pickup system in Kris' basses is very similar in design and function to the system in the original Ampeg Baby Basses. Each foot of the bridge sits on a small round steel diaphragm. Under each diaphragm is a round coil with a magnetized steel core; a magnetic pickup. When you pluck the strings, the bridge bounces on the diaphragm, which wiggles in the magnetic field, which creates a small current in the coil, etc. The two coils are wound and oriented as a humbucking pair, and the signal goes through a simple passive circuit with Volume and Tone controls. It's very similar to a passive electric bass, except that the diaphragms are wiggling in the magnetic field, instead of the strings. It's that motion of the diaphragms that gives the Baby Bass-style pickup its unique, powerful thumping sound.

    Anyway, I think I've figured out why the KK pickup system is weak, and a simple way to fix it. Kris' design of the coils, diaphragms, and control circuit are all fine. Surprisingly enough, the fix involves adding steel washers to the bottoms of the feet of the bridge.

    This does two things: The steel washers add iron content into the mass that's bouncing in the magnetic field. Kris has the diaphragm just right, in its thickness and spring rate. Mechanically it works fine, but it doesn't have enough iron mass to create a strong enough signal in the coil. Adding a steel washer or slug on the top side of the diaphragm significantly increases the signal level in the coil, as well as the sensitivity of the pickup. It increases the overall output level as well as widening the frequency range, top and bottom.

    The other problem with Kris' design is those big flat feet on the bridge. They span almost all the way across the diameter of the diaphragms. They effectively restrict the diaphragms from moving, and doing their job. I don't get it. Putting the steel washers under the feet raises up the corners of the feet, allowing enough clearance that the diaphragms can deflect and bounce, like they are supposed to. That brings back the big Baby Bass thump.

    Here's the quick and dirty way to do this fix: Use double sided tape to attach a pair of steel washers to the feet of the bridge. They must be steel washers, not stainless, but they can be zinc plated. The thicker, the better. These ones I used are #10 Heavy Washers, which are about 1/2" OD x 0.100" thick. Stick them on there and set the bridge back in place. You'll have to readjust the action slightly, because the bridge will be sitting a little higher. And no harm is done. If you don't like it, you can peel them back off.

    IMG_3215B.

    I've added the washers like this on 4 KK Baby Basses so far. On each one of them, it significantly improved the sound. Louder, fuller, and more Ampeg-like.

    I had another KK in here this weekend, a brand new one. A beautiful bass. Same problem. While he was standing here, I added the washers and showed him the difference. It completely transformed the sound of the bass. He wanted me to do a more elegant and permanent version of the fix, so this is what I came up with.

    IMG_3578B. IMG_3579B. IMG_3581B.

    I machined up some steel slugs, 7/16" dia x 0.200" thick and recessed them into the feet of the bridge, attaching them with small screws. Note how I slightly rounded the bottoms of the feet, and left the slugs sticking out slightly. This configuration worked even better than the simple washers; louder and fuller. I assume that it's because there's even more iron wiggling around. I believe that I'm on the right track in understanding why this works.

    The owner picked up the bass this morning and is thrilled with how it sounds now. He's a pro, and plans to use it for extensive gigging.

    I offer this info here to help any of you KK owners. And yes, I've talked this all over with Kris. He said that it got him thinking in some new ways, and he's working on some design improvements.
     
    DoubleMIDI, nouroog and Eric Hochberg like this.
  2. mchildree

    mchildree Supporting Member

    Sep 4, 2000
    AL/GA
    Bruce, this is OUTSTANDING information. Many thanks for sharing it! I have a fairly new KK, and have been wrestling with the low output. I just bought a K&K Bass Max and was about to widen a bridge wing slot to fit it....kind of a PITA, and would leave the stock pickup system going unused. I'll try this first, and will report my results.
     
  3. NickyBass

    NickyBass Supporting Member

    Nov 28, 2005
    Southern New Jersey
    I had an Azola bass that benefited from a similar fix. I tried a few different washers under the bridge and was surprised with the results. I used bigger ones but probably would have had better results with smaller ones. I've since sold the bass.
     
  4. mchildree

    mchildree Supporting Member

    Sep 4, 2000
    AL/GA
    Success! I actually had the best results using washers that were a bit larger in diameter than the ones used by Bruce....about 3/4". The appearance isn't as clean, since the washers show underneath the bridge feet, but the output was quite a bit increased. Definitely more usable for my doubling gigs.
     
    jesperhansen likes this.
  5. Bruce Johnson

    Bruce Johnson Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    That's great, Mike! I don't know what the optimum point is in the tradeoff between increasing the signal level (by increasing the size of the slug/washer) versus increasing the diaphragm motion (by decreasing the footprint of the bridge foot on the diaphragm). It may be personal taste of punch vs clarity.

    And there are other design possibilities too. For example, I could make a thinner diaphragm, which would be a little more flexible, and sandwich it between a pair of smaller, thicker steel slugs. One over, one under, riveted together through a small hole in the middle of the diaphragm. Then drill a small recess in the bottom of the bridge foot that would locate over the top slug, which would keep the bridge correctly located. And round up the corners of the bridge feet for clearance. I think that something like that would be the best permanent design change to this pickup, and what Kris should do.

    Lowering the stiffness of the diaphragm, while adding inertial mass and iron to it, would lower the frequency of the "warble" that happens just after the initial pulse of the note. In my experience with tuning the percussive pickups in my Scroll Basses, getting that warble clear and slow is a real important part of making an electric bass have an upright bass like character.

    I'm hoping that some KK bass owners will experiment with all this themselves, and post their results here. Like you have. Thanks!
     
    Last edited: Nov 14, 2014
  6. mchildree

    mchildree Supporting Member

    Sep 4, 2000
    AL/GA
    Here's what I ended up with. I have my shop dismantled for remodeling at the moment, or I'd probably try your second idea, Bruce.
    image.
     
  7. Bruce Johnson

    Bruce Johnson Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    Mike;

    Next time you get a chance to mess around with it, try smaller diameter washers, but stacking two or three. Double stick tape between a couple of washers isn't going to hurt anything. A stack of smaller washers should give you the necessary iron volume to increase the output level, while the smaller diameter will increase the diaphragm motion and the punch.

    The washers that have worked well for me are Heavy series washers, which are 0.100" thick. That's more than twice as thick as standard washers. When I went with the machined slugs, I made them 0.200" thick, and it increased the output level and clarity even more. I suspect that going much beyond that would be diminishing returns.

    But, think of that as being about the volume of iron that you want; 0.200" thick x 7/16"-1/2" diameter.
     
  8. mchildree

    mchildree Supporting Member

    Sep 4, 2000
    AL/GA
    I actually thought about stacking two, Bruce. I couldn't find any washers as thick as .10, in a diameter as small as yours. My only fear was that it might not allow me to adjust the action low enough. I'm on vacation from work next week, so I'll experiment more and try to record the results.

    Having my shop dismantled SUCKS! ha!
     
  9. NickyBass

    NickyBass Supporting Member

    Nov 28, 2005
    Southern New Jersey
    Bruce, maybe this is a step towards a Johnson BB??? ;) I'd be the first in line.
     
  10. Bruce Johnson

    Bruce Johnson Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    Nicky, there's no way I could get a Baby Bass style EUB developed and into production any time soon. I'm overwhelmed with development projects for several new horizontal basses, and all the work I do for other Luthiers.

    Also, I couldn't come close to competing with the KK bass on price. If I built basses just like them, I'd have to sell them for about $4000. I don't know how Kris does it.

    The only thing reasonable that might happen is for me to work with another Luthier who wants to get into building EUB's with the percussive-type sound. I could develop and supply the pickup system.

    Mike;

    Yeah, to me life without a shop full of tools and machines and projects isn't.....life.
     
  11. mchildree

    mchildree Supporting Member

    Sep 4, 2000
    AL/GA
    Did a little more experimentation. Tried two 1/2" diameter washers stacked, and also tried two of the same size washers you see in my photo above, stacked. For whatever reason, both those setups resulted in lower output and a thinner tone. So far, the first washers I used (.95 diameter, .065 thickness) have yielded the best results for me.
     
  12. Bruce Johnson

    Bruce Johnson Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    Okay, that's interesting information. I'll try that experiment myself, comparing washers that are larger diameter and thinner vs smaller dia and thicker. The customers' KK bass that I did the recessed slug feet on is back in my shop for some minor fingerboard surfacing. I'll do a few more experiments with it while it's here.

    It may be that the extra added iron is more effective in increasing the signal strength when it's located further out horizontally from the center of the coil, than it is when stacked up vertically right above the magnet.
     
  13. NickyBass

    NickyBass Supporting Member

    Nov 28, 2005
    Southern New Jersey
    Did you adjust the pickup height when you stacked the washers?
     
  14. mchildree

    mchildree Supporting Member

    Sep 4, 2000
    AL/GA
    Nicky, no I didn't change the pickup height at all. I was going for an apples-to-apples comparison with the stock configuration, and with the various washer sizes, so I needed to keep it constant.

    Bruce, I'm not sure if this makes any difference between what your results and mine, but my bass is a new model that KK just added to the line.....KK Baby Junior 1/2 size. I wouldn't think that the pickup internals are any different, but I'm not sure about it.
     
  15. Bruce Johnson

    Bruce Johnson Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    Nicky;

    On each of the customers' KK basses that came to my shop with weak sounding pickups, the first thing I did was to check the adjustment of the height of the pickup coils, to be sure that that wasn't the problem. Then I kept the same adjustment when I added the washers under the bridge feet.

    Mike;

    Kris has been making some changes in the pickup system. The one that I made the recessed-slug mod to is new, barely a month old. The pickup coils on this one uses threaded machine screws as the pole pieces up through the centers of the coils. They aren't adjustable, they are just steel bolts holding the coil bobbins to the cross bracket. Then he has two ceramic ring magnets stuck to the heads of the bolts, under the coils, to charge them and create the magnetic field.

    The previous basses of his that I worked on were 1-2 years old. They used alnico rod magnets as the cores of the coils, rather than the steel bolts. That's how the old Ampeg coils are made, using alnico rod magnets. I don't know why he changed away from that construction. Maybe he's trying increase the field strength with the stronger ceramic magnets? But, as I've described above, I don't think that the field strength is the cause of the weak output of his pickups. I couldn't do a side by side comparison, but it seemed to me that this recent bass was just as weak sounding as the older ones. And it responded exactly the same way when I added the washers.
     
  16. bajocallao

    bajocallao Supporting Member

    Jul 13, 2006
    Woodside, New York
    Endorsing Artist: D'addario Strings, Aguilar Amplifiers
    just a thought
    Why doesn't his pickup discs have nipples on it like the original Ampeg pickup?
    I believe this would give sort of the same elevated effect as washers under the bridge feet. Also I believe concept of disc nipples and fitted holes under original Ampeg aluminum bridge feet are for the vibration
    Why do KK bridge feet go passed disc?
    I believe this also hurts the sound.

    How's 990 Bruce? Ha!
     
  17. Bruce Johnson

    Bruce Johnson Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    Hey Abraham;

    Yeah, the diaphragm disks in the Ampeg pickup have a little pressed nipple bump in the center, and there's a small round recess in the bottom of the foot of the bridge. So, it doesn't sit up on top of the bump. But notice that the footprint of the foot is relatively small and round, about 1/2" diameter. I think Ampeg understood how the diaphragm had to be able to move, in order to get that percussive sound.

    Now the Ampeg's bridge is metal, but it's cast aluminum. No iron in it. An Ampeg Baby Bass may benefit from the steel washer trick, to increase the signal level output and sensitivity of the pickup. I don't own one or have one here in my shop right now (although I have several of the necks here), so I can't test the idea. If one of you owners out there wants to try it, let us know what you find. Same trick; steel washers and double-stick tape.

    In the Ampegs that I've worked on, I've noticed that many of them showed up here with two and even three diaphragm disks stacked on top of each other, on each side. And a few appeared to come that way from the factory. That doesn't make sense to me, in my knowledge of how the pickup operates. It's like putting a really stiff drum head on a drum. In each case, when I took out the extra stacked disks, leaving just one on each side, the bass sounded better overall. Better percussive pulse and good signal level. The stacked disks are a mystery to me. One owner told me he heard that it reduces feedback. Well, yeah, throttling the pickup will do that.

    The idea that I presented above, of a diaphragm with an attached iron slug on the underside, and a bump on the top side to fit the bridge foot, could be a simple upgrade for an Ampeg pickup too.
     
  18. bajocallao

    bajocallao Supporting Member

    Jul 13, 2006
    Woodside, New York
    Endorsing Artist: D'addario Strings, Aguilar Amplifiers
  19. Bruce Johnson

    Bruce Johnson Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    I don't see the exact washers that I've been using on Amazon, but here's the listing at McMasters:

    http://www.mcmaster.com/#standard-washers/=urloli

    The part number for the #10 size is 91201A011

    They are Extra Heavy Plain Steel Washers, #10 size. The ones I have came from a surplus hardware place in Burbank. They measure 0.100" thick.

    As I mentioned above, if you can't find the Extra Heavy washers, you can stack up two or three standard #10 washers.
     
  20. Bruce Johnson

    Bruce Johnson Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    I had a nice call from Kris today, the owner/builder of the KK basses. We talked all about these issues with the pickups, ideas that he's been working on, and what I've been doing here. He definitely is open for ideas and feedback from owners to improve his basses. He encouraged me to go ahead and figure out my own "hot rod kit"; something that will improve the sound and be simple for owners of his basses to install themselves. If he likes it, and customers like it, then we can work something out. Maybe he'll have me make the parts to put on new basses, or buy the design from me. I'm happy to help. I like his basses, and I think he's got a good thing going with them.

    My thinking right now is to make up a kit of replacement diaphragms, which have the iron slugs attached to them. They could be directly swapped into the bass in a few minutes, with no permanent mods. Just a minor readjustment of the coil height and neck tilt.

    So, this is a call out to KK Baby Bass owners here in the US. If you want to check in here on this thread, I'll get together a small list. I'll make up some experimental sets to send out to you, and let you try them out.

    Any of you who are near me here in the NW Los Angeles area are particularly welcome. We could arrange for you to stop in my shop and do some A/B testing in person.