Diaphragm-pickup from the old ampeg baby bass

[Fast Freddie]

Best info I read thus far. Thanks Bruce! I am a fan of your work. Now this affirms why.

Mucho thanks bro!

[Luigi]

Here i am other time, without solving my question.
I was lookin for rewinding my bobbins or buying new ones because i have this problem:
When i'm playing (live!) in every moment the signal deads for some, then i shoot the bridge and it starts again, but this is not a solution.
I though there were the bobbins, broken in some point, but a liuthier here told me not.
Then i redid the weldings, and it seems to go, but it's not so.
Now i would to try to change the magnets, but buying from that site is very expensive because shipping costs with UPS.
Now: Anyone can sell me a pair of that magnets at a reasonable cost? I live in Milano, Italy.
Thank you.

[Dave Kerr]

Magnets won;t intermittently lose their charge - try swapping out your switch?

[Luigi]

I will do, thank you!
However, if someone has those magnets, i want to try them, because the ones i have are very bad..

[Bruce Johnson]

Luigi;

If the pickup is cutting in and out when you're playing, one possible cause is that there isn't enough clearance between the diaphragms and the magnets. If they're too close, then sometimes when you play up high or hold down two strings, the diaphragm will contact the magnet. When that happens, you get no sound. On most diaphragm style pickups, you need about 1/16" of clearance between the underside of the diaphragm and the tips of the magnets.

On the Baby Bass, the coils and magnets are mounted on an aluminum bar, which is adjusted up and down by the two chrome knobs beside the diaphragms. You tighten the knobs to bring the coils up until the magnets contact the diaphragms, then back them off until the sound comes back and the tone is good.

[mambodoc]

Devil Bass

David,

As teenager, tinkering with electronics, magnets, coils and guitar pickups, I met up with a custom guitar maker in Newark, NJ (Down Neck Section, Esther St) named Steve Blozen who initially made Yugoslovian stringed folk instruments in about the 1960s. He expanded to making guitars as the market for his folk instruments was rather limited once everyone in the performing folk group had one.

I was building my first laptop guitar when I met his son, who was looking for electronic paths for his father's first electric guitars, at Lafayette Electronics on Central Ave (I believe?). There was also a near by auto paint store where he purchased all the auto paint lacquer that were used to spray all his guitar bodies. Candle apple red with a black trim was a favorite and that was also used on the Ampeg Devil Bass.

I met Mike Roman, the inventor of the Devil Bass, at Steve's house/shop when I first saw the Devil Bass prototype. It was neck heavy with the long neck, scrolled head with heavy bass machine heads. I suggested to Mike that the horns may need to be extended to keep the beast balanced once you let go of the neck. I even showed him that if he extended the top horn by about 6", the bass would balance better. I recall being blown off by my balance observation as if he was saying, "What the hell does this kid know".

The Ampeg Baby Bass was introduced and popular with jazz/standards players as being something that is more portable and with a clean-sounding Ampeg amp, could get a respectable sound even using non-metalic gut strings. Here is where the hidden disk pickup comes into play.

Mike incorporated Jess Oliver's (Ampeg's then Vice President, real name Oliver Jessup) patent of the Baby Bass pickup into his Devil Bass design. I was too young to recognize the politics of all of this at that time. The prototype Baby Bass emerged as a candy apple red version with black hand sprayed overlay accents that was different from instrument to instrument, some with more or less black overlay, depending on the mood of the spray operator.

One summer, soon after obtaining my driving license, so I must have been about 17, I met Jess Oliver through Steve and Mike Roman who offered me a job at Ampeg in the Lindon, NJ factory. I worked the amp final assembly line which was near a factory entrance door to the Ampeg offices and could easily hear Everett Hull, the Ampeg President, and Jess Oliver jamming with visitors in their offices with Everett playing his popular Baby Bass. Mike Roman was working on his prototypes trying to get people to try using his new Devil Bass. Eventually I saw a Devil Bass prototype sitting next to a Baby Bass in Everett's office.

The big thing they were pushing about the Devil Bass was that it did not need to use metal strings, just like the Baby Bass, as the bridge was sitting on two metal disks. The authentic, amplified sound of an acoustic bass was still their priority. Each disk was mounted over a coil of 12,000 turns each of AWG 42 wire wound in series opposing with a N and S .25" diameter X 1" long magnet, wired like a series-connected humbucking pickup. These 12,000-turn coils were very good hum detectors if not set up as humbuckers.

Steve was building a metal string bass guitar and wanted some pickups for it. I took 4 Baby Bass coils, put them in custom made plastic pickup housing with two rows of two coils, staggered to fit under the strings and wired two series sets in parallel to keep the hum bucking effect. Later, I added miniature volume controls right in the pickup housing to adjust the volume of each pickup. The output was high enough that using series resistors to mix the individual string outputs worked pretty well.

I was very happy doing the final assembly on the amps that one Summer. I got to play with different models and see how the whole amp was constructed; assembly line chassis soldering, the wood shop to make the cabinets, the Tolex covering room, and then me, putting the final touches on a completed amplifier.

One day, while looking into the open chassis of a reverb and tremo-equipped amplifier, I was fasinated by a flashing light that I later found out, by looking at the schematic, was the low-frequency oscillator that works with a photocell creating the pulsating volume effect known as tremolo. I took an allegator test lead and placed it from the photocell output and attached it to the reverb output and suddenly now the reverb was pulsating. I walked into Jess Oliver's office after work and said: "I have something to show you". He walked with me back to my assembly station near the offices, and I showed him how the tremolo is now on the reverb sound. He was impressed and that is how the reverb repeat feature was added to later Ampegs amplifier models. As a kid, it was a nice feeling being listened to! What did I know about Patents?


Ampeg got their reputation for making guitar and bass amps that were extensions of high fidelity amplifiers with a clean sound. They catered to the traditional players still using gut bass strings. I do not recall any players other than Jazz or standards players making music out of the front offices when I was there one Summer. It took a while for Ampeg management to recognize that some people liked loud amplifiers with even-harmonic-distortion that amplifiers like Fender etc. add to the sound.

It was at Ampeg, with their Burns Guitars, that I got introduced to low impedance guitar pickups and the wide variety of sounds they can produce.

Joseph Rogowski

I have no idea how I arrived at this forum, but I was looking for Mike Roman info on a whim and found this. I met Mike through my dad who worked NY Brass & Copper in Hillside NJ. He sold Mike Brass and Copper stock for his electronic work. I have a Devil Bass made by Mike as well as an acoustic guitar with a modified sound hole to hold tone longer...as he explained it to me. I remember him with an everpresent quart of Colt 45, working in his basement shop, in Scotch Plains NJ think. Is he still alive? Anyone with info...don't hesitate to e mail. Thanks. Ed: mambodottoreATbellsouthDOTnet

[frankytorres]

coils different amount of turns, help please

i have some questions for those experts on the diaphragm pickup used on the ampeg baby bass. #1.- what happens if one of my coils has a resistance of 5k ohms and the other one 6k ohms? #2.- diameter of the diaphragm; what effect does it have on the sound, lets say one being 1" vs 1.5"? #3.- about the magnet what if i wanna use neodymium instead of alnicoV? how will it affect the sound?

[Bruce Johnson]

I guess this question is directed at me?

Here are some approximate answers:

#1: I haven't done much detailed testing of Baby Bass coils to have any data on standard turns counts, DCR readings, etc. So, I can't help you with what the coils are supposed to be or what's typical. I will say from experience that Ampeg's 1960's instrument shop was not a tightly controlled tolerance-driven operation. I've seen parts all over the place in dimensions and construction details. As compared to operations today, they just weren't that fussy about holding tight specs on all of the individual parts. Their QC evaluation was on the finished instrument. If it didn't sound right, they'd go back in and shuffle a few parts until it did. My point is that it wouldn't surprise me at all to find one factory coil reading 5K ohms and the other reading 6K ohms. What's the result? The one with higher resistance might have a little higher output level and slightly less high end response. But almost all of that would probably be compensated for by a tiny adjustment in the coil height adjustment screws.

#2 As I described further up in this post, think of the diaphragm as a drum head. When you increase the diameter, while keeping the thickness and everything else the same, the resonance peak and the hump of the frequency curve move down lower. Just like you were working down through a set of toms, from smallest to largest. Also, the larger the diaphragm, the more effective travel there is at the center. So, the output level gets higher, because there's more movement of the metal through the magnetic field. Making the diaphragm from a thinner metal has a similar effect to going larger in diameter.
Larger and/or thinner = deeper, boomier, louder
Smaller and/or thicker = brighter, clearer, quieter

#3 I dunno. If the overall magnetic field strength and shape was about the same, I doubt that it would make much difference in the overall tone. If you radically increase the field strength, it'll mostly blow up the output level. How it would affect the tone curve I don't know, but I don't think it would be a radical change. Remember that the majority of the tone curve and attack curve of this pickup system are determined by the diaphragm and the mechanical geometry. The coils and magnets play a much smaller role. I used the analogy before of putting a microphone inside a drum. You can play around with swapping different model microphones, and their position inside the drum, and it'll make some change to the sound. But overall, it still sounds like the same drum.

If you're interested, sometime soon I'm going to be offering a "tuners kit" for Ampeg Baby Basses. It'll be a set of various diaphragms and associated parts (with instructions!) that will allow Baby Bass owners to mess around with their pickups to get the sound they want. In my working with Baby Bass players, I've found that you guys have a lot of different playing techniques and tone preferences. There isn't one perfect setup. And there's a lot of difference from one instrument to the next. So, I'm going to provide a kit to help you adjust yours as you please. You can contact me directly at brucejohnson100....at....att...dot..net