Any tips on where to find an Ampeg-style baby bass magnetic diaphragm pickup?

[mturkis]

I build my own double basses. up til now they've all been acoustic, amplified with the realist pickup, but I'm building myself an ampeg style baby bass.

I've corresponded with some makers in Colombia, who'll sell me their version of the design, but it's quite pricey with shipping. One of them actually mentions on his website that he has his manufactured in Miami, but I can't find any info on who, specifically, makes them. I've also tried to contact Steve Azola, but I never hear back from him.

Anyone know who in Miami (or anywhere else in the States) makes these? Or does anyone have any experience themselves? I've read another thread on the subject of making them which waxed historical and, being that I'm pretty ignorant when it comes to electronics, went over my head pretty quickly. I'd be interested in trying my own hand at it if I can't find any for a reasonable price, I'm a pretty quick study.

Any information will be greatly appreciated!

[Bruce Johnson]

Well, the important thing to understand about diaphragm pickups is that they must be customized and fine tuned for every application. Small changes in mechanical things in the instrument structure itself can cause dramatic differences in the tone that comes out of a diaphragm pickup. Everyone who builds basses with this style of pickups (Ampeg, Azola, myself, etc.) has had to develop the pickup for their own specific instrument, to get it to sound right. That's why there aren't any aftermarket diaphragm pickups for sale (that I know of). Even if one of us sold you a kit of parts, you'd probably still have to modify it extensively to work in your bass. Diaphragm pickups are very fussy mechanically.

So, you're going to have to build your own. The electronic/electromagnetic end of it doesn't have to be complicated. The simplest thing I can recommend is to get a Seymour Duncan Quarter Pounder P-Bass pickup. That pair of coils are already about the right physical size, configuration, and magnetic strength to work as a baseline. They're already wound as a split humbucker set, and can be wired up in a simple passive circuit with a volume and tone control.

The diaphragms are where you'll have to do the experimenting. The diaphragms should be some kind of spring steel (probably, but not absolutely). Ideally, you want them to have about 1/16" of up and down movement over the top of the magnets as the bass is plucked. They also need to have about 1/16" clearance from their lowest position to the tops of the magnets. You'll have to play with the thickness and size of the diaphragms to get there. The diaphragms are reacting to the download from the bridge, which is dependent on the break angles of the strings over the bridge, string gauges, scale length, etc. You'll probably end up making up a benchtop "mule" instrument to use as a testbed.

Once you get the spring rates, travel, and clearances in the right range to give you a reasonable output level, then other issues come up. Diaphragms, or any other spring system, will have resonances at various frequencies that can cause weird notes at random places. It'll take more tinkering to dampen or shift those resonances around.

Anyway, that's the basic story on diaphragm pickups. There aren't any easy off-the-shelf answers. So, make your own!

By the way, I call these things percussive pickups, because of the general thumpy nature of their tone. The version that I developed for my own Scroll Basses uses a framework of spring steel rods instead of diaphragms. In my application, that's what worked best, but it's not necessarily the same for you.

[mturkis]

Thanks Bruce,

Very, very helpful information. That definitely gives me a place to start from. We'll see how this whole project goes! Metal and electronics are a whole new bag for me!

Marty

[frankytorres]

here is a link to the manual for the ampeg's baby bass. with drawings:
http://www.direct.ca/west/demo/bb/AmpegFrame.html

also here is the patent for it:
patent # 3244791

I hope this helps,

Franky Torres

[mturkis]

Thanks! That patent is especially helpful. I might come in to Roccupulco this Saturday if you're in there to pick your brain. Where did you get the parts such as the aluminum plate, diaphragms, etc.? Did you make them yourself or have someone else manufacture them? That's the part I'm least sure about.

[frankytorres]

I made the plates myself, aluminium is the easiest to work with. I won't be there on friday but for sure i'll be there on saturday, call me or tell one of the security guys at the door to go get me so I can let u in for free.

[Bruce Johnson]

Just a reminder that the diaphragm(s) need to be steel. Or, if you want to use some other material, then some steel part has to be attached to the diaphragm over the magnets. You need to have some iron atoms wiggling in the magnetic field to get any sound!

Aluminum is fine for the cover plates and mounting brackets.

[mturkis]

Thanks again Bruce! I know you said it will take some playing around with, but any tips on where to start with the thickness of the spring steel for the diaphragms?

[David Schwab]

Just a reminder that the diaphragm(s) need to be steel. Or, if you want to use some other material, then some steel part has to be attached to the diaphragm over the magnets. You need to have some iron atoms wiggling in the magnetic field to get any sound!

Aluminum is fine for the cover plates and mounting brackets.

Have you ever tried sticking the magnet on the plate and just having steel poles in the coil? I don't know how well it would work, but would allow other materials to be used for the diaphragm. I saw a banjo pickup that worked like that.

[David King]

Mturkis,
Start with the steel you have or can get easily. 22 guage is pretty common and will be a reasonable starting place.

[Bruce Johnson]

David (Schwab);

The percussive pickup that I developed for my current model Scroll Basses is similar to that. 1/4" dia x 1" Alnico V rod magnets dangle down from the sprung mechanism that holds the bridge. The coils are hollow and the magnets hang down almost all the way through them, with clearance to move freely. The signal output this way is much higher, clearer, and more precise than the old Ampeg design. I don't know why Ampeg went with the design that they did. It has so many inherent problems and there are obvious (to me anyway) better ways to arrange things.

mturkis;
The Ampeg diaphragms are made from two layers of 22 ga (0.028") spring steel attached together. They made a fuss about how it was some kind of special magic steel alloy, but I've tried several grades of spring steel and couldn't tell any difference. A single layer of 16 ga or 18 ga will probably be in about the right range too.

[mturkis]

Thanks for all the help, guys!

I checked out one of Franky Torres' pickups and seeing it up close & personal was very helpful, so I think I'm ready to go on the construction/materials front.

Now, to display the true depth of my ignorance, would anyone be able to direct me to a source that would lay out what electronic parts I need to set up a passive circuit with tone and volume controls (& how to wire them)?

Thanks in advance!

Marty

[mturkis]

Found the wiring info. Thanks for all the previous tips! We'll see how she sounds. Got the metal on the way from McMaster Carr.

[David Schwab]

David (Schwab);

The percussive pickup that I developed for my current model Scroll Basses is similar to that. 1/4" dia x 1" Alnico V rod magnets dangle down from the sprung mechanism that holds the bridge. The coils are hollow and the magnets hang down almost all the way through them, with clearance to move freely. The signal output this way is much higher, clearer, and more precise than the old Ampeg design. I don't know why Ampeg went with the design that they did. It has so many inherent problems and there are obvious (to me anyway) better ways to arrange things.

That's good to know. I had considered doing something like this for an electric URB that I plan on building... eventually.

It's good to see that you are using one of these types of pickups on your scroll bass instead of just a magnetic pickup. More work, but truer to the original design.

[mturkis]

I'm about to wire up my pickup. I'm using components from a P bass circuit. Does anyone have an opinion on whether I should follow standard P bass wiring procedure, or wire it exactly as the Ampeg patent shows it, which is slightly different. Does anyone know how much it will affect the tone?