Alumitone lookalike

[bbsailor]

Greetings,

I've been following the discussions on LoZ pickups with interest. Great stuff.
After seeing the work of Bajaman, decided to make one and see what it sounds like. Please see attached pictures and sound clip.

The sound clip was recorded straight into the LoZ input of the mixer with a flat response setting, no tone or effects editing. Plugging the pickup into a 200 Ohm to 50K mike transformer and playing into the guitar amp gives quite nice output level, however, it sounds quite different than playing through the mixer (different impedance matches I guess) .

My pickup uses a VITEC 57P184 current transformer that I had laying in my junk box. I believe it uses a 1000 turn toroid. The magnetic strips are like Bajaman described --- mine charged up to about 230 Gauss. I wired it for XLR conventions and found it extremely quiet.

Thanks for all the good work and sharing of ideas.

Regards.

JBF.

JBF,

Here are a few more tips to help you get the best sound out of your current Transformer (CT) based guitar pickup.

The current developed in the low Z string loop is based on having very low resistance electrical connections. Ensure that all connections are clean.

Try using two CTs, one on each end of the pickup. Then try wiring them in series/parallel/single using an on-on-on miniature switch. This will give you some tonal variation when using either the microphone matching transformer or the XLR input of a microphone preamp. If you do this, please post the tonal variations in an mp3. The mixer will have a flatter and wider band response than the guitar amp.

Your mp3 sample has a nice upper frequency response without the classic midrange hump in a high impedance pickup.

Do you plan on putting volume and tone controls on you guitar that match the CT output?

Nice Job!

Joseph Rogowski

[bbsailor]

Bajaman,

I have searched the Internet for "miniature current transformers" and found the following link. yuanxing electronics transformers These miniature current transformers have 5000 turns (the highest turns I have seen so far) and should produce a higher output level, especially if you use a current transformer on each end of the pickup.

Joseph Rogowski

[Michael]

Hi, Guys,
OK I'm new to this forum but have been following with fascination the subject of CT single turn primary sensor technology. I have a couple of questions; I have been exploring the idea of having a totally integral ( one piece) primary loop with the sensing coil embracing this structure, similar to what Lace does. Is there available or could one make, a moldable liquid or paste ferric substance that could be custom molded as the inductor core around the primary turn and including the secondary? The first thing that came to mind is an epoxy / steel mixture such as J B weld which is mildly magnetic. Another approach might be to hand wrap a toroidal core from coated iron wire or ribbon such as in a toroidal power trans. If this is do-able then an specific coil could then be wound to the necessary parameters. What do you think?
Thanks ,Michael

[bbsailor]

Hi, Guys,
OK I'm new to this forum but have been following with fascination the subject of CT single turn primary sensor technology. I have a couple of questions; I have been exploring the idea of having a totally integral ( one piece) primary loop with the sensing coil embracing this structure, similar to what Lace does. Is there available or could one make, a moldable liquid or paste ferric substance that could be custom molded as the inductor core around the primary turn and including the secondary? The first thing that came to mind is an epoxy / steel mixture such as J B weld which is mildly magnetic. Another approach might be to hand wrap a toroidal core from coated iron wire or ribbon such as in a toroidal power trans. If this is do-able then an specific coil could then be wound to the necessary parameters. What do you think?
Thanks ,Michael

Michael,

The key to a good CT pickup is a low impedance current string (primary) loop typically measured in hundreds of micro ohms. If you are trying to match an XLR mixer input or an XLR to high impedance matching transformer you need a CT with an output impedance below about 500 ohms. Here is how you calaculate this. Take a CT with a turns ratio of 1 to 500 and you have an impedance transformation of 250,000 (500 squared). Also assume that you are plugging into a mixer with a 2K ohm input impedance. 2000 ohms divided by 250,000 equals .008 ohms being reflected in parallel back to the primary loop impedance.

The key to getting a good low impedance output from a CT is to use AWG 12 down to AWG 6 solid wire. Surplus sales of Nebraska has some nice square AWG 6 insulated magnet wire that is good for CT pickup experimentation. You simply make a sharp "U-shaped" bend about 2.25" deep to accomodate the string width. Drill two holes in AWG 6 square wire to snugly fit the CT primary prewired loop arranged with the U-shaped primary winding facing up or vertical to form a full loop with the bent string loop of AWG 6 square wire. The AWG 6 wire has 25.9 micro-ohms per inch of length. The typical 500 turn CT such as the CSE187L has a prewired primary loop of about 250 micro-ohms that must be added to the other part of the string loop to be able to estimate the output impedance. Use the Extech LCR meter model 380193 to see how the resistance of the primary string loop directly affects the output impedance of the CT secondary output. Prem Magnetics makes an off-the-shelf CT model SPCT250 and SPCT251. The SPCT 251 has a more expensive core and produces a little higher signal output than the SPCT250. The nice trhing about this transformer is that it has a square opening to loop the user supplied primary loop through. These SPCT transformers nicely fit the AWG 6 square wire to form a very low primary loop impedance.

It is best to use a toroid CT with between 500 and 1000 turns to generate an output within the typical range of a microphone mixer. You can control the output impedance range by how many primary loops are put through the toroid. If you half the turns ratio by putting two turns through the CT you reduce the output impedance by about 4 times. The core material is critical for transforming the primary current in the CT to a useful output. You can try to use interlocking "C-shaped" laminations to intersect the primary loop such as what Lace does on the alumitone. Note that the CT is attached to the summation point where the two humbucking primary loops combine and drive the two miniature coils (under the alumium housing) with about 10,000 turns each wired in parellel.

The type of CT that you choose to use will affect now you approach making a low impedance string loop. The core inductance per coil turn is a listed CT characteristic. Zettler makes the ACST 200 series with turns ratios of 1 to 50, 100, 150, 200, 300, 500, 1000, 1500. The single primary loop has a AL of 2500nH or 2.5 uH. You will not get a molded substance to perform well enough to be practical in this application.

Solid copper wire, solder and copper tubing seems to be a fast way to make a low impedance loop. Two pieces of square AWG 6 wire can be drilled sideways on each end to make a loop using short pieces of AWG 12 wire and a pair SPCT 251 CTs, one on each end of the string loop. Measure one CT while the other CT is open and then short out the other CT and the impedance of the primary loop changes. Here is where the ear is the best test equipment to find the sweet spot of CT turns ratios, CT primary loop impedance, secondary output impedance and the loading effect on the CT secondary. http://www.mmgca.com/apps/MMG-ctdesign.pdf

I hope this helps?

Joseph Rogowski

[ola_strandberg]

Hi Everyone,
I hope you will excuse my barging in - hopefully it my question is close enough to the topic at hand!

I build guitars, primarily extended range and mixed scale. Always lightweight. For the purpose, I have developed my own modular hardware, which allows me to accommodate any number of strings and any scale lengths by simply mounting the desired number of tuners/bridges in the desired locations.



I now need a pickup that has the same flexibility... I realized when thinking about it that the transformer/bobbin assembly in the Alumitones and the weight of them is small enough + light enough that I could stack one for each string in whatever location I choose along the string's length. Many of my customers really want the bridge pickup close to the bridge for a particular sound and I can't offer it with standard technology. I do not want to develop a pickup that is tied to a certain angle or number of strings.

What do you think? And more importantly, is there anyone who can partner up with me and make them? My backlog is too long for taking a pickup design timeout.

Thanks in advance,
Ola Strandberg, Strandberg Guitarworks
guitar-only site: .strandberg* Guitars | Headless, multi-scale and extended range guitars crafted for your unique requirements
development blog: Strandberg Guitarworks

[David Schwab]

You have to realize that the Alumitone is patented, so you can't legally make pickups like that and put them on guitars for sale. Some alternatives would be a narrow pickup that you can angle anyway you like, or individual coils for each string.

[sihama]

any more information on this? what happend to the pictures? did I awaken the dead?

[bbsailor]

any more information on this? what happend to the pictures? did I awaken the dead?

sihama,

It appears that some older photos posted by Bajaman have been lost. Do you have any specific questions? Tboy is this web site maintainer, ask him about the lost photos.

I can answer any questions about Alumitione-like pickups.

Thanks for dropping by.

Joseph Rogowski

[sihama]

ok!!!.... first you can see the fotos if you google this pages link on the top .
i spend alot off hours re-reading this thread and this one http://music-electronics-forum.com/t5447/ to try to clear things in my head...smoke ..... lots of smoke... ok i get the idea now kindof
1. I use amp simulation on the pc alot if i go directly from the ct will it "work" except the different bandwith??
2. I would like to buy a ct but i probably wont be able to find something in my city in Greece i will search for the" as 104" do you think is common? I am making a very cheap 7 string fanned guitar and i need a angled pickup in the size of an 8 string and these alumitone style pickups seem like something i could make by recycling garbage....
3.i have a lot of 32 avg wire left over from when i was making a halo wah inductor can i use it for a diy ct
4.the main loop must go thru the center of the ct? i think bbsailor your original design was diferent
5 .i would like to make a coil to go directly to an amp like an alumitone ,is there a way around ordering from ebay the really thin 42 wire witch is the reason i got interested in this pickups in first place ?
thanks bbsailor for your quick respons on my last post

[bbsailor]

ok!!!.... first you can see the fotos if you google this pages link on the top .
i spend alot off hours re-reading this thread and this one http://music-electronics-forum.com/t5447/ to try to clear things in my head...smoke ..... lots of smoke... ok i get the idea now kindof
1. I use amp simulation on the pc alot if i go directly from the ct will it "work" except the different bandwith??
2. I would like to buy a ct but i probably wont be able to find something in my city in Greece i will search for the" as 104" do you think is common? I am making a very cheap 7 string fanned guitar and i need a angled pickup in the size of an 8 string and these alumitone style pickups seem like something i could make by recycling garbage....
3.i have a lot of 32 avg wire left over from when i was making a halo wah inductor can i use it for a diy ct
4.the main loop must go thru the center of the ct? i think bbsailor your original design was diferent
5 .i would like to make a coil to go directly to an amp like an alumitone, is there a way around ordering from ebay the really thin 42 wire witch is the reason i got interested in this pickups in first place ?
thanks bbsailor for your quick respons on my last post

sihama,

The output impedance of the CT which is attached directly to the string loop is determined by the wire gauge used in the string loop. So yes to question 4, the main string loop must go through the CT either through the center of a Toroid type of connected directly to the "U-shaped" loop on the CSE-187L E-I core type. Thicker wire provides a lower resistance that should produce an output impedance in the 200 to 500 ohm range to match the bridging input impedance of either a mic matching transformer (about 3000 ohms) (answer to question 5) mounted directly into a guitar amp input (to eliminate the cable capacitance effects) or an XLR input in the 2000 to 3000 ohm mic mixer input impedance. You should try to be using a wire gauge either AWG 10 or as low as AWG 6. The wire gauge affects the tone of the pickup with thicker wire favoring the bass frequencies. Since you will be spanning more than six strings, your primary string loop will be a little longer. I would suggest a string loop wire in the AWG 6 to 8 range. Use copper tubing to make a good low resistance string loop joint with silver solder if using a toroid CT or simply drill out the center of the AWG 6 wire to match the diameter of the "U-shaped" primary on the CSE-187L CT.

What input impedance and signal level does your PC input require (the answer to question 1 depends on your answer to this question)?

Most electronics mail order places (Mouser, Digikey, Jameco, Allied Electronics) ship world-wide. Look for a retailer in your country or a nearby EU country (question 2). If you use a CT in the 500 turn range (Triad CSE187L) the output impedance will be easier to keep in the XLR mic input range. If you use a toroid CT with 1000 turns (Triad CST-1000) and AWG 6 string loop wire, the output impedance will be about 300 ohms. Mic matching transformers are common and you only need one along with a matching 3-pin XLR connector and some 2 conductor shielded wire.

I do not recommed you making a DIY CT as obtaining the the right core material will be more difficult than purchasing either of the two CTs recommended above (Question 3).


I hope this helps.

Joseph Rogowski

[sihama]

yeh... i looked in 3 electronic suply stores and they thought i was an alien when I asked them for the ct
so ordering would be the only way... unless i wind that coil my self any diractions would be great!! or any alternative dead cheap diy desent pickups design! thanks again for your quick answer on my last post
!