Is the transition between current-mode and voltage-mode pickups continuous?

[earthtonesaudio]

Hi, first post here.


I have been reading about low impedance/current sensing pickup designs like the Lace Alumitones, and I was wondering if there was some sort of continuous function or relation between the number of turns/thickness of wire, and the mode in which the pickup operates most efficiently?

Obviously the low impedance pickups use few turns of thicker wire and are optimized for current output, and the high impedance pickups use many turns of thinner wire for optimal voltage output.

Is this just some basic electronics theory that I have overlooked?

Thanks,
Alex (EarthTonesAudio)

[bbsailor]

Hi, first post here.


I have been reading about low impedance/current sensing pickup designs like the Lace Alumitones, and I was wondering if there was some sort of continuous function or relation between the number of turns/thickness of wire, and the mode in which the pickup operates most efficiently?

Obviously the low impedance pickups use few turns of thicker wire and are optimized for current output, and the high impedance pickups use many turns of thinner wire for optimal voltage output.

Is this just some basic electronics theory that I have overlooked?

Thanks,
Alex (EarthTonesAudio)

Alex,

That is a great question because it gets to the heart of how low impedance pickups, wire size, transformers turns ratios, transformer losses, and matching all come together when trying to optimize low impedance pickup designs.

Think of it like this. If a traditional high impedance voltage based pickup uses AWG 42 wire with 8000 turns then a low impedance pickup using a microphone matching transformer with a 500 to 50,000 ohm rating, with a 1:10 turns ratio would need an 800 turn coil with an impedance that matches the 500 ohm rated load side. Typically you will want a wire that has ten times the area of AWG 42 to scale equally (excluding transformer and matching losses). Now there are some voicing options available by changing the wire size, and coil turns due to matching the transformer primary, transformers losses and reflected load impedances.

The Jack Casady Bass low impedance pickup uses AWG 28 wire and has a 23 ohm resistance rated at 24.87mH. This represents a pickup design that is somewhere between a high impedance pickup and the other end with current transformers using very low impedance string loops.

Now if you want to experiment, see the link below for the SPCT251 current transformer that has a nice core size for better low frequency operation.
Prem Magnetics, Inc. - Interconnect Transformers
It has a 2000 turn secondary at 305 ohms. The primary is an open core of 0.160 inch square so you can use a very thick single loop of AWG 4 wire to make an Alumitone-like pickup. You can experiment with using multiple primary loops of thinner magnet wire like AWG 12 to 18 and play with different voicings.

The less obvious thing to consider is that the primary loops are measured in micro ohms and require very good connections to form the primary loops. I use copper tubing to join heavy wires into loops and solder the connection.

Some current transformers (CT) like the CSE187L use a prewired single loop of AWG 12 wire (250 micro ohms) that can be joined to a single string loop of wire that has a resistance about 5 to 10 times lower than 250 microohms to minimize losses. This is where playing with different size string loop wire sizes can help voice the pickup to suite your ear to be more efficient in the higher or lower frequency ranges. The CSE 187L has about a 20 ohms DC resistance output and matches well into an XLR microphone input (rated between 150 to 250 ohms with about an actual 2K ohms input impedance) and has an output in about the 5mv range. Start with a thin wire single loop like AWG 18 and progressivly go to using a thicker wire loop that is up to about AWG 6 or 8. This will be well worth your time.

These tranaformers are very inexpensive and allow you to quickly try different coil arrangements. Just take good measurements to see (with a scope on the CT output) and listen to which frequencies are favored by changing the wire size of the string loop. You can even try making a string loop with a CT on each end of copper tubes about 2.5" long to fit the string width. The you can switch the two CT outputs in series and parallel to listen to matching differences. You can even bend the CTs down 90 degrees to fit the CT CSE187L pickup into a single coil pickup space.

I use 2" long by .25" wide neo magnets from K&J magnetics to nicely fit in the CT string loop width. Just put shrink wrap over these neo magnets to prevent shorting the magnets conductive surface against non-insulated wire when experimenting. I use old scraps of solid household electrical wiring for the heavy wire string loops.

I hope I have answered your question and encouraged you to experiment.

Joseph Rogowski

[earthtonesaudio]

Hi Joseph,

Thanks for the reply. You've given me a lot to think about.

[Xaar]

Mr Rogowski , I have a few questions in regard to this famous alumitone pickup (the humbucker sized one only)




A LOT of questions

-What differences are there in the transformer section essentially between a humbucker sized alumitone and the new "death--bucker" alumitone?

-Concerning the C-transformer, what charecteristic should be considered for the laminated core:

high permeability or high flux saturation??
Apparently audio transfos in microphones are of the same type and have a core (considering a similar output at the secondary) made of high-permeability--low-saturation alloy as a 80%nickel-20%iron (permalloy etc) or even pure nickel. Would this do?

Which volume should the core represent in metal...
Any method to calculate this?

-More importantly, in the patent number 5831196 we can see the twin bobbins (of the c-transformer) wound in opposite direction (which seems normal since it's supposed to like an "interrupted" toroid transfo) but wired in PARALLEL ! How come not wired in series? And why do both bobbins have their wire ends soldered at one end on the CORE lamination itself ( the other wire ends in parallel are soldered together as the "hot" lead) ???

In resume: why in parallel, and secondly doesn't this interfere with magnetic flux through the core to solder both bobbins ends to the laminations as if it were GROUNDING leads?

Also, WHERE should the main ground of the pickup be soldered (or attached) on the aluminum frame exactly? does it have any importance?

I'm not an expert in transformers so please excuse my questions if they seem stupid.

Thanks in advance.

[David Schwab]

-What differences are there in the transformer section essentially between a humbucker sized alumitone and the new "death--bucker" alumitone?

More turns on the transformer. The regular Alumitone humbucker is 3.4K, and the Deathbucker is 5K.

[Xaar]

More turns on the transformer. The regular Alumitone humbucker is 3.4K, and the Deathbucker is 5K.

I read that on Lace's site, but I wondered just if there was something more (or different) than just a few turns more: different core, wire diameter and bobbin shape.

Geez, 5K is just in filtertron territory, of course the freq range has nothing to do.

Perhaps it's just like you think: the same old transfo with a few more turns.


Doesn't anyone here have this pickup (or any other alumitone) unassembled for studying it?

[David Schwab]

Perhaps it's just like you think: the same old transfo with a few more turns.

In this case the transformer will alter the tone of the pickup. The aluminum primary coil seems the same.

Doesn't anyone here have this pickup (or any other alumitone) unassembled for studying it?

I have a Transsensor P bass pickup I got used on eBay. The cover is so worn that it doesn't have the Lace logo anymore.

The pickup is epoxied into the case, but I have been thinking of peeling the case off and taking a peek.

The Transsensor pickups are the ones in the patent.

[bbsailor]

Mr Rogowski , I have a few questions in regard to this famous alumitone pickup (the humbucker sized one only)




A LOT of questions

-What differences are there in the transformer section essentially between a humbucker sized alumitone and the new "death--bucker" alumitone?

-Concerning the C-transformer, what charecteristic should be considered for the laminated core:

high permeability or high flux saturation??
Apparently audio transfos in microphones are of the same type and have a core (considering a similar output at the secondary) made of high-permeability--low-saturation alloy as a 80%nickel-20%iron (permalloy etc) or even pure nickel. Would this do?

Which volume should the core represent in metal...
Any method to calculate this?

-More importantly, in the patent number 5831196 we can see the twin bobbins (of the c-transformer) wound in opposite direction (which seems normal since it's supposed to like an "interrupted" toroid transfo) but wired in PARALLEL ! How come not wired in series? And why do both bobbins have their wire ends soldered at one end on the CORE lamination itself ( the other wire ends in parallel are soldered together as the "hot" lead) ???

In resume: why in parallel, and secondly doesn't this interfere with magnetic flux through the core to solder both bobbins ends to the laminations as if it were GROUNDING leads?

Also, WHERE should the main ground of the pickup be soldered (or attached) on the aluminum frame exactly? does it have any importance?

I'm not an expert in transformers so please excuse my questions if they seem stupid.

Thanks in advance.

Xaar,

You asked a lot of good questions.

Mr Rogowski , I have a few questions in regard to this famous alumitone pickup (the humbucker sized one only).

Both the Humbucker size and the Strat size Alumitone pickups use dual low impedance loops with a single magnet of opposite polarity in each loop. Since the magnet only is located under three strings it sounds more like a single coil with the strings only going over a single magnet. This is unlike a true humbucker high impedance pickup where a string goes over two sets of magnets or magnetic fields.

Looking at patent # 5831196, figure 17 you can see that the transformer coils are locared on one side of the center channel of the dual loops. This makes the two loops configured in a humbucking configuration.


A LOT of questions

-What differences are there in the transformer section essentially between a humbucker sized alumitone and the new "death--bucker" alumitone?
I have not seen the "deathbucker, but i can speculate how it might be configured. If you have a pickure of it's underbelly, please post it.

The Deathbucker may have two sets of coils, one on each leg of the inverted "U" shaped body shell. The current Alumitone shell has a provision for another set of coils on the opposite side. This is how the DDeathbucker could be configured to allow series and parallel connections of the output.

David's answer could also be correct in that it simply has more windings. A photo of the Deathbucker would help understand how tdis might be done.


[I]-Concerning the C-transformer, what charecteristic should be considered for the laminated core:[I]

high permeability or high flux saturation??

Yes

Apparently audio transfos in microphones are of the same type and have a core (considering a similar output at the secondary) made of high-permeability--low-saturation alloy as a 80%nickel-20%iron (permalloy etc) or even pure nickel. Would this do?

Yes. You can experiment with CSE187L (1:500 turns ratio) low frequency Current Transformers (CT) to make an Alumitone-like pickup with one of two transformers to form a low impedance primary loop. Then, send the CT secondary to a 500 ohm to 50K ohm microphone matching transformer at the amp or a microphone mixer input with a 250 ohm rating and a actual 2K ohm input impedance. Switching the CTs in series and parallel will change the tonal balance.



Which volume should the core represent in metal...
Any method to calculate this?

The size of the core structure has the primary purpose of coupling the high current low voltage going through the low impedance loop where it passes through the "C - shaped" laminates which from a toroid-like transformer around the metal low impedance loop shell.



-More importantly, in the patent number 5831196 we can see the twin bobbins (of the c-transformer) wound in opposite direction (which seems normal since it's supposed to like an "interrupted" toroid transfo) but wired in PARALLEL ! How come not wired in series? And why do both bobbins have their wire ends soldered at one end on the CORE lamination itself ( the other wire ends in parallel are soldered together as the "hot" lead) ???

I believe the coils could be wired either in parallel or series to change the pickup voicing. Also, this may help keep the noise level down on the high impedance side.

In resume: why in parallel, and secondly doesn't this interfere with magnetic flux through the core to solder both bobbins ends to the laminations as if it were GROUNDING leads?

I don't know why the coil would be attached to the lamination except to ground one side of parallel coils to the metal shell to minimize noise. If the coils were put in series then this laminate connection would not be desireable. I suspect thewse coils coil be wires to 4-conductor shielded cable like a 4 wire humbucker to have series and parallel wiring options.



Also, WHERE should the main ground of the pickup be soldered (or attached) on the aluminum frame exactly? does it have any importance?

It should be connected to the aluminum metal shell. Typically the leads of the Alumitone are two conductor shielded so that phase reversals of two alumitone pickups can be done easily.


I'm not an expert in transformers so please excuse my questions if they seem stupid.

Jameco sells the CSE187L CTs cheap so you can experiment. The size of the primary low impedane loop helps to voice the pickup tone. Start with AWG 12 and go up to to AWG 6 copper wire to experiment.


Thanks in advance.

No problem.

Joseph Rogowski

[David Schwab]

The Deathbucker may have two sers of coils, one on each leg of the inverted "U" shaped body shell. The current Alumitone shell has a provision for another set of coils on the opposite side. This is how the Deathbucker could be configured to allow series and parallel connections of the output.

David's answer could also be correct in that it simply has more windings. A photo of the Deathbucker would help understand how tdis might be done.

I'm just guessing, of course, based on the higher CD resistance. That's interesting about the second set of coils.

They mention on the site that the Deathbucker also has patents pending. I haven't looked to see what they might have filed.

I've been meaning to get one of those transformers to mess with.