Ultra Low Impedance Pickups

[tbryanh]

You could also use three transformers and go up one string and back to the string next to it, with the strings being in series.

Yeah, that looks like it would work.

I am wondering which strings would be best to pair off as far as noize and tone goes?

[tbryanh]

How would the sound of 3 transformers differ from the sound of 6 transformer?

[tbryanh]

As the string impedance changes depending on which fret is used (the length of the string chages), how does this affect the tone?

[bbsailor]

Yeah, that looks like it would work.

I am wondering which strings would be best to pair off as far as noize and tone goes?

The problem is that you have three sets, an odd number, that will not balance as well as if it has an even mumber to reverse the phase to make it humbucking.

Just play with it to see which strings balance best.

From my string measurement impedance here are six string measurments for a set with a 11 high e string set on a Gibson scale using the Extech LCR meter at 1KHz.

low E: .679 ohms
A: .892
D: 1.095
G: .774 (plain)
B: 1.008
E: 2.014

Joseph Rogowski

[bbsailor]

As the string impedance changes depending on which fret is used (the length of the string chages), how does this affect the tone?

It should not change the matching too much as the transformer will still be 5 to 7 times higher than the actual string impedance.

Joseph Rogowski

[bbsailor]

How would the sound of 3 transformers differ from the sound of 6 transformer?

The only thing you give up is independent control of each string.

Joseph Rogowski

[JohnnyBravo]

Hi Mr Joe Rogowski!

First of all I must say that i'm not academically prepared to understand most of the contents you share in this forum. I'm a musician and a formal student of Sciences of Comunication, so this topics are hard for me to understand obviously, but I still want to understand what is going on in my guitar. I own a set of alumitone pickups in my strat and pretty in loved with them. But I don't understand clearly what means and implies the fact that this pickups work based on current rather than voltage. Perhaps it's a silly question but I would really aprecciate an answer.

Regards from México, Thanks beforehand
Fernando Alpuche

[bbsailor]

JohnnyBravo,

Guitar pickups have been made for the past 50 years around the idea that the pickup must produce enough voltage to drive the input impedance of tube type amplifiers with a high input impedance of about 1 meg ohms. Generally, in order to produce enough voltage to drive this type if input impedance a voltage output level of 100mv (one tenth of a volt) to about 500mv (0.5V). The pickup output voltage had to be higher than the noise to produce a relatively noise-free signal. In order to achieve this the early designers of pickups: Rickenbacher (spelling?), Fender, Les Paul, and others chose to use the available magnets of their time and wind enough turns (5000 to 10000 turns) of very fine wire (AWG42 to 43) to obtain enough voltage output to drive tube-based public address (PA) amplifiers with high impedance pickups. Guitar amps, both tube-bases and solid state, then evolved using the same PA tube-based input impedance designs but still needing 100 to 500mv pickup output levels. This fundamental concept has driven guitar pickup and amp designs to this day.

Microphones produce an output of about 2 to 5 mv, a very low voltage. However, they do this using a balanced line, low-noise design to use additional amplifier gain rather than many turns of wire around the magnets. Transformers are used in dynamic and ribbon microphones to increase the low impedance of voice coils or ribbons in microphones (look up "ribbon microphone" on the web) to produce an output impedance in the range of 150 to 250 ohms. The input impedance of microphone input circuits is in the range of 1500 to 2000 ohms, use three pin connections to produce a low noise "balanced line" (look up this term also on the web) and use a higher amount of gain to raise the lower level of microphones (compared to guitars) to produce a higher quality output.

Why higher quality? The high impedance guitar pickups have a high frequency impedance in the range of a few hundred thousand ohms at resonance and the capacitance of a common coax guitar cable affects the tone of a guitar, like turning down the tone pot slightly. Microphones with a low impedance output (150 to 250 ohms) are not affected by the connecting cable and can be a few hundred feet long with minimal tonal affects. Les Paul designed his recording guitar model using about 500 to 1000 turns of AWG 28 wire and used a microphone matching transformer at the amplifier end of the of the guitar cable to minimize high frequency losses. Unfortunatly, the high impedance pickup design took hold and this continues to this day. See: Current Electric Guitar Design Deficiencies for more details.

The Alumitone pickups use a very unique design in that the alumium frame of the pickup actually acts like a single turn, very low impedance loop around the magnets. On the side you will notice a laminated transformer core wrapped around the alumium frame that acts like a transformer with the primary (low impedance alumium loop) being transformerd into a higher impedance and higher voltage to match a high impedance guitar amplifier but with less wire than a traditional high impedance pickup. This minimizes the affects of high impedance guitar cables as the Alumitone pickups have a lower impedance. The current generated in the Alumitone alumium frame by the string vibrating over the magnets produces a high current but a very, very, very low voltage. The coils under the pickup frame actually transform that higher current to a higher voltage based on the amount of turns or very fine wire wrapped on the coils under the Alumitone frame. Look up "transformer turns ratio" on the web.

When you put a matching transformer (4 ohms to 10,000 ohms or higher) across a guitar string (connected behind the nut and bridge), the voltage generated on the string is transformed to a higher voltage, enough to hear the vibrating string on a guitar amp but only when a magnetic field is near the vibrating string. Try it!

If you wind a guitar pickup with 600 turns of thicker wire (AWG 28 to AWG32) and then connect the output of this to about a 500 to 50,000 ohm microphone matching transformer (Look up "Shure A95U") you can make a Les Paul-like recording low imepdance pcikup where the transformer trurns ratio of 1 to 10 makes the 600 turns look like about 6000 turns.

If you are interested in guitar pickups and follow my web look up recommendations, you will begin to see that very low impedance coils have high current generated in the very low impedance loop (less than one thousandth of an ohm) of heavy wire and the "current transformer" transforms this to a level that can feed a 3-pin XLR microphone input with a wider bandwidth for a better high frequency response.

I cannot respond to any more questions until about the middle of August.

Thanks for your interest in this.

Joseph Rogowski

[Tubebass]

Many years ago.....

I'm a longtime live sound guy. Back in the 80s I did sound for a prominent Canadian folkie who had his Martin set up this way as I understood it at the time. All strings in series, and three magnets on the body, one for each pair of df strings. Output taken at the bridge end of the E strings with NO transformer, just straight to the endpin jack. It worked well into my DI and sounded great as I recall.

How about connecting all 6 strings in series and using one ribbon-mic transformer?

This would work with only one transformer.You could use thin copper foil in the nut between adjacent strings to short them together between the E-B, G-D and A-E and shorting the B-G, and D-A at the bridge.
If you make a plexi bridge, you could build the transformer into the bridge and even put a stereo mini 1/8" jack to connect to an amp with minimal guitar mods for a balance output to feed a mic mixer rather than a guitar amp.

I think I would like to try it this way first.

Good plan!! You could quickly build a mock up and play with it this way.

If the strings were connected to each other in a zig-zag fashion, it seems there might still be a humbucking effect.

I don't think so, but give it a try.
This puts all the strings in series and you could use an 8 ohm 70 volt line matching transformer 1 or 2 watt is about a 1" cube. MCM part number 555-7117 for $2.52 VIP price in catalog #SC12.

Have fun.

Joseph Rogowski

[Tubebass]

How about connecting all 6 strings in series and using one ribbon-mic transformer?

I'm a longtime live sound guy. Back in the 80s I did sound for a prominent Canadian folkie who had his Martin set up this way as I understood it at the time. All strings in series, and three magnets on the body, one for each pair of of strings. Output taken at the bridge end of the E strings with NO transformer, just straight to the endpin jack. It worked well into my DI and sounded great as I recall.

[bbsailor]

How about connecting all 6 strings in series and using one ribbon-mic transformer?

I'm a longtime live sound guy. Back in the 80s I did sound for a prominent Canadian folkie who had his Martin set up this way as I understood it at the time. All strings in series, and three magnets on the body, one for each pair of of strings. Output taken at the bridge end of the E strings with NO transformer, just straight to the endpin jack. It worked well into my DI and sounded great as I recall.

Tubebass,

You are better off using some form of input transformer to convert the low impedance of six-in-series-strings to something like 1.5 to 2K to feed a microphone low-Z XLR input. Feed the output of the transformer balanced and ground the strings to the XLR ground for the lowest noise. The actual voltage generated on the strings themselves (input level to transformer) is in the range of a few milliivolts so a transformer will help improve the sighal to noise ratio and bring the output well into the 10 to 30 millivolt range depending on magnet strength, location along the string length over the body and closeness to strings. Use heavy wire between the outside E to E string series connection and mount the transformer close to the rear of the bridge either on top for testing purposes or under the bridge for a more permanent and less visible mounting.

Play with positioning magnets on the various body positions betwen the neck and bridge to emphasize different harmonics. Two flat type magnets 1" X .75" X .187" with a .187 hole in the middle (See RadioShack.com for a package of 5) work well near the bridge, mounted with double sided foam tape. Add to that the same magnets on a custom wood bar that mounts in the sound hole, like an add-on pickup and you can get some variation in sound quality. Use .125" thick rubber under the magnets and you can mount them with a screw and fine tune the magnet height to balance the sound output. This is a great setup for tonal experimentation.

You should get a sound that is closer to an acoustic sound than a traditional electric guitar sound as there is no classic resonant hump in the middle of the audio spectrum where the ear is most sensitive.

For even more sound control, you can use three transformers with adjacent string pairs shorted together at the nut to have three outputs that can be electrically and mechanically (with magnet position and closeness to strings) adjusted.

Most microphone preamps are designed to work with inputs in the range of a few millivolts up to about 25 millivolts. Keep the noise level low and the full fidelity of the strings acting as the active elements of a ribbon microphone can be done very easily.

Let us know how your experiment works out?

Joseph Rogowski

[Tubebass]

Had an opportunity to speak to the aforementioned Canadian folkie as his tour came through our town last night. Turns out that (big surprise!) my memory sucks! Apparently his guitar was set up as follows: Brass nut, strings in pairs (E and A, D and G, B and E) with the three pairs in parallel. It did use a Jensen transformer but I didn't get a model number. He said the magnets were ceramic, with the poles alternating, that is, the outer two magnets had the north pole up while the center one had the north pole down. He also confirmed that the gain before feedback with this setup was very good.

[jrfrond]

Bass players are more open to the more hi-fi tone of low Z pickups.

Of course, Alembic's State-Variable LPF with it's switchable resonant peaks allow you to go the other way if you'd like, i.e. taking the low-Z pickup sound and allowing you to dial-in whatever resonant peak amplitude and frequency you'd like.

[bbsailor]

Had an opportunity to speak to the aforementioned Canadian folkie as his tour came through our town last night. Turns out that (big surprise!) my memory sucks! Apparently his guitar was set up as follows: Brass nut, strings in pairs (E and A, D and G, B and E) with the three pairs in parallel. It did use a Jensen transformer but I didn't get a model number. He said the magnets were ceramic, with the poles alternating, that is, the outer two magnets had the north pole up while the center one had the north pole down. He also confirmed that the gain before feedback with this setup was very good.

Tubebass,

No problem with your memory as it happens to all of us. The key thing is that you remembered a unique way the strings were used as moving coil pickups, much like the ribbon in a ribbon microphone. Look for a ribbon mic transformer on the Jensen web site. It has a higher turns ratio than normal input transformers. The transformer must be mounted near the bridge so the wire resistance between the three sets of parallel strings and the transformer is as low as possible. If the transformer has a low impedance output. like to feed a mic input, then the turns ratio will be about the square root of .5 ohm divided into 150 ohms or about 1 to 17, or possibly higher. With this setup you would be sending between 10 and 20 mv into the mic input after the transformer.

I am still trying to wrap my mind around the alternate polarity: E-A outer pair (north), D-G center pair (south, B-E outer pair (north). He might have reversed the phase of the center pair in an attempt to minimize hum?

Maybe others can comment on this?

Thanks for the update.

Joseph Rogowski