How is the Suhr BPSSC working?

[Chuck H]

but you can't shield the top and that's where noise comes in.

The way this reads it looks like you believe that pickups only "hear" magnetic noise the same way they "hear" a guitar string, and this is certainly not the case. Magnetic noise can get into a pickup any way it hits the coil of wire. If the pickup cavity and pick guard weren't shielded there would be A LOT more noise getting to the pickup. (wood, as it turns out, is a poor shield against magnetic fields)

I think Lace has this covered. They have steel or iron bracket around all sides except the top. But that change the sound also.

Absolutely. I don't know what the phenomenon is called, but shielding tight to any inductor forces that inductors own EMF back upon itself, changing the inductance. I've tightly shielded pickups and heard this for myself. The pickup became less open sounding and a little squarky in the top end. It did reduce noise though.

[Mike Sulzer]

The way this reads it looks like you believe that pickups only "hear" magnetic noise the same way they "hear" a guitar string, and this is certainly not the case. Magnetic noise can get into a pickup any way it hits the coil of wire. If the pickup cavity and pick guard weren't shielded there would be A LOT more noise getting to the pickup. (wood, as it turns out, is a poor shield against magnetic fields)



Absolutely. I don't know what the phenomenon is called, but shielding tight to any inductor forces that inductors own EMF back upon itself, changing the inductance. I've tightly shielded pickups and heard this for myself. The pickup became less open sounding and a little squarky in the top end. It did reduce noise though.

The pick guard and cavity are shielded against noise made by elecric fields, not magnetic fields.

[Chuck H]

Right. Thank you for making the distinction... I was indeed talking about electric fields. Such as might be caused by transformers or motors. Pretty much anything that is an electromagnet.

Wouldn't a strictly magnetic field strong enough to cause noise also effect string vibration? and what makes a magnetic field like that? I always assumed that EMF meant electromagnetic field. Shielding does work against it.

[Steve A.]

Always late to the party!

I experimented with dummy coils in my LP Jr back in 2003. That was before the Chiliachki patent used in the Suhr system so I had a lot of misconceptions like thinking that the dummy coil should be as similar to the sensing coil as possible. P-90 coils are very easy to convert into dummy coils- just remove the screws and magnets and you are done. Although I haven't tried it yet the screw coil on a PAF-style humbucker should work, with perhaps half of the DC resistance of the P-90 coil. In most cases it is a lot easier to mount a thin bottom. On my LP Jr I put the dummy P-90 coil on the bottom of the pickup cavity which required some routing to allow for full adjustment of the sensing coil. I wired the dummy coil between the grounded lead from the real P-90 and ground, with a P-P pot switch wired as a shunt to remove it from the circuit. I posted sound samples on my site which I thought were impressive. With the added dummy coil the sound was a little bit more compressed and with more midrange but otherwise sounded like a P-90 to me.

Hum and noise and buzz. IMO it all depends on our electrical/magnetic environment. I'm not sure what is electrical and what is magnetic but I figure that covers most of the bases. If you are a very noisy E/M environment it will probably make your single coil pickup hum and buzz like a mofo. Spin yourself around 360 degrees and you may find a horizontal orientation that minimizes the noise. Or not if the E/M noise is coming at you from all directions like in a bar where the owner decided to put up strings of clear Christmas tree lights all over the place hooked up to cheap dimmers. BTW in a bar like that you may get some noise even playing a guitar with humbuckers. However if the guitar is properly shielded and the pickups have metal covers that should minimize that noise. For a moment consider a properly shielded guitar with P-90 pickups with metal covers (like on my '90's Epiphone Casino)- in that noisy E/M environment you are still going to get a lot of noise despite all of the shielding. When the E/M noise is not omnidirectional, if you rotate around in a circle you will probably find an orientation that minimizes the noise. And all of that shielding will reduce the remaining noise considerably.

My condo is a good example of E/M noise. About 10 years ago the damned neighbors had their TV cable outlet moved from the far side of their living room to the wall in common with my music room which had formerly been very quiet in terms of E/M noise. Whenever they turned their TV on all of my single coil guitars would hum like a mofo unless I oriented them in the right direction. That situation was what inspired me to screw around with dummy coils, and between that and the "bar from hell" mentioned above I had many opportunities to see what worked and what didn't work.

Since switching to lap steel with the pickup facing my ceiling I get noise even if I spin around on my pseudo-medical office stool. If I orient the lap steel vertically (like a regular guitar) it will reduce the noise considerably. But that is not an option for me.

I planned on adding a dummy coil to my new 10 string lap/console non-pedal steel but the one I just whipped together from 400 feet of 32GA magnet wire will not fit without routing which would weaken the body where two of the legs screw in. I reread the Chiliachki patent again and see that to follow his design I would have had to use something like 39GA magnet wire wound to 250 ohms to match a 7K pickup. I wound the wire on an aluminum soft drink by hand about 100 turns and then dipped it in a 16 oz Crock Pot I use for wax potting pickups to hold the wraps together. And then I crumpled the can and cut the top half off to allow me to slide the dummy coil off the can. After more dipping I bent the coil in the shape I wanted and wrapped black electrical tape around the coil.

The finished coil was bigger than I figured so it won't fit in my lap steel but I came up with a new idea that might work even better: I'm going to put the dummy coil in a Hammond box used for FX pedals, with two jacks, a footswitch and a 10k pot wired as a variable resistor across the dummy coil leads to adjust its intensity. Since dummy coils need to be wound in the reverse direction of the sensing coils, for some pickups the jack on the right will be the input, with others the output.

Having the dummy coil flat on the floor would be no good with a regular guitar, but it is perfect for pedal steels and non-pedal console steels mounted on legs since it will be parallel to the top of the pickup. Which works out good because most of the vintage console steels had single coil pickups, which need the dummy coil more than regular guitars that can usually be upgraded to hum-cancelling pickups. I am going to start with a metal box since strong E/H noise will penetrate shielding; if that doesn't work I will switch to a non-metallic box. And I will need to experiment with different dummy coils to see which one works the best with my menagerie of steels. I was just thinking that if the stomp box was a cube you could turn it on its side and use it with a regular guitar.

Now to test out this idea... I'll start a thread posting my results.

Steve Ahola

P.S. Here is a link to the Chiliachki patent used in the Suhr system:

http://www.blueguitar.org/new/misc/p...chiliachki.pdf


P.P.S. And here are links to some recordings I made demonstrating the noise reduction of the dummy coils:

http://www.blueguitar.org/new/mp3/sa...coil_strat.mp3

http://www.blueguitar.org/new/mp3/samples/p90_w_dc.mp3

http://www.blueguitar.org/new/mp3/sa...90dc_noise.mp3

[Steve A.]

Always late to the party!

I experimented with dummy coils in my LP Jr back in 2003. That was before the Chiliachki patent used in the Suhr system so I had a lot of misconceptions like thinking that the dummy coil should be as similar to the sensing coil as possible. P-90 coils are very easy to convert into dummy coils- just remove the screws and magnets and you are done. Although I haven't tried it yet the screw coil on a PAF-style humbucker should work, with perhaps half of the DC resistance of the P-90 coil. In most cases it is a lot easier to mount a thin bottom. On my LP Jr I put the dummy P-90 coil on the bottom of the pickup cavity which required some routing to allow for full adjustment of the sensing coil. I wired the dummy coil between the grounded lead from the real P-90 and ground, with a P-P pot switch wired as a shunt to remove it from the circuit. I posted sound samples on my site which I thought were impressive. With the added dummy coil the sound was a little bit more compressed and with more midrange but otherwise sounded like a P-90 to me.

Hum and noise and buzz. IMO it all depends on our electrical/magnetic environment. I'm not sure what is electrical and what is magnetic but I figure that covers most of the bases. If you are in a very noisy E/M environment it will probably make your single coil pickup hum and buzz like a mofo. Spin yourself around 360 degrees and you may find a horizontal orientation that minimizes the noise. Or not if the E/M noise is coming at you from all directions like in a bar where the owner decided to put up strings of clear Christmas tree lights all over the place hooked up to cheap dimmers. BTW in a bar like that you may get some noise even playing a guitar with humbuckers. However if the guitar is properly shielded and the pickups have metal covers that should minimize that noise. For a moment consider a properly shielded guitar with P-90 pickups with metal covers (like on my '90's Epiphone Casino)- in that noisy E/M environment you are still going to get a lot of noise despite all of the shielding. When the E/M noise is not omnidirectional, if you rotate around in a circle you will probably find an orientation that minimizes the noise. And all of that shielding will reduce the remaining noise considerably.

My condo is a good example of E/M noise. About 10 years the damned neighbors had their TV cable outlet moved from the far side of their living room to the wall in common with my music room which had formerly been very quiet in terms of E/M noise. Whenever they turned their TV on all of my single coil guitars would hum like a mofo unless I oriented them in the right direction. That situation was what inspired me to screw around with dummy coils, and between that and the "bar from hell" mentioned above I had many opportunities to see what worked and what didn't work.

Since switching to lap steel with the pickup facing my ceiling I get noise even if I spin around on my pseudo-medical office stool. If I orient the lap steel vertically (like a regular guitar) it will reduce the noise considerably. But that is not an option for me.

I planned on adding a dummy coil to my new 10 string lap/condole non-pedal steel but the one I just whipped together from 400 feet of 32GA magnet wire will not fit without routing which would weaken the body where two of the legs screw in. I reread the Chiliachki patent again and see that to follow his design I would have had to use something like 39GA magnet wire wound to 250 ohms to match a 7K pickup. I wound the wire on an aluminum soft drink by hand about 100 turns and then dipped it in a 16 oz Crock Pot I use for wax potting pickups to hold the wraps together. And then I crumpled the can and cut the top half off to allow me to slide the dummy coil off the can. After more dipping I bent the coil in the shape I wanted and wrapped black electrical tape around the coil.

The finished coil was bigger than I figured so it won't fit in my lap steel but I came up with a new idea that might work even better: I'm going to put the dummy coil in a Hammond box used for FX pedals, with two jacks, a footswitch and a 10k pot wired as a variable resistor across the dummy coil leads to adjust its intensity. Since dummy coils need to be wound in the reverse direction of the sensing coils, for some pickups the jack on the right will be the input, with others the output.

Having the dummy coil flat on the floor would be no good with a regular guitar, but it is perfect for pedal steels and non-pedal console steels mounted on legs since it will be parallel to the top of the pickup. Which works out good because most of the vintage console steels had single coil pickups, which need the dummy coil more than regular guitars that can usually be upgraded to hum-cancelling pickups. I am going to start with a metal box since strong E/H noise will penetrate shielding; if that doesn't work I will switch to a non-metallic box. And I will need to experiment with different dummy coils to see which one works the best with my menagerie of steels. I was just thinking that if the stomp box was a cube you could turn it on its side and use it with a regular guitar.

Now to test out this idea... I'll start a thread posting my results.

Steve Ahola

P.S. Here is a link to the Chiliachki patent used in the Suhr system:

http://www.blueguitar.org/new/misc/p...chiliachki.pdf


P.P.S. And here are links to some recordings I made demonstrating the noise reduction of the dummy coils:

http://www.blueguitar.org/new/mp3/sa...coil_strat.mp3

http://www.blueguitar.org/new/mp3/samples/p90_w_dc.mp3

http://www.blueguitar.org/new/mp3/sa...90dc_noise.mp3

[Mike Sulzer]

It is not a misconception that the dummy coil should be as much like the sensing coil as possible. That gives the best cancellation over the widest frequency range. However, you have to add actively if you want to avoid inductance increases. Why do you take the screws out of the P-90 coil? Steel in a coil affects the sensitivity to magnetic fields. With a humbucker pickup in a strong magnetic field, you can hear the removal of each screw, and so you must be having an effect of at least one db or so. Take out all six and you have a significant difference. To get best cancellation leave the screws in.

[Steve A.]

It is not a misconception that the dummy coil should be as much like the sensing coil as possible. That gives the best cancellation over the widest frequency range. However, you have to add actively if you want to avoid inductance increases. Why do you take the screws out of the P-90 coil? Steel in a coil affects the sensitivity to magnetic fields. With a humbucker pickup in a strong magnetic field, you can hear the removal of each screw, and so you must be having an effect of at least one db or so. Take out all six and you have a significant difference. To get best cancellation leave the screws in.

I believe that the main goal of the Suhr system is not just cancellation of the hum, but doing so transparently so that the single coil sound is as unchanged as much as possible. By using a dummy coil of considerably lower resistance than the signal sensing coil (like 250R vs 7k) when it is wired in series it has a lesser effect on the sound of the pickup. The Suhr system also has a 10k pot wired as a variable resistor which shunts the signal from the signal sensing coil to ground thus bypassing the dummy coil allowing you to fine-tune the hum-cancelling effect. There is a second 10k pot wired as a typical guitar tone control with a .047uF cap but from my experiments with series wiring I believe that it actually boosts the treble rather than cutting it. (That really freaked me out when I wired up a 2HB/2V/2T hollow body jazz guitar with a harness that optionally linked the two pickups in series with all of the volume and tone controls active. When I tried it out in series mode I thought that I had wired up the tone pots backwards and took everything out of the hollow bodied guitar to see where I screwed up, only to find that I hadn't made a mistake other than pulling out the harness needlessly. )

It was my understanding back in 2003 that a dummy coil was like a pickup but without a magnet or pole pieces. I guess that there are other varieties. In any case the Chiliachki patent used by the Suhr system uses a large area coil with no magnet or pole pieces. I liked the idea of making a coil with a heavier gauge wire with fewer turns since it could conceivably be something made without any kind of winding machine. Something that might be tedious but could be done on your dining room table with no equipment at all. When you need to stop or take a break a piece of tape can keep it from unraveling (do not try that with 43GA wire!)

Steve Ahola

P.S. My idea of putting a dummy coil in a floor pedal box per the Suhr System will not be as simple as I had thought it would. For the dummy coil to be connected in series you would need a TRS output from your guitar which would have to wired with signal ground and "chassis" ground isolated. Actually not necessarily an unworkable idea- when a mono guitar cable was plugged into the guitar the signal ground and chassis ground would be shorted together by the sleeve of the plug. You would need to use a TRS cable from the guitar to the dummy coil box which would have a stereo jack for the input and a mono jack for the output along with a switch to reverse the polarity of the dummy coil.

Another upgrade for the floor box- volume and tone controls for the output signal. Many pedal steel guitars lack volume and tone controls, figuring that you can just adjust them on the amp. One problem is that some PSG players switch back and forth between the steel and a regular guitar using the same amp which may make it necessary to readjust the controls every time that they switch. Also if there is a particularly strong output signal from the pickup it could push the input stage of some amps into distortion. If you plug a mono plug into the TRS input jack of the floor box, it would take the dummy coil out of the circuit so it could be used with mono output guitars strictly to control volume and tone.

[Mike Sulzer]

It is primarily the inductance of the dummy coil that needs to be kept low. It is inductance that sets the impedance of a pickup over most of the range, and so if you use a similar coil for a dummy, you are about doubling it. This lowers the resonant frequency with the cable capacitance. Thus the need for either an active circuit or a large coil.

I believe that the main goal of the Suhr system is not just cancellation of the hum, but doing so transparently so that the single coil sound is as unchanged as much as possible. By using a dummy coil of considerably lower resistance than the signal sensing coil (like 250R vs 7k) when it is wired in series it has a lesser effect on the sound of the pickup...

[Steve A.]

It is primarily the inductance of the dummy coil that needs to be kept low. It is inductance that sets the impedance of a pickup over most of the range, and so if you use a similar coil for a dummy, you are about doubling it. This lowers the resonant frequency with the cable capacitance. Thus the need for either an active circuit or a large coil.

Is there any particular circuit that you would recommend to amplify the signal from the coil?

I don't know if anyone has tried putting a dummy coil in a floor box but it does allow for much more experimentation than you might want to do on a guitar. It would be of little use except for a steel guitarist whose steel will be in a fixed position parallel to the floor. I'm going to go ahead and use a P-90 coil for the dummy but with the volume and tone controls of the Chiliachki patent added at top panel controls. I did get a little humcancelling action with the 65 ohm coil (you could hear the hum level drop a little bit but nothing to write home about.)

Transparency is not a requirement in this particular project as long as the end result is something usable musically***. Right now the only option that most steel guitarists have is the EHX Hum Debugger which evidently is a very narrow notch filter centered around 420hz (it could have other frequencies as well- I believe that 420hz is the 7th harmonic of 60hz.) There is a hollowness to the sound and with an open chord strum you can hear that a lot of the richness is gone. (It would be great if it had a blend control to mix in some of the original unprocessed signal- in many cases eliminating half of the hum would be fine if the sound was more natural.)

I wanted to button up my new 10 string console steel so I wired pickup lead that would normally be grounded to the ring terminal of a 1/4" stereo jack. Plug in a regular guitar cable and it will connect the ring to the grounded sleeve for normal operation. Plug in a stereo cable going to the floor box and it will allow a dummy coil to be wired up in series.

Steve

*** We all have preconceived ideas about how a guitar should sound but not so much with steel guitars.