Suggestion for Brad Sarno

William Peters · Post by **William Peters** » 8 Sep 2004 3:25 pm

Brad,

Knowing how you like to engineer audio equipment for steelers, I have a product suggestion for you.

This would be for solving the hum problem with single coil pickups.

Here's my idea.

1) Create a dummy pickup (sensor) that could be mounted on the guitar, as close to the real pickup as possible. The purpose of this sensor would be to sense the electrical noise that impinges upon the actual pickup. It would not need to be anywhere near as large, or need the have the same impedance.

2) Add a sense coil input to your Black Box circuitry that it would take this signal, and mix it in (180 degrees out of phase) with the buffered signal from the guitars pickup, thus nulling out the hum or other noise.

The sense coil could be standardized, not individualized for different guitar pickups, as long as your BB had a phase adjustment for the sense coil. With a little help from a PIC microcontroller, it could be made self-nulling.

This came to me while reading another thread about hum, TrueTones, and NV112s.

------------------
Bill

http://www.wgpeters.com
Mullen RP SD12U, ART-SLA, Tubefex, Vamp-Pro

Ken Fox · Post by **Ken Fox** » 8 Sep 2004 4:24 pm

Kind of sounds like my Bill Lawrence Tele pickups. They are really a stacked humbucker arrangement, but the bottom coil does not pick up any sound, just cancels out the hum. Still sound a lot like a Tele, too!

Will Holtz · Post by **Will Holtz** » 8 Sep 2004 6:54 pm

I was not aware of how a humbucking pickup works, so I looked it up. If anyone else is interested this has a nice little write up.

Ken Fox · Post by **Ken Fox** » 9 Sep 2004 7:08 am

Thanks Will, that is a great article!!!

Brad Sarno · Post by **Brad Sarno** » 9 Sep 2004 10:12 am

Wow Bill, pretty fascinating idea. I've done a small share of pickup winding in my time, but what you suggest sure feels beyond my field of expertise. It seems feasable on the surface though. Since the humbucking is about phase cancelling out the noise outside of the magnetic field while the strings inside the field induce the in-phase current in the coils, your idea seems to make sense. I'm personally not really equipped to experiment in that realm, but I'd love to see someone take it there.

What I do know is that after all these years (50+) of seeking that holy-grail of making a humbucker sound as sweet as a single coil, it seems that someone would have refined that technology by now. But here we are, still seeking. I have heard about a guy who is experimenting with an extra coil underneath a unique magnetically shielded plate to accomplish the same thing, but I don't know where that research stands today.

As far as implementing that idea into the Black Box, it seems a bit complex electronically since the Box is currently so basic of a circuit. Maybe this is something for Jerry Wallace or Bill Lawrence to delve into even further.

I'm kind of simple. I use a True-Tone when I can, but if the gigs are full of hum and buzz, I'll use an E-66 humbucker.

Brad Sarno

Bill Terry · Post by **Bill Terry** » 9 Sep 2004 10:17 am

Alembic has been building basses with 'dummy' noise cancelling pickups for years.. Here's one..

http://www.bassnw.com/Special%20Order%20Basses/Basses/Alembic/alembic_series_I_8_st.htm

[This message was edited by Bill Terry on 09 September 2004 at 11:19 AM.]

Kevin Mincke · Post by **Kevin Mincke** » 9 Sep 2004 10:40 am

Brad, your email is not working.

William Peters · Post by **William Peters** » 9 Sep 2004 1:23 pm

Brad,

Ok, I thought it might be up your alley.

I'm a radio frequency person myself, hardly ever get below 30 mhz.

Bill,

Its pretty easy to build the dummy pickup, but the problem is that it has to be made to match the active pickup, and since it is no doubt passive, will result in a change to the active signal.

What I was thinking of was using some active electronics like Brads tube buffer circuit to subtract out the hum without affecting the single coil tone.

Well the idea's out there if anyone wants to jump on it.

------------------
Bill

http://www.wgpeters.com
Mullen RP SD12U, ART-SLA, Tubefex, Vamp-Pro

Don Walters · Post by **Don Walters** » 9 Sep 2004 2:08 pm

Isn't the hum due to the 60 Hz provided by the power company? And isn't that frequency maintained very precisely, at least in North America? Couldn't a very narrow filter of that frequency somewhere after the signal leaves the pickup eliminate or at least reduce the hum, without degrading the rest of the pickup's spectrum?

This may be a naive thought from a layman, but ... ?

If my True Tones had half the hum they have now, I'd be very happy.

Brad Sarno · Post by **Brad Sarno** » 9 Sep 2004 3:25 pm

My email is working again.

Brad Sarno

Donny Hinson · Post by **Donny Hinson** » 9 Sep 2004 3:42 pm

You're right, Don. The 60-cycle line frequency is maintained to within thousandths of a percent. A 60-cycle notch filter could be designed into the circuitry of the average solid-state amp for only a couple of dollars. I'm really surprised no manufacturer has offered it.

Maybe the manufacturers who are devoting all that time and money attempting to "model" different sounds will get smart and start "modeling" silence too!

Brad Sarno · Post by **Brad Sarno** » 9 Sep 2004 5:25 pm

Yea, but if you try to notch out 60Hz, you'll also be notching out any musical notes played near that notch. That happens to be real close to an A# and B. Those notes would disappear when you played them. Also, even though the AC noise comes from a 60hz sine wave, there are the overtones of that frequency that are often louder and noiser than 60Hz itself. You've got the whole harmonic sequence coming from the 60Hz. If you remove 60Hz only, you'll still be left with a loud 120, 180, on up and also some buzzy high frequencies that are harmonic artifacts of that tone. To truly notch out the 60Hz hum, it would take some very fancy multi-pole filters, and at each pole, you'd be also removing musical notes along with the hum and buzz, not to mention you'd be adding loads of nasty EQ phase distortion into the sound. If it were as simple as just filtering out 60Hz, we'd probably see it implemented in all kinds of gear.

Brad Sarno

William Peters · Post by **William Peters** » 9 Sep 2004 5:40 pm

Brad,

How right you are, its not just 60 hz, but a broad spectrum, not to mention those pesky police radio receptions..

The Peavey Tubefex has a 60 cycle hum filter. Its effect designator is HF, but like you say, it takes a lot of good stuff out too. The first time I tried it, I slide my bar over the frets, and found there is a dead spot where almost all sound disappeard. Not what I was expecting.

------------------
Bill

http://www.wgpeters.com
Mullen RP SD12U, ART-SLA, Tubefex, Vamp-Pro

Donny Hinson · Post by **Donny Hinson** » 11 Sep 2004 4:36 am

A properly designed notch filter would put the 60-cycle hum component 25-30db down. It would have little or no effect above 62 or below 58 cycles. Yes, you can make the notch that deep and narrow, and it's not really sophisticated, either. All it takes is an op-amp, and a precise R/C network.

In some environments, sure, the harmonics of the line frequency generated by neon lights, flourescent lamps, and dimmers would still create noise...but I could live with them.

Half-a-loaf is better than none!