PG Music Home Forums General Discussion Off-Topic OT, wide band audio amp with a 5Hz bottom end?

I know there are a number of people here that work in the audio industry and others that just know a lot more about it than I do so I'm posting here.

It's for a future project I'm working on. I'm looking to build something that will create a pulsed electromagnetic field in discreet frequencies from 5Hz to 200Hz. The 200Hz is easy but the 5Hz is the problem. I found a "reference amp" that went down to DC but the price range was out of this world.

It needs to be 100W, preferably mono or stereo bridged. 2 or 4 ohms would probably be perfect.

Any suggestions? I'd like to also minimize the cost.

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I figure I could create the square wave input with a computer or Arduino board, feed it through the amp, and build a coil to create the electromagnetic field. I might need help with the coil too, but I figure I can wind a coil, buy or preferably rent a gaussmeter and do some experimentation.

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You might ask what I'm building? I want to build a PEMF (PEMFt) device (google that if interested).

Here is the back story:

My mother-in-law has Parkinson's disease. Brother-in-law Bill works to connect venture capitalists with people needing investments. Brother-in-law Kevin is a world famous doctor (lectures other doctors all over the world).

So Bill was trying to connect investors with a guy who is building PEMFt machines to be sold to the medical profession. PEMFt is approved for pain clinics, bone repair, and veterinary medicine in the USA and a lot of other uses in Europe, Australia and other countries. In some of those other countries PEMFt has shown to help a large percentage of Parkinson's patients. Kevin says it definitely won't hurt to use the machines and there is a chance it might help.

Parkinson's isn't curable and the medicines that treat the symptoms have less and less effect as time goes on, so anything that can slow the eventual decline and perhaps even show some slight improvement is a good thing.

I read a lot about PEMF/PEMFt and it seems like proverbial "snake oil" - too good to be true. But Kevin says it definitely won't hurt.

The guy building the machines that Bill is trying to connect to investors doesn't have FDA approval to sell them yet (it's a loooooooong process), but is letting people use them while he takes notes and evaluates the progress or lack of progress of the people that come in. He isn't allowed to charge money, so he has a tip jar to help pay for the electric consumption.

OK it's getting like a B movie, isn't it??? Waiting for the "Bride of Frankenstein" to appear at any moment (she was hot, wasn't she? -- and that hair-do -- wow!)

OK to get serious again...

So we figure, it won't hurt, and we bring mother-in-law down for a month's worth of treatment. The problem is that it's 2 hours each way in moderate traffic, and another hour for treatment - and at 5+ hours used up, the day for us is shot - as self-employed people that means no income generated. But mom is worth it. So we did it for a month.

Problem was complicated by mom needing surgery for arthritis in the neck and got a portable PEMF device to help the bones grow back. The portable device was programmed to die in 90 days.

While we were taking mom Leilani and I figured, it wouldn't hurt so why not spend the hour getting zapped instead of sitting in the waiting room. After a month I noticed much better eyesight. I'm farsighted and even when these glasses were new, I couldn't read tiny type. Now with my glasses I can read things I couldn't read with a magnifying glass and my glasses when they were new! I also noticed a little finger that I injured many years ago that gave me pain while playing guitar and certain notes on the saxophone doesn't hurt at all an more. Also a sharper and quicker mind. Leilani noticed improvements as well. So maybe it isn't snake-oil after all.

Well they sell home units, but (1) they are underpowered by comparison and (2) at least $4,000 each. The ones they use that are proper powered for pain clinics and race horses cost $20,000 and up. OUCH!

So I figure I can build something that creates an electromagnetic field, after all, that's what the voice coil in a speaker does. So I contact an engineering friend who gave me a few pointers, reassured me that my thinking is right, and I'm out to build a PEMFt machine that isn't 4 hours away. They won't have the automatic control for frequency and timing that the expensive units have, but I can set frequency with the signal generator and use an alarm clock for timing.

At least investigating if it is affordable. I figure I can produce the square wave. I've even seen old Heathkit devices for sale on eBay.

So the biggest problem now is an affordable power amp that can go down to 5Hz. Once I locate that, then I'll investigate the gaussmeter and coil construction.

Any help with the amp?

Thanks,
Notes

First thing to know is the Impedance of your coil...

The Impedance is important because any amplifier you find will have to be able to develop your required 100W into that impedance.

So what is the size of this coil, what is the gauge of presumably copper wire of this coil, does the coil have a ferrite or iron core in it or is it an air core?

For something as you describe, I'm thinking that a full on Audio amplifier may not be needed, although it is "off the shelf" -- what you describe likely does not need to be a High Fidelity amplifier. That could then make the entire process a lot less expensive. Could be as little as a couple or four FET outputs on a heatsink with a small driver board. (For pulsing a coil with sqarewaves from the given ~5hZ to 200KHz, a signal generator or waveform gen would be $$$ OVERKILL. A 'Triple Nickel' LM555 IC and a handful of components can be used as the generator. And FETs may not be the best route, either, I'd consider the lowly SCR (Silicon Controlled Rectifier) as the driver, definitely.)

Feel free to PM me, Bob.


--Mac

Square wave pulse? Sounds like good old CW to me.But faster.LOL. Find an old Crown DC300. They went down to DC.

I would think that portable Pain Management devices would be of interest to the Veteran's Administration (VA) or Disabled American Veterans (DAV) and they have $$$ to throw at it. I will help in any way possible, Bob. Another idea might be to contact medical schools and get the school involved, perhaps as a doctoral thesis project.

Addendum: I have one VA Dr friend who is a Psychiatrist and fellow musician who, if nothing else, could open some doors for you.

I have no intent on marketing this thing. FDA approval is both expensive and time consuming. There are already approved devices out there used in pain clinics in the USA and for other purposes in other civilized countries. Plus I don't want the responsibility for anyone else's health.

If you google PEMF and PEMFt you will find the applications for this to be widespread. Arthritis, vision problems, bone regeneration, nerve regeneration and tons of others including to relieve the symptoms of Parkinson's Disease. PD is a brain disease. Among other things it causes limb tremors, which the drugs mostly control, but also, PD patients fall a lot as the brain and the legs sometime don't coordinate. This is a severe problem as mom hurts herself when she falls. She lives alone and refuses to go into an assisted care facility.

So if I can build this thing, it will definitely continue to help my eyesight, finger injury, and brain quickness, and if it relieves mom from one fall, it's worth the money.

And I forgot to mention. I've had bursitis in my hip since I was a teenager. It's a family thing on my father's side (thanks Dad). All traces of it are gone. PEMFt is supposed to work for arthritis too.

I'd still be taking her to the already invented machine, if it were not a 5 or more hour day and a half tank of gas.

The Crown amp looks good, and there are a lot of them for sale. Thanks John.

I might go with the signal generator instead of the computer as then I could rack everything together.

All and all I want the field to be 20 - 30 Gauss. I haven't investigated which frequencies do which job yet. There is a lot of research to be done before I start, and I'm gigging a lot this time of year, so I don't expect to have it done next year.

And Mac, a PM is coming your way.

Thanks all.

Any more info is appreciated.

Bob

One more thing, I read that NASA uses PEMF for manned space flight as human life is depending on the natural PEMF of planet earth which is much weaker in orbit. The more I research PEMF the more amazed I am. Like I said, if I didn't have first hand experience with the benefits, I'd think this kind of thing to be akin to quackery.

It's Monday, no gig today, so I'll catch up on some Norton Music stuff. Birthday gig tomorrow and then more holiday parties. Life is good!

I think all I need now is the formulas or advice on winding the coils. The will be air core (or human body part core), big enough to fit a human head into, and 4 ohms impedance. I'm supposing the variables are wire gauge, number of windings, and diameter. The field should be 20 - 30 Gauss, and I need to find the formulas for that.

Notes

How about a rack mount analog synth set to square wave. Not sure if it'll go down to 5 Hz.

Notes, yes, the good old Crown DC300/DC350 series amps will go right down to DC.

Take a look at "function generators" rather than "signal" generators, too.


--Mac

Another thought I also have is this:Are you going to want and rectify the output so that the coil always sees the same polarity. I may not be saying this right but I think you know what I mean. If the output is actually AC even though square wave the magnetic field will also switch poles North/South based on this oscillation. Maybe what you really want is pulsating DC? AKA rectified AC but unfiltered.

Hmm, not sure. Rectified DC seems to make more sense and switchable N or S polarity.

Thanks again.

Just had a quick look - couldn't find a NASA patent but did find a trademark..?

This patent information did come up though - haven't read 'em so I don't know if they'll help:
http://www.google.com/patents/US6132362
http://www.google.com/patents/US5181902
http://www.google.com/patents/US5743844
http://www.google.com/patents/US6443883

Thanks Lawrie - this could be a gold mine.

I also found these:

http://patentscope.wipo.int/search/en/de...r=&maxRec=1

http://patft.uspto.gov/netacgi/nph-Parse...p;RS=PN/7335156

Found a book translated from German that says this cures tinnitus in a large percentage of cases. This might make this thread on topic, since many musicians suffer from tinnitus.

Notes

I think I'd REALLY like to see the details of what you eventually come up with...

I'll share, but of course, you accept full responsibility and use at your own risk.

Of course, if anyone wants to help with the research, we can make it a group project.

The possibility of reducing tinnitus, relieving arthritis, improving nerve conduction speed, regenerating nerves, better vision, and speedier brain functions are things that many musicians can benefit from.

Early gig today, so I don't have much time to google. My next step is to find out if it's really a square wave or pulsed on/off. Gigs straight through Sunday too. It's a great time of the year to be a musician in Florida.

Notes

Notes, there's an online square waveform generator here: save to .wav is part of the page. Burn to CD. Done.

http://www.audiocheck.net/audiofrequencysignalgenerator_squaretone.php

-Scott

Thanks Scott. They are of short duration, but I'm sure audacity can fix that after downloading.

Plus I'll have to make sure the CD player will go down to 5Hz

I also found a "Spectro Signal Generator" - shareware for about $10 - I could use a laptop if the USB to Audio interface has a wide enough bandwidth. I checked the manual for my Edirol units but bandwidth is not noted in the specs. I suppose I could go computer to computer and use Audacity for a check.

Right now I'm trying to find out if I really need a square wave or more of a pulsed wave (for lack of a better term: a square wave with no zero crossing).

But I've got a one-nighter gig every day until Christmas Eve so my googleing and/or testing will be limited until after Christmas.

Bob

Haven't had a lot of google time, but so far this is what I suspect:

The source is not really a square wave that goes from + to - but either from + to 0 or - to 0.

More googling next week. Early setup for another gig today.

Notes