The XR7 Pickup Identity Case... (so far)

Dix_

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NOTE: Due to the 10,000 character limit I've had to split this post into 2 parts. Also, I guess you need a certain number of posts before your posts can go live instantly. So, for those of you hoping for actual physical evidence, hold onto your shorts, that's in Part 2

Over the years I've seen questions now & then about what a good replacement for a bad XR7 pickup might be, or what one sounds like.

Since Gary alluded to it a bit ago in another topic, I figured I might as well go ahead and give everyone else here my case for the XR7 pickup being nothing more than the Dimarzio Super2 with a set of different looking polepieces.

That conversation was a part of a greater one that led to me being the new caretaker for the blue '82 X-79 featured on his website. I now have a trio of X-79s. 2 genuine excellent condition "survivors" (including Gary's), and the battle worn "player" that I play on a semi-regular basis with the usual headstock repair, and the finish literally worn off the neck in places.

Now, let me start by saying that I'm by no means a pickup expert. However, I do know just enough about electronics to be really, really dangerous.... Meaning, I'm just dumb enough to have something go "poof" when I turn it on, & then be able to follow a schematic just enough to figure out where I effed it up & fix it.

That coupled with the fact that in a former 1980s life I spent enough time as a bass-player-turned-live-concert-sound-engineer to learn just a little about how all that electron-flow stuff related to what moves our auditory receptacles and the sometimes shapely backsides of certain females of the species.

Also, perhaps just as important as all that, I'm old enough to have been around back then with just enough technical curiosity to be paying attention. Because, in my mind, just as important to the actual physical similarities & the numbers, is the historical evidence & circumstances of the time.

For those of you who prefer to sleep through history, feel free to skip down to the numbers & pictures below in part 2.... if it’s there... if it isn't yet, go take a nap & come back later. Suffice to say that, IMO, you can't approach a 1970's mystery with a 21st century mindset. If you weren't alive back in the 1970's and/or don't know anything about the history or the times, then maybe the 1st part of this will help you make some sense of how the reality of 2019 bears little meaning in what happened a full 40 years ago, when the whole replacement pickup industry was still crapping in it's diapers.

On that note, for those of you who might care, I related an abbreviated version of the history to Gary, which I'll expand on here.

Begin dream sequence....

The year is 1978. A young guitar player sees an ad in a magazine that his rock star hero uses a certain pickup in his guitars. He calls his local music store, orders a pair of the pickups, and then installs them in his cheap import Les Paul copy. He plugs in the guitar expecting magic. He gets no real apparent difference from the pickups that he took out of it.

But, why????


Return to present day....

As we sit here in 2019, your options for pickups are nearly endless. Dimarzio, Duncan, EMG, the list goes on... and each of them has dozens, or even hundreds, of models. All in minute varying degrees of dark to bright, mid-scooped to mid-boosted, and outputs from tens of millivolts to well over half a volt.

20, or even 30, years ago the situation wasn't really all that much worse. Dimarzio's 1989 catalog featured 17 different humbuckers & 11 different single coil options.

But, if we charge up the flux capacitor, jump in the Wayback Machine, & drop ourselves in the middle of the 1970s it was a whole different ballgame.

Prior to 1976 the aftermarket pickup market was pretty much non-existent. If you had a pickup that went bad or wanted "something different" back then you had very few choices... You salvaged one out of a repair shop bone pile, ordered a replacement from the manufacturer (which may not have been possible with some odd/off brand guitars), or you knew someone who could rewind it for you. And you could count those guys on the fingers of one hand. They had names like Bill Lawrence, Larry Dimarzio, & Seymour Duncan. & they were busy guys with a pretty exclusive clientele... I hope you knew somebody, who knew somebody, who... well... you get the idea.

In Dimarzio's case he was hand winding custom pickups in his Staten Island shop. The first being the now famous Super Distortion. As he relates it, high-gain amps just didn't exist in the early 70s. To get that real "high gain" sound that we all became familiar with you put a boost pedal in front of the amp or jumpered the channels of your Marshall. The Super Distortion was designed for one thing... to put out twice the voltage of the usual humbuckers of the day & push the front end of the amp harder. Marshall concocting the higher gain single channel 2203 & 2204 was still a couple years away. The formula was pretty straightforward, use a stronger magnet (ceramic), pile on copious wraps of wire & presto... more voltage output... not exactly rocket science.

As luck would have it, one of his former collage buddies was the bass player of a New York band that was starting to get some national traction. Yup, it was Gene Simmons who introduced Larry Dimarzio to his lead guitarist Ace Frehley. And the rest is, well.... KISStory.

Next thing you know, this crazy Californian named Bernie Rico calls, he wants to know if you can make that pickup with a 4-wire cable so he can use it with a series/parallel switch. This was the dawn of the "Dual Sound" pickup and a 12-year relationship with BC Rich guitars.

Take that pickup, give it to a kid from Berklee who's just landed a job playing alongside Chick Corea in Return To Forever, & the jazz world starts calling in.

OK, so lets fast forward a couple years... business has grown pretty quick in the little Staten Island shop. In addition to the Super Distortion/Dual Sound, there's now a direct Gibson replacement based off of Dimarzio's own 1959 Les Paul called the PAF, and an even higher output humbucker but that one isn't quite ready for primetime just yet, it needs some tweaking (that'll be the X2N). There's also the Gibson "EB" sized bass pickup design kicking around that Simmons was using, as well as a couple single coil Strat replacements currently being wound. He starts thinking maybe this whole replacement pickup thing, could be a thing...

Dimarzio decides to take the next logical step & start marketing replacement pickups to the rest of the general guitar playing world. And oh, by the way, just coincidently that other guy, Seymour Duncan, out on the west coast is in near the exact same boat... and the aftermarket pickup industry as we now know it was born.

Not too long after this point Kiss' other guitar player wants something with more high end in it than the Super Distortion. Or, as he put it in a 1978 Guitar Player magazine interview, "Like a PAF, only hotter".

In another more recent interview about his preferred guitar tone, "I like jangly guitars, but it still has to be able to rattle my nuts".

Yes boys & girls, that's a quote.

1978_ad_s.jpg

And thus, the "Super II" was concocted. OK, so it's not as Stanley alludes, an over-wound PAF. That trick will have to wait for some Dutch kid named Van Halen to conjure up. Nope, the magnet is ceramic, not alnico. The reality is, it's just an under-wound Super Distortion. No magic really, same magnet, same bobbins, same wire, just less of it.

In fact, all of Dimarzio's humbucking pickups of this era used the same wire, bobbins, & nickel plated setscrews for polepieces. The difference was simply the number of turns of wire wrapped around the bobbins. Except in the case of the PAF, that got an alnico magnet & polepieces that more resembled Gibson's. Not a lot of ultra-secret tricky stuff going on. The process of being able to carefully & perfectly sculpt the exact sonic signature of a pickup to the nth degree was still quite a few years off.

Now, for anyone wanting to know what a Super2 (or an XR7, since that's what we're accusing it of also being) sounds like, grab a copy of Paul Stanley's 1978 solo album. Super2 loaded guitars are all over it (which he stated in that same GP interview). Except for most of the solos, the majority of which were done by the now famous Kiss "fifth wheel" Bob Kulick. That noted, there are a few done by Paul himself, & the difference between Kulick's Les Paul & Stanley's solos are sonically obvious. The outro solo of "Hold Me, Touch Me" is a particular favorite of mine for what a Super2 can sound like in solo mode.

Other later perpetrators of the Super-II sound were Lita Ford, & Quiet Riot's Carlos Cavazo.

So, it's now 1978 and Dimarzio has grown to a 16 page catalog that's added "P" & "J" style bass pickups, a couple acoustic models, & a Tele replacement. But the humbucker lineup still consists of the same 4 options... well, OK, 3 actually, with a 4 wire option on one of 'em. Your endorsers list reads like a Who's Who of pop & rock radio. You've got a pretty good thing going, & your reputation has gotten the attention of the entire guitar industry... even if you are still something of a "small business". Remember, we're not talking about a multi-million dollar company here yet, with hundreds of employees. Just a small company chugging along making handfuls of pickups at a time. Super fast computer controlled winding machines don't exist yet. The machines that do exist are still manually operated here.

(to be continued...)
 
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adorshki

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Keep it coming !
Awesome read so far!
"Boy Howdy"!
(And I promise not to muck it up with bad jokes)
(Unless the topic's finally petered out to that stage where it's ok)
But, if we charge up the flux capacitor, jump in the Wayback Machine, & drop ourselves in the middle of the 1970s it was a whole different ballgame.

Prior to 1976 the aftermarket pickup market was pretty much non-existent. If you had a pickup that went bad or wanted "something different" back then you had very few choices... You salvaged one out of a repair shop bone pile, ordered a replacement from the manufacturer (which may not have been possible with some odd/off brand guitars), or you knew someone who could rewind it for you. And you could count those guys on the fingers of one hand. They had names like Bill Lawrence, Larry Dimarzio, & Seymour Duncan. & they were busy guys with a pretty exclusive clientele... I hope you knew somebody, who knew somebody, who... well... you get the idea.

And funny you should mention that but yes, my best buddy got his CBS-era Strat's p/u's rewound at a little hole-in-the-wall shop in the crumbling retail core of downtown San Jose where rents were dirt cheap, in '74 I think it was, by a guy named Dan Torres who eventually carved out his own little niche in the Bay Area:
https://www.eastbaytimes.com/2004/09/12/torres-amps-up-sound-of-electric-guitar/
He explained to me that CBS cheapened up the builds with less winding on the p'ups and that's why older Strats sounded better(like Hendrix), but there was this guy who re-wound 'em for ya.
Maybe a myth built around a seed of truth (about CBS' build standards), but it always stuck with me. I liked that kind of stuff.
Anxiously awaiting pt 2.
:friendly_wink:
 
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Dix_

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When we left off, we had a butt-load of the gold & platinum recording artists of the day doing so with our pickups. We’d upped our game enough to start offering our wares up to the general public. The future looks pretty good from our little niche in the music biz we’ve carved out for ourselves.

Then the phone rings, a guitar company wants to put our pickups in their guitars, but, unlike BC Rich they don't want the most expensive pickup in the inventory. Nor do they want to be like Guild & a few others of the time & make any of our usual suspects optional upgrades. They need it to be more cost effective. They want to market inexpensive guitars to young wannabe rockers, & be able to tout that the pickups are "made by Dimarzio". Seems we do indeed have a reputation at this point. One that’ll help sell guitars... or so these crazy folks seem to think. And, by the way, they want 'em by the boatload... literally.

Hello, Korea calling.

Quick, hit that hold button on the phone. OK, opportunity knocks. But we've got to figure out how to make 'em some cheap pickups that are at least semi-worthy of having our name attached to 'em with our 1970's technology & production methods.

So, what to do?

Wait!... I've got it!!!... We'll take the lowest cost pickup in the lineup, the one with the cheapest magnet and the least amount of wire, & rather than adjustable setscrews, pop in 12 slugs that cost next to nothing, call it the "K-10" & stick 'em on a boat... That just might work.

Sort of...

Only thing that didn't fly was the name. Hence, they came back across the Pacific renamed as "SD-2" (as if "Super Distortion 2") in cheap knockoff guitars with brand names like "Hondo", and import versions of S.D.Curlee guitars.

As verified by Larry Dimarzio himself in a 2010 Q&A session over on Premier Guitar, the Korean OEM K-10/SD-2 was nothing more than a Super2 with slugs for polepieces. This sets an interesting precedent in the timeline. It also means the next time I see the SOB I'm tellin' him he owes me a Bennie.... plus interest... adjusted for inflation. (remember my tale of how the Super2s didn’t’ sound any different than the SD-2s I took out of that cheap LP knockoff?.... now we know why.)

Lets jump ahead to 1980, & Guild now wants a Dimarzio pickup of their own too. The standard full-size humbucker lineup has grown from 4 to 6 (or 3 to 5 depending on your point of view) & that Super2 is still the best bargain of the lot. Price is obviously a concern. But we're talking about Guild, not Korean knockoffs, so they can't look exactly like those "SD-2"s that are now associated with that market... hmmm.

Considering that we already have LD on record confessing to prostituting the Super2 out to the Koreans, is it really a stretch to believe that slotted setscrews were substituted for the standard hex & a small "adapter plate" gets soldered on one of the mount tabs to fit Guild's mounting rings? Added cost might be what?... less than 5 minutes?

Nope, it ain't... take a look.... Remove the polepieces of a Dimarzio Super2 and a Guild XR-7 & you'll find they're nothing more than the same nickel plated #10-32x5/8" setscrews incognito.

polepiece_screws.jpg

Take a deeper look & you'll find the exact same bobbins (just slightly different color), same magnet, and what appears to be the same gauge wire with the same number of turns. Also, one of the single screw mount tabs on one side literally has a 2-screw adapter plate soldered onto it.

Now, I haven't taken things to the point of peeling wire off the bobbins, but, there's no need, if you can physically see that the bobbins look like they have the same amount of wire wrapped around them, a simple DC resistance test verifies wire gauge.

Dimarzio Super II: 8.7k (advertised – most measure between 8.35 & 8.6)
XR-7s I've tested or known verified: 8.34 – 8.56k

An inductance measurement verifies the combination of magnet strength & magnetic mass. Unfortunately, simple handheld LCR meters are notoriously inaccurate when it comes to measuring pickup inductance. The only one I know to be even close is a now discontinued meter by Extech Instruments. To be truly accurate measuring the inductance of a pickup calls for a dual channel scope, testing to find the resonant frequency, & doing some math.

I tested the two pickups I had on the bench at the time when I took the above polepiece pics & my Extech meter came up with 5.34H & 5.31H. Since that time I've actually gotten to the scope & tested them both again.

Dimarzio Super II: 5 henrys (advertised – 5.56H measured)
Guild XR7: 5.37 henrys

If that ain't close enough for Rock & Roll, I don't know what is.

At this point I'm pretty comfortable calling the XR7 simply a Dimarzio Super-II with different setscrew polepieces, charcoal-ish bobbins, & an adapter plate soldered on one of the mount ears.

Now, there IS a difference in the stray capacitance between the two that you can call significant if you really want to split hairs. The Super2 measured 109.4pF while the XR7 came in at 58.5pF. That difference is likely due to the era the pickups come from. The XR7 was obviously made back in 1981-82, while the Super2 used in these tests came from this century. A difference in simply the insulation of the wire used (which is very likely) can account for that.

Remember "p" = "pico"... or a difference of 0.000000000051 farads.

Also, stray capacitance by itself isn't going to amount to a difference any human is going to hear regardless if you're one of those with ears made of gold & myrrh. 10 feet of guitar cable amounts to 5-10 times the pickup's capacitance (roughly 30-50pF/foot on average). Since capacitances in parallel are additive, unless you are never going to plug your guitar into your amp with nothing more than a 2 foot cable, the pickup's capacitance becomes next to meaningless.

So, there you have it. There's everything I know thus far about the origins of the XR7 & Super-II. Which are extremely likely, one in the same.

The good news here is, if you need to replace a failed XR7 & don't care about what is engraved on the backside, your replacement is still being made as we speak. Buy a Dimarzio Super-II, swap the polepieces, desolder the adapter plate, stick it on the Dimarzio & you're back in business. If all you care about is the sound, I seriously doubt you even need to bother with the polepiece swap.

While I'm at it, if you're not caring about keeping everything all original for resale value, you can improve the look of an XR7 equipped Guild by swapping the mounting rings with a pair of old Ibanez 3-screw mounting rings. Guild used the same pickup rings for the XR7 they used for the larger HB-1, while the Ibanez version have the openings sized more appropriately, leaving much less gap between the pickup & ring. All the screw holes are in the exact same locations so the swap is simple plug & play. Only downside is that the Ibanez rings are slightly smaller in outside dimension. So if the original rings left marks of their footprint in the body finish, that will show slightly around the Ibanez rings unless you take the time to buff it out.

Andrew Giomi at reproguitarparts.com usually has a few in stock in flat or carved top and black or cream color versions. He's also got single to dual hole mount adapters if you don't want to bother with desoldering the XR7 mount tab.

Now of course, the final proof is going to be an actual, honest A/B comparison between an XR-7 & a Super-II installed in the same guitar. That plan is in the works. However, in conjunction with that before I go through the exorcise of swapping & recording the two, there is a way to actually measure the frequency response of a pickup that I want to try while I have one of each not actually mounted in a guitar. But, it involves a few parts, some tinkering to coming up with a reasonable facsimile of a test jig, & then wiring the test circuit in it. I should be able to get to that sometime when life stops getting in the way so much. For now, the wife is still breaking in her second new hip of the year. Guess I should have gotten an extended warrantee. Talk about expensive repair bills... McLaren & Ferrari ain't got nuthin' on this bunch.

So... stay tuned. (to be continued at a later date...)

(And I promise not to muck it up with bad jokes)
(Unless the topic's finally petered out to that stage where it's ok)

Oh, don't let that stop you.... muck away!!!

IMO, there's no time for a bad joke like the present.

Maybe a myth built around a seed of truth
The best myths with the longest legs always have one of those.
 
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Dix_

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Thanks, Guys.

I actually meant to put up something like this years ago but it kind of slipped through the cracks.

Been a long time X-79 fan. Ever since the 1st day I picked one up in a PA shop, immediately fell in love with the neck feel & walked out the door with it about 20 years ago. I have a few other guitars around here, Les Paul Studio, BC Rich Eagle, & a PRS SE Custom 24, but I keep going back to the X-79 'cause every damn time I pick it up that neck just feels like home.

Guess I just like skinny necks.

The only other neck I've tried that feels similar (in fact, real damn close) to my hands was the Kramer Nightswan. For those who don't know, that was originally a signature model for Vivian Campbell when he was with Whitesnake, & designed by Buddy Blaze. If you've ever seen a Floyd Rose locking nut size chart & wondered what the hell an "R1" nut with an E-E center width of only 1.3" & 10" radius might be used on... now you know. (well, technically, it was actually originally made for anyone putting a Floyd on a Norlin era Flying V. Campbell & Blaze likely used it because it was the smallest one in the FR lineup)

& yes, I kick myself in the asterisk every time I think about the fact that I walked out without buying it.

At any rate, as an X-79 fan I've kind of read through posts in this joint occasionally since it first popped up on my radar 10-12 years ago or so. & I actually was going to join & comment back when I saw the one (& only I think) time someone surmised that the XR7 might be a Super-II in Guild clothing.

I did a quick search & actually managed to find it: http://www.letstalkguild.com/ltg/sh...-80-Write-Up&p=1743026&viewfull=1#post1743026

Supposedly the XR-7 pickups were very close to if not exact re-labels of the DiMarzio Super Distortion 2 - which is similar to the regular Super Distortion...

By the way, I really should issue a minor technical correction. I mentioned above that a pickup's inductance is a function of magnet strengh & magnetic mass. Umm... that SHOULD read: magnet strength & INDUCTIVE mass.

OK, so my fingers were workin' faster than my brain. Oh well, women I used to date when I was younger had that same complaint. Go figure.

It's of some significance because ceramic magnets, while a very good source of magnetism, have about the same inductance as air. As in, none.

The upshot of that is, for two pickups of equal magnetic strength one with an alnico magnet will have more inductance than a ceramic. Hence, ceramics will tend to be brighter sounding. However, for magnets of equal size the ceramic will be stronger than the alnico. Which makes them perfect for higher output pickups, as you can pile on more wire & still have some top end to speak of. A PAF style pickup with enough wire on it to get its output up to Super Distortion level would be a rather dark sounding pickup.

Which makes for an interesting side note that most don't know.

Most everyone knows the story about how Eddie Van Halen originally scavenged Gibson pickups & overwound them for his "Frankenstrat" experiments. That and working out how to wax pot 'em caused him, as he says, "proceed to ruin many, many pickups."

He experimented a lot between those early ablbums. In addition to the various color & pickguard versions of the Frankenstrat, It's had more than a few different pickup versions in it. Sometime between Van Halen II & Fair Warning (if memory serves) he started running out of sources for cast-off Gibson pickups. A tip he got from Seymour Duncan was to get Dimarzio Super Distortions, replace the ceramic magnet with alnico, & remove windings until he got the sound he was looking for. This actually turned out to be easier than adding wire to a Gibson. So "Frankenstrat Pickup version 8.92" or whatever, is a Dimarzio Super Distortion with a magnet swap & windings removed.

True story. Or, as Mike Rowe would say... That's "the way I heard it".

If you look at enough old pictures from the 1980-ish era you'll eventually trip over a few where Frankie's polepieces are those tell-tale allen head setscrews.

adorshki mentioned myths up above. Just for giggles, here's my favorite guitar myth...

Ever hear that the difference with how a 24-fret vs 21 or 22-fret guitar's neck pickups sound is due to the string's "anti-node" occurring right above the pickup on the non-24-fret?

Horse hockey!.. Barbara Streisand!... Bovine Excrement!

For openers, that MIGHT be true if, and ONLY if, you tune your guitar to something like open G (or any other open tuning) and never play anything but that one open chord.

Basic physics kind of gets in the way of this one... meaning... once you fret a string you have effectively changed the length of that string, thus, that particular anti-node of that particular note of that particular string has also moved (toward the bridge).

However, string anti-nodes and where they may be, or not be, isn't a big deal really. The pickup has a wide enough "window" to work with. It's pickup "pattern" is more like a shotgun than a sniper rifle. Or in the case of humbuckers, we're talkin' blunderbuss territory, & thankfully so. If it were so tight that an anti-node would cause a frequency to disappear you'd never get away with bending strings during a solo.

At any rate, here's a response trace of a Les Paul's low E string & neck pickup. If the string's anti-node was a major player, the harmonic at 320Hz wouldn't be anywhere near that strong.

open_e.png


However, if you search around on the subject you'll see that anti-node myth repeated over and over again... even by some who really should know better.

The brighter sound of a 24-fret's neck pickup is simply the effect of the pickup needing to be closer to the bridge because a 24-fret fretboard is longer. Nothing more complicated than that.

A bit of an update on my "project"...

The theory I'm workin' on is that you should be able to measure a pickup's output (both output voltage and frequency response) without the need to use a bunch of filtering on the output (other than optionally simulating the loading of the controls & maybe 10 feet of cable if you like).

Well... I ran an 80Hz to 8kHz sweep through v1.0 and exported the results to Excel. Which generated this frequency graph. How's this for "proof of concept"?

test.png


Now remember, this is an "unloaded" pickup (that's also too close to the driver, more on that in a minute). There's no volume or tone control circuit, and no guitar cable attached. Once that would get added/simulated, the prominence of the resonant peak would be drastically reduced. So, this graph isn't really representative of how it would sound in application. But it is a decent enough "proof of concept" that's at least close enough for redneck work in my potentially warped world.

For this whole thing to work the way I want, the coil that drives the pickup has to have a flat frequency response (impedance) through the critical band. Meaning, in this case 80Hz to 8kHz. In order to get an inductor of that value in a practical size you have to use an inductive core. An air core inductor of that value would be bigger than my coffee cup.

So, my test subject was a DC choke for a tube amp power supply. Problem is, at the limit of my signal generator (about 2v RMS) I end up with the pickup so close to the driver that the choke's inductive core alters the pickup's inductance just enough to move the resonant peak a few hundred Hz.

So, that whole "inductive mass" thing is something that's chewin' on my asterisk at the moment. However, I believe it can be overcome with that time-honored redneck engineering technique known as brute force.

Which means... it's either going to work, or I'm gonna blow some sh*t up. Fun times!
 
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Nuuska

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Hello

Interesting reading.

How about getting a full-range speaker and tearing that apart to get the voice-coil? You will need an amp to drive it.

Or if you wanna connect directly to your signal generator - how about a coil from electric guitar pick-up without magnet ?


keep the stuff coming - we'll be reading.
 

Dix_

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Using a power amp to boost the voltage is the "brute force" part I was talking about. If my calculations are correct (which are always highly suspect) to get the signal levels I'm looking for, at the minimum distance from the driver coil (at least 1/4"), I'm looking at 20v minimum.

I'd like to see 400mV out of the pickup. I got 117mV out of it, but that was with it in contact with the driver. From 1kHz on down is no problem (less than 0.2H difference). But, once you get closer than 1/4" to the driver the pickup's inductance at 10kHz starts getting significantly altered. To the tune of near 1 full henry difference from 1/4" to contact.

Speaker voice coils usually have a rather large impedance curve in the audio band with a low resonant frequency. This is by design. Normally in a speaker, you want the resonant frequency to be below the audio frequencies it needs to reproduce. Above the resonant frequency the impedance will be a rising curve. A speaker's rated impedance is an "average" among the frequencies it's designed to reproduce. Which is kind of the opposite of what's needed for this circuit. The resonant frequency needs to be up above 10kHz for this purpose.

Using a stripped out pickup as a driver is a method that's been done. The issue there again is signal strength & if you pull the magnets out to make an air core inductor so as not to effect the pickup's inductance, your driver coil's inductance is now so low that you need to create a 20dB/decade filter to apply to the result. Not to mention that you still have an issue with getting any kind of "real world" number to use for an output voltage rating.

The DC choke should work fine as a driver, it'll surely handle all the voltage I can throw at it, as it's made for a tube amp power supply, which is hundreds of volts. They just don't like a lot of current. So as long as I keep the current under half an amp it should work. Power resistors can work as current limiters. So then it's just a matter of doing the math & finding the right combination of inductor & resistor values. Triad Magnetics has fairly cheap Chinese made chokes from 0.3H & up.

When I get some time I'll throw up a post on the theory & what's been done that started all this rattling around in my cranial cavity of short-circuits & malfunctioning synapses.

If need be I've got an old Peavey DECA 1200 power amp sitting in the basement collecting dust. Lack of power shouldn't be an issue.

Lack of brain cells.... well... that's a whole 'nuther sermon.
 
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Nuuska

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The DC choke should work fine as a driver, it'll surely handle all the voltage I can throw at it, as it's made for a tube amp power supply, which is hundreds of volts. They just don't like a lot of current. So as long as I keep the current under half an amp it should work. Power resistors can work as current limiters. So then it's just a matter of doing the math & finding the right combination of inductor & resistor values. Triad Magnetics has fairly cheap Chinese made chokes from 0.3H & up.


Hello

Even though the DC choke coil is used in high voltage circuit - it is a series component in tube amp PSU and voltage drop across it is usually fairly low - only tens of volts. Limiting factor is current as you write.
 

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OK folks... here we go... another 2 parter.

WARNING!!! Elevated levels of pickup & electronics theory & geekness follows. If that kind of stuff causes your eyes to glaze over & your head to spin, proceed at your own risk.

A quick overview of the problem...

For testing pickups I'd like to see 2 things that matter in the real world.

- 1. What does it sound like (frequency response)
- 2. Output strength (voltage generation)

Now, you wouldn't think that should be too difficult. But the reality is, it's not that simple really. I'll get back to #1 in a minute, but let's start with #2.

Dimarzio started listing the output of it's pickups in millivolts sometime in the mid 80s. However, for the longest time, Duncan refused to list the output level of it's pickups. For which they received continual pressure to do so ("because Dimarzio does it") since they day they launched their website's user forum.

Their reasoning was actually sound...

The key is that yes it is frequency dependent. Suppose you had a warm sounding humbucker, vs. an overwound single coil with a lot of upper midrange. If you play hard, the guitar's strings could deliver more "signal peak" to the amp on that Strat pickup than the Humbucker. But an RMS test would show the HB as producing more mV. OR, let's say that with some standardized test method the HB reads higher across a broader frequency range, but the overwound single coil makes more "distortion" on your amp because it drives that key upper midrange area harder. You'd think the Strat was "louder" but it's not.

IF and when we have a suitable method of measurement that produces results we think have value to the majority of consumers, then we'll probably post it. Right now I can take a pickup to a certain "machine" we have and get a mV reading, and different versions of the same pickup produce very similar (consistent) mV readings. But if I take 3 of the same Dimarzios to it, they're all 20mV different from one another. That might not mean the three I'm testing are inconsistent. It may simply tell me that my method is somehow frequency deviant to theirs, and these three would be consistent with one another if tested on their machine, whatever it is.

If we do ever post mV ratings, we will probably also post some details about our method. I'll also want a bunch of Dimarzios for calibration purposes, maybe we'll let you guys trade your Dimarzios for Seymour Duncans...

(05-24-2011)

Dimarzio's method for coming up with an output rating was (and is) this...

we measure the RMS voltage from the pickup into a 20K ohm load 333 ms after the initial voltage peak using only the A string with all other strings muted.

The pressure on Duncan was kept up & finally in 2014 they relented & started posting the output rating of their pickups on their website. They posted the test method they used in their forum...

Good afternoon forum friends, as many of you know we are deep in the midst of a website design (and yes for those of you rolling your eyes, it has been an extraordinarily long journey as we completely re-design, record and sample our many, many pickups). I wanted to give you guys a peak at some upcoming mV data. You all know the limitations of using DC resistance as an indicator of output, a much better indicator is mV. We've devised a precise and repeatable method for testing pickup output which we believe corresponds closely to actual playing. We start with a Telecaster that has an oversized cavity routed to allow easy pickup installation. The guitar is carefully tuned to standard tuning (consistent tuning is important). We add a custom machined, mechanical, spring loaded strum arm with a tempered, .004" thick spring steel pick. We install the pickup, setting the distance from the top of the pickup to the string to .093" +/- .010" (consistent set-up is essential). We then load and release the strum arm, capturing the result on a digital storage oscilloscope. We perform this process 5 times for a 3 pickup sample lot and average the results. This is repeated for every model we make.

I'm happy to be able to share some of this data with you today. I appreciate you guys being cool and patient with us as we work to give you all the tools you could ever want to make the best selection.

(07-31-2014)

That "listing" got more than a few mixed reviews. For example....

That list is really surprising. Full Shred has more output than Distortion and Invader. 59 has more output than Screamin Demon and Custom Custom. The standard Perpetual Burn has a lot more output than the trembucker version.
It's very strange. I think some of the data might be wrong.

I'm tempted to use the old "be careful what you wish for" line here... but... ah, well.

I think what may have confused most is that they were hoping for something they could use to directly compare a Dimarzio to a Duncan. But a quick review of the "listings" showed that Duncan's output specs were on average about double the average of Dimarzio's.

Well, there is no (and never has been) any kind of "standard". The method Duncan used & the method Dimarzio uses are worlds apart. Dimarzio plucks one string & measures the output a given amount of time past the initial attack. While Duncan doesn't specify if the rating they used is the "peak" (initial attack) or something a number of milliseconds later. Even so, their method is all 6 strings, which will generate more output than a single string regardless of what exact period of time we're looking at.

Duncan has since stopped actively displaying the output in actual millivolts, but now rather use a "bar graph" display allegedly representing output. But, that millivolt number is still in the page code for each pickup. If you want to see it right-click a page & "view page source", search for the term "salsa-specs" & you'll see it.

Both methods have their advantages & drawbacks. If you're a lead player you may prefer Dimarzio's method. While others may consider Duncan's more realistic. If I were devising a method & trying to minimize various effects that would cloud comparisons my idea would be to inject bandwidth limited noise (80Hz to 8kHz) at a given level & then measure the output.

In my (maybe somewhat limited/warped) view, this would yield the best of both worlds. No frequency dependent transient attack spike that could be deceptive, yet is more realistic than the post-attack sustain of a single string. Put the entire frequency band in, at a constant level, & measure the output. Seems like a reasonable approach to me. But, what do I know?

However, let's leave that one on the table for a moment...

(continued, next post)
 

Dix_

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If measuring output isn't confusing enough, that's nothing compared to the 3-band Lo/Mid/Hi frequency graphs you find on spec pages. Those are more subjective than a Van Halen "brown sound" discussion.

The problem, in theory anyway, is that a guitar pickup & cable as far as your amp is concerned, is nothing more than an RLC circuit. (RLC = Resistor/Inductor/Capacitor) In other words, when you plug a guitar into an amp this is what the amp "sees"....

pkup_c.png


Now, if you do an analysis of a signal though such a circuit with values that mimic a pickup, you get what appears to be a low pass circuit with a resonance "hump" or peak.

pkup_r.png


So, in theory, any pickup's "low frequency" response should be meaningless, as they would all be identical with the "variables" being the midrange & highs. Those varying based on the width, magnitude, & frequency of the resonance peak.

Now, that's all well & good in theory, but as I'm fond of saying, theory & real world application don't always play well together... or as Yogi Berra once put it...

In theory there's no difference between theory & practice. In practice, there is.

Simulations aren't of much use. Sims assume "perfect" inductors & capacitors. Both of which are never perfect. Losses, which exist, can only be guessed at.

You can apply a signal directly across a pickup & measure that result. However, that's not going to give you any basis for output level. Nor would it measure how the various losses & imperfections might filter in with the translation from vibrating string to output signal.

So, this leaves us with generating an appropriate disruption in the pickup's magnetic field to measure. Doing that with some method that at least tries to approximate the real world is where things get tricky.

Obviously Duncan's & Dimarzio's methods generate very different output voltage results. How they are generating their frequency response "graphs" is likely just as different (not to mention possibly highly subjective as well). Comparing a Dimarzio to a Dimarzio or a Duncan to a Duncan, while requiring a bit of "faith" on the part of the shopper, is possible. But, comparing a Duncan to a Dimarzio (or anything else for that matter) via listed charts & graphs is utterly pointless.

So, why not use the same principles as a transformer? In other words, disrupt the magnetic field of the pickup with another inductor's magnetic signal.

This can work. And, there are a couple examples of this that have been put into practice. However, both are flawed IMO. If what you want is BOTH frequency response AND output strength.

The first was published by Peter Hiscocks at Syscomp Design (makers of the "CircuitGear" line of USB oscilloscopes). While a valid "proof of concept", the results he generated have a fatal flaw. That being the inductor he used for a driver (a junk doorbell solenoid), which has a distinct frequency response (impedance) "curve" in the critical guitar audio band (80-8kHz) that would be rather difficult to filter out.

The other method, devised by Ken Willmott of the GuitarNutz forum, uses a much smaller driver coil. One with an inductance measured in microfarads, and is current driven rather than voltage driven. Now, while this moves the "curve" of the driver's impedance out of the audio band, this method however, also leaves the voltage output vs frequency with a -20dB/decade "slope" which needs to be filtered out. That's rather easy to do with a simple 6dB/octave filter. The shortcoming of this method however, is that the output you're generating from such a weak driver is barely able to get you a signal above the noise floor of the circuit.

So, while this may work for comparing just the frequency response, it's not very helpful for looking at output voltage at anything that even vaguely resembles real world application.

That's what started this whole hair-brained scheme rolling around amongst the static of that murky area between my ears.

So the upshot of this whole little semi-back-burner project/experiment is to be able to get BOTH frequency response and voltage output via a standard, repeatable, and simple method, & come out with results that make some kind of sense to real-world application.

Put a pickup in a test fixture, run bandwidth limited noise (pink) through the driver at a predetermined standard level. That would give an output level. Then run an 80Hz to 8kHz sweep, plot the result on a frequency graph (probably "normalized" at some particular frequency vs voltage) & done.

Whole operation from Start to finish shouldn't take more than 5 minutes.

At least, that's the theory... the reality... to be determined.
 
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GAD

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I have pages and pages of articles about pickups that I've not published because, as you state, it's just not that simple. (Ask Frono - I've almost trademarked that phrase when trying to explain pickups).

IMO publishing mV values for pickups is meaningless without an industry agreed-upon standard for driving the pickup, and that will never happen.

I've spent countless hours doing exactly what you're doing. Here's a pic from one of my experiments:

TestingJacksonGuitar-1.jpg



I look forward to your updates because so far, you've gone the same place I have, which is down the dark path to madness. :encouragement:
 

adorshki

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So the upshot of this whole little semi-back-burner project/experiment is to be able to get BOTH frequency response and voltage output via a standard, repeatable, and simple method, & come out with results that make some kind of sense to real-world application.
Put a pickup in a test fixture, run bandwidth limited noise (pink) through the driver at a predetermined standard level. That would give an output level. Then run an 80Hz to 8kHz sweep, plot the result on a frequency graph (probably "normalized" at some particular frequency vs voltage) & done.
Whole operation from Start to finish shouldn't take more than 5 minutes.
At least, that's the theory... the reality... to be determined.
Freakin' magnificent stuff.

I look forward to your updates because so far, you've gone the same place I have, which is down the dark path to madness. :encouragement:

From the usual source:
"In the mid-1920s George Beauchamp, a Los Angeles, California guitarist, began experimentation with electric amplification of the guitar. Originally using a phonograph pickup assembly, Beauchamp began testing many different combinations of coils and magnets hoping to create the first electromagnetic guitar pickup. He wound his earliest coils using a motor out of a washing machine, later on switching to a sewing machine motor, and eventually using single coiled magnets."
If only he'd hooked up with Kenneth Stricklander, things might have developed in a more scientifically rigorous progression:

early-days-strickfaden-assembling-a-mad-scientist-apparatus.png


colin-clive-ernest-thesiger-the-bride-of-frankestein.jpg


colin-clive-frankenstein-1930.jpg


the-cosmic-ray-diffuser.jpg
 

GAD

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I so going to put a Cosmic Ray Diffuser on my pedal board.
 

Dix_

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I look forward to your updates because so far, you've gone the same place I have, which is down the dark path to madness. :encouragement:

Oh, I've been living down rabbit holes for years.... just ask my wife. :highly_amused:

Another issue where things get "fuzzy" (that "subjective" thing I mentioned above) is what exactly do those "graphs" you see consider "midrange"?

If we're talking guitars, & you're askin' me, I'd call it somewhere around 500-600Hz.
Marshall it seems, tends to agree with me.
Fender however, seems to think it's 300Hz.
The bass & treble controls on a Vox are centered around 500Hz.
The "middle" frequency of an Ampeg midrange selector switch is 800Hz or 1kHz depending on model.
If you go by old Dimarzio catalogs, they list impedances at 100Hz, 1kHz, & 10kHz.
Duncan?... who the h*ll knows what they're callin' it? No evidence exists.

If we call 82Hz to 8kHz the guitar's bandwidth, that's roughly 6-2/3 octaves. 3-1/3 octaves above 82Hz puts you in the 800Hz ballpark. (826Hz)

The argument can also be made that 8k is a bit of a stretch to use for the bandwidth of an electric guitar. So, if you peel that back to the 6k that some consider more realistic, then you end up with 700Hz for a middle of the range.
 
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Rocky

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While I'm at it, if you're not caring about keeping everything all original for resale value, you can improve the look of an XR7 equipped Guild by swapping the mounting rings with a pair of old Ibanez 3-screw mounting rings. Guild used the same pickup rings for the XR7 they used for the larger HB-1, while the Ibanez version have the openings sized more appropriately, leaving much less gap between the pickup & ring. All the screw holes are in the exact same locations so the swap is simple plug & play. Only downside is that the Ibanez rings are slightly smaller in outside dimension. So if the original rings left marks of their footprint in the body finish, that will show slightly around the Ibanez rings unless you take the time to buff it out.

Andrew Giomi at reproguitarparts.com usually has a few in stock in flat or carved top and black or cream color versions. He's also got single to dual hole mount adapters if you don't want to bother with desoldering the XR7 mount tab.
Necro-post (Thanks Greg)

Has anybody verified the above information regarding pickup rings?
 
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