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Topic: Low Impedance Pickup Wiring |
Bruce Bindeman
From:
Illinois, USA
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Posted 5 Mar 2007 7:35 pm |
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I'm experimenting with a low impedance single coil pickup. First, I custom wound a pickup to 125 ohms and ran three wires out - the two ends of the windings and a ground. Then I terminated them in a stereo plug.
I used a stereo jack-to-XLR adapter with a lo-to-hi 1/4" microphone plug. Then I just plugged into my amp. It sounds good, no problem.
Now, I would like to figure out how to wire standard on board volume and tone controls with such a pickup. I'm thinking I will keep the three wire configuration with a stereo jack on the pickguard and a stereo cord to my adapter.
What value pots would be best?
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Harbor Lights clone, Quilter MicroPro Mach 2 HD |
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Jim Sliff
From:
Lawndale California, USA
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Posted 5 Mar 2007 8:32 pm
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| Quote: |
| I used a stereo jack-to-XLR adapter with a lo-to-hi 1/4" microphone plug |
It sounds like the "adapter" you used is actually a low impedance to high impedance transformer. If you want volume or tone controls before the transformer, the usual way is to install a complete active (i.e. preamplifier) circuit - this is the usual setup for guitar and bass low-impedance pickup systems. A low impedance signal normally should be boosted before (or in the process of) running it through volume and tone shaping circuits). There are quite a few miniature preamp boards around for low-impedance pickup systems, but you'll probably have to ask some questions to get one that matches up well with your idea. Tweak it right and you could end up with essentially a zero-noise, very hi-fi signal with wide tone shaping possibilities (and with an active circuit, boosting of frequency ranges rather than simply cutting them as in standard passive systems).
I don't know if anyone's done it on steel before, but it would seem an ideal platform for an active system.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
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Lee Jeffriess
From:
Vallejo California
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Posted 5 Mar 2007 9:36 pm
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Sounds like, the Les paul recording guitar, Mark neil has been telling me thats the way to go, for about fifteen years.
He wanted to do a 50ohm coil like LP, the skys the limit, you could pretty much have an open pallett of voiceings.
Lee |
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Bruce Bindeman
From:
Illinois, USA
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Posted 6 Mar 2007 8:23 am
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Jim, that's right, I'm using a low-to-high impedance transformer. I had not considered active electronics.
Lee, I did get the idea from reading about the Les Paul Recording model.
I didn't think the LP Recording used active electronics and I 'assumed' I could use regular passive components. |
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Mike Wheeler
From:
Delaware, Ohio, USA
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Posted 6 Mar 2007 10:59 am
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Jim is right on the money. Active electronics is the way most lo-Z systems are designed. But, you can use passive components. The signal loss may, or may not, be tolerable. The transformer used will determine how much signal quality, and level, is lost...better transformer, better signal quality.
As long as the high impedance cable lengths are kept to somewhere around 20 feet or less, noise and hum should be very tolerable. Of course, a strong signal fed to the transformer will help swamp out the noise.
Keep experimenting. Many of the greatest inventions came from people who thought "what if I .........."
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Best regards,
Mike |
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Bruce Bindeman
From:
Illinois, USA
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Posted 7 Mar 2007 4:42 pm
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Mike,
You're right. I wired it up with the old volume and tone pots and there is no problem getting sound.
The Volume goes from ON to OFF in just a fraction of a turn and the Tone really doesn't function.
They are standard 500K pots. I'll try something like 5K and see what happens.
Thanks
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Harbor Lights clone, Quilter MicroPro Mach 2 HD |
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Jim Sliff
From:
Lawndale California, USA
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Posted 7 Mar 2007 5:28 pm
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I did not mention using passive components, because having experimented with them over the years they are simply rendered to "on off" devices. If you don't go active, you're really wasting time/money IMO.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 7 Mar 2007 5:37 pm
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About 99.99% of the guitars made don't use a low impeedance system. Hmmm...I wonder why?  |
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Dave Mudgett
From:
Central Pennsylvania and Gallatin, Tennessee
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Posted 7 Mar 2007 6:52 pm
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| Quote: |
| About 99.99% of the guitars made don't use a low impeedance system. Hmmm...I wonder why? |
IMO, because properly amplified, low-impedance pickups have a real clear, clean tone and show all your mistakes.
Seriously, traditional high-impedance pickups were designed for high-input-impedance tube amps, and sound fine through them. But in comparison to something like a Les Paul low-impedance pickup, they're real midrangey sounding, and tend to distort like crazy. That's great if it's what you want - most guitar players do - and that is the way electric guitar grew up.
I had a Les Paul Recording model for some time - through a nice clean, full-range, solid-state amp with a little reverb and echo, it sounded great. Listen to "Chester and Lester" - no problem with Les' sound, to my ears. That's one of his fancy versions of that guitar with low-impedance pickups, which I'm pretty sure is what he still uses.
Active is certainly an option, but my old guitar was strictly passive, with transformer impedance matching. I believe Les' guitar can use XLR cables, if I'm not mistaken, which means he must have a center-tapped transformer. That is not standard in the Les Paul Recording, but a real good idea for making long cable runs and noise reduction.
Donald Brosnac's Guitar Electronics for Musicians has the circuit diagrams for 1971 and 1977 versions of the LP Recording. An interpreted version - without the impedance matching transformer - is here.
The bass and treble pots are linear 2.5KOhm and 1KOhm respectively, and the volume control is 2.5KOhm - it doesn't say, but I think the volume pot is audio. My guitar was stock, and sounded very good for country, jazz, and rockabilly. The only reason I sold it was that it, like most of them, was boat-anchor heavy.
The 3rd page of the above link shows how that guy put active boost and a Keeley-style overdrive circuits into his LP Personal - a slight variation on the LP Professional and Recording models. Looks interesting. I think these are very under-rated guitars. |
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Bruce Bindeman
From:
Illinois, USA
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Posted 7 Mar 2007 8:05 pm
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Dave,
That's a great page. It answered my suspicion about the tone capacitors, too. Much higher values need to be used.
I wired up the 5K pots and the volume works pretty well. The tone is ineffective.
Donny,
It was probably the cost of the transformer and/or circuitry in the 50's and 60's. High impedance made more sense, even with the hum, etc. with single coils.
Jim is right that on-board modern circuitry (op-amps) make the most sense today. |
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Lee Jeffriess
From:
Vallejo California
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Posted 8 Mar 2007 12:42 am
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Bruce, I think your dead on Im sure it was more of a financial consideration, from what I understand it took Les 20 years too finaly get a production recording guitar and, the amps.
Its like a ribbon mic PU.
Bruce, could you keep us posted.
Lee |
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