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Post new topic Half volume problem: Lawrence 705s wiring in Sho-Bud Pro III
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Author Topic:  Half volume problem: Lawrence 705s wiring in Sho-Bud Pro III
Ben Standefer


From:
San Francisco, CA
Post  Posted 6 May 2019 9:56 am    
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I'm in the SF Bay Area and recently decided to take lessons with Kerry Johnson (he's great so far!). At our first lesson, Kerry helped me setup the guitar, and Kerry was surprised at how much quieter my guitar was than his. We tried changing out cables, volume pedals, etc. but he's convinced that my pedal steel is at about half volume than it should be. I never noticed this because I've always played by myself, so just turned my amp up more. It's definitely a lot quieter than his guitar. I had to keep my volume pedal floored just so he could hear me along with him during the lesson!

After the lesson, we took a look at the pickup wiring. He was scratching his head a bit about the jack and thought it was worth asking around to see if anybody has any ideas or noticed anything obviously wrong based on photos.

What we know:
* 1970s Sho-Bud Pro III (D10)
* After-market Lawrence 705s
* Produces half volume than is expected
* Kerry and I agree the signal might sound a little "phasey"... maybe that's just because it's quiet though
* There was a little loose electrical tape that was falling off on some of the wiring

Does anybody have any ideas on what could be going on? Here are some pictures: https://imgur.com/a/PFqcrH8. I'll probably take it to my local luthier to inspect (non-steel expert), but I wanted to figure out if anybody here had ideas on why these pickups might be at about half volume.

Pictures link: https://imgur.com/a/PFqcrH8

–Ben Standefer
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Jon Light


From:
Saugerties, NY
Post  Posted 6 May 2019 10:17 am    
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Poke around where you see those tiny frayed bits of braided cable sticking out. You can use a tiny jeweler's screwdriver or even a pencil point. See if any of those hair-sized bits of wire aren't falling over and shorting on another contact. 'Comb' them aside, clear of anything metal. If you have tiny cutters, even better is to cut away any stray 'hairs'.
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Ben Standefer


From:
San Francisco, CA
Post  Posted 6 May 2019 11:41 am    
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Jon, thanks for the reply.

Yes, when we first looked there was some old, loose electrical tape completely falling off. (You can see it in one picture where it's just sitting there.) Maybe before taking it to the shop I'll isolate the exposed wiring with electrical tape, then see if the volume problem is resolved.

It's difficult to tell in isolation (i.e. without Kerry's pedal steel next to mine) if the volume is "too low". Is there a way I can test the pickup with a multimeter? I'm thinking I could test some values from the pickup leads, then test for the same values at the jack (with the switch turned the right way). Presumably that would isolate the cause of any potential problem to either (1) the pickup itself or (2) to the switch/switch wiring. But I'm not sure what values from a multimeter I should be looking for.

–Ben
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Ken Fox


From:
Nashville GA USA
Post  Posted 7 May 2019 3:41 am    
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I’ve seen several pickups in guitars and even one in a Tele display lower volume and a thin tone. All three had a break in the windings

Plug in a guitar cable and then check with an ohm meter from tip to ground of the cable
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Jim Kennedy


From:
Brentwood California, USA
Post  Posted 7 May 2019 10:48 am    
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You have an input Jack with contacts on the ground side. Make sure those contacts are clean. Signal loss and poor ground is common with this type of connector. You can get a burnishing tool for this, or you can use some notebook paper. There seems to be a bit of surface corrosion on your guitar. Not uncommon but can cause problems like yours if it gets into your wiring or switches. Make sure all of your ground connections are clean and tight, and look for cold/loose solder joints. The signal from a pickup is very low. Any corrosion, loose connection, or cold solder joint will cause signal loss.
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Jim Kennedy


From:
Brentwood California, USA
Post  Posted 7 May 2019 10:57 am    
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My mistake. The multiple contacts next to the input are for switching pickups. Cleaning still applies. I have run into this on old Gibson guitars. The contacts corrode over 30 or 40 years and will pass less to know signal. Good luck.
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Michael Brebes


From:
Northridge CA
Post  Posted 9 May 2019 6:30 am    
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Do you have the volume problem with both necks/pickups? If the problem is with both necks, chances are it is after the neck switch. Definitely measure the resistance with a multimeter. Depending on the pickup, it will usually measure somewhere between 10K and 25K ohms. It's hard to tell from the pictures, but the one shielded cable coming up from the neck closest to the jack looks like the shield might not be attached. Too hard to tell from pics.
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Kerry Johnson


From:
Bay Area, California
Post  Posted 12 May 2019 11:34 am    
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Hey Ben,

I just saw your posting and the closeup pics.
Thanks Jon, Ken, Jim and Michael for your suggestions.
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Last edited by Kerry Johnson on 13 May 2019 3:57 pm; edited 1 time in total
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Ben Standefer


From:
San Francisco, CA
Post  Posted 13 May 2019 1:21 pm    
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Jon, Ken, Jim and Michael, thank you very much for your feedback. I've been taking my time to research and wrap my head around what the best route forward is here.

Here's my current plan:

* Test the pickups themselves. Get a multi-meter and test each pickup's output (~20k ohms for Lawrence 705s according to the original spec, give or take). Rule out problems with the pickups themselves. If there is a problem with the pickup, there's now a remake of the Lawrence 705 narrow mount pickups (the remake has non-chrome surroundings).
* Replace the 3-way DPDT switch/jack & wiring. Just replace the 3-way DPDT switch/jack with the new version from SwitchCraft. It's $20. This will (1) require rewiring/resoldering cleanly, (2) eliminate any potential issues with corrosion, (3) eliminate any problems with the switch design or aging/wear of the switch.
* Optional: Hook up wiring for the single coil tap. My guitar has switches mounted on it for single coil tap, but there's nothing connected to them now. Using the wiring diagram here: https://bb.steelguitarforum.com/viewtopic.php?t=156334&sid=d5d9171a6055b95d21cea3e5f9dfb12b it seems trivial to connect the single coil tap switches.

Questions:
* For wiring, what gauge/type of wire should I use?

I'm starting to understand that this wiring is very nuanced for pedal steel I probably just want to get good at doing the wiring myself vs. trusting a 6-string shop to decide what to do here.

Thanks again for your input!

–Ben

Parts:
* New 3-way DPDT switch, long version for my guitar: https://www.stewmac.com/Pickups_and_Electronics/Components_and_Parts/Switches/Switchcraft_Toggle_Switches.html
* Knobs for the switch: https://www.stewmac.com/Hardware_and_Parts/Knobs/Switch_knobs/Toggle_Switch_Knob.html
* Remake L-705s: https://www.sillmusicsupply.com/Brand-New-Lawrence-705-pickup-narrow-mount_p_51.html

Helpful threads:
* Guitar in similar state as mine, plus Ricky Davis' wiring diagram of 3-way DPDT switch with single-coil taps: https://bb.steelguitarforum.com/viewtopic.php?t=156334&sid=d5d9171a6055b95d21cea3e5f9dfb12b
* Discussion around 3-way DPDT switches on Sho-Buds: https://bb.steelguitarforum.com/viewtopic.php?t=268330&sid=5046bbbd8b2326d6723eccffe60f3ebe
* Original Lawrence 705 spec sheet: https://bb.steelguitarforum.com/viewtopic.php?p=1655770
* Craig Baker question about Lawrence 705s with 500k volume pot: https://bb.steelguitarforum.com/viewtopic.php?t=288107&sid=4bfdd3bbcdfdcdb20274fc38407ceb96
* Mike Scaggs wiring diagram: https://bb.steelguitarforum.com/viewtopic.php?t=324624&sid=2f0db73f40e91c937784dedb8f52599e
* Bob Lawrence original wiring diagram: https://bb.steelguitarforum.com/viewtopic.php?t=165330&sid=14c7ef8db500506cb7f39984a1dd6d52
* Bruce Derr wiring diagram for Lawrence 705s, parallel and series humbucking option: https://bb.steelguitarforum.com/viewtopic.php?t=275792&sid=e5f155fc2cb77007569aa378ee8281ff
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Dan Beller-McKenna


From:
Durham, New Hampshire, USA
Post  Posted 14 May 2019 6:09 pm    
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Ben,
I am having an issue with the wiring on my Sho Bud, needs a complete resoldering (maybe a new selector switch). Anyway. it's at the point where sometimes the C6 neck doesn't come on unless I jiggle the pick up wire. Occasionally, it only comes to half volume unless I jiggle it some more. Could well be a loose wire issue on yours.
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Ben Standefer


From:
San Francisco, CA
Post  Posted 28 Jun 2019 12:34 pm    
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Dan, note that Michael from pedal steel guitar parts recently came across OEM stock of 125 original Sho~Bud selector switches: https://www.psgparts.com/Switch-Selector-Neck-ShoBud-85-001.htm?categoryId=-1

I ended up doing this to solve this half volume problem:
* The Lawrence 705 pickups seemed to have been damaged. The C6 could not produce an ohm reading, and the E9 gave a very low reading around 12K ohms, when it should be 18-20K ohms.
* I decided to replace both Lawrence 705 pickups with Truetone pickups, as recommended by Ricky Davis (legendary Sho~Bud restorer!). These are single coil pickups similar to the original pickups on a guitar, but hand wound by Jerry Wallace himself. Ricky David told me to ask Jerry Wallace to wind the pickups to 17.5K. Ricky and Jerry have done a lot of research with pickups+Sho~Buds and have found that to be the ideal pickup. (IT SOUNDS GREAT!!!)
* When the Truetones came, I installed them and resoldered everything myself. Someone had made a mess of the previous wiring/switching, and I'm pretty sure there was some kind of unintentional ground leak going on.
* I used a new jack and a new switch.
* I didn't know about the OEM switches Michael from pedal steel parts had, so I used the tall variety of the modern Switchcraft switch: https://www.stewmac.com/Pickups_and_Electronics/Components_and_Parts/Switches/Switchcraft_Toggle_Switches.html
* I'd recommend getting the original part from Michael to keep your guitar historically accurate!

With the wiring, jack, switch and pickups replaced... the crappy volume problems are now completely gone and everything sounds amazing. The reading from my guitar cable is spot on, 17.5K. Learn how to use a multimeter to test this stuff (YouTube can teach you multimeter + soldering). It was actually a fun project and I'm proud of the work!!!
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