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Topic: Please help with old Oahu wiring problem |
David Hayes
From:
California, USA
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Posted 14 Jan 2012 2:52 am |
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Hi all:
I have an old Oahu (see pic below) that has had the pots changed. It doesn't sound right - the higher e string is much lower volume - less twang that a usual lap steel and it is very bassey on the low e string. I have the original pots. They are stackpole W618 and one of them (I think the tone pot) has two resistors on it - one resistor bridges two of the three posts and the other resistor comes off one of the posts. The replacements are new 500k allparts pots without any resistors on either of them. Does anyone have any information on how this should be wired properly, what parts are correct even a referral to a tech who is knowledgeable but not too expensive would be appreciated. I am in Orange County California. I would like to get this thing sounding the way she should - any help appreciated.
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David Venzke
From:
SE Michigan, USA
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Michael Lee Allen
From:
Portage Park / Irving Park, Chicago, Illinois
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Posted 14 Jan 2012 9:28 am
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Deleted
Last edited by Michael Lee Allen on 2 Aug 2012 12:05 pm; edited 1 time in total |
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Steve Ahola
From:
Concord, California
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Posted 14 Jan 2012 1:11 pm Re: Please help with old Oahu wiring problem
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| David Hayes wrote: |
| I have an old Oahu (see pic below) that has had the pots changed. It doesn't sound right - the higher e string is much lower volume - less twang that a usual lap steel and it is very bassey on the low e string. I have the original pots. They are stackpole W618 and one of them (I think the tone pot) has two resistors on it - one resistor bridges two of the three posts and the other resistor comes off one of the posts. The replacements are new 500k allparts pots without any resistors on either of them. Does anyone have any information on how this should be wired properly... |
If you can post pictures of the old and new controls it would help in diagnosing the problem with your steel. I think that what you are calling "resistors" are actually capacitors. In addition to pictures, it would be a big help if you can tell us what is stamped on all of the parts.
You might want to compare the wiring in your steel to a typical diagram for one pickup and two controls:
http://www.seymourduncan.com/images/support/schematics/1phat1v1t.jpg
Some of the early lap steels have unusual wiring but in most cases you should be able to get a decent sound with the above diagram. (Note: the wire going from the vol pot to the tone pot could alternately be connected to the middle terminal of the volume pot rather than the outside terminal. Some people call that the "50's wiring mod" and is usually a definite improvement over modern wiring. Many vintage lap steels were wired that way from the factory.)
From your description it sounds like there is too much capacitance in the tone control circuit.
Steve Ahola
_________________
www.blueguitar.org
Recordings on electric guitar:
http://www.box.net/blue-diamonds
http://www.box.net/the-culprits |
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Frank James Pracher
From:
Michigan, USA
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Posted 14 Jan 2012 3:27 pm
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David. I have an Oahu Tonemaster that is very similar to the one you have there and mine had the same problem. All mine needed was:
1) A string change. (The former owner had a real light string for the high E)
2) I adjusted the pole pieces on the pickup. On mine it was real easy. They were just screws and you just needed a flat blade screwdriver to adjust them in or out of the pickup. ( The closer the plole piece is to the string the more output)
A few minutes of of playing around with it and I had the output nice and even.
_________________
"Don't be mad honey, but I bought another one" |
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David Hayes
From:
California, USA
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Posted 14 Jan 2012 4:25 pm
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| Will post pics soon when I can light things so details are visible. - thanks for the help diagnosing the problem. I will also try to adjust the poles if I can figure out how to get to them (the wood piece covers them). THANKS for all the help fellas! |
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David Hayes
From:
California, USA
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Posted 16 Jan 2012 2:37 pm
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A better description of the problem is that the tone is less bright so the low E overpowers the high e - kind of muddy. Here are the pics of the circuit. I have hi res versions if those help. The original pots have "Stackpole W618" inscribed. Replacement pots are new modern allpart 500k - any help appreciated.
Overall wiring
Tone pot wiring
Filter/Capacitor attached to tone pot
Original Tone pot
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Blake Hawkins
From:
Florida
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Posted 16 Jan 2012 7:00 pm
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The two resistors on the original pot are:
The green one is 500,000 ohms and the red one
is 200,000 ohms.
They are very old and use the "body-end-dot"
resistor color code system from the '30's and
'40's. |
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Steve Ahola
From:
Concord, California
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Posted 17 Jan 2012 1:27 am
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| David Hayes wrote: |
| A better description of the problem is that the tone is less bright so the low E overpowers the high e - kind of muddy. Here are the pics of the circuit. |
For starters you might try running the output from the pickup directly to a guitar cable bypassing all of the circuitry (which looks like a rat's nest!  ) If you have a guitar cable with a bad plug on one end you can turn it into a test cable by replacing the bad plug with alligator clips. If the pickup sounds muddy run straight into a guitar amp, it probably needs to be rewound and/or remagnetized.
You might try replacing the capacitor with a modern cap of 0.047uF- those old wax and paper ones sound great but they don't last forever. If you don't want to deal with this yourself a good tech should be able to diagnose the problem fairly quickly.
As for the resistors on the original pot, the 500k ohm one between the two outside terminals was probably used to lower the resistance of the tone pot. (I have no idea why the 200k resistor was used, or where it was connected. The terminal that it is connected to is normally not used on a tone control.)
Good luck!
Steve Ahola
P.S. I'd imagine that the wooden pickup cover is secured with some of the nuts on the back of the steel.
_________________
www.blueguitar.org
Recordings on electric guitar:
http://www.box.net/blue-diamonds
http://www.box.net/the-culprits |
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Steve Ahola
From:
Concord, California
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Steve Ahola
From:
Concord, California
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Steve Ahola
From:
Concord, California
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Steve Ahola
From:
Concord, California
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Steve Wilson
From:
Morgan Hill, California, USA
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Posted 18 Jan 2012 4:59 pm
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I found this useful info a few months back regarding changing the value of pots by using different value resistors. I think this is what is going on with your Oahu (Kay)as mentioned before.
http://www.projectguitar.com/tut/potm.htm |
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Steve Ahola
From:
Concord, California
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Posted 19 Jan 2012 12:58 pm
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| Steve Wilson wrote: |
I found this useful info a few months back regarding changing the value of pots by using different value resistors. I think this is what is going on with your Oahu (Kay)as mentioned before.
http://www.projectguitar.com/tut/potm.htm |
Adding a resistor between the outer terminals will reduce the total resistance of the pot, but I find it even more useful to add resistors between the middle terminal (the wiper) and the outer terminals (one or another or both).
If you start off with a 1M linear taper pot, adding a 220k resistor between the wiper and the cold/ground/CCW terminal will create an 180k audio (logarithmic) taper pot. Adding the 220k resistor between the middle terminal and hot/CW terminal of the pot will convert it into an 180k reverse audio taper pot. Adding 220k resistors between the wiper and both outside terminals will create a 180k audio/reverse audio dual taper pot
Here is a great article on The Secret Life of Pots by R.G. Keen:
http://www.geofex.com/article_folders/potsecrets/potscret.htm
So what do all of these tapers mean? Audio taper means that the volume increases gradually as you turn the control up from 0. Reverse audio taper means that the volume decreases gradually as you turn the control down from 10. Audio taper is great for volume swells, but I usually prefer the reverse audio taper as it gives me more control over the volume as I turn it down from 10. A dual taper audio/reverse audio pot would combine those two properties. (A tapering resistor of 20% of the value of the linear pot will give you the best simulation of an audio taper.)
Steve Ahola
_________________
www.blueguitar.org
Recordings on electric guitar:
http://www.box.net/blue-diamonds
http://www.box.net/the-culprits |
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David Hayes
From:
California, USA
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Posted 19 Jan 2012 1:05 pm
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| THANKS for all the help guys - I have some parts on the way - will let you know how things turn out. |
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