Would this be a reasonable thing to do?

We are fortunate to count Paul Gagon as a member here, so it seemed natural to give him a home to stretch out in and relax a little. Maybe exercise the grey matter and present a little history of the guitar and bass (amps too!) from his perspective as one of the eminent designers of our time.

Got questions? Great! Good questions might be, "What are the EQ mappings for the M Series preamps?" Or, "What was the thought process behind the MJ-4?" Troubleshooting questions should remain in the regular forums (he reads those too). Finally, please be mindful of how I feel about tech questions via PM or email.

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Would this be a reasonable thing to do?

Postby jglunt2112 » Sun Sep 27, 2020 2:15 pm

I love my Fullerton SB-2, but I'm partial to basses with one volume control. (Probably the result of playing a P-bass for a thousand years.) The SB-2 has two, one for each pickup, and the balance between those pickups is how you set the bass's tone. (Of course, you all know that.) So if you have to turn volume up or down during a song or set, you have to do it by adjusting one pickup at a time and, at least for me, tweak it several times to get that tonal sweet spot back. Of course, said tweaking also changes the volume as well, so it can all start over. I thought of this possible solution that wouldn't require any routing or other "heavy lifting." Run the volume for both pickups through the first pot, making it a master volume. Change out the second pot for a fader control to dial in how much of each pickup goes to the output. The bass would look exactly the same as it does now, but volume adjustments would be simpler and more consistent tonally. Could this work? Has anybody tried this? Is there a diagram showing the wiring for this with pot values, etc.? Diagrams I can follow; an electronic innovator I am not. Thanks...Jim
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Re: Would this be a reasonable thing to do?

Postby Ken Baker » Sun Sep 27, 2020 6:57 pm

Reasonable? Sure!

Here you go. Click the image for a PDF suitable for printing.

Image

Pots are both 250KA (250KΩ Audio taper). Those downward pointing arrow thingies represent a connection to ground. Arrange the leads as needed. The final connection to ground is to the sleeve connection on the jack.

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Re: Would this be a reasonable thing to do?

Postby jglunt2112 » Sun Sep 27, 2020 8:12 pm

Beautiful. I just might have to give this a try. Thank you...Jim
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Re: Would this be a reasonable thing to do?

Postby jglunt2112 » Sun Sep 27, 2020 10:07 pm

I have had no luck finding a 250k-250k audio taper blend pot. Everything I find is linear. I've checked All Parts, Stew Mac, Amazon, and even G&L. Does anyone have an idea where I can find one of these? Thanks!...Jim
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Re: Would this be a reasonable thing to do?

Postby Ken Baker » Mon Sep 28, 2020 12:16 am

jglunt2112 wrote:I have had no luck finding a 250k-250k audio taper blend pot.


I was working off a really old set of notes.

A standard 250K-250K blend should be fine.

Sorry about that.

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Re: Would this be a reasonable thing to do?

Postby jglunt2112 » Mon Sep 28, 2020 7:52 am

No problem. Even the diagram you sent me states plainly a 250kA pot for the blender. I was wondering if I was going crazy. Now there's no more need to wonder...I know for sure that I am. Thanks...Jim
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Re: Would this be a reasonable thing to do?

Postby Ken Baker » Mon Sep 28, 2020 11:15 am

The diagram was hand scrawled by yours truly. ;)

Just get a 250K blend pot.

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Re: Would this be a reasonable thing to do?

Postby jglunt2112 » Wed Feb 24, 2021 12:07 am

I finally installed a 250k blend pot into my SB2, so it's wired as master volume & blend. I used a linear taper pot, as I couldn't find an audio taper pot. (See previous messages.) I had a hum problem, which I figured out thanks to you guys, but it just isn't acting right. The blend is not smooth at all. It kind of changes as if it were a notched switch, not changing at all, then taking a jump, then repeating that. Is that because of the linear taper? It also somehow seems to have affected the volume control, as it very slowly increases volume until it's about 3/4 full, then it jumps up much louder. I tried an MN taper blend pot, which was a disaster. It literally sounds like I have a 3-way switch installed. I did find a seller on Ebay that had one 250kA blend pot, which I ordered, but I'm curious if any of you might have some thoughts on this...Jim
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Re: Would this be a reasonable thing to do?

Postby jglunt2112 » Wed Feb 24, 2021 10:49 am

Here is a follow-up question (or two) to my follow-up question (see previous post on this thread). Ken, I notice on your wiring diagram that the ground from the "X" on the blend pot just shows going to ground. Is it supposed to be connected to the chassis of the blend pot? I read some articles elsewhere that say not to do that, but (1) doesn't that introduce the possibility of hum, and (2) isn't the blend pot grounded anyway because it's against the foil on the back of the pickguard, as are the jack and the volume pot, both of which are grounded? I grounded both the "X" to the blend pot chassis and ran a ground wire across from the volume pot chassis to the blend pot chassis. I also grounded the bridge pickup and the bridge to the chassis of the blend pot. Am I wrong in doing all that? My feeble and inquiring mind wants to know :ugeek: ....Jim
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Re: Would this be a reasonable thing to do?

Postby Ken Baker » Wed Feb 24, 2021 1:27 pm

jglunt2112 wrote:I finally installed a 250k blend pot into my SB2, so it's wired as master volume & blend. I used a linear taper pot, as I couldn't find an audio taper pot. (See previous messages.) I had a hum problem, which I figured out thanks to you guys, but it just isn't acting right. The blend is not smooth at all. It kind of changes as if it were a notched switch, not changing at all, then taking a jump, then repeating that. Is that because of the linear taper? It also somehow seems to have affected the volume control, as it very slowly increases volume until it's about 3/4 full, then it jumps up much louder. I tried an MN taper blend pot, which was a disaster. It literally sounds like I have a 3-way switch installed. I did find a seller on Ebay that had one 250kA blend pot, which I ordered, but I'm curious if any of you might have some thoughts on this...Jim


Sounds like there's something odd going on in the pot. Possibly taper, but impossible to check without a replacement. You have one coming, so we'll wait for that.

jglunt2112 wrote:Here is a follow-up question (or two) to my follow-up question (see previous post on this thread). Ken, I notice on your wiring diagram that the ground from the "X" on the blend pot just shows going to ground. Is it supposed to be connected to the chassis of the blend pot?


Any ground point that connects to the sleeve of the jack is good.

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