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Jack Bruce (ish) EB3 / SG Bass


Andyjr1515
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[quote name='FuNkShUi' timestamp='1476703726' post='3156389']
Cracking job mate.
I shall remember they're Swifts from now on too!
[/quote]
No problem :lol:

The brass nut arrived this morning................. but it was a 6-string electric. Hopefully a replacement is on the way.

Two bits of further progress: Popped a strap button on the back and did a few checks. Great news - a more conventional strap button position is fine and it balances and sits beautifully




Second bit of progress, I did a few quick soundclips - [url="https://soundcloud.com/andy-rogers-6/eb-3-style-custom-bass-sound-files"]this is Bridge; Both; Neck[/url] No point in trying the notch settings yet - you would hear my breathing louder than what's coming out of the amp :lol:

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What value choke are you using? IIRC the Gibson circuit diagrams only give a Gibson part number rather than the actual value of the choke.

When I built my first electric guitar in 1979, I fitted a varitone that used every version I could find circuits for because I wanted to use all 11 positions on the speed knob I had. TBH most of them sounded crap and there was a significant volume loss on all but the most subtle variations.

Edited by BigRedX
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[quote name='BigRedX' timestamp='1476725506' post='3156696']
What value choke are you using? IIRC the Gibson circuit diagrams only give a Gibson part number rather than the actual value of the choke.

[/quote]

A further element of subterfuge / chicanery was alleged on the part of Gibson: The inductance values were stated incorrectly on the circuit diagrams to mislead other manufacturers. I have picked up this statement from internet research so it may have no credence whatsoever. Do you have a multimeter that will measure inductance?

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[quote name='BigRedX' timestamp='1476725506' post='3156696']
What value choke are you using? IIRC the Gibson circuit diagrams only give a Gibson part number rather than the actual value of the choke.

When I built my first electric guitar in 1979, I fitted a varitone that used every version I could find circuits for because I wanted to use all 11 positions on the speed knob I had. TBH most of them sounded crap and there was a significant volume loss on all but the most subtle variations.
[/quote]
[quote name='3below' timestamp='1476725918' post='3156703']
A further element of subterfuge / chicanery was alleged on the part of Gibson: The inductance values were stated incorrectly on the circuit diagrams to mislead other manufacturers. I have picked up this statement from internet research so it may have no credence whatsoever. Do you have a multimeter that will measure inductance?
[/quote]

My head goes squiffy when I try to get it round the difference between henrys and ohms inductance value :rolleyes:

It is a 1.5H induction coil with induction values quoted at 4k ohm primary (presumably therefore 2k ohm tapped) and 600 ohm secondary coil. In terms of resistance, they are quoted as 148 ohms primary and 64 ohms secondary. I've got a 100k resistor and 0.022uF capacitor making up the rest of the circuit

I think I need to check my components wiring diagram against the original circuit diagram before I do anything else (and double check I actually physically wired it up that way!). This is the components diagram I used:


If one of you can give it a glance for a quick sanity check that would be great :)

Edited by Andyjr1515
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In fact, have I spotted the error? Presumably the notch circuit is supposed to be a bleed off the main volume? I've realised, I have the feed from the neck p/up in positions 4 / 5 & 6 ONLY going through the capacitor/resistor circuit. Presumably I should be taking a line direct from the volume hot to the 6 \\ position on the rotary switch?

It'll take 2 mins - I'll try it

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[quote name='Andyjr1515' timestamp='1476785128' post='3157152']
In fact, have I spotted the error? Presumably the notch circuit is supposed to be a bleed off the main volume? I've realised, I have the feed from the neck p/up in positions 4 / 5 & 6 ONLY going through the capacitor/resistor circuit. Presumably I should be taking a line direct from the volume hot to the 6 \\ position on the rotary switch?

It'll take 2 mins - I'll try it
[/quote]
OK - well I think that has worked to an extent. In position 4 (intended to be neck going through notch filter using full primary induction coil) I now have a sound that is different to the other positions, more trebly and lower volume (bit like the equivalent of putting a mute on a trumpet) but OK. The other two positions still lose most of the volume.

But I'm still not convinced I've got the notch circuit right...

- or if it is, I might use the other switch positions in a different way :D

Whatever, it is an interesting diversion. Also - in all other ways - I'm really pleased how the bass is turning out. I've been playing it this morning and it sits so nicely both on the strap and on the knee and, with the neck volume at about 9 and bridge on 10, the three main position sounds are phenomenal.

Can't wait to get the proper nut on and hear it through a bass amp :)

Final tweak I might do is take the neck back down to wood and restain/reoil it....I've got it silky smooth but I've gone a little too enthusiastic with the slurry and buffing and the mahogany colour is showing through a bit through the dye. I might try Pete out with it first, because it is lovely to play and he might prefer it as it is.

Edited by Andyjr1515
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Thanks, folks :)

Showed the progress to Pete last night - he's delighted with it (phew)

He's a good player - it sounded great! It's light, it balances beautifully, the neck is the same profile as his favourite bass and it looks quite classy in the flesh

Very few things to do now:
- re-stain the neck. Easy job. I tried a variation on my experiments with the slurry method which didn't really work, so I'll redo it the way I did my LP junior so that the buffing doesn't start to reach the mahogany (which is what it's doing at the moment)
- sort the varitone notch or alternatives for switch positions 4-6
- fit round-wounds
- fit the brass nut that should be arriving in the post today
- get him a hard case

On the basis that there's plenty of time for those jobs before his November birthday, I've started getting my head round a couple of smaller mods and a very exciting full build, all for Basschat members :). I'll kick off threads at the appropriate times ;)
Oh...and after I've finished those, then Pete wants me to build him ANOTHER bass...piccolo (c 25" scale, to boot...maybe fanned frets...)!!!!

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The filter circuit appears not to be a 'notch' but is a [b][low pass] WRONG[/b] . The idea that it is a 'notch' filter is stated elsewhere on websites/forums. Using this website [url="http://sim.okawa-denshi.jp/en/RLClowkeisan.htm"]http://sim.okawa-den...LClowkeisan.htm[/url] [b][edit for correct link] [/b]and the following values: R = 220 Ohms, C = 0.02 uF and L = 1.5 H gives a low pass filter result. I used 30Hz to 12000 Hz as the frequency limits. I would like to model it in some other simulations before drawing firm conclusions. Quite why you would want to low pass the 'mudbucker' is debatable (and counterintuitive). More research to follow.


[b]Edit for sense and correctness: [/b]After thinking and exploring the correct simulation I have realised that it is a low pass filter. The digram on the website takes the output voltage across RC. The Gibson EB3 circuit modelled takes the output voltage across the inductor L. This 'inverts' the filter to a high pass filter. My rhetorical question at the end of post was right.

Edited by 3below
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Surely the varitone circuit should be a high-pass filter?

Certainly the one I made copied (and expanded) from a Gibson 355 circuit sounded that way. The more usable settings made my DiMarzio Super Distortion humbucker sound as tinny as a Telecaster single coil!

Edited by BigRedX
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[quote name='BigRedX' timestamp='1476909342' post='3158463']
Surely the varitone circuit should be a high-pass filter?

Certainly the one I made copied (and expanded) from a Gibson 355 circuit sounded that way. The more usable settings made my DiMarzio Super Distortion humbucker sound as tinny as a Telecaster single coil!
[/quote]

This is what 'surprised' me when I put the LRC configuration and values into the simulator. More so when you think about the 'mudbucker' in an EB3, why would you want to further remove high frequencies. I have treated the pickup simply as a source of ac emf and not factored the pickup's resistance (impedance) and inductance into the circuit. I wonder if my simulation was too simple. More research / exploration needed (or an EE on BC).

Edited by 3below
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I don't know if it has any relevance, but the outfit in the states that sell an 'improved' Eb-3 pre wired loom (can't remember their name but I'll post a link in a bit) apparently aim for a 800hz mid point...they don't say how they achieve that, though ...

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[quote name='Andyjr1515' timestamp='1476912030' post='3158497']
I don't know if it has any relevance, but the outfit in the states that sell an 'improved' Eb-3 pre wired loom (can't remember their name but I'll post a link in a bit) apparently aim for a 800hz mid point...they don't say how they achieve that, though ...
[/quote]
Got that wrong. The site is here, Rothstein Guitars http://www.guitar-mod.com/rg_eb3.html

I think what they are saying is that is is supposed to be a notch that lets all frequencies though except the target range? Their range they say they are trying to block are the frequencies around the 800hz, if I've understood their blurb correctly.

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[quote name='Andyjr1515' timestamp='1476913347' post='3158518']

Got that wrong. The site is here, Rothstein Guitars http://www.guitar-mod.com/rg_eb3.html

I think what they are saying is that is is supposed to be a notch that lets all frequencies though except the target range? Their range they say they are trying to block are the frequencies around the 800hz, if I've understood their blurb correctly.
[/quote]

Your understanding is correct in my world of Physics / Electronics, you have described a notch filter. They have a very interesting looking varitone wiring diagram for the 'CT' bass on the website. Might be useful? http://www.guitar-mod.com/wiring/ctimages/ctbass_wiring.gif

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