Gibson SG Bass mod

[fraco]

I`ve ordered a couple of Curtis novak bisonic pickups for my Greco Eb720 (Gibson SG bass copy). I`m gonna change all the wiring and pickups.

The original has a 4way rotary switch for pickup selection and vol+tone for each pickup.

the plan is a 6way 4pole rotary switch for series/paralell and phase in/out switching, and independent volum and tone for both pickups. the tonepot is going to be a modded fender tbx pot. wich will be able to cut bass or treble on both pickups independently.

the rotary switch is going to be wired like below. the rest of the wiring is in the wiring schematic. this is my first mod and wiring schematic, so it may be a bit off, and I do have a few questions...

does this look like a workable mod? I know the volum and tone for the neckpup will not work out of phase (pos 5 and 6). but will there be other complications?

what about the series wiring, will the bridge volum and tone pots suck to much tone for the series mode to work well? other complications because of this?

In pos 3 (bridge only) shall I ground the neck pickup, or does this not matter?

about the schematic. the black wiring is ground. I was unable to show the solding on pots, but hope you`ll understand.. the green wire is the hot signal. the square plate in the middle is the common ground, and the extra ground that connects to the middle of pickups are for the metalcovers of the pickup.

I have showed some of the rotary switch in the schematic. hope you`ll understand the details when you look at the seperate picture. the tbx tonepot is also not very detailed in schematic. see pic for a closer look.

I would really like some help and thoughts about this..

thanks

PS. page about the TBX mod here:

sites.google.com/site/phostenixwiringdiagrams/modified-tbx-tone-control

[ashcatlt]

The rotary looks fine.

You should wire the N V and T across the pickup itself - between the N's green and black rather than the green and common ground. Then it should continue to work even when out of phase. It should also allow you to get broadbucker tones.

That many pots in general can cause some loading issues and kill some treble in series mode, but there's kind of no way around it.

[JohnH]

Hi fraco and welcome to GN2

There's nothing wrong with your intent, it's all quite do-able. The diagram needs some staring at though, since its an assemblage of partial diagrams.

The rotary controls have two things to check IMO. I have some similar 4 pole 5way's in an LP copy. They are Alpha brand, not expensive but quite solid and reliable units. But they are fairly stiff to turn. This was OK in my guitar, since they were used on each pickup and I still had a standard toggle for quick changes. But in your case the rotary is the main selector. Do you need to do any quick changes with it mid song?

An SG, in guitar form, has a very thin body. Is it the same with your bass? (the bass player in our band has an Epiphone one, i like the sound of it but Ive never had a good look at it). Will the twin deck rotary fit in the body cavity?

There are also smaller plastic bodied rotaries available these days. Dannyhill had some on a complex design for a dannilectro - and had some trouble getting a reliable result with them.

On your general scheme - since you are having out of phase and series options, I think there is a huge advantage if you can keep your volume/tone circuits still acting independently on each pickup through those changes. Apologies but I haven't figured out whether your scheme is intended to to that - but you could have it that way. Then you can control the balance of phased pickups.

You could wire each pickup with its volume and tone controls as an independent separate module, with two wires coming out to go to the rotary, from each volume pot. Then the rotary takes these and does the series/parallel and phasing. I have this on my Gibson LP (different guitar to the LP copy) and it works fine. It solves the excess loading problem in series mode and gives you full mixing control in all modes. Its this:

LP modular wiring

Actually, that LP design has a few variations presented, and one of them ends up with a rotary for the output control.

I suggest treble bleed on each volume pot 150k and 1nF in parallel if you use 500k log pots, or 120k 1nF with 250k pots.

John

[newey]

Fraco-

[shadow=red,left,300]Hello and Welcome to G-Nutz2![/shadow]

It looks like ashcatlt and JohnH have you pointed in the right direction. You should mind John about fitment, check and double-check that before you pull the trigger on ordering the switches.

BTW, I tried to fix your link to the TBX diagram, but the link seems to be broken. Can we assume it's the same as what you have posted?

[fraco]

thanks a lot for the comments! ;D

the link is now fixed. and I`ve hopefully made a better wiring diagram.

oh.. some thinking made me decide to use a blend knob and master volum instead of two independent.. the blend comes before the rotary and is wired independently. and the master is after the rotary.

You could wire each pickup with its volume and tone controls as an independent separate module, with two wires coming out to go to the rotary, from each volume pot. Then the rotary takes these and does the series/parallel and phasing.

I don`t see how this is doable with one rotary switch.. and it is basically what I have done. except in order to do the phases and series switching I also had to add the ground from the Npup. but when the phase is reversed( inside the switch), of course , the Neck V and T comes before the pup in the path of the signal.. and that is the problem.. otherwise everything shall be independent.

I took the wiring of the rotary from another source, and I don`t have the skills to figure out a better way to do this. Maybe I`ll come up with a solution, but i figured that I`ll probably not use the phasing positions much anyways.. afterall this is a bass.. and besides, with the master volum I`ll be able to do some independent volum stuff as well:)

but If anyone can come up with a solution for this problem, by a different wiring, It`ll be much appreciated




the parts are already ordered(except blend pot... :, and my bass is thicker than an SG guitar, It has enough room I think..

You should wire the N V and T across the pickup itself - between the N's green and black rather than the green and common ground. Then it should continue to work even when out of phase. It should also allow you to get broadbucker tones.

Isn`t this what I have already done? problem is when phase is reversed, the V and T comes before the pup.. Or do you mean that the actual pots (the metal) should not be grounded to common ground, but included in the pupground? wouldn`t that cause a lot of hum in series and phasereverse mode?

[JohnH]

if you hold off on ordering that blend pot - Ill sketch what I had in mind later
J

[fraco]

thx! I was a bit impatient when I made that first order(week ago). I just assumed I`d find a way. but didn`t know how.. but doing it that way also inspired me to learn a lot

the way the blend switch is wired, it actually works like two independent volumes anyway, doesn`t it? got it from here.. the "stereowiring" www.stewmac.com/freeinfo/Electronics/Pots/i-4137.html I figured it was better with a blend and MV when that`s possible.. it is nice to have a master volum when playing live.. but if you sketch it with two V`s instead, I don`t mind. that is not the issue here

got to go to bed. thanks for the feedback and help!

[newey]

Fraco-

I don't know about the rest of it-it's late and I'm done for the day. But your master volume control is wired as only a two-wire rheostat, you need to ground the third lug.

[sumgai]

fraco,

Hi, and to the NutzHouse!


Since you're an admitted newbie, I'll break this down into non-threatening chunks for easy digestion.

1) Your drawing(s)..... You need to do a couple of things to make it easier for anyone (even us Nutz) to read it:

a) Don't hide any lines at all, I'm speaking specifically to the black, allegedly ground, wires, but this applies to every wire. If you make the viewer infer the path of a wire, mistaken assumptions will follow, trust me on that.

b) Number your rotary switch terminals. Some of us would like to help you, but we have to guess at which terminal is which, trying to match them up with the first image (the 6T4P rotary switch). I tried, but no matter how I looked at it, I seem to find several connections missing, and more than a few that I'm pretty sure should not be there....

c) While we're looking at that rotary switch.... don't let wires touch any terminals except the necessary ones, not even a tiny bit,. Right now, I see the lower pickup's green wire passing through several terminals, and I'm left scratching my head as to whydidhedodat.

d) I guess, after going cross-eyed, I should just blurt out "Label Everything." Which control is V, which is T? Which pickup is which? (Your first diagram had it pretty close to easy to guess, your second one is.... let's just say, challenging. )


2) Your first diagram showed the output jack being fed by the selector switch, the usual and standard way of using a 2P,2V,2T arrangement. However, your second diagram shows that same jack getting its signal from a pot (which one - I dunno!), decidely not the customary way. Keep in mind that this isn't necessarily bad, it's just not easy for us to discern why you might want to do this, that's all I'm saying here.

That was the bad news, now for the good stuff:

We've certainly seen "first posters" that were less prepared than you, much less! But we're all pretty friendly here, that kind of thing doesn't bother us at all. But what we're all about is helping each other get past tuff problems, and learn how to solve similar problems in the future. Really, that's it - helping others to learn how to figure out what's going on, and how to either fix it, or make it better... aka, modding it!

So what I've done, hopefully, is give you a nudge towards putting more detail into your drawings, so that we don't get Excedrin Headache #8 trying to put two and two together. Along the way we'll ask questions, you'll ask questions, and everybody will benefit from the answers.... even those posted by gumbo, our own notorious thread-derailer! ;D

HTH (Hope That Helps)



sumgai

[fraco]

about the master volume. I simply forgot to draw the ground wire.. and I didnt notice until I posted.

and about the drawing. I have a lousy program for drawing wiringschemes.. and I`m from norway. So on top of lacking a solid foundation in English writing, almost no experience, I have a problem with the program. However it is fairly easy to lay out a rough diagram on it. so I think it`s ok when trying out ideas, Its called DIY Layout creator.

But I have only two "bendable" wires to choose from. Black and green. and they are also a bit hard to "mold". you have to connect the wires. and then "shape it". thats why the green wire from the MV is touching the rotary. And on top of that; the black wire ALWAYS goes below anything else.. dont know why.. oh, did i mention I cant write on the diagram? haha..

needless to say, I need to find a new program and draw the whole thing better...

thx for honest feedback.

[JohnH]

fraco

This is the thought I wanted to describe:



Its based on the diagrams that you are using, but I'd suggest you redraw it if you are interested.

Both sets of controls stay effective and independent in parallel, series and out of phase modes.

The top part shows how to adapt the TBX/volume circuit to get all the signal wires separate from those connecting ground to the cases, so when it goes in series with the other, or out of phase, grounds stay correct.

I added the treble bleed to the volume control. This is the key to keeping the mixes in series consistent if you use in-between settings, with one or both pickups not at maximum.

You can wire up both sets identically, then combine them with your rotary as in the lower diagram.

I'm confident this works in principle, with the two volume controls, but I'm not sure how consistent the tone would be if adapted to the blender then master tone - it adds another pot to the system.

Anyway, good luck!

John

[fraco]

I don`t understand all things about your wiring, but from what I can tell, only the volum will function out off phase, right? but I also see you have connected the tonecap to the pup cold.. this is the part I don`t understand.. will this make the tone work in OOP mode as well, or is this only because of grounding issues in series mode?

anyways,

thanks! this helps a lot

[fraco]

There.. I`m still not sure if your wiring has the TBX pot working properly out-off-phase. but anyways. I`ve constructed a new diagram. this time it is hopefully understandable to all of you.. and it`s a bit changed.

the difference is. I have added push-pulls to the volum pots.

one does phase switching on Npup before the signal reaches any pots. the other is a stereo/monoswitch.. wired so I can have T V on each source of course..

now, because of two spare "slots" on the rotary, I came up with the Idea of adding a midchoke to series and paralell mode. I think this is my final take on the wiringscheme..

but I would still like some feedback on it:) beeing a newbie, i`m not so sure if everything works properly...

the DPDTs on push/pull is drawn upside down to make it easier to see where all the wires are going.. kind of stupid, I know..

also another reason for using push/pull on phase is I can easily experiment with HOOP (adding a cap in series to the lead in OOP)



anyways, here goes..

[JohnH]

fraco - that's a good diagram to work with - you are definitely embracing this rather specialized subject of guitar wiring that we do around here!

OK, comments:

I don't think you need the extra phase switch, if you also have the phased options on the rotary.

The way I suggested to amend the TBX/Volume wiring, creates a 'black box' with two wires coming out and a signal output across them. All the volume and tone functions are within the box so always work in any mode. The two outputs, red and blue, are not dedicated to being ground and hot, they can be either. Neither of them are directly grounded within the 'black box'. the ground for the back of pots etc is not on the signal path.

So you can flip the phase of the whole lot, after-wards, at the rotary, and this works (though its not the usual way). I have this phase after volume/tone on my LP.

But, if you prefer to have a push/pull for phase, then you can drop two positions on the rotary, and reduce it down to a three pole four way switch. This is a simpler thing, more common and is only a single layer instead of two layers. It will be easy to work out a diagram for this, let me know if you want to go this way and if you want help, what order would you have the settings? eg neck, both series, both parallel, bridge?

With your stereo switch - all fine. Here's a couple of things to consider:

Is it more useful to have a stereo socket as you showed, or two mono sockets - in terms of the amps and leads that you will use? (I don't know)

If you are using a mono set up, and pull the stereo switch, it will cut to one of the pickups, which is the neck as shown. This effect could also be useful for changes mid-song, if you find turning the rotary is fiddly and pulling a knob is easier. In which case, is it better to have it default to neck or bridge?

When you draw a push pull, its better to show it at 90 degrees to how you have it, with two of the outer lugs facing the pot. In that case, the default pushed-in setting has each centre lugs connected to the lugs furthest from the pot.

John

[fraco]

about the mid choke: on a gibson series 2 EB3, the inductor is about 2,5-3 H. and the cap is .47MFD. it is wired as I have drawn with an inductor and a cap in series to ground, and the rest of the signal goes to output. However the series 2 EB3 used 300k pots. I`m gonna use 500k. the Gibson midchoke was tested a lot, and I think I`m gonna try to duplicate that as a start..

. but do I need to go up or down in cap and inductor values to compensate for the different V pots? I guess I need to try different values because of different pups, tonepots etc. as well. but it`s nice to know where to start.. and the TDX pots do have a center detent...

the Series 2 Eb3 has two 250k T pots, and 2 300k V pots in the circuit

[fraco]

There.. you have already answered.. as you can see I`m currently figuring out how to do the midscoop. the thing is; I`ve already ordered the rotary. and with a midscoop and modded TBX, I can in a way have a three band EQ.

I would like one stereojack. mostly because i don`t want to make permanent changes to the bass. plan is to change all the guts, with the possibility to install it and perhaps sell it as a vintage original guitar..

Neck is also my desired Pup. so everything is like I want it to be.. the phase switch also comes in handy in stereomode.. especially If I`m gonna use two channels on one amp

I`m gonna make a better drawing soon.

[JohnH]

on your mid scoop idea, is this to go on the rotary control? being after the volum epots, its effect on tone may varry according to the volum esetting, beacuse it will be either mor eor less connected and able to interact with the pickups.

But, if you have an inductor and cap in series, their main effect is that, at a particular frequency, they have very low impedance, thus shunting your signal at that frequency resuklting in a mid scoop, the depth of which is controlled by the resistance. So, if you have some starting values to apply from something you have seen befoer, I'd think they will probably still wotrk much the same.

The notch frequency will be at f= 1/(2Pi. sqrt(LC))

John

[fraco]

Ok, don`t know If I`m gonna start doing the math, just yet. but thanks anyway

I think I`ll start with the inductor that is originally in my Grecobass. then probably .47 in pos 6(series) and .22 in pos 5 (parallel).

If I`m gonna add resistors, shall i do it in series or paralell, and what difference does it make to the sound? I guess you can have a lower cap value but same overall resistance, not making the notch to deep right?

my last schematic(with added variable midscoop)

[newey]

fraco-

I see some issues with your diagram at position 6 of the rotary. First, IIRC, you first had this as an OOP setting, but now it's to be BN * B with the choke, correct? If so, you've still got OOP because the B "hot" is wired to the N "hot.

But even more basically, you've got the B "hot" connected to both N "hot" and N "ground", meaning you'll get no output from the B pup at that position. This connection occurs via the red jumper between lug 6 on the upper deck, bottom pole (which connects to neck - in Pos. 6) and lug 1 on the upper pole (which connects to neck + via lug 6 on the upper pole, and also to output via lug 4, upper pole).

You need to rewire that position so that it mirrors position 4, but with the choke added.

Other than that, it looked OK to me.

[fraco]

thanks! It`s the first time I`ve drawed on a rotary wiring.. the other one, with OOP, I just found..

I believe I have fixed it now...

[JohnH]

fraco
If you want to investigate values for your mid scoop, then the 'GuitarFreak' spreadsheet in the reference section could help.

It runs the maths for working out frequency response of typical guitar/bass circuits, and the tone control section includes a tone pot, cap and an inductor (which would normally be set at 0H).

So you could use this to play with values.

It doesn't do is also model a normal tone circuit at the same time, there's only one tone control built in - but it will still give you a clue.

To control the mid scoop, a resistor in series is what you want.

This is the set up, modelling a Jazz bass pickup, a 3H inductor, a 0.047 cap, and the tone pot set at 4.4% of a 250k pot, ie 11k (10k or 12k are the nearest standard fixed values). The pickup inductance for P bass would be higher, say 6H according to data.



If you reduced the tone pot Resistance to 0, this would happen:



What I thought was, if you have excel, maybe you could download the spreadsheet, set it up to replicate the first view, then play around with the tone values to see if you want to do this.

Note: the blue trace is the basic tone with the tone control at max, press the 'snap-shot' button to capture it. Next to is is a 'volume match' button - uncheck this.

cheers

John

[fraco]

Ok. my logic tells me that in order to imitate a pot turned f. ex. halfway down, you could then add a resistor in series, right? I have searched the net and the forum for info on midscoops, but almost everyone, except the one on the vintage SG bass, seems to be based on adjusting the amount of cut with a potmeter (thats why i wonder if I can imitate a potmeter with a resistor)..

I`m not so good at understanding the Resistance and elctronical theory stuff.. but my logic tells me that the series mode will need more resistance than the parallel. to aquire a goodsounding midscoop. this because of the pickups beeing wired in series.. or is it the other way around? that I need more resistance on the parallel?

I guess I only have to try and experiment to find two midscoop settings that work. because of midscoop comes after tone and volume.. and that is not the way it usually is done, right?. but in a way, I think that can make the midscoop more versatile and adjustable by itself also..

but anyways the prosess of finding a good midscoop will be a lot easier if I know what I`m doing.. and that program looks like it will help me understand:) thanks for all the help, info and link!

[fraco]

I`ve recieved most of my parts except the pickups, so I`ll guess I`ll start the wiring soon, to have everything ready for the pickups arrival. However, I came across the Villex passive mid boost, and decided I wanted to have that instead of the midscoop.

anyone here with any info on how this booster work? www.villex.com/internal_booster.html

here is a wiring schematic in pdf. only one I found... www.villex.com/downloads/switch%20boost.pdf

I`ve tried searching the net (incl. this forum) for info on this but the only info I find is that it is probably transformer or inductor based.. But It has gotten really good reviews also for basses, and thats what I really care about.


I have a question about the wiring. do I need to wire the output from the toneboost straight to the jack output as showed, or can I just wire it to join the other outputs on the rotary? see pictures

[fraco]

last version without stereo/mono switch, but with the midboost on the push/pull and midscoop.. perhaps this is the version I finally end up with. but I`m first going to try midboost and stereoversion. to see if Stereo comes in handy and because of not having to go through all the hassle of finding midscoop values.

[newey]

fraco-

I'd neither heard nor seen the Villex module before, so no experience with it, and no one has discussed it since I've been hanging around this joint. So, you're the guinea pig with this unit.

As a passive device, it can't really "boost" anything. Any perceived increase in the mids is apparent only because other frequencies are attenuated. IOW, it's a relative boost, not an absolute boost.

That's not to say it isn't a worthwhile thing to have; again, I have no experience with it.

We can't tell much more about it since the circuitry is presented as a "black box"- we don't know what's inside. The manufacturer undoubtedly wants it that way. It's probably a fairly simple circuit inside there.

As far as wiring it up, you've shown two different diagrams, so I'm not sure what exactly you're showing us there. The maker shows two different applications- one switched and the other unswitched (constant "on").

It looks like you've used the "constant on" wiring, and are using the rotary to cut the output of the device. That may well work just as you show it, but since we don't know what's inside the "black box", it's hard to say for sure.

I would suggest wiring it differently. Use the diagram showing the switched version of the wiring, and use the unused pole of your rotary switch.

The mfr. shows it with a SPDT toggle switch (On-On). The center terminal as shown on their diagram corresponds to the "common" terminal of your rotary- use the unused commons terminal on the unused pole of the rotary.

The "boost" connection, as shown for the toggle, then goes to the terminal where you want the "boost"; the "bypass" terminal as shown is then wired to the positions where you don't want the unit to operate. Output and ground connections are then as shown.

In that way, you're wiring it for switched output just as the maker shows, and it's no problem to do so since you have the free switch pole sitting there unused.

As you have shown it, I would be concerned that simply cutting the output line and leaving the unit connected to ground may leave it loading things when not used, since we don't know what's inside. It would probably work as you show it, but I think you're better off following the directions for the switched version.

[fraco]

thanks.. that makes perfect sense. You save me again newey! I simply forgot that it was connected to ground and thought only about the hot poles. wich are connected to nothing in pos 4-1.. Of course when the unit is connected to ground it makes sense that some of the signal might also goes to ground.

[fraco]

btw. here is a graph of a 4way rotary version of the midboost. my mod will only include the 7db version (red graph).



wonder how this works...

[newey]

Your latest diagram is what I meant, anyway, not sure there would be any difference either way, but I think it's just a "cleaner" install using the empty pole of the rotary.

You also posted another version using a separate switch, which I didn't see before I posted. That would allow the midboost to be used in all settings, or to be off in all, so is more flexible- but of course requires another switch.