Pots to switches

[Mk90]

I had an old Ibanez gio jazz bass that I made to a project bass to tey out different things. I pulled the frets and made it fretless and I'm more than happy with the result and can definately see myself gigging with this.

Now I'm thinking of modding the electronics. I generally find one or two sounds I use for any given gig. This means a couple of different blends on pickups and maybe one or two flavours with the tone pot. I thought maybe using switches with pre-selected values in place of the pots.

The bass is basic vol-vol-tone. The idea was to maybe have switches with on-off-minipot for each pickup to have them on/off and one pre-selected value. Tone could be just fully open and minipot.

I'm handy with soldering iron and can make basic repairs easily, but I have zero understanding on designing electronics and how to make something like this.

 

[MidlifeBeginner]

Circuit wise, you can think of push poll pots as a separate switch and pot. The two parts work as independent circuits.

Grounds always stay connected.

Assuming your pickups are wired parallel, each switch should cut off the signal between the pot on the jack.

In the circled spots, you wire the cutoff switch between the pot and the wire.

 

[dwizum]

Keep in mind that the controls are a major factor in determining the tone of a passive bass, even when they are fully on. The volume and tone pots act as a resistive load in parallel with the pickup, even when fully on, which tends to roll off high frequencies and cause an upper-mid frequency resonant peak. That tone is what our brains have been programmed to accept as a natural tone for a bass, and it's very different than the tone you get if you literally wire a pickup straight to a jack with no pots or other controls involved at all.

As a result, if you design controls using switches in order to create a "full on" option, and your on option doesn't include the pots at all, you'll find it sounds very different than a normal bass with the controls turned all the way up. Of course, you may find you really like that tone, but it'll be different, and if you want a natural full on tone you won't get it that way.

If you want your on option to sound like a normal bass with the controls turned up, you can wire the controls such that the on option includes a resistor in parallel with the pickups, of the same value as the pot. So, basically, a "volume bypass" switch would swap between a pot and a resistor of the same value as the pot. Then you'd dial the pot to your desired setting, and you'd be able to switch between that setting and a normal passive bass full volume tone.

 

[Jerry Catanescu]

I had an old Ibanez gio jazz bass that I made to a project bass to tey out different things. I pulled the frets and made it fretless and I'm more than happy with the result and can definately see myself gigging with this.

Now I'm thinking of modding the electronics. I generally find one or two sounds I use for any given gig. This means a couple of different blends on pickups and maybe one or two flavours with the tone pot. I thought maybe using switches with pre-selected values in place of the pots.

The bass is basic vol-vol-tone. The idea was to maybe have switches with on-off-minipot for each pickup to have them on/off and one pre-selected value. Tone could be just fully open and minipot.

I'm handy with soldering iron and can make basic repairs easily, but I have zero understanding on designing electronics and how to make something like this.

I once used a rotary switch in place of a pickup blend pot. I think it was a 5-position. It allowed me to select neck, bridge, both, and two pre-selected "in between" positions (basically, a full pickup plus the other pickup through a resistor). Much easier to recall "sweet spot" positions than by turning a blend pot just right. Especially when recording, when you try to recall the tone you used a week ago. I did that to a Status Graphite bass, if it's any encouragement to try it with your Gio.

Alpha makes some nice little green rotary switches that look like mini pots and won't break the bank.

 

[micguy]

The volume and tone pots act as a resistive load in parallel with the pickup, even when fully on, which tends to roll off high frequencies and cause an upper-mid frequency resonant peak.

The inductance (in your pickup(s)) and the capacitances (in the pickups and especially in your cable) are the circuit elements that create the upper mid peak, and the rolloff above that. The resistances mostly (it's a bit more complicated at less than full volume) damp the resonant peak - higher resistances damp the resonant peak less, which means (with the volume and tone controls full up) that your instrument will be a bit brighter sounding.

 

[Mk90]

Googling now, I realise I might have used somewhat wrong terminology here. By mini pots, I mean really mini mini pots, as in trim pot type. Is there any reason these wouldn't work provided that I find ones that are the correct type and resistance? I would like to have the sweet spot dialed in and not change accidentally exactly for the reasons Jerry mentioned above, but I know I will want to fine tune it from time to time also.

Am I understanding this correctly here? Green would be the resistor or possibly just the straight connection (?), and blue is the "preset pot". Middle position cuts the signal completely. Tone switch would just lose the middle position. These switches would be wired in the circled red spots mentioned earlier:

 

[dwizum]

A "really really mini" trim pot would work fine if you want to tuck it in the control cavity and use it as a set and forget adjustment.

In terms of your diagram above with the red circles. They're not quite in the right place. And there needs to be some adjustments to your other diagram. For the volume pots, think of the pot as having three connections - two ends, and a middle. One end is on hot, the other end is on ground. The middle is on the pickup. When you turn the pot, you change how much resistance is in series versus parallel. Full on has all the resistance in parallel. Your yellow wires on the toggle switch basically need to connect to the pickup's hot wire and the black hot wire that goes to the jack. Then, you can switch to the dialed-in pot, or a resistor connected to ground to simulate full on.

Here's a modified diagram:

If you use an on-on mini toggle, this will give you a preset volume position, and a "full on" with a resistor for a parallel load to simulate the pot. With an on-on-on mini toggle, this will give you those two in the outside on positions, and the middle on position will be a wonky kinda kill switch where that specific pickup will be killed, but the other pickup (if it's in an on position) will have an additional load in parallel from the resistor and the preset volume pot. I can't think of a way around that, but it might be fine for you.

For the tone pot, I'd just use an on-on and have it make or break a separate wire connected from the jack hot to the tone pot middle terminal.

 

[Lostgallifreyan]

A pot is a potential divider. All you need to do is emulate it accurately. Set the pot how you want it, then isolate it (unsolder all but one wire, the last won't interfere with testing). Measure the resistance between the wiper terminal and each end. Note the values, taking care to avoid accidental reversals. Repeat for other settings you want. Tedious, but only needs doing once.

At this point you need to find a rotary switch that has TWO poles, and as many ways as you need settings for. A standard form is a 6-way 2-pole switch, and they come in sealed forms with high reliability, ideally with 1/8'' diameter metal shafts.

Each of the resistor pairs should have one end wired to a contact for one pole, and the midpoint of the pair wired to the matching contact on the other pole. The other end of each pair must be commoned together and connected to the ground-most end of the where the original pot connects in the circuit. The midpoint common on the switch goes to where the wiper terminal used to connect, and the other common terminal on the switch goes to where the far end of the pot used to connect.

A diagram might be easier to read, but harder to make than writing this, so I left it at that. You'll get up to 6 reliable settings based on the original pot if you do this, with no complications involving parasitic effects.

Taking real measures, using close matches in real resistors, is the key to accuracy. Use 1% metal film resistors. Getting the RATIO of resistances in each pair is more important than exact matches for value.

 

[Mk90]

A "really really mini" trim pot would work fine if you want to tuck it in the control cavity and use it as a set and forget adjustment.

In terms of your diagram above with the red circles. They're not quite in the right place. And there needs to be some adjustments to your other diagram. For the volume pots, think of the pot as having three connections - two ends, and a middle. One end is on hot, the other end is on ground. The middle is on the pickup. When you turn the pot, you change how much resistance is in series versus parallel. Full on has all the resistance in parallel. Your yellow wires on the toggle switch basically need to connect to the pickup's hot wire and the black hot wire that goes to the jack. Then, you can switch to the dialed-in pot, or a resistor connected to ground to simulate full on.

If you use an on-on mini toggle, this will give you a preset volume position, and a "full on" with a resistor for a parallel load to simulate the pot. With an on-on-on mini toggle, this will give you those two in the outside on positions, and the middle on position will be a wonky kinda kill switch where that specific pickup will be killed, but the other pickup (if it's in an on position) will have an additional load in parallel from the resistor and the preset volume pot. I can't think of a way around that, but it might be fine for you.

For the tone pot, I'd just use an on-on and have it make or break a separate wire connected from the jack hot to the tone pot middle terminal.

Thank you so much. I can definately work with this. I think I also understand Midlifebeginners image better now and I see why it's different. The additional load with "kill switch" is something I'll just have to experiment with. So I wouldn't be able to get full volume (or the same range of frequencies) with only one pickup this way?

I could see myself using a rotary switch if I could find one that could affect both pickups at the same time. So I could have "presets" of pickup combinations with just one knob (kind of overly complicated version of blend). But for now toggle switches is the way to go. Both esthethic and tactile feel of switches over knobs is far superior in my opinion

 

[StereoPlayer]

Like this. Tapped pu’s. On full/off for each PU. Stereo/mono switch.

 

[StereoPlayer]

Like this. Tapped pu’s. On full/off for each PU. Stereo/mono switch.
View attachment 4848872

Edit to the above..
That’s…full volume/off/half volume for each pu switch.

 

[dwizum]

So I wouldn't be able to get full volume (or the same range of frequencies) with only one pickup this way?

The kill switch position in your diagram disconnects the pickup and puts resistance in parallel with the rest of the wiring. Basically, yours will behave more like a bass with volume knobs for each pickup - in the kill switch position for a given pickup, it'll be like that pickup's volume knob is turned all the way down. Basically, it'll behave like a VVT jazz bass. If that's what you're after then you're all set! I made the comment to differentiate it from a "traditional" kill switch, which is typically just a short to ground.