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Help wanted with wiring diagram

Dave_2000

Dave_2000

Feb 11, 2013
24
8
#1
Alco-4PDT.png Wiring Diagram - Rotary copy.jpg Wiring Diagram - Toggle copy.jpg I have made my best shot at a wiring for scheme for two magnetic pickups (master volume/blend) and a piezo pickup (separate volume) with a 3-way switch (mag only/both/piezo only). Additionally, I want the 3-way switch to turn off the piezo preamp battery when in the mag only position.

I have one scheme with a toggle and another with a rotary switch, which are otherwise identical. I also attached a diagram of the internal connections for the toggle (Alco version) to verify those connections. My questions are:

1. Will this idea work?
2. Have I drawn anything incorrectly? (I intend to give this diagram to a luthier & don't want anything wired the wrong way around, etc.)
3. Will the treble bleeds on the blend do anything?
4. Should I remove the grounds on the blend pot?

Any comments, corrections, suggestions, etc. are very appreciated.
 
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#2
Firstly, you can't mix a buffered signal with passive magnetic pickups, unless the impedance is the same, and it usually isn't. You need to buffer the magnetic pickups if you intend to use them with the piezo elements.

Second, battery switching is not a good idea. Personally, I would ditch the switching, and let the output jack disconnect the battery when the bass is unplugged.

Third, the value of the treble bleed caps may need to change, depending on the impedance of the signal you end up with after you've buffered the signal.

Other than that, the only thing to be aware of is that you have a choice in the way in which you wire the volume pots. The way you have it is arguably the preferable way, because it allows the best taper, but the drawback is that rolling either volume down too far will mute the signal. The other method compromises the performance of the volume controls, but allows fully independent control.

I would definitely consider removing the grounds on the blend pot, to avoid loading the signal.
 
#4
Thanks for replying line6man, I was actually hoping you were going to be the one to review this.

But now, just to make sure no good deed goes unpunished, I have a few follow up questions:

1. There are 3 reasons I wanted to have the battery switched. I leave the cord in my bass all the time at home, I don't want to drain the battery when I'm just practicing & one mistake in the wiring diagram is I want to have the piezo on a stereo jack which would mean I couldn't use that to switch the battery right?. Can you tell me why switching the battery is a bad idea?

2. I thought the whole idea of a preamp for the piezo was precisely to get it to match the impedance of the magnetic pickups. I don't want to pester you but what am I missing?

Thanks for any help you can offer me.
 
#5
Dave_2000 said:
Thanks for replying line6man, I was actually hoping you were going to be the one to review this.

But now, just to make sure no good deed goes unpunished, I have a few follow up questions:

1. There are 3 reasons I wanted to have the battery switched. I leave the cord in my bass all the time at home, I don't want to drain the battery when I'm just practicing & one mistake in the wiring diagram is I want to have the piezo on a stereo jack which would mean I couldn't use that to switch the battery right?. Can you tell me why switching the battery is a bad idea?

2. I thought the whole idea of a preamp for the piezo was precisely to get it to match the impedance of the magnetic pickups. I don't want to pester you but what am I missing?

Thanks for any help you can offer me.
Click to expand...

1. The main problem, in your case, is that switching between pickups will result in loud pops, as the piezo preamp receives power. These pops are not only annoying, but not good for your amp and speakers.

2. Piezo preamps have a few different purposes. Firstly, because of the high output impedance of piezo elements, you need to get the signal buffered before it leaves the bass, to avoid the effect of cable capacitance. Second, because the output impedance of the piezo elements is so high, you can't drive a standard 1M Ohm amp or preamp input without loading the elements with a relatively direct resistance. Piezo preamps provide a more appropriate input impedance, which is usually around 5 or 10M Ohms. As far as output impedance is concerned, there probably are some piezo preamps out there with output impedances similar to passive magnetic pickups, but it wouldn't make very much sense to do that, because magnetic pickups are usually buffered before being combined with piezo signals, to allow the two signals to play nicely when mixed, and allow the total output impedance of the bass to be very low.
 
#7
If I may: what about adding a second, 'dummy' battery? Add resistors to reduce switch click, and when you flip the Piezo "off," it'll still read a power load, but it won't matter if it's drained; so long as it's not dead? Bonus points for wiring an LED ala Audere.

What'd'you think '6?

Rob
 
#8
Awesome Sauce said:
If I may: what about adding a second, 'dummy' battery? Add resistors to reduce switch click, and when you flip the Piezo "off," it'll still read a power load, but it won't matter if it's drained; so long as it's not dead? Bonus points for wiring an LED ala Audere.

What'd'you think '6?

Rob
Click to expand...

You would need to be sure the switch is of the make-before-break variety. (Meaning that when switching from NO to NC, or vice versa, the common connects both terminals for a brief moment, before disconnecting one of them.) If the bass is always left plugged in, the battery life for the dummy battery will not be good, however. You will need a new battery a couple of times a month, if not, even sooner. That's a lot of money and hassle for something that can be avoided by following the proper procedure of unplugging the bass when it is not in use.
 
#9
line6man said:
You would need to be sure the switch is of the make-before-break variety. (Meaning that when switching from NO to NC, or vice versa, the common connects both terminals for a brief moment, before disconnecting one of them.) If the bass is always left plugged in, the battery life for the dummy battery will not be good, however. You will need a new battery a couple of times a month, if not, even sooner. That's a lot of money and hassle for something that can be avoided by following the proper procedure of unplugging the bass when it is not in use.
Click to expand...


Sir 6,
The way you phrased that response makes me uneasy about something. When you say that unplugging the bass is the proper procedure do you mean it's proper to avoid draining the battery or do you mean I should even be unplugging my completely passive bass as well? If so, why?
 
#10
Dave_2000 said:
Sir 6,
The way you phrased that response makes me uneasy about something. When you say that unplugging the bass is the proper procedure do you mean it's proper to avoid draining the battery or do you mean I should even be unplugging my completely passive bass as well? If so, why?
Click to expand...

Unplugging prevents battery drain. There are other advantages, as well. If you don't unplug, the cable can twist up. If you leave the bass on a stand, there is a tripping hazard. On the other hand, some might argue that unplugging a passive instrument presents unnecessary wear on the jack.
 
#11
line6man said:
You would need to be sure the switch is of the make-before-break variety. (Meaning that when switching from NO to NC, or vice versa, the common connects both terminals for a brief moment, before disconnecting one of them.) If the bass is always left plugged in, the battery life for the dummy battery will not be good, however. You will need a new battery a couple of times a month, if not, even sooner. That's a lot of money and hassle for something that can be avoided by following the proper procedure of unplugging the bass when it is not in use.
Click to expand...

Ah, yes. I forgot the OP wanted to leave the bass constantly plugged in. My idea was meant for practice/performance purposes.

Rob
:bassist:10001110101:thumbsup:
 

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