Wiring Woes.

[Chris Thomasi]

I am close to completing two five string basses, one fretted, one fretless.
Both have a three band graphic with standard 9v battery supply. There is a graphic on/bypass switch and a power on/off switch. Each switch is dpdt and each has an indicator LED above it.
Have been racking my brain to figure out the wiring but to no avail. Can anyone help?

[Peter Wilcox]

I have some questions:
Does the EQ have its own volume control, or will the volume pot control that?
Do you want the output to be from either the EQ or directly from the pickups, or from both mixed together too?
You show 3 wires going to the output jack - is that some kind of stereo output from the EQ?

The power could be controlled by a SPST switch, or a switching jack - or you can use a single leg of the DPDT switch. You'll need a resistor in series with the LEDs.

[Chris Thomasi]

The third wire to the jack socket is for cutting power when bass is not plugged in.
The blend pot and volume pot are part of the eq unit, but ideally I would like to retain these functions and just bypass the three band pots. The thinking behind the dpdt switches was to use one side for function and the other for the relevant LED, although a spdt would probably work for the power on/off switch.

[Peter Wilcox]

It seems that the "eq unit" is probably a preamp, and the volume, blend and eq pots are all wired internally, so you'd need the schematic to see if it could be done (which is unlikely). If you have a switching jack already, why would you want to cut the power with the bass plugged in (unless you're just forgetful like I am)?

[Joshua Levin-Epstein]

As peter asks, what do you want to accomplish? Many makers with preamps wire their instruments so they have a passive mode. If the blend pot and volume control are passive, you can send the (passive) output to either the preamp/eq or directly to the jack. If this were the case, I would use a 3 position switch: Active/passive/ passive with a cap to ground, like a tone control turned all the way down.

If the volume and blend controls are active, then you'll need some passive controls that are in when you totally bypass the preamp. Maybe stacked volume and tone.

(My opinion) you want to use only the switching jack. You will get a nasty thump if you switch the battery off while the volume is up.

[Chris Thomasi]

Have got power switch working and bypass almost there, it seems to be the simple bit i.e. the LED'S, that are giving me the headache.

[Chris Thomasi]

Have got power switch working and bypass almost there, it seems to be the simple bit i.e. the LED'S, that are giving me the headache.

[Peter Wilcox]

For the power on indicator, wire a LED in series with ~1K resistor from V+ (positive battery terminal) to the jack lug that will be grounded when the plug is inserted. The LED will turn on when you insert the plug.

Assuming you've figured out how to use one pole of a DPDT switch to bypass the EQ, wire a LED and resistor from the second pole of the switch to V+, and connect the other lug of the same throw of the switch to ground. When you throw the switch, the EQ will bypass and the LED will turn on.

[David King]

Just keep in mind that each LED uses about 20mA to operate. That's about 10-40 times the power used by the preamp. Your battery life will go from months to days which is why you don't see a lot of LEDs on instruments. You can radically cut power consumption by having the LED flash very fast via a PWM circuit so that it's only on a fraction of the time. LED power management chips do this very inexpensively.

[Chris Thomasi]

All sorted eventually. Both LED's have a current limiting resistor in series as they were way brighter than necessary anyway, so battery drain isn't too much of an issue.
Capacitors sort switch clunk.

[Peter Wilcox]

Maybe you could draw out the circuit and post some pics to show us how you did it.

[Chris Thomasi]

Will do that next time I take the control cavity cover off and trace through the spaghetti.
The main cause of the confusion was the lack of a schematic for the eq unit. The epiphany came when I realised I needed to be switching the output from the eq and not trying to interrupt the input.

[Dan Smith]

LEDs have become very efficient these days.
We typically apply 0.5mA current to them on our test equipment.
They can be blinding at 20mA.