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Degrading a Battery's Output

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saiyuki

New Member
Hi. first off i have absolutly no idea about electronics, but i do have a good musical ear which brings me here. Lemme explain...........

I have a 1978 MusicMan Sabre2 guitar which goes through a Boss GT-3 Processor. The guitar has a built-in active circuitry for the Dual Humbucker Low Impedance Output Pickups, and it also provides a seperate bass and treble system.

The guitars active circuit runs off of a 9V square battery which is housed within the guitar body. Over the years of playing, i prefer the sound when the 9V battery has degraded and outputting between 7.5V and 8.5V. So here's the question........

Is it possible to either purposly degrade the battery to the required output prior to usage, or add an additional circuit (or whatever is needed), to the guitar, so that i could manually select between 7.5V and 8.5V output of the 9V battery. Obviously this is needed only when the battery is new, but a new battery can take anything from 1 year onwards to degrade to the point of the sound output i enjoy.

In the past i have relied on other people to donate their old batteries when they become useless for their purposes, but they are now becoming hard to obtain. Fearing the worse, i've posted here in the hope someone could help.

Thanks
 

Hero999

Banned
This sounds like bad design to me.

The operation of the circuit shouldn't change until the battery voltage falls below 6V.

The obvious solution to me would be a low drop-out regulator.
 

mramos1

Active Member
Maybe drop a diode or two inline with a battery leg.

How much space is in the battery compartment? Each diode will drop .7v roughly from the new battery.
 
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Nigel Goodwin

Super Moderator
Most Helpful Member
Don't mess about with diodes or anything, add a resistor in series with the battery - essentially as a battery goes 'flat' it's internal resistance rises, adding an external one will give the same effect. You can calculate the resistor using ohms law by measuring the current taken by the pedal, or simply try different values.
 

saiyuki

New Member
If the circuit is a faulty design, then i'm glad it's in my guitar. Having discovered the voltage problem(?) a long time ago, it has saved me probably hundreds, if not thousands of pounds, in purchasing different guitars to achieve the kind of sounds for which this guitar can produce.

The battery fits quite snug inside the rear body cavity, but the controls cavity in the front of the guitar has room for additional switches/components. The circuit inside the guitar produces a low impedance output, and is the only unit powered by the 9V battery. The Boss Processor pedal has it's own 240V power supply.

Using the resistor suggestion, could i employ a small circular switching unit that allows e.g.. 8.5V, 8.0V, 7.5V resistance selection?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
If the circuit is a faulty design, then i'm glad it's in my guitar. Having discovered the voltage problem(?) a long time ago, it has saved me probably hundreds, if not thousands of pounds, in purchasing different guitars to achieve the kind of sounds for which this guitar can produce.
Presumably all it's doing is producing distortion as the battery goes flat, the level of distortion also probably varies as you play, as the supply rails vary.

It's a similar effect to what you get with valve amplifiers using valve rectifiers.

The battery fits quite snug inside the rear body cavity, but the controls cavity in the front of the guitar has room for additional switches/components. The circuit inside the guitar produces a low impedance output, and is the only unit powered by the 9V battery. The Boss Processor pedal has it's own 240V power supply.

Using the resistor suggestion, could i employ a small circular switching unit that allows e.g.. 8.5V, 8.0V, 7.5V resistance selection?
Yes, you could easily do that, or use a variable resistor to allow a fully variable adjustment - but this does depend on the wattage of the variable resistor been high enough.
 

Mr RB

Well-Known Member
Hi Saiyuki, I've heard this before, that some people prefer the sound of the active tone controls when run with flat batteries. I have an old Washburn Bass with active EQ but it likes full batteries, for more "punch". People say the flat batteries give a "mellower" sound which is probably less treble.

Anyway you can do it with a 5v low dropout regulator (it's a 3 pin IC) and control it with a small trimpot. That way you can adjust the regulated voltage from 7.0 volt to 8.5 volt or whatever and find the sweet spot that you like. The voltage will remain fixed at exactly the volts you set it to.

Most 5v 3-pin regulators are not low drop out type, you might have to look around a bit, maybe Digikey has them.
 

saiyuki

New Member
Hi. I thought i replied earlier but the post hasn't appeared :confused:

The sound with a new battery is bright, clean and crisp. It was designed to output this tonality at half-volume. Cranking it to full volume overdrives the amp, but with solid state amps it doesn't really sound good, hence the Boss GT-3.

After 30 years of playing each other, the Sabre is still the only guitar i would use :) The sabre has a coil reverse switch and when the battery becomes too low, it becomes ineffective, and sadly, this is the time i have to either use a new one and put up with it for a long time, or scrounge an old one from somewhere. :D

I was on the verge of putting an advert in a shop window asking for old 9V batteries, but now i have 2 more options to investigate.

Thanks for the info
 
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