Stupid question - why do some basses have two batteries?

[GoodShowSir]

Right stupid question, and probably something I should have figured out a while ago.

 

Why do some active basses need two 9v batteries? I think I get it for something like a dual humbucker, but there seems to be others that have it and only single coil?

 

 

 

[Newfoundfreedom]

Because they run an 18 volt preamp system instead of 9 volt.

[Ed_S]

I've seen some with two where there's a built-in effect or fret marker LEDs etc. as well, so one is for the preamp and the other is for the accessories. Don't think I've ever seen a production bass with two wired for 9v just to extend the runtime, but I believe EMG used to suggest it as an option in their wiring guide alongside the 18v system for increased headroom.

[fretmeister]

18V operation is the main reason for increased headroom

 

Quite a few basses with that now. The new Stingray Specials are 18V with 2 batteries for example.

 

 

[TheGreek]

My Spector 6er has two 9v. I think the only other bass I can recall having two was my Overwater 

[Hellzero]

Fodera, Sire, Warwick, MTD, Ibanez, Ken Smith, Status (the Hellborg model was even running on 4 batteries, so 36 Volts...), loads of luthiers basses, ... have an 18 Volts preamp installed.

[itu]

Simplified background: Operational amplifiers (opamps) need double sided power. Positive (+), negative (-), and the zero point.

 

A preamp can be built with one sided (with a single 9 V battery), or two sided power (2 x 9 V). Two sided is easier to build, because it is simpler and requires less components (the first battery is the lower side from -9 V to 0 V, and the second from 0 V to +9 V). If a preamp is functional with both options, the circuitry is based on a one sided power, and "an artificial zero point".

 

+9 V

0 V

-9 V

 

The preamp sees the lower side (- connected to negative, + connected to 0 V) as negative voltage, and the higher side (- connected together with the first battery to 0 V, + connected to +9 V) as the positive. Opamp is happy with this arrangement. If there's just one battery, the voltage has to be divided with components to positive, negative, and 0 V.

 

More voltage equals more headroom (Status has a preamp running at 4 x 9 V = 36 V, like @Hellzero mentioned), but the output of an ordinary bass is in the ballpark of 1 V (peak to peak). Even a single 3 V battery could be enough to drive a pre. True: depending on the pickups, some transients could reach few volts (peak).

 

[Sometimes it would be wiser to have two batteries in parallel. Then the last drops of the batteries would be used till the very end.]

Edited July 29, 2023 by itu
additions

[Newfoundfreedom]

9 minutes ago, itu said:

Simplified background: Operational amplifiers (opamps) need double sided power. Positive (+), negative (-), and the zero point.

 

A preamp can be built with one sided, or two sided power. Two sided is easier to build, because it is simpler and requires less components. If a preamp is functional with both options, the circuitry is based on a one sided power, and "an artificial zero point".

 

More voltage equals more headroom (Status has a preamp running at 4 x 9 V = 36 V, like @Hellzero mentioned), but the output of an ordinary bass is in the ballpark of 1 V (peak to peak). Even a single 3 V battery could be enough to drive a pre. True: depending on the pickups, some transients could reach few volts (peak).

 

[Sometimes it would be wiser to have two batteries in parallel. Then the last drops of the batteries would be used till the very end.]

 

I'm glad you made that simple. 🤔

[fergs40]

My Westone Thunder 1A (the later one with the big - Magnabass? - pickup) has two 9v batteries - and that dates from 1986…

[pineweasel]

24 minutes ago, fergs40 said:

My Westone Thunder 1A (the later one with the big - Magnabass? - pickup) has two 9v batteries - and that dates from 1986…

My 1983 Thunder 1A does too, they all had an 18v preamp

[Hellzero]

I think Alembic started the "18 Volts" preamps way back in the 70's... In fact they started active basses.

[theyellowcar]

I had a Fender Deluxe P/J with an 18v preamp - believe the equivalent models these days (Player Plus) still do as well. 

[GoodShowSir]

Amazing!

 

Thank you everyone!

 

 

[Stub Mandrel]

Being cynical, it's to provide sufficient headroom for the excessive gain of some active basses.

 

I'd love to know what benefits are gained by the higher output level of active basses beyond generating the requirement for lower gain input stages on amps to compensate.

 

I hardly think it's justified as improving signal to noise ratio or microphones would be boosted to similar levels.

[itu]

59 minutes ago, Stub Mandrel said:

Being cynical, it's to provide sufficient headroom for the excessive gain of some active basses.

 

I'd love to know what benefits are gained by the higher output level of active basses beyond generating the requirement for lower gain input stages on amps to compensate.

This is not that simple. The output level doesn't have to be super high, not at all. Some hi-Z ("passive") basses may even have higher output level.

 

A 9 V battery is an easy option, because it contains enough energy to drive a tiny preamp (usually the tone stack only) for a year or so. The voltage is suitable for an opamp or few.

 

The low output impedance (Z) requires some energy. If the Z is lower, more energy is needed. An NE5534 consumes pretty much energy compared to say, TL07x family, or much newer (and better) opamps. But it is also a very lo-Z output opamp. Alembic used the NE 553x family, and chose an external PSU to drive the high current consumption circuitry. I am not sure, but the PSU could be two sided, someone could maybe verify this?

 

Once more: battery voltage is not directly connected to the output level. Battery powered lo-Z preamp does not have to have higher output than its hi-Z sibling. With all settings maxed out (treble, bass etc.) it is possible, but not a must.

[Woodinblack]

Just easy to make an amp with a proper centre zero voltage, rather than one made by making a half 4.5 rail on a 9v system.

Doesn't have to be 18v, the original ibanez actives are 2 1.5V but 9v are convenient battery size.

[Hellzero]

@itu The Alembic DS5 is a two sided power supply and the bass can also be powered (not that long) with two 9 Volts batteries.

 

[Newfoundfreedom]

14 minutes ago, Hellzero said:

@itu The Alembic DS5 is a two sided power supply and the bass can also be powered (not that long) with two 9 Volts batteries.

 

 

Thanks. That's much clearer. 🙄

[Stub Mandrel]

3 hours ago, itu said:

This is not that simple. The output level doesn't have to be super high, not at all. Some hi-Z ("passive") basses may even have higher output level.

 

A 9 V battery is an easy option, because it contains enough energy to drive a tiny preamp (usually the tone stack only) for a year or so. The voltage is suitable for an opamp or few.

 

The low output impedance (Z) requires some energy. If the Z is lower, more energy is needed. An NE5534 consumes pretty much energy compared to say, TL07x family, or much newer (and better) opamps. But it is also a very lo-Z output opamp. Alembic used the NE 553x family, and chose an external PSU to drive the high current consumption circuitry. I am not sure, but the PSU could be two sided, someone could maybe verify this?

 

Once more: battery voltage is not directly connected to the output level. Battery powered lo-Z preamp does not have to have higher output than its hi-Z sibling. With all settings maxed out (treble, bass etc.) it is possible, but not a must.

 

I'm not convinced. The majority of pedal effects run happily on 9V. I'm not sure why you should need super low output impedance (unless you want to run old 40R headphones dirct from your bass). Even the venerable 741 is 75 ohms, nothing compared to any amp input. Mic level is usually 2k and line 10k.

[itu]

True. But a 741 is a noise machine compared to the low noise NE5534. There are several parametres that require energy.

 

Long ago had a Washburn (a copy of Status) which preamp had a single opamp. It was filed blank, so the actual type was unknown. I decided to try several types, because it was easy, and such ICs were (and are still) pretty cheap. TL071 was just fine, the sound was quite close to the original. Power consumption was just slightly larger. The last in line was this NE. Superb sound, deeper bass, wider response, everything was better. Except it was power hungry (OP series wasn't available at that time). Battery (batteries, to be honest) cried, and I had to change batteries pretty often. Later I studied electronics, and started to understand the details.

 

No, I haven't been very active with designing circuitry, although some time ago I fell in love with the designs of our own @Passinwind. His work is very interesting. I wish at least one preamp will find its way to the basses I work with.

[kodiakblair]

Several of my Peaveys needed 2 x 9v, suspect it was the pairing of active pickups with internal preamps .

[White Cloud]

On 29/07/2023 at 11:13, GoodShowSir said:

Right stupid question, and probably something I should have figured out a while ago.

 

 

For what it's worth I don't think this was a stupid question at all. 

[Gasman]

MM Bongo runs 18v...

[ahpook]

I've converted my Spector basses to run at 18v rather than the stock 9v.

 

Any excuse to switch on the soldering iron

[kodiakblair]

1 hour ago, ahpook said:

Any excuse to switch on the soldering iron

What did you solder ?