Advantages of an 18V pre amp?

[carl0s]

[quote name='BigAlonBass' post='369653' date='Jan 4 2009, 12:17 AM']Nope, not an Urban Myth. Quoting Official N.H.S. statistics - An average of Nine people die every year in the U.K. from testing a PP3 with their tongue. Apparently, it's a fool-proof way of finding out if you were born with a weak heart. Thank goodness I wasn't. I'd been doing this for years before I read the article. [/quote]

What you should do is lick your index finger - nice line of wetness, then put PP3 terminals on one end of finger and tongue on the other..

[Davebassics]

At peak, my P bass measured roughly 0.6Vpk (gave it a right twonk). Line level is 1.737Vpk. So after a few calculations, roughly 9dB of gain is needed to bring instrument level up to line level. Obviously this will vary significantly every time you repeat it but it offers a fundamental starting point.

For single supply rails you have to DC bias the signal to allow full swing through an op amp. Biasing a 9v battery at 4.5v theoretically gives you 3.9Vpk of gain to play with. Practically it will be less, more like 3Vpk because op amps wont swing fully to their supply rails. Don't take my word on this but I think your average 9v battery can kick out around 12dB before distorting.

Thus deducting, a 9v battery will suffice. 18v means you can push a much greater signal out of the bass for driving the next stage if required.

[flyfisher]

[quote name='BigAlonBass' timestamp='1231024629' post='369653']
Nope, not an Urban Myth. Quoting Official N.H.S. statistics - An average of Nine people die every year in the U.K. from testing a PP3 with their tongue.
[/quote]

So that makes PP3s more dangerous than railway crossings, yet they are allowed to be openly sold - to children, no less - without any warning labels or fancy interlocking safety devices.

Funny old world.

[Al Heeley]

Can I ask: 2 batteries better than one? I have a apir of SB basslines pickups powered by a 9V pp3, it has pasive controls (JB wiring). I'm taking the passive pots pout and adding a 3-band eq pre-amp, also 9v. Do i use a separate battery for pickups and pre-amp, single 9V to power both, or 18V in series to power both? Can't seem to find any recommendation in the literature about this.

[neepheid]

[quote name='Al Heeley' timestamp='1328622881' post='1530126']
Can I ask: 2 batteries better than one? I have a apir of SB basslines pickups powered by a 9V pp3, it has pasive controls (JB wiring). I'm taking the passive pots pout and adding a 3-band eq pre-amp, also 9v. Do i use a separate battery for pickups and pre-amp, single 9V to power both, or 18V in series to power both? Can't seem to find any recommendation in the literature about this.
[/quote]

Unless it is documented that either of these components will take 18V then I don't think you should feed it to them. Also if you stick at 9V then I would just take the feed off one battery, otherwise when it stops working how will you know which battery is dead? It is unlikely that the pickups and the preamp drain power at exactly the same rate...

[Al Heeley]

Thx, running fine on one battery powering both

[Davebassics]

incase anyone is interested I discussed this on my blog last night:

[url="http://allthatjazzbass.blogspot.co.uk/"]http://allthatjazzbass.blogspot.co.uk/[/url]

[alstocko]

The way to think about this is, is that if you have two 9v circuits (pickups and a preamp) all it needs is 9v. If you have something which needs 18v give it 18v.
Use the "does what it says on the tin" analogy.

[flyfisher]

Having just re-skimmed this thread I'm surprised nobody queried whether "18 volts" is actually "-9 to +9" volts. Op-amps require a +/- power supply around a 0v reference level. The audio waveform will alternate around this 0v reference level. Thus the "0v" output level of an op-amp powered by a single 9v battery will be 4.5v (known as a DC shift) and the audio waveform can alternate between 0v and 9v.

With two 9v batteries, the op-amp power supply can be arranged as -9v and +9v with and the "0v" reference level will actually be 0v. Thus the "0v" output level will be 0v and the audio waveform can alternate between -9v and +9v.

This might seem a subtle difference but it means the amp can be DC-coupled to the next stage(the bass amp). A pre-amp with a 4.5v DC shift would need to be AC-coupled to the bass amp in order to eliminate the 4.5v offset.

Having said all that, I'm not that familiar with guitar pre-amps but the above certainly holds true for op-amps.


As an aside, AC-coupling is commonly used in audio (and video) equipment, specifically to avoid the build up of DC offsets between connected equipment, and such capacitors will have some effect on the 'flatness' of the audio signal. In some circumstances, comparisons between the 'sound' of 9v and 18v preamps might be little more than the comparison between AC and DC coupling.

[flyfisher]

[quote name='Dr.Dave' timestamp='1230373034' post='364072']
I'm no sparky but I should think an 18v is more reliable. 2 batts are less likely to die a sudden death than one so there should always be more nosebag for the eq circuits to feed on. That's how it was explained to me anyway.
[/quote]

I can't see that myself. If the circuit needs 18v then it's unlikely to work very well with 9v. This is especially true if the two batteries are connected as "-9 : 0 : +9" where one dead battery will mean the loss of one power rail and a very nasty sounding output.

It would be possible to combine two 9v batteries for redundancy, but that would be no different to using a 9v pre-amp with a larger battery.

Besides, if you have two batteries you have twice the chance of a failure than with just one - so there's no great reliability advantage.

[LiamPodmore]

No idea on the difference (i'm no electro-tech-nerd, though i wish i was) but what i do know, is that the 18v pre-amp in a Musicman Bongo sounds f*cking HUGE!!!!!!!!!!

Liam

[Davebassics]

Perfect world theoretical scenario:

A active bass output should be around +4dBu line level, 9v is more than enough to give +12dBu output.

A 18v preamp you could theoretically push +18dBu. This is regardless of the class operation of the preamp. Most input stages can handle a +24dBu input so this shouldn't be an issue.

[Guest bassman7755]

Most audio signal paths feature some "line level" connection at which point the signal voltage is at most 1.4v or thereabouts so I really cant see how 18v vs 9v at the front end is going to make any difference.

[BassPimp66]

More is better. 18 v is better than 9 v / 5 string is better than 4 string / 3-finger pluck, is better than 2-finger pluck ... etc...
This being said, I don't need more than 9v on my Sadowsky. I have a John East preamp on 18v on my jazz bass to compare with.

[Conan]

[quote name='LiamPodmore' timestamp='1334931024' post='1623665']
what i do know, is that the 18v pre-amp in a Musicman Bongo sounds f*cking HUGE!!!!!!!!!![/quote]

So does a Spector tonepump @ 9V!

[Chiliwailer]

I got my first 18v preamp recently, blown away by it.

I had been meaning to buy a compressor pedal for some time, this bass ensured that I got one straight away!

[jazzyvee]

I have a 36v ( + - 18v) pre-amp in my bass powered from an external 240v ac to 36v dc rackmounted power supply. Without the psu plugged in it operates at 18v with internal batteries. It'a very powerful sounding bass when compared to my 9v basses so I'd say it certainly gives me more clean headroom.

Jazzyvee