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18v and 9v active circuit

munkonthehill

By munkonthehill,
in General Discussion

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stingrayPete1977 Grand Master

stingrayPete1977

Posted
Posted

That sounds much more like it to me nice one! :rolleyes:
Like I said I have a little knowledge, enough to get what you are saying but I imagine with no knowledge it will always be a bit of a mystery and most folks round here just work on the more is better theory anyway.Im trying to think how that can be put into a simple way for someone with no electrical/electronic knowledge to get?

Lets say- There are 2 plates with cakes on, With a 9v system you are only allowed to eat cakes from the left hand plate yet with the 18v sytem you can enjoy cakes from either plate whenever you like. How does that sound?

Although for some and me included on this one the old circuit still has its place because it produces a sound we are familiar with and still using.Im still a sucker for a 2 band Ray when it comes to funk and Disco it just sounds right, Maybe in those instances the other plate of cakes is just too much and the likes of Larry Graham and co never had a problem just eating from the one plate :)

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EdwardHimself Proficient

EdwardHimself

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Posted

[quote name='munkonthehill' post='950125' date='Sep 9 2010, 12:25 AM']so whats the diffence between 18v and 9v active circuits????

About 9v............. Ba Boom



All joking aside, is the extra voltage purely to keep the circuit active as it needs 18v or is it to give the circuit extra power?

Im a lawman myself so have no real or very little knowledge of electronics (except having an NC in electronic engineering, however that was 12years ago!!!!!!!!!!!! god am getting old :) )

So just checking this bit of info,,,,,the bongo im using just now seems to overload my preamp a bit more than the stingray I had or either of my fenders. This may of course be down to EQ settings, however im sure some BC'ers may have more info for me.

Cheers
Steven[/quote]

an 18v curcit basically gives you more headroom.

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ahpook Grand Master

ahpook

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Posted

[quote name='flyfisher' post='953283' date='Sep 12 2010, 01:15 AM']I rest my case. :)


Think of it this way. The waveform from the pickup is an AC signal and it will alternate around zero volts (ground). An amplifier - either a bass power amp or a guitar pre-amp - must therefore amplify both the +V and -V portions of the waveform. It is not possible to amplify the -V portion of the waveform if there is no negative voltage rail to supply the amplified negative signal voltage. With an 18V system, the two 9volt batteries are connected together to give 18 volts across the voltage rails BUT the connection between the batteries will be connected to the ground of the power amp, which means that the pre-amp voltage rails are actually +9V and -9V with respect to ground. This configuration allows the AC pickup waveform to be correctly amplified on both its positive and negative cycles. Such a design allows the pre-amp to be DC-coupled to the power amp and eliminates the requirement for a DC-blocking capacitor, which is a good thing as far as frequency response is concerned (for the reasons described in the above quote).

With a single 9V battery as a power supply, the pre-amp output can only swing between zero and +9v, so how can the -V portion of the pickup waveform be amplified? The answer is to apply a DC bias voltage to the input of the pre-amp so that the AC pickup waveform is centred around 4.5V instead of zero volts. The pre-amp can now amplify the AC waveform and the output will be a larger AC signal, but still centred around 4.5 volts.

The bass amp input will be expecting an AC signal centred around zero volts (ground) so, to remove the 4.5V DC offset of the pre-amp output, the pre-amp is connected to the bass amp via a capacitor, which will only allow the AC signal to pass through it and will block the 4.5V DC voltage offset (hence the term 'blocking capacitor').

Unfortunately, this capacitor will have some effect on the AC waveform, as mentioned in the above quote, which may not be desirable. Hence the advantage of an 18V system, more accurately referred to as a -9V, zero, +9V system, which allows direct DC-coupling of the pre-amp output to the bass amp input.

Apologies for the ramble but although simple in principle it's not easy to describe purely in words.[/quote]

techy, but perfectly correct....

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Dood Grand Master

Dood

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Posted

[quote name='lowdown' post='953568' date='Sep 12 2010, 02:33 PM']I am glad you asked - it's been a comical read...with a bit of mines bigger than yours thrown in :)

Garry[/quote]

:lol: :rolleyes:

[quote name='EdwardHimself' post='953629' date='Sep 12 2010, 03:37 PM']My advice would be to not worry yourself about it and get whichever you think sounds better whether it be 18, 9, 2, 27v whatever...[/quote]

Or!!! PASSIVE :o

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stingrayPete1977 Grand Master

stingrayPete1977

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:) Lots of experts round here! I clearly said I didnt know enough and a little bit of knowledge is dangerous but I do know enough to see if someone else doesnt! Its like asking about a car problem then someone writing 2 pages all about it then telling you they didnt realise your car had an engine!
Im not going to get anymore drawn in now I promise :rolleyes:
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Daquifsta Apprentice

Daquifsta

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Just to throw a spanner in the Donkey, the EMG pickup set I have in my bitsajazz, which came with a pre-wired loom, said to use 9v, OR 18v for 'more headroom'.

Now, despite being a mechanical engineer, and not a 'lecky one - I do get the idea of the whole -9, 0, +9 situation, since we're in the context of AC voltage here, but there is definitely not a connection to the 0v between my two batteries. Have EMG done something clever?

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Dood Grand Master

Dood

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Posted

[quote name='stingrayPete1977' post='953855' date='Sep 12 2010, 07:07 PM']:) Lots of experts round here! I clearly said I didnt know enough and a little bit of knowledge is dangerous but I do know enough to see if someone else doesnt! Its like asking about a car problem then someone writing 2 pages all about it then telling you they didnt realise your car had an engine!
Im not going to get anymore drawn in now I promise :rolleyes:[/quote]

{actually - I'll remove this post - I can't be arsed..}

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Dood Grand Master

Dood

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Posted

[quote name='Daquifsta' post='953864' date='Sep 12 2010, 07:19 PM']Just to throw a spanner in the Donkey, the EMG pickup set I have in my bitsajazz, which came with a pre-wired loom, said to use 9v, OR 18v for 'more headroom'.

Now, despite being a mechanical engineer, and not a 'lecky one - I do get the idea of the whole -9, 0, +9 situation, since we're in the context of AC voltage here, but there is definitely not a connection to the 0v between my two batteries. Have EMG done something clever?[/quote]

Yes, you are quite correct - it is also possible to derive a '0V' line by using a simple circuit design without the need to take a third cable from the batteries.

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Dood Grand Master

Dood

Posted
Posted

[quote name='ahpook' post='953915' date='Sep 12 2010, 07:57 PM']/backs away waving hands/

this is electricty folks....someone could get hurt !

:)[/quote]


Yup - I'm out - better things to do than have a p*ssing match.

[/unsubscribed]

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flyfisher Experienced

flyfisher

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Just to clear up a few things . . .

Yes, in general, 18V will give more headroom than 9V - assuming those are the actual voltages used by the pre-amp circuit (see below). This may or may not be significant, depending on the pre-amp output signal voltage.

There are many different ways of creating a 'plus-and-minus' power supply. Two 9v batteries make it very easy. A single battery makes it a little more complex, but certainly not impossible. Indeed, a single 9V battery could be made power a voltage converter circuit that provided an 18V (or even higher) voltage supply to the actual pre-amp circuit (search for 'charge pump voltage converters' for more info).

In other words, extrapolating the "quality" of a pre-amp on the basis of how many batteries it uses is about as valid as using the rated power output of a speaker to determine how loud it will be.

Also, consider the overall signal chain from pickup to speaker. If the guitar uses a powerful pre-amp then the main amp will have less work to do, assuming a constant volume from the rig. This might be a good or bad thing depending on the relative characteristics of the preamp and main amp.

Engineering is the art of compromise and electronic engineering is no exception. But all the techy stuff pales into insignificance compared to the role of marketing and fashion in such things! After all, we all know that an amp that goes to 11 must better than the run-of the-mill amps that only got to 10, so 18 volts must also be better than 9. :)

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BigRedX Grand Master

BigRedX

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Posted (edited)

I don't see what the problem is.

flyfisher has explained the advantages of using 18v to power an on-board pre-amp and the best way to do it in [url="http://basschat.co.uk/index.php?showtopic=102019&view=findpost&p=953283"]this post[/url] and [url="http://basschat.co.uk/index.php?showtopic=102019&view=findpost&p=953983"]this post[/url] and done it much better than the entire [url="http://basschat.co.uk/index.php?showtopic=35505"]stickied thread in Repairs and technical Issues[/url] which TBH contains no useful information whatsoever, and why it is stickied is beyond me...

And while we're on the subject of on-board pre-amps maybe someone with a good knowledge of electronics (flyfisher?) can explain the attraction to me. I already have tone controls on the pre-amp in my rack, and I would have thought that it's much easier to build a good noise-free tone-shaping circuit when you don't have to worry about getting it small enough to fit into the control cavity of a bass and having to be powered by batteries?

Edited by BigRedX
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lowdown Grand Master

lowdown

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[quote name='BigRedX' post='954380' date='Sep 13 2010, 09:16 AM']And while we're on the subject of on-board pre-amps maybe someone with a good knowledge of electronics (flyfisher?) can explain the attraction to me. I already have tone controls on the pre-amp in my rack, and I would have thought that it's much easier to build a good noise-free tone-shaping circuit when you don't have to worry about getting it small enough to fit into the control cavity of a bass and having to be powered by batteries?[/quote]

Not sure what a tech reason would be.
But for me, i have done plenty of stuff where i just plugged the Bass into a DI box and had to use headphones,
and the onboard pre-amp gave me the extra tone shape control, and with that a signal bump.



Garry

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