Why not 18V???

[JimiLL]

I was just wondering if anybody could tell me if there was any drawbacks to using an 18V pre amp instead of a regular 9V. I know the 18 has more headroom, and Ive noticed that when I play fingerstyle with a heavy attack (much like Trujilo plays), my 18V EMG pre has a tendency to overdrive my amps pre a little bit. I play through a Genz benz 1200.

Gain is set relatively moderate on the amp (12 o'clock, both channels), and the rest of the volume contols are at ~ 9 o'cock.

I noticed I didnt seem to have this problem when I played the bass and it was wired 9V.

Bass is Spector Euro 5

[HEADLE]

Does that have a regular tone pump in it? If so and you are attaching two 9 volt batteries you are actually running it at 36 volts as the tone pumps have a doubler built into them. Yikes! better see what pre you have.

H

[line6man]

I honestly never understood the appeal of 9V over 18V, when there are virtually no disadvantages, provided the bass in question has room for two batteries.

You might pay twice as much for batteries, but honestly, how often do you have to change the batteries in a bass...

[Burlington]

I'm curious about this myself. If my preamp was wired 18v, would my amp have more of a tendancy to clip or be closer to clipping?

[bassbenj]

Originally Posted by Burlington

I'm curious about this myself. If my preamp was wired 18v, would my amp have more of a tendancy to clip or be closer to clipping?

Yes it would because the bass would have more voltage out if played hard. But these are two separate issues. What you want is to have clipping nowhere in ANY part of the signal chain.

Thus an advantage to running 18 volts is it helps keep the bass from clipping especially if you like to have the volume up near max (like say you play a couple of basses and you'd like the knobs set to the same positions on all of them for consistency). Often this is a good thing to do because it also can keep your tone more pure and the bass running longer as the batteries go dead.

Point is that many bass preamps have semiconductors that often have voltage ratings of 20 or 30 volts. In this case you can raise 9 volts to 18 and basically nothing changes in the circuit or signal except you can get a larger output from the preamp.

Note that the output of a preamp is AC. It goes positive and negative. Now some Integrated circuits used in basses are NOT rated to handle much more than 9 volts. These can NOT be souped up with 18 volts of supply. But the problem with 9 volts of battery is that because bass output goes positive and negative. The 9 volts is split to Plus and minus 4.5 volts. But it's worse than that. We usually use alkaline batteries longer life and those can be a bit lower voltage than ordinary ones. And of course, batteries go dead with the voltage dropping as they age. So our plus and minus 4.5 volts may drop to 4 or even 3.5 volts. But wait. There is more. The circuits, especially integrated circuits used in bass preamps typically will not drive the output to the full supply values. Usually it will only give you an output a volt or so lower than the max voltage and a volt or so higher then the minimum negative voltage. So now when we thought the bass was pumping out 9 volts in reality it may have just a max value of only plus or minus 2 or 2.5 volts. You play hard and the preamp starts clipping.

But of course this doesn't really have to happen. You can simply play at a lower output level and crank the gain on your head. Nothing clips! So 18 volts isn't NECESSARY, it's just a bit of protection against inadvertent clipping. But since there is only one problem with going to 18volts and no down sides, why not? There is only ONE reason. And that one reason would be if the specs on your preamp do not allow it to run with 18 volts for power. If that is the case you MUST stick with 9 volts.

OK?

[JimiLL]

Originally Posted by HEADLE

Does that have a regular tone pump in it? If so and you are attaching two 9 volt batteries you are actually running it at 36 volts as the tone pumps have a doubler built into them. Yikes! better see what pre you have.

H

LOL no its a EMG BQS pre amp. Definitely able to run 18V.

One more question: Say I play with a certain attack with a 9V pre, and the pre "bottoms out" and peaks in signal thats sent to the amplifier. Now, if I leave amp setting alone, and install an 18V with same playing style, will the 18V allow more transients to "pass through" the bass and on to the pre of the amp, causing distortion??

[agedhorse]

The additional supply voltage will not change anything unless you were exceeding the maximum output that's possible from a 9 volt supply. That is typically about 2 volts RMS or over +4dBu clean. As you go to an 18 volt supply, you will increase this (potential) maximum undistorted output level by over 6dB (some of the losses in the initial 9 volts do not carry over into the voltage increase) so now you are closer to +12dBu.

Most bass amps can not handle +12dBu without clipping the preamp, but often there is an output level trim on the pick-up electronics that allows this level to be reduced down to a more reasonable level. Kind of like downgrading an upgrade.

There are some valid reasons for goig to an 18 volt system depending on the architecture and topology of the pickup circuits, but increased output level headroon is not one of them.

[SGD Lutherie]

Going from 9V to 18V will not make the bass louder. You will hear a less compressed tone though.

If the amp is clipping on loud attacks, turn down the gain on the amp, or use a limiter before the amp.

I always use a little compression or limiting. Every recording you hear has the bass compressed a bit. You get a more even tone without the transients getting out of hand.

I also like to run my gain hot on my amps and preamps, so the limiter stops me from clipping.

[realbadgroove]

I hear no difference in tone with 9 compared to 18v. The 18v seems a little hotter on the output but not so much that it would clip your amp. Just turn your gain down on the amp. Just because both knobs are at 12 o'clock does not mean you are matching your input and output gain. Ive wondered why heads never have a meter for input and output gain.

[SGD Lutherie]

Originally Posted by realbadgroove

Ive wondered why heads never have a meter for input and output gain.

They should. Some have an overload LED like my Trace Elliott. You turn the gain up until it lights on your hardest picked notes, and then you back the gain down until it doesn't light.

So any clipping means you need to turn the gain down. The input gain and output level do not have to match.

[agedhorse]

Originally Posted by SGD Lutherie

Going from 9V to 18V will not make the bass louder. You will hear a less compressed tone though.

Only if you are driving the internal preamp hard enough to run into the limits of the 9 volt supply. That is still typically a higher level than what most bass amps need (by maybe 10-20dB) to reach full output.

One reason for using an 18 volt supply is to be able to overcome large losses in a passive tone control network without make-up gain at the output. Not a great design philosophy (like putting a band-aid on an amputation) but stranger things have been done in the bass world IMO.

The absolute input overload limits for most bass amps on the market are around +8dBu, an 18 volt supply (with a good preamp design) can do well beyond this. It's also WAY beyond what (most) pedals can handle.

[SGD Lutherie]

Originally Posted by agedhorse

Only if you are driving the internal preamp hard enough to run into the limits of the 9 volt supply. That is still typically a higher level than what most bass amps need (by maybe 10-20dB) to reach full output.

Most circuits use a bipolar supply, so when you are runing a preamp off of 9 volts, that's +/- 4.5V. If you are running it off 18 volts, you get +/- 9 V.

But some circuits don't need more than 9, such as JFET preamps. They can actually get more noise and distortion at higher supply voltages.

I was basing the more compressed tone observation on EMG pickups and preamps. If you are using those, and have room for a second battery, then by all means try it. You will hear an improvement in dynamics.

One reason for using an 18 volt supply is to be able to overcome large losses in a passive tone control network without make-up gain at the output. Not a great design philosophy (like putting a band-aid on an amputation) but stranger things have been done in the bass world IMO.

18 volts will not increase the gain without a change in the circuit. If you have to use large amounts of gain in the circuit, then I agree that's not the way to do things.

But headroom is not a bad thing.

The absolute input overload limits for most bass amps on the market are around +8dBu, an 18 volt supply (with a good preamp design) can do well beyond this. It's also WAY beyond what (most) pedals can handle.

Even a 9 volt JFET buffer can do a gain of 10. I've clipped Eden preamps with one of my basses that was using one of these buffers set with the gain up to line level.

[BassLife77]

I switched back and forth between 9 and 18v and I can hear a difference. The output isn't louder but the tone is better with 18v

[agedhorse]

Originally Posted by SGD Lutherie

Most circuits use a bipolar supply, so when you are runing a preamp off of 9 volts, that's +/- 4.5V. If you are running it off 18 volts, you get +/- 9 V.

Doesn't matter if it's bipolar or not, the dynamic range is 18 volts, single ended just means that the common reference is biased to 1/2Vcc or at 9 volts in an 18 volt single ended system. Other than that, it's exactly the same.

Originally Posted by SGD Lutherie

18 volts will not increase the gain without a change in the circuit. If you have to use large amounts of gain in the circuit, then I agree that's not the way to do things.

Not referring specifically to gain but absolute signal level. Noise figures can be improved (somewhat) driving a lossy passive eq with a higher input voltage, so a higher power supply would make this more possible. Gain is not a function of supply voltage, maximum output level is.

Originally Posted by SGD Lutherie

Even a 9 volt JFET buffer can do a gain of 10. I've clipped Eden preamps with one of my basses that was using one of these buffers set with the gain up to line level.

Don't think "gain" is what you mean here, especially with a buffer which has a gain of 1 (otherwise it wouldn't be a "buffer", though these terms have been blurred by markering and non-engineer geeks distorting the definition. Maximum output level of a JFET, regardless of gain, can approach 2 volts RMS, same with low voltage rail-to-rail opamps.

My point here is that there is plenty of signal level here for most applications using a 9 volt supply. Many pedals are also 9 volts and manage the same signal dynamics. 18 volt supplys without output level trim controls often cause more problems than they solve. Too much of a good thing is usually not good.

It's all part of the overall gain structure and managing the dynamics of each stage of the pickup electronics. Doing min and max signal dynamics analysis will quickly show where gain and rail levels need to be to obtain the best overall compromises for most players.

[SGD Lutherie]

Originally Posted by agedhorse

Doesn't matter if it's bipolar or not, the dynamic range is 18 volts, single ended just means that the common reference is biased to 1/2Vcc or at 9 volts in an 18 volt single ended system. Other than that, it's exactly the same.

We said the same thing using different words. Also not all waveforms are symmetrical.

Don't think "gain" is what you mean here, especially with a buffer which has a gain of 1 (otherwise it wouldn't be a "buffer", though these terms have been blurred by markering and non-engineer geeks distorting the definition. Maximum output level of a JFET, regardless of gain, can approach 2 volts RMS, same with low voltage rail-to-rail opamps.

That would be a unity gain buffer. A buffer is anything that offers a high impedance input and a low impedance output. In this particulat case the JFET circuit is able to do a gain of 10.

My point here is that there is plenty of signal level here for most applications using a 9 volt supply. Many pedals are also 9 volts and manage the same signal dynamics. 18 volt supplys without output level trim controls often cause more problems than they solve. Too much of a good thing is usually not good.

Generally yes. In the case of EMG's circuit, they even advise the use of 18V. It all comes down to how the circuit was designed. As I'm sure you know, some 9V circuits wont run at 18V.

Increase the power supply to 18V on these circuits will not yield more output, but it also wont clip when pushed hard. That can mean it can pass a louder signal though without distortion, but in actual practice changing from 9 to 18 volts wont seem any louder.

[KJung]

Originally Posted by JimiLL

I was just wondering if anybody could tell me if there was any drawbacks to using an 18V pre amp instead of a regular 9V. I know the 18 has more headroom, and Ive noticed that when I play fingerstyle with a heavy attack (much like Trujilo plays), my 18V EMG pre has a tendency to overdrive my amps pre a little bit. I play through a Genz benz 1200.

Gain is set relatively moderate on the amp (12 o'clock, both channels), and the rest of the volume contols are at ~ 9 o'cock.

I noticed I didnt seem to have this problem when I played the bass and it was wired 9V.

Bass is Spector Euro 5

There is no relationship between 9 versus 18 volt and output level. If your bass has a very hot output and you have 'strong' attack with your technique, turn the input gain of the amp down, or in extreme cases, use the 'active' intput or 15db pad switch (depending on the amp).

Also, many on board preamps have internal trim pots to set the output level of the pre.

The only advantage of an 18volt circuit is that it allows a bit more headroom prior to the on board preamp clipping. This would only be an 'advantage' if you crank a tone of low end with the pre and play VERY aggressively, but again, has not impact on the output level of the pre.

[Jamie_Funk]

I wonder if the moderator can make this a sticky? The 9v vs 18v, and especially the incorrect perception of increased ouput, comes up a LOT.

J

[FunkMetalBass]

I wish it were easier to fit 18V into control cavities or to find room to put 18V's worth of battery compartments. I have EMGs in 3 of my basses and OBP-3s in the other two with passive pickups, and only one of them runs with an 18V circuit.

While typing this and simultaneously searching DigiKey, I came aross this:
http://search.digikey.com/scripts/Dk...X1044CSA%2B-ND
http://www.geofex.com/circuits/+9_to_33.htm

It's a charge pump converter. Has anybody ever tried using this to pump 18V from a single 9V battery? I realize battery life would be considerably shorter (theoretically, ~half the normal length), but it could solve clipping issues.

[okcrum]

Not to add to the confusion, but I've seen preamps using a single 9 volt battery that could swing 18 volts p-p - the preamp contains a DC-DC converter to step up the battery voltage.

[agedhorse]

For clarity's sake, generally a (voltage) buffer amp is considered a unity gain device or a voltage follower. When voltage gain is involved, it's generally referred to as a voltage amp or VAS, which may or may not have a (very) low impedance output. Where both functions are provided, it's generally referred to as a buffered voltage amp. This highlights the problem of slang use of terms in one industry that may have a more precise use in other industries. Both are "correct" within the context of the application.

Signal symmetry does not matter for single ended versus bipolar operation either, all that matters (all the signal cares about) is the abount of available dynamic range above and below wherever the reference ground is placed. If it's placed at 1/2Vcc on a single ended supply, it's electrically equal to a bipolar supply of equal voltage rail to rail.

I have not mentioned DC-DC converters, but that is a completely different approach that can yield whatever design voltage the designer wishes, from a 9 volt battery. In fact, with the appropriate circuit, a bipolar supply can be derived as well. The chief drawback to these devices (including charge pumps) is that they tend to be electrically noisy and require careful design and layout for good perfomance. I have designed a couple of circuits using such devices successfully, but they usually require agency approvals for RFI emissions due to the switching frequencies involved.