Active pickups in newer bass guitars tend to use 2 x 9v batteries to give 18 v, whereas effects pedals traditionally have used (and continue to use) a single 9v power supply.
If there a good technical reason as to why 18v is preferable for an onboard preamp, and if so are there any design issues that 9v powered effects pedals have to deal with because of the relatively low voltage?
If there a good technical reason as to why 18v is preferable for an onboard preamp, and if so are there any design issues that 9v powered effects pedals have to deal with because of the relatively low voltage?
My first best guess would be that the move to 18v from 9v is to increase voltage swing from the pickups. Remember, the theoretical maximum RMS output using a 9v supply will only net you [ 9 / 2.82 = ] 3.2v RMS. Practically speaking, it's a whole lot less.
That still sounds like an awful lot of room at first glance. However, if you take a reasonably high output pickup -- say the bridge humbucker from a Gibson ES-335 -- and connect the guitar directly to a good oscilloscope, you'll see the pick transient from each string will peak at 3-4 times greater than the amplitude you get as the string slowly decays.
Now whether that much headroom is musically desirable is another topic entirely. It would be 100% dependent on your style of playing, what you prefer to play, and whether you prefer a basically clean sound or want to crunch it up.
The folks that slap bass strings around would probably die for such an increase, as slap bass is basically clean. A power chord from a metal head? Not so much.
Dave
That still sounds like an awful lot of room at first glance. However, if you take a reasonably high output pickup -- say the bridge humbucker from a Gibson ES-335 -- and connect the guitar directly to a good oscilloscope, you'll see the pick transient from each string will peak at 3-4 times greater than the amplitude you get as the string slowly decays.
Now whether that much headroom is musically desirable is another topic entirely. It would be 100% dependent on your style of playing, what you prefer to play, and whether you prefer a basically clean sound or want to crunch it up.
The folks that slap bass strings around would probably die for such an increase, as slap bass is basically clean. A power chord from a metal head? Not so much.
Dave
The traditional valve preamp triode typically runs on 300V - 350V, and has an awful lot of output headroom compared to 18V circuitry. What's more, when triode outputs do overload, they tend to do so more gracefully than solid-state circuitry.
I think the 18V rail is to keep the solid-state bass preamp from clipping, which usually produces quite nasty harsh sounds.
In another thread, one person posted oscilloscope captures showing that he can generate 10 volt transient peaks from his humbucker-equipped guitar. 😱
That is atypical, but 1 volt peaks are not. If you assume a pedal running on 9V can only put out a max output of maybe 6V peak-to-peak (typical of many opamps running on 9V), and therefore only 3V peak, you really don't have a lot of room for gain - any gain larger than 3x (roughly + 10 dB) will cause clipping of the transients.
I think the 9V standard for guitar pedals was set by historical precedent, simply because small 9V batteries were available, and that was the highest voltage you could conveniently get in a battery small enough to fit in a typical guitar FX pedal case.
Today many FX pedals (and bass preamps) are built around op-amps, and when electronics engineers can, they traditionally run op-amps off +/- 15 V rails - equivalent to a single 30-volt power supply rail!
So even 18V is a compromise, really. Better than 9V, but it would be nice to have the extra breathing room of 30V if it were possible.
-Gnobuddy
I think the 18V rail is to keep the solid-state bass preamp from clipping, which usually produces quite nasty harsh sounds.
In another thread, one person posted oscilloscope captures showing that he can generate 10 volt transient peaks from his humbucker-equipped guitar. 😱
That is atypical, but 1 volt peaks are not. If you assume a pedal running on 9V can only put out a max output of maybe 6V peak-to-peak (typical of many opamps running on 9V), and therefore only 3V peak, you really don't have a lot of room for gain - any gain larger than 3x (roughly + 10 dB) will cause clipping of the transients.
I think the 9V standard for guitar pedals was set by historical precedent, simply because small 9V batteries were available, and that was the highest voltage you could conveniently get in a battery small enough to fit in a typical guitar FX pedal case.
Today many FX pedals (and bass preamps) are built around op-amps, and when electronics engineers can, they traditionally run op-amps off +/- 15 V rails - equivalent to a single 30-volt power supply rail!
So even 18V is a compromise, really. Better than 9V, but it would be nice to have the extra breathing room of 30V if it were possible.
-Gnobuddy
So would it be reasonable to assume that 9v effects pedals designed for bass guitars either have an attenuator on the input, or have a voltage doubler in the power supply?
Hello.
More voltage => less intensity in cable to the amp => less disruption due to Jack contacts.
I honestly don't know - I haven't really studied the schematics of bass guitar pedals. Particularly with older pedals, maybe they just keep the voltage gain very low (so as not to clip), and mostly just EQ and buffer the pickups (rather than amplifying the signal a lot)?
-Gnobuddy
I'll side with Gnobuddy and say that I honestly don't know either, but I've got a really good guess that's based on a couple sound engineering practices.
mjbmikeb2, I think you may have the right idea but just the wrong end of the stomp box with your comment about having an attenator on the input. Good engineering practice says that for maximum signal to noise ratio, you want to maximize the amplitude of the input signal as much as possible right up front in the first gain stage. That practice applies to any multi-stage amplification system, regardless of its intended function or purpose.
Having an attenuator at the input before the first gain stage would defeat that practice, because among other things, you would be deliberately increasing the signal to noise ratio by padding down the signal before it was amplified. Instead, you want to run the signal hot through to the output of the stomp box, and if you have to have some attenuate somewhere, you put the attenuator at the tail end of the amplification system as a volume control.
Now I must admit that you've got the right kind of thinking going, because most every channel in a recording studio has the ability to pad down a hot signal before it goes into the board, but the operative word is hot. But that usually means that you're taking a direct signal from the speaker output of an amp or some other high voltage source that would immediately cause the first gain stage in the board to distort.
A stomp box shouldn't need to have an input pad, because it is designed to be connected directly to an instrument. The problem is our previously-mentioned guitar with a humbucker pickup and our slap-bassist (who also may have a humbucking pickup). As Gnobuddy pointed out, he recalled another poster stating he was able to achieve a 10 volt transient peak from a humbucker. I'd have to do it over again to make sure, but I swear I was able to get a 12 volt spike out of my ES-335 by doing the same thing. That slap bass probably makes an even larger transient when our bass player pulls the low E string an inch up in the air and lets it slam back against the fingerboard during a hot riff.
An interesting off-this-topic discussion is that if you put three or four series-wired diodes across the input before the first gain stage and play a guitar through it, you can't really hear that it clipped off the transients, both bass and guitar. I actually series-wired three diodes one direction and another three series-wired diodes in the other direction across one of the channels of an old Vox Royal Guardsman for a time, and the guitar sounded just fine because of its Attack-Decay-Sustain-Release (ADSR) envelope. Other instruments with a different ADSR profile -- like an organ -- wouldn't work well.
Now back to the 18 volt question...........if you double your B+ to 18 volts, your input stage can suddenly handle those nasty pick or slap transients quite handily without clipping. Not only that, 18 volts provides you with an input stage that can offer a small bit of amplification for the rest of the stomp box to work with. If things need to be tamed down, you can easily attenuate things at the output of the stomp box with a volume control.
Dave
mjbmikeb2, I think you may have the right idea but just the wrong end of the stomp box with your comment about having an attenator on the input. Good engineering practice says that for maximum signal to noise ratio, you want to maximize the amplitude of the input signal as much as possible right up front in the first gain stage. That practice applies to any multi-stage amplification system, regardless of its intended function or purpose.
Having an attenuator at the input before the first gain stage would defeat that practice, because among other things, you would be deliberately increasing the signal to noise ratio by padding down the signal before it was amplified. Instead, you want to run the signal hot through to the output of the stomp box, and if you have to have some attenuate somewhere, you put the attenuator at the tail end of the amplification system as a volume control.
Now I must admit that you've got the right kind of thinking going, because most every channel in a recording studio has the ability to pad down a hot signal before it goes into the board, but the operative word is hot. But that usually means that you're taking a direct signal from the speaker output of an amp or some other high voltage source that would immediately cause the first gain stage in the board to distort.
A stomp box shouldn't need to have an input pad, because it is designed to be connected directly to an instrument. The problem is our previously-mentioned guitar with a humbucker pickup and our slap-bassist (who also may have a humbucking pickup). As Gnobuddy pointed out, he recalled another poster stating he was able to achieve a 10 volt transient peak from a humbucker. I'd have to do it over again to make sure, but I swear I was able to get a 12 volt spike out of my ES-335 by doing the same thing. That slap bass probably makes an even larger transient when our bass player pulls the low E string an inch up in the air and lets it slam back against the fingerboard during a hot riff.
An interesting off-this-topic discussion is that if you put three or four series-wired diodes across the input before the first gain stage and play a guitar through it, you can't really hear that it clipped off the transients, both bass and guitar. I actually series-wired three diodes one direction and another three series-wired diodes in the other direction across one of the channels of an old Vox Royal Guardsman for a time, and the guitar sounded just fine because of its Attack-Decay-Sustain-Release (ADSR) envelope. Other instruments with a different ADSR profile -- like an organ -- wouldn't work well.
Now back to the 18 volt question...........if you double your B+ to 18 volts, your input stage can suddenly handle those nasty pick or slap transients quite handily without clipping. Not only that, 18 volts provides you with an input stage that can offer a small bit of amplification for the rest of the stomp box to work with. If things need to be tamed down, you can easily attenuate things at the output of the stomp box with a volume control.
Dave
mjbmikeb2,
My apologies -- I'm betting that with all the activity on this thread, we still haven't truly answered your question. The reason I say that is that I just read all of the posts, start to finish, including your original question.
You wanted to know why Active Pickups In Bass Guitars tend to use two 9v batteries in series for 18 volts, whereas most stomp boxes use 9v. Here is a shorter answer for you that may get to the meat of what you wanted to know:
Pickups (active or not) generate a very "fragile" signal. Fragile in this sense means High Impedance, meaning the output of any given pickup can be several volts, but it contains very little current. Lack of current in the signal means that anything -- volume control, tone controls, or even a long cable back to the amp -- is going to selectively attenuate parts of the signal and make it NOT what the pickups originally generated. There is only one sure fire way to get the original signal into the amp -- no volume, no tone controls, and an extremely short guitar cord.
Quite comically, I've already lived that scenario. Years ago, I bought a Squire P-Bass from the Shop Goodwill website for 47 bucks. The neck was fine but the volume and tone controls literally fell apart after I got it, so I simply removed them and wired the pickup directly to the jack. The doggone bass literally came to life -- it sounded sooo outstanding without the volume or tone controls loading down the signal that I haven't even installed replacements!
Thankfully, electronics came to the rescue for the situation above. A simple buffer circuit built into the bass can add current to the signal without increasing the output voltage and without causing any frequency degradation, and from there the "stronger" / Lower Impedance signal can easily handle a volume control, tone controls, and long cords without issue.
Then........people got clever, not only with the kind of electronics installed in the instrument but also the kind of playing bassist started doing. Instead of simple passive volume / tone controls, manufacturers started adding "active" circuits where increasing the treble or bass control actually increased the amplitude of that part of the signal (as opposed to passive controls that work by actually attenating the signal).
Adding active controls worked okay with a single 9 volt battery as long as the bassist used a pick or "walked" up and down the strings with his / her fingers. The reason is that both styles are reasonably "gentle" and kept the transients at a minimum. The 9 volt supply could handle it.......just barely.
Things fell apart quickly with the advent of slap-style playing, because the style dramatically increases the amount of headroom required (and by implication, the supply voltage) to faithfully reproduce the output of the pickups as the buffer circuit(s) add current. The only way to rectify the situation was to increase the voltage applied to the electronics, so they could keep up with the pickups when the strings are slapped.
Hope this got closer to the point.
Dave
My apologies -- I'm betting that with all the activity on this thread, we still haven't truly answered your question. The reason I say that is that I just read all of the posts, start to finish, including your original question.
You wanted to know why Active Pickups In Bass Guitars tend to use two 9v batteries in series for 18 volts, whereas most stomp boxes use 9v. Here is a shorter answer for you that may get to the meat of what you wanted to know:
Pickups (active or not) generate a very "fragile" signal. Fragile in this sense means High Impedance, meaning the output of any given pickup can be several volts, but it contains very little current. Lack of current in the signal means that anything -- volume control, tone controls, or even a long cable back to the amp -- is going to selectively attenuate parts of the signal and make it NOT what the pickups originally generated. There is only one sure fire way to get the original signal into the amp -- no volume, no tone controls, and an extremely short guitar cord.
Quite comically, I've already lived that scenario. Years ago, I bought a Squire P-Bass from the Shop Goodwill website for 47 bucks. The neck was fine but the volume and tone controls literally fell apart after I got it, so I simply removed them and wired the pickup directly to the jack. The doggone bass literally came to life -- it sounded sooo outstanding without the volume or tone controls loading down the signal that I haven't even installed replacements!
Thankfully, electronics came to the rescue for the situation above. A simple buffer circuit built into the bass can add current to the signal without increasing the output voltage and without causing any frequency degradation, and from there the "stronger" / Lower Impedance signal can easily handle a volume control, tone controls, and long cords without issue.
Then........people got clever, not only with the kind of electronics installed in the instrument but also the kind of playing bassist started doing. Instead of simple passive volume / tone controls, manufacturers started adding "active" circuits where increasing the treble or bass control actually increased the amplitude of that part of the signal (as opposed to passive controls that work by actually attenating the signal).
Adding active controls worked okay with a single 9 volt battery as long as the bassist used a pick or "walked" up and down the strings with his / her fingers. The reason is that both styles are reasonably "gentle" and kept the transients at a minimum. The 9 volt supply could handle it.......just barely.
Things fell apart quickly with the advent of slap-style playing, because the style dramatically increases the amount of headroom required (and by implication, the supply voltage) to faithfully reproduce the output of the pickups as the buffer circuit(s) add current. The only way to rectify the situation was to increase the voltage applied to the electronics, so they could keep up with the pickups when the strings are slapped.
Hope this got closer to the point.
Dave
The funny thing is that electric guitars were invented before there were any of today's good audio engineering practices, so they come with a signal attenuator built right in: the guitar's volume control!
That high-impedance passive attenuator right where the signal is weakest would be a big no-no today, except that it's been there so long that no guitar manufacturer would dare to take it off. Guitarists would revolt if they didn't have a volume knob!
Interesting factoid: Leo Fender stole his 12AX7 preamp gain stage design from the back of a (RCA?) tube catalog. It was designed for standard "mid-fi" audio of the day, maybe a radio or gramophone, not an electric guitar. The standard 1.5k cathode resistor and 100k anode resistor biases up with the grid at about (-1.5V) with respect to the cathode.
This really only allows maybe +/- 1V input headroom before grid current starts to flow, and starts to distort the high-impedance guitar signal.
I have two guitars that show this is more than a theoretical problem: both of them will audibly overload the input of my Princeton Reverb if you turn the volume to full, and strum a six-string chord. You don't have to strum hard, either.
The same two guitars will also overload the input of my Super Champ XD. That one has a solid-state preamp, but being a Fender product, may only have the same amount of headroom as their more traditional valve designs.
That poster did more than just state this - he attached oscilloscope screen captures showing more than 10 volt peaks from his guitar. Real engineering data, not just unsubstantiated claims!
I don't think I would have believed 10V peaks without seeing the 'scope captures for myself, I would have figured he just set his scope probes wrong or something, and was thinking he had a 10x attenuation in the probe when he actually didn't.
My two guitars that overload the input of the Princeton Reverb are both, shall we say, heavily influenced by the ES-335. Both have thin hollow bodies with f-holes and a solid centre block running down the middle of the body, both have a pair of humbuckers. One is an Ibanez, the other a Korean-made Agile.
The courts have said that neither is violating any copyrights - the basic concept of a semi-hollow, thin-body electric guitar is no longer protected by copyright - but I'm sure our foul-tempered friend Mr Henry Juszkiewicz would love to sue both manufacturers if he could.
As an aside, the Agile feels better to play than the "real" Gibsons I've tried out in music stores in the last five to ten years. What a shame Gibson's manufacturing quality has fallen so low.
Was this for clean tones, or was the guitar sound distorted? I would think clipping off the transients would be more noticeable for clean tones.
I actually suspect that one reason valve preamps sound better for guitar clean tones is that the multiple preamp valves progressively soften and "sandpaper away" the harsh spiky transient at the start of each guitar note before you hear it.
-Gnobuddy
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