Is 18V electronics just a myth?

[magic papa]

Hi,

There's a lot of hype about 18V electronics in pedals, preamps etc.

What I found so far is that 18V pedals are pain in the backside to power on pedal boards whlist not really offering any measurable improvement in anything.

If we assume that the pickups of the passive bass will give you about 2Vp-p than 9V should have enough headroom as the main pupose of the effect pedals is sound modelling and converting high impedance to low, not driving the power amps or getting a lot of gain.

Does anybody drive a power amp with a stompbox preamp? Is that really a practicable thing to do?

So I think 18V is a just a marketing thing not really worth worrying about. The prime example is an MXR Blowtorch. Why would anybody need extra headroom there? It's gonna clip the signal anyway, that's what it's for. Am I missing something?

Your opinions? (perhaps we should get the Mythbusters to check this myth out ).

MM

[bongomania]

It's not a myth, it's just a subtlety. Sometimes the subtlety is worth the hassle, sometimes it's not. Also, there is a difference between headroom and gain.

[magic papa]

Sure, though my point was that if you reduced gain then you'd get more headroom and unless you are after heavy gain, there no compelling reason for higher voltage.

[bongomania]

Take the Diamond Compressor for example. It has exactly the same output levels whether you run it at 9V or 18V; but at 9V it's fairly easy to clip the input with low frequencies, while at 18V it is difficult to clip the input. Headroom refers to the levels that a component can handle without clipping--which is only sometimes related to gain.

[behndy]

Originally Posted by magic papa

Does anybody drive a power amp with a stompbox preamp? Is that really a practicable thing to do?

i've done that for years. a lot of people do. when i was younger it was ADA MB-1's into power amps (because i wanted to be Les) and now it's SansAmp stuff into power amps.

gives you a nice, modular setup and i can get the tones i'm looking for.

[M0ses]

I drive my power amp with a DHA VT1-EQ-Bass, running at 12V. Sounds fantastic.

[bigchiefbc]

Originally Posted by magic papa

Sure, though my point was that if you reduced gain then you'd get more headroom and unless you are after heavy gain, there no compelling reason for higher voltage.

Headroom is about being able to handle a hot signal (such as an active bass, or maybe even a line-level signal from an fx loop) without clipping. Most pedals don't allow you to control the amount of input gain going into the pedal. This is where 18V electronics are useful. They can usually take in a really hot signal without clipping.

[magic papa]

Originally Posted by bongomania

(...)Headroom refers to the levels that a component can handle without clipping--which is only sometimes related to gain.

Hmmm, not sure I understand, perhaps I have some misconception about how things work.

I always thought that gain and headroom are inseparable. Bascially more gain = less headroom and less gain = more headroom. In all situations. As far as my (perhaps incorrect) understanding goes the gain is just the amplification ratio of the input signal voltage. All the headroom is - is how big the signal can become without clipping. In other words - how much can you amplify the singal so it's peaks aren't clipped.

So with my theory - if the compressor clips at 9V - decrease the gain and it won't clip. You don't need the output signal to be higher than 9V unless you want the output signal i.e to drive a power amp. Although if SansAmp can drive a power amp than 9V is enough even for that.

I still stand by my first statement - you don't need 18V for a guitar pedal of any sort if you design it correctly

Cheers

MP

[bongomania]

Nope. Think about headroom like a doorway, where if it's too low you bonk your head walking through. The gain of an opamp/transistor/tube/etc. can make your signal taller, so it bonks its head (clips); but the doorframe already had a fixed height regardless of gain. So a tall-enough input signal will bonk its head even if the gain stage is set for low (or no) gain. A high-gain opamp can still have low headroom, and a high-headroom opamp can still have low gain.

Yes you can "duck down" by turning down the output of your instrument before it hits the pedal, but most people would rather use an 18V adapter than mess with the volume knob on their instrument, to get the right results from a pedal.

[magic papa]

Originally Posted by bongomania

Nope. Think about headroom like a doorway, where if it's too low you bonk your head walking through. (...).

Right, I think I'm not far from the truth. In your example I would see gain as a parameter that describes how tall I am. I guess my entire thinking was around the idea that both doorway size and my height have to be in sync and that's all. It doesn't really matter how big one or the other is. In other words we can build a huge doorway that should fit people of any height, but there's always a chance somebody will want to drive a crane through it. On the other hand you could build a doorway for a hobbit that would confortably fit in it.

The only hard limit here is the voltage generated by pickups, so there is no way that we could power a pedal with say 2V. However if you go over a certain voltage (which I thought was about 7-9V) than it really doesn't matter that much how high you go becasue you should have enough to play with.

So going further we could design a high-voltage active bass that outputs say 240V and you have to play in rubber gloves not to get zapped, but the improvement will be none.

I'm trying to design a preamp, so this is a valuable discussion for me.

Cheers

MP

[bongomania]

Sure, and in case it's not clear, I'm only trying to be helpful, not argumentative. A couple of further considerations: Many common IC's are designed to be powered at 5V, and the pedal circuits built around them are designed to chop the 9V down to 5. So that's a big part of why there can be headroom issues even when using a 9V supply. Also, the amount of voltage powering an IC doesn't always translate into a literal voltage of signal level; they're obviously related, but it's not always 1:1. And there can be clipping issues even in some components that are not gain devices. It's not as common outside of gain devices, but it's one of those things that can drive you batty when hunting for the cause of unwanted distortion.

[Ben Clarke]

My only direct experience with this is with a Fulltone OCD that I use with guitar. I played it quite often with 9v, 12v and 18v supplies. It sounded noticably different with each supply. As bongo said, it is in the subtlety category. Fuller talks some about it on their site. As you increase the voltage, dynamics & harmonic "openness" increases with that pedal. I still happily use it with whatever voltage is convenient, usually 12v from a Voodoo Labs PP2.

Circuits vary and so will results.

I corresponded with David Barber after purchasing the Linden EQ for bass use and asked him about higher voltage supplies. He said to only use 9v, but pointed out that those 9 volts are converted to 25v by the circuit (and an 18v supply would result in a 56v supply to the circuit). Remember things are not always as they seem.

[bongomania]

True true! Lots of pedal builders these days are incorporating those "charge pump" circuits that increase the voltage internally.

[magic papa]

Originally Posted by bongomania

Sure, and in case it's not clear, I'm only trying to be helpful, not argumentative.

Sure thing, and similarily - I'm not trying to banter - just really trying to understand the issue

Originally Posted by bongomania

A couple of further considerations: Many common IC's are designed to be powered at 5V, and the pedal circuits built around them are designed to chop the 9V down to 5. So that's a big part of why there can be headroom issues even when using a 9V supply.

Aha, that explains a lot. But you can design around that. Pad the input to go below 5V with a decent headroom and then boost it on the output to whatever (9V minus the headroom).

I guess that's what I meant previosuly by saying "if you design you pedal right". Obviously if the voltage is dropped the clipping may occurr. With 9V we get 4.5 Vp-p which is quite healthy. With 5V we get 2.5Vp-p, which assuming 2Vp-p from pickups can certainly be a problem.

I also understand that it is possible to boost voltage internally. Obviously this complicates the circuit and chews the battery much faster, so firstly there has to be a real need for higher voltage.

Still can't see it . Not for a stompbox anyway. Even if I chain many pedals together, providing I set up the output volumes right on all of them I should get no clipping unless I've got a badly designed pedal (or a high voltage bass )

[Ben Clarke]

Originally Posted by magic papa

...What I found so far is that 18V pedals are pain in the backside to power on pedal boards whlist not really offering any measurable improvement in anything...

That really depends on what's being measured.

Besides, we're producing tone here, who's to say what constitutes an improvement? I know a guy who likes the OCD best with about 8v on it. He says it kind of just collapses everything down and squashes the harmonics that I like to get really dynamically from it.

It comes down to whether or not there is a discernable difference. If so, then it's up the designer to make a decision.

[silky smoove]

magic papa: I think the bit that keeps getting missed is that bongo is describing the amount of signal voltage that occurs when it hits the pedal. You're describing what happens after the signal hits the pedal and you adjust the gain control.

[boomertech]

You are correct that you can turn down the instrument to prevent clipping. You can also design a circuit that attenuates the signal to keep it below the level of circuit clipping. But there are benefits to a higher voltage circuit.

Headroom… I have measured the raw signal from a MM Stingray with slap and pop style with the initial signal exceeding 6V peek-peek. The typical (non rail to rail) op-amp can only output within a few volts of its supply voltage. With a 9V supply this would limit the op-amp to approximately 6-7V peek to peek output. This would be just on the edge of clipping the op-amp without attenuating the signal.

Noise… Every circuit component creates noise. Many circuit designs try to keep a large S/N ratio by keeping the signal as large as possible. If you increase the signal level early in the path then you can increase the S/N ratio for the rest of the circuit and output. If you attenuate the signal to prevent clipping your S/N ratio is reduced and noise levels go up.

Components…. Some pedals are designed with IC’s that require more than a 9V supply to operate correctly.

EQ/Gain… Let’s say that your passive bass with hot pick-ups can output a 2V p-p signal. If you add 12dB of gain you have boosted the signal to 8V p-p. An 8V p-p signal will be clipped in a 9V op-amp circuit and 12dB boost is not uncommon in boosters and EQ’s.

There are excellent 9V circuits designed for bass that will be hard to clip and there are 18V pedals that you can clip easily. Often bass pedals are from a prior guitar pedal design that needs 18V to accommodate the larger dynamic signal. The way the signal is processed is up to the designer and they are all bound by the laws of physics and measured compromise.

Most charge pump IC's have efficiencies reaching 98%. So that is a myth that they use gobs of battery current. You can design a 9V and 18V circuit that uses exactly the same current with the only difference being the headroom.

Why do almost all SS preamps operate at +/-15V or more when the power amp can reach full output power with a 1Vrms signal?

[Eric!]

Also, Tronographic Rusty Box takes 24-40 volts. Holy BALLS.

[TOOL460002]

my final bass teacher modded most of his basses to run on two 9v batteries instead of one, so it must be better.

heh... well, in all seriousness, there is a solid reason why some pedals need 18v, and why some can operate from 9-18v for more headroom. i essentially use parallel loopers with volume knobs as a preamp, and have tried running different ones at 9v, 12v, and 18v. there is a difference (i play an active bass).

the wall wart does suck though, especially the one for the mxr eq. its friggin huge.

[Timi]

Originally Posted by Eric!

Also, Tronographic Rusty Box takes 24-40 volts. Holy BALLS.

...and ships with a 40V. It actually gets warm!

Question: Is it safe to assume that pedals which can run at 9V or 18V can also be run anywhere in between?