In quest of perfect guitar tone

Passive electric guitar pickups with their extremely high source impedance (‘Hi-Z’), have lead most manufacturers of quality top-end amplifiers to adopt a standard ‘1000 Ohm impedance input’,  to, as far as possible, neutralize all the problems associated when high impedance sources are connected with relatively how impedance inputs.

This said, if you are using passive single coil pickups the difference between using a 500 Ohm guitar input and a true 1000 Ohm guitar input is going to be more obvious than if you are using humbuckers, or active pickups, such as EMGs.

What the ‘technical specs’ often fail to note is that it is the very start of each note that has the most high end transients.  The ‘pick attack’. And anyone who really loves the sound of an electric guitar will appreciate just what a tragedy is is to lose these attack transients high frequency fidelity. This is key to understanding the full implications of impedance in relation to guitar tone.

Most of the big named guitar amplifiers have been using 1000 Ohm guitar inputs for decades. Truly ‘Hi-Z’ inputs.

For example a Fender Twin Reverb has a 1M Ohm input. A Fender Bassman 59 has a 1M Ohm. A Marshall Bluesbreaker has 1M Ohm.

As to guitar effects pedals, all Boss pedals are 1M Ohm, while many Fender Pedals are 1M Ohm (but some are as low as 150k).

[Retailers of sub-optimal audio interfaces, though, will tell you that ‘lots’ of guitar amps have 470 kOhm as input impedance. That this input impedance of470K Ohm is a compromise solution to allow both Low impedance or Mid- impedance sources to be used on the same input without trouble. They will then add that any signal loss will be minimal, a few dB at most, so you will lose little tone, and add very little by way of noise, when using the 470K Ohm as compared to the 1000 Ohm (1 M Ohm)].

Sadly, lots of retailers will use the term ‘Hi-Z’ to refer to values as low as 600 Ohm. Sometimes retailers will refer to their product at ‘Hi-Z’, even though it is considerably lower. But don’t be fooled. Guitar amps produce the tone we are after. The tone that the algorithm modellers who produce the best guitar effects plug-ins try to emulate. So if you use anything less than the ‘real deal’, you will probably be disappointed with your final sound.

The dream of guitar amplifier, cabinet, and effects simulator designers is to match the true warmth, tone, punch, and clarity (just to name a few of those other ‘qualitative’ ‘subjective’ words) of their analog counterparts.

To make passing your guitar intput, your guitar signal, through their ‘algorithm’, as close as possible to plugging your guitar into ‘the real thing’.

I won’t go into the details of just how many different processes have to be modelled to even approach that level of realism. Luckily I don’t have to, as this guide deals with things we, the users of that software, can do to avoid ‘stuffing up’ the final (technical) stage of the process. Which is, ironically, mostly the input stage. The very first stage of the signal flow.

Setting up a guitar.

And then plugging it in.

Getting the signal to reach those clever algorithms that turn AC current into all those tasty subjective impressions guitarists, and all lovers of music, relate to like a wine connoisoire relates to wine.

Tone, warmth, crunch, squeal, sustain, ‘bell harmonics’, chimes, oomf, dull thud, and scream. Just to name a few of our ‘favorite things’.

One thing all quality hardware has in common is a 1000 Ohm guitar input.

[But it is interesting to note that the pots in guitars tend to range between 220k and 470k Ohms].

Most guirists will use a D.I box between their guitar and the amplifier, to ‘match impedances’. And if they don’t have a dedicated D.I box, at least one of their guitar effects pedals will act like a high impedance boost, and thus be performing the same function, whether or not the guitarist realises this. 

If you have a guitar effects pedal without a ‘true bypass’,  you may find that it works pretty well as a  D.I, as a  high impedance preamp, if you put it  in ‘bypass’ mode.

So the amp gets, receives, the full benevolence, the full measure, the bounty of fullness and completeness, and  is able to ‘drink’ up, down to the very last ‘drop’, every milliliter of power and glory you are able to sqeeze out of your axe.

So you won’t be limited by other factors ‘bottlenecking’ and ‘dampening’ and ‘filtering’ and ‘blocking’ the flow of your musical genius, as it blocks the flow of electrons carrying the pixie dust of guitar tone.

Think of it like trying to fill up a big tank of water using just a little narrow hose. You have a huge tank of inspired electrons flowing in waves of Alternating Current. You want to get this magic stuff into the Amp. To make it louder. Better. To add that ‘magic’ that words fail to describe. But which the ears hear. And the heart feels. That ‘rock’ and ‘roll’ your very soul. And reach out to the ‘Super-Soul’ within all creation.

But it has to somehow pass through that narrow, thin hose. It just doesn’t work. It’s going to slow you down. Block the flow. Lots of ‘water’ is going to be splashing about, splashing out over the floor. It just won’t make it into the ‘magic machine’, the ‘black box of goodness’ we refer to as an ‘Amp’.

Then imagine being able to exchange that narrow hose with a big thick fat hose.

You get the idea. The hose is the ‘weakest link’.

But the hose is not the cable. Though a good quality cable is also key.

[Refer to ‘Sound Foundations’ for details, if you are not reading this chapter in that guide right now. You see it took me a long time to work out what needed to be saying about Impedance, and how to say it. So I will add this chapter to ‘Sound Foundations’, along with a chapter on setting up electric guitars].

The hose, in this analogy, is your Audio Interface’s guitar input.

You want to get 1000 Ohms of water into your computer, but it will only let in maybe 600 Ohms at best. Often much much less.  Often as low as 250 Ohm. And we are talking within a very limited bandwidth.

If you were to measure the Impedance across the active bandwidth that your guitar pick-ups are outputting, those figures would suffer badly. Slump. [They’d look as bad as your 401K and other investments are going to look when the financial crisis that the Banksters have been keeping up their sleeves for ‘just the right moment to cause the most damage’, occurs. For the same reason. You can ‘hide’ ‘facts’ by ‘spinning’ them. Mis-direction. The sort of ‘spin’ and ‘mis-direction many audio interface retailers use with their ‘specs’].

No matter how hard you ‘pump’ that axe of yours, no matter how much ‘water’ leaves your guitar, being forced out by your finger tips, as your pound and squeeze out those magical licks and chops, maybe half of it is every going to reach the algorithms. The ‘guitar amp, cabinet, and effects simulators’.

[If you can ‘contain’ the water, under pressure, so it doesn’t leak, (great guitar cables and connectors) you can then ‘amplify’ it using a water pump (D.I or other form of amplifier).  This increases the water pressure. The same force of a tank of water over a large area, is now applied over a much smaller area, making the force that much greater. So it is really ‘pumped’ into your laptop. No part of the signal lost. Everything intact. And at really tasty levels making it possible to record with peaks around -12dB, ensuring not a single high energy transient is ever clipped. All those tasty frequencies intact, and now ready to be ‘processed’ in your laptop into pure sonic effulgence worthy of any celestial axe].

Note that, roughly speaking, impedance describes how ‘fat’ the hose is. How much water it can carry. A thinner hose will reduce how much water can be transferred from A to B per second.  So the ‘thinness’ of the hose is analogous to the ‘impedance’ of an electrical component.  It ‘impedes’ the flow of water. It impedes the ‘current’ of water. 

That was just rough anology. Forgive me if I miss the mark. Because water is pretty homogenous. AC currents are not. Impedance is more or less at different frequencies, within the same electrical component.

This is why you have to test any hardware with an AC power source. Preferable an actualy guitar. Impedance is frequency dependent. When specifying an impedance you have to specify the frequency at which that impedance was measured.  Otherwise it is more or less meaningless. For example a 1 ohm impedance at 1000 Hz might be 10 ohms at 10 Hz, or...