This unique pedal combines a looper with a nice delay modeler. It doesn’t do everything my old Echoplex did, but it’s a nice leap forward in technology- with stereo recording, tons of memory (and SD card expansion), stereo recording, USB connectivity and software librarian, not to mention some really nice delays.
But before we get to happiness, let’s first talk about a major manufacturing issue, nearly a total deal-breaker. If I hadn’t figured out a solution, I would have had to return the JamMan Delay and seek looper nirvana elsewhere. More
Here’s a great reference image, which clearly shows the differences between the typical A (audio/log), C (reverse audio/log), B (linear), and W (s curve) tapers. Less common are the K, D, and G tapers.
Here’s another excellent article on guitar pickups, courtesy of Pete Biltoft at Vintage Vibe Guitars. Thanks Pete for the permission to post this here!
August 2011
DC resistance measurements are widely used as a gauge of the “output” of passive magnetic pickups. This use of DC resistance is both technically incorrect and often misleading; to find out why, read on…More
A reader recently asked me a question about the low pass filter in a guitar tone circuit:
Will a 250k tone pot with a .02uF capacitor sound the same as a 500k pot with a .01uF capacitor (all else being equal)?
This is an interesting thought experiment, and the answer is simultaneously obvious and non-intuitive.
At first glance, you might be tempted to look at this standard low-pass filter schematic (borrowed from the LPF wiki), and the associated formula for cutoff frequency as 1/2piRC, and conclude that the two circuits would behave identically (since 250k*.02uF is the same as 500k*.01uF). However, the problem there is that the R in the formula is not the tone pot! That R is really the internal resistance of the guitar, or the resistance of the pickup.
In the tone circuit, the pot actually sits above the capacitor C, but below the branch to the output Vout, as shown at left. So, the formula for the cutoff frequency is more complex. In this analysis by a guitarist/mathematician named Bill, he suggests a formula for the cutoff frequency as follows:
How’s that for insanely non-intuitive?! Bill points out that the lower square root term only works with tone resistances less than about 20k (since otherwise the value would go negative producing imaginary numbers in the square root), thus explaining the often limited useful range of tone pots, and why log taper pots are more useful for tone than linear. Nevertheless, this seems to be an over-idealized formula, since in practice, I do see more variation in the tone pot even at higher resistances. This formula doesn’t seem to capture the full complexity of the reactive network made up of pickup inductor, and overall circuit resistance and capacitance (including cable capacitance).
Ok, so math is clearly the wrong way to think about this!! Too complicated! Back to the original question. Let’s think of it more simply. Imagine you turn both pots down to zero- you’re basically eliminating the variable resistance pot and wiring the cap directly to ground. Of course, the larger capacitance .02uF will sound darker than the .01uF. So they’re obviously not equivalent circuits.
Next up, experiment! Grab a couple pots, caps and some alligator leads and try it out! You’ll find that they do indeed sound quite different. The larger capacitance with the smaller pot resistance sounds darker, no matter how you slice it, when compared to the 500k pot and .01uF cap. Even with both pots up full, the larger capacitance with the smaller pot sounds a bit darker.
This all begs the question, why do guitar manufacturers often pair a 250k tone pot with a .047uF cap, versus the .022uF cap with 500k pots? The former will produce a darker sound both because of the larger capacitance but also because of the increased load on the pickup from the smaller resistance. “Double whammy” as Bill points out at the end of his paper.
Following last year’s All About Pickup Magnets, here’s another excellent article on guitar pickup magnets, courtesy of Pete Biltoft at Vintage Vibe Guitars. Thanks Pete for the permission to post this here!
In this article, Pete consolidates his own expert research on pickups, along with a bunch of information from the Wikipedia magnet entries and Magnet Kingdom, to give us an overview of magnets in general, as well an in-depth look at AlNiCo magnets for guitar pickups.More
I’ve been asked a number of times whether the polarity makes any difference when connecting the common guitar tone cap, and I always answer No.
Electrolytic caps are polarized, and can fail or explode if you connect them up backwards. But we don’t use electrolytics for guitar tone – the caps we typically use (polyester film, paper-in-oil, etc) have no significant polarity.
Now, film and foil caps (like Orange Drops and Mallorys) do have an outside foil-wrapping which is used for shielding and is connected on one of the leads of the cap. Ceramic and silver mica caps aren’t built with an outside foil wrap.
I haven’t noticed it myself, but it obviously depends on the guitar, pickups, amp, wire, capacitors, and the ears 🙂
Caps aren’t typically marked for which is the outside foil end- and I don’t know of any way to tell which is which. So, in short, try your tone cap both ways and if you hear that one way sounds better than other, then go for it. If you don’t hear a difference, don’t worry about it!
There are a variety of expensive “boutique” guitar tone capacitors out there, which I haven’t tried and didn’t include in my tone cap comparison project.
I just came across this audio comparison by “Kernel of Wisdom” which examines a bunch of the more expensive tone caps including a vintage bumblebee, modern bumblebee, Jensen Paper-In-Oil, Vitamin Q, and Luxe Grey Tiger.
Steven at S. K. Guitar Specialties has an interesting article comparing tone caps of different material types (PIO, Ceramic and polyester), with overlaid frequency plots. Check it here.
Here are the recordings lifted from my most recent Tone Cap Comparison Video, split into individual files. The files are named using generic numbers, rather than labeling them by cap type – so you can listen to these without being influenced by preconceived ideas of what a particular material type should sound like.
Or try this. Before checking the legend (linked below), listen to the examples and choose the one you like best. After you’ve decided what you like, only then check the legend which says what cap type is used for each recording.
I wrote about my love of looping back in 2010, when the new JamMan Solo and JamMan Stereo were announced.
