hammer Stupidly Wonderful Tone Control 7/12/2005 10:16 PM
A simple and pleasing way of getting nice treble rolloff tone control. Details included in GIF.

hammer Multi-Flanger 5/25/2005 3:56 PM
This is an older Japanese schematic someone posted in a huge zipfile a while back. It is one of the more experimental flanger designs I've seen. Not so much in terms of the circuits themselves, but in terms of what it encourages the user to tinker with.

The unit has the standard LFO and regen possibilities, but it also has LFO shape, sum/difference outputs, and a whole truckload of modulation capabilities, including envelope-driven sweep. A *lot* of knobs and switches on this one.

As far as parts go, the only hard to get things would be the BBD chip (MN3009 256-stage BBD) and clock driver (MN3101) and a 2SA798 matched PNP pair. The MN3009 can be subbed with an MN3007 to some extent (though with a shift in delay time), and the other two are available, just hard to find from any of the typical industrial suppliers. Everything else either uses easily available parts or parts that are easily subbed for.

A PCB layout is included, flipped around for using PnP etching/resist method, however I cannot vouch for the scale of the layout. You may have to adjust the prinout size on your machine before printing it to your choice of transfer sheet. The traces have been digitally thickened a bit but I don't see any spots where there is big risk of traces bleeding into each other. That being said, you may want to touch up the resist pattern yourself before printing to transfer sheet.

The flaw in the circuit, if there can be said to be one, is the absence of companding for both level and noise control. On the other hand, there is pretty good lowpass filtering of the BBD (2-pole before and 5-poles after), and a input-level gain control so noise and distortion should not be too much of an issue.

This looks like a really interesting circuit.

hammer Simple downward expander 5/25/2005 12:58 AM
This is a downward expander. Where noise gates make all output below a certain level equal zero, a downward expander simply reduces the output proportionately. This has the pleasing side-effect of not chopping the attack and decay/trail of notes as much as a gate does.

The schematic comes from a collection of Japanese schematics that someone posted a while back. I cleaned it up a bit and flipped the PCB layout so that it is compatible with PnP transfer techniques. The PCB is probably not to scale so be careful in re-scaling it.

The diodes can be replaced with 1N914 without changing the circuit much. The 2SC1222 transistors are listed in my data book as the complementary unit for the 2SA640. I suspect that the 2N5088 would sub for the 2SC1222 just fine, meaning that a 2N5087 would sub for the 2SA640. It's your option to include the indicator built around TR4 or not.

Haven't built it, but it looks good.

hammer Fast-Slow mod for envelope-controlled devices 4/15/2005 10:01 PM
This is a nice quick and dirty way to simultaneously change the attack and decay time constants of any side-chain driven device that uses a half-wave-rectifier, using a simple SPDT toggle.

The principle is illustrated using the Nurse Quacky clone of the old E-H Doctor Q pedal. Added components are shown in red/blue.

hammer The Crank - a not so clean booster 1/9/2005 2:29 AM
This is my attempt to make a high-ish gain booster that is intended to push a tube amp but adds just a hint of its own dirt. It needs a dual-ganged 10k pot, but the payoff is that it appears to retain subjective bandwidth as gain gets cranked and the dirt appears. Some serious volume boost. More design details are provided in the GIF.

(NB: I was searching for a font for the title and stumbled across one in my collection named "Centaur". That's not an indication of any clandestine schematic, just wishful whimsical thinking.)

hammer A different sort of panning tone control 9/29/104 6:39 pm
The classic Big Muff Pi tone control pans between the outputs of a simple lowpass and highpass filter. The corner frequencies are set so that: a) there is reasonably equivalent output level from each extreme of the tone control (i.e., changing the tone won't drastically change the volume), and b) the "middle" position delivers a gentle mid-scoop.

While elegant in its own way as a do-all control, you can't have more bottom without losing bite, and can't get more bite without losing bottom. Personally, I find that a nuisance.

While looking over some schematics from various Shin-Ei fuzzes, various Univox Superfuzz issues, and the Roland Bee-Baa, I saw that many favourite fuzzes incorporated a switch to go from a mid scoop sound (which would accentuate buzz and octaves above by de-accentuating the fundamental) to a "normal" full-bandwidth sound. This started me thinking about replacing the switch with a panning control similar to the Big Muff's. The big question was what would be at the non-scoop end of the control's rotation. To simply fade in a mid-scoop was a bit too plain and the sort of thing you could easily do with a resonant boost-cut control/stage.

At the same time, I started pondering what eventually turned into the Rosey-Ray fuzz (see a few entries below). There, I wanted a control that would pan between two different fuzzes, and I wanted the pan control to blend between the best that each had to offer. What I ended up with was a bizarre control that incorporated a lowpass filter on one side, much like the BMP, plus a mid-scoop at the other side, and a little twist that inserts more variation into the control with a single component.

What I've posted here is the essential design idea, without any posted values. You can look at the Rosey-Ray for one implementation of it, but note that the values chosen were arrived at by trial and error to complement the two distortion stages and produce roughly equal volume. I thoroughly expect other component values to be more appropriate in other contexts. For the Rosey-Ray, the two parallel signal paths to be panned between were coming from different sources. What I've shown in the schematic here assumes that a single source (e.g., the output of a high gain device like any of Joe Davisson's excellent designs) is simultaneously filtered in two ways and you adjust how much of each you want.

The lowpass side should have a rolloff somewhere in the 2-3khz zone. This will yield a nice warm distortion tone, a bit of bite but with all the edges sanded down smooth and round. It will easily stand out in a mix and you will know that it is a distortion, but with a more relaxed bluesier feel suited to a humbucker-equipped solid body or semi-acoustic. The mid-scoop/notch can be whatever you want it to be. The essential thing is that it retain both top end and bottom. I recommend the articles that Jack Orman has at his www.muzique.com site in the lab notebooks, concerning notches and scoops. Myself, I just started with a known quantity: the Superfuzz notch.

The neat quirk I stumbled onto is the addition of the cap between wiper and ground. Bear in mind that cap, in tandem with each leg of the pot, forms a low pass filter whose rolloff is set by the capacitance and pot-leg resistance. Let's say, for instance, the pot was a 100k linear, just like the BMP, and the wiper-cap was .001uf. With the pot rotated completely in any direction, the pot and cap make a LPF with a 1.5khz rolloff which is ADDED to the action of whatever filter precedes it. When the pot is rotated fully towards the lowpass side, the cap is paralled with the existing treble-cut cap to form a single-pole lowpass with a lower rolloff.

Rotate the pot 10k away from the end, and you'd have a 6db/oct rolloff at 2.3khz, followed by a second 6db/oct rolloff at 16khz. Of course, at the same time, the signal coming via the notch filter side is also rolled off at 1/(2*pi*90k*.001uf)= 1768hz.

The nifty thing here is that as you rotate the control, you not only change the relative balance of each source, but you also change the spectral content it is contributing as the LPF rolloff for each side keeps changing. The result is a control where a couple of degrees rotation gets you an audibly different sounding tone, with a different character, not just a little brighter or a little duller, more boomy vs more nasal. It's not quite a "clickless switch" like those pots that double as program switchers in many digital FX boxes, but there is a big increment to the amount of clear variation can be introduced by a single pot. Again, the nice thing is that you don't have to trade off bite for bottom. If you need more bite, you can simply up the value of the cap labelled C1.

It may well require a lot of tinkering to get it to work right in your circuit, but this is a circuit that is well worth tinkering with.

hammer Another Leslie 8/11/104 4:46 pm
Dean Hazelwanter sent me these pictures for posting, showing another rotating speaker arrangement. The baffle is more complex than the styrofoam "cheese wheel" shown in the entry below this one. The speaker is also bigger.

Dean has taken it apart to give a better sense of how the mechanism works. Like the smaller unit I have, this one also operates by belt drive.

The zipfile contains a number of jpg files and is about 1.5meg in total. Thanks Dean.