Multimode filters, Part 2: Pole-mixing filters

Posted by & filed under Filters, Matrix12, Oberheim, Synth DIY, Vintage synths, Xpander.

Last time we looked at reconfigurable filters, filters that include switches to rearrange parts of the circuit during normal use. However, that’s not the only way to produce different responses from a single filter circuit. This time, we’ll look at another approach: pole mixing. “Pole mixing”? It sounds like stirring a cake with a broom handle… Either that or a DJ doing a set up a flagstaff, right? Nope! You’ll have heard people talking about filter “poles”. Without going into the… Read more »

Design a Eurorack “Vintage VCA” with the LM13700

Posted by & filed under Projects, VCAs + Amplifiers.

The LM13700 is a bonafide classic synth chip, plus it’s cheap and *still* available decades after it was originally introduced. Ok, it’s no longer the state of the art, and its noise and distortion figures are pretty poor, but that’s actually a part of its charm. It’s definitely got that “vintage sound”. So let’s have a look at how we’d actually use it. We’ll design a simple linear “Vintage VCA”. A Eurorack VCA with the LM13700 Let’s assume we want… Read more »

Coronavirus Covid-19

Posted by & filed under Uncategorized.

Update: 17 April 2020 We’re still here! International mail is very slow currently. We’re seeing some packages take three or four times the usual amount of time to arrive. However, everything does seem to get through, soon or later. The major part of the problem is that there are almost no international flights to take mail and things seem to be getting very backlogged. We’ve still got stock and haven’t yet had supply difficulties. If you don’t mind being patient,… Read more »

A look at the TR-909’s noise generator

Posted by & filed under Noise, Roland, Synth DIY, TR-909, Vintage synths.

The TR-909 uses a hardware implementation of an LFSR as its noise generator. We’ve dealt with LFSR noise generators in a few other articles, but we’ve only looked at firmware implementations, so it might be fun to see how the same thing is done in hardware. The circuit is composed of three parts; the shift register itself, a clock, and a start-up circuit. Firstly, here’s the whole thing: Three ICs are used, two 4006 18-stage shift registers, and a 4070 quad-XOR… Read more »

Building the Electric Druid pedals

Posted by & filed under BBDs+Delays, Distortion, Overdrive, and Fuzz, Flanger, Stompbox stuff, Wah, Autowah, and Filters.

  This page collects together just the information you need if you’re intending to build one of the Electric Druid effects pedal/stompbox projects. For each pedal, you only really need the construction guide, which includes the full bill of materials (BOM) and a wiring diagram for the PCB in the enclosure. We also provide a drilling template for your enclosure. Each of these pedals has a separate page about it, usually with a lot more information about the development of… Read more »

Roland “Cross Mod” and “Metal Sync” – What do they actually do?

Posted by & filed under GR-700, Jupiter 6, Jupiter 8, JX-10, JX-3P, JX-8P, MKS-30, MKS-70, MKS-80, Oscillators, Roland.

What do Roland’s “Cross Mod” or “Metal Sync” really do? There are quite few people asking this question on the internet, but no-one has much of an answer. Here’s a few forum discussions I found about it: Ok, so Harmony Central was never going to provide a solid technical answer, but the Roland Clan forums or (even better) Stack Exchange might have turned up someone who actually knew what they where talking about. No luck this time. So what’s… Read more »

Which noise chip do I need?

Posted by & filed under Noise, Synth DIY.

The Electric Druid range of chips now includes four noise generators, so the table below summarises the differences between them to help you select the best chip for your application.   White Noise Outputs Pink Noise Outputs Digital Control? MN5837 replacement? NOISE1B 1 0 No Yes NOISE 2 1 1 No No PENTANOISE 5 0 No No KIJIMI NOISE 3 (1 at once) 0 Yes No   The original NOISE 1B generator provides a single white noise output and was… Read more »

NOISE2, a white and pink noise source in a single chip

Posted by & filed under Noise, PIC/Programming, Synth DIY.

It’s been around ten years since I developed the original Druid NOISE 1B chip to produce good quality white noise. Finally it gets an update, and the new NOISE2 chip can produce pink noise as well as white noise, so there’s no need for external “pinking” filters. Here’s what it sounds like, white noise and pink noise:   Here’s the spectrums for the two outputs. Note the scales on these two graphs are different, so you can’t compare one to the… Read more »

FilterFX – 12dB/oct LP/BP/HP LFO filter with 8 waveshapes

Posted by & filed under Stompbox stuff, Wah, Autowah, and Filters.

The FilterFX project uses the Druid STOMPLFO to control a 12dB/oct state variable filter. A state variable filter (SVF) is chosen because this filter design offers highpass, bandpass, and lowpass outputs which gives us the greatest range of different effects. The LFO offers eight waveforms, including two random waveforms (one does those crazy sample-and-hold effects like the Maestro FSH-1). Furthermore, the PCB provides for addition of an expression pedal to allow the filter to be used like a wah pedal… Read more »

An LED bargraph audio level display

Posted by & filed under PIC/Programming, Projects.

Replacing the LM3914/LM3915/LM3916 with a PIC Most designs you see for audio level LED bargraph displays use the LM3914/LM3915/LM3916 series chips that are no longer made. However, the chips are simple, so we can replace them with a PIC and build a nice LED bargraph driver on a single chip. So why do you need this thing? You need this if you want to display an audio level and make sure it doesn’t go above some well-defined threshold, usually the level at… Read more »