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 »

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 »

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: https://www.harmonycentral.com/forum/forum/Keyboards/acapella-18/330134- http://forums.rolandclan.com/viewtopic.php?f=59&t=54410 https://music.stackexchange.com/questions/57210/what-exactly-is-the-cross-modulation-on-roland-jupiter-and-jx-analog-synthesiz/71048 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 »

Experiments with variable rate drum sample playback

Posted by & filed under DMX, Linn, LinnDrum, Oberheim, Projects, Synth DIY, Vintage synths.

Or how to get a vintage 1980’s drum machine sound without selling your kidneys! There was a discussion on the SynthDIY mailing list recently about how the early digital drum machines like the LinnDrum or the Oberheim DMX used to change the pitch of drum sounds by simply changing the sample rate. They literally just played the samples back faster or slower, exactly like speeding up or slowing down a tape recording. At the time, this was relatively easy because… Read more »

One-shot Event Generator

Posted by & filed under Envelope Generators, LFOs, Projects, Stompbox stuff, Synth DIY.

Here’s something slightly different! Is it an LFO? Is it an envelope generator? Well, it’s a bit of both. It produces a one-off event like an envelope generator, but it has a selection of waves more like an LFO. It works by producing a single “ping” when triggered. A ping is like a mini-envelope. The rate and waveshape of that ping are variable (from 55 msecs to 2.5 seconds, and eight different shapes), and the single ping can be augmented… Read more »

TAPLFO 3C – Squashing the bug

Posted by & filed under LFOs, Projects, Stompbox stuff.

We’ve recently discovered a bug in the recently-released TAPLFO 3 code (how embarrassing!). The problem only affects the tap tempo feature of the TAPLFO3. Other chips like the VCLFO or STOMPLFO aren’t affected. We’ve fixed the code, and while we were working on it, we also improved the switch debouncing routine to be more tolerant of bouncy switches. We’re offering anyone who has an affected chip (a TAPLFO 3) a free replacement with the TAPLFO 3C. Please get in touch and send us your… Read more »

Electric Druid chips: The Next Generation

Posted by & filed under Envelope Generators, LFOs, Projects, Stompbox stuff, Synth DIY.

In the last six months, we’ve been very busy here in the Druid workshop, developing and testing new versions of our PIC-based chips. This work is now complete, so I’d like to introduce the new chips. Why bother? What was wrong with the old ones? Ok, there wasn’t anything much wrong with the old ones, but things have moved on since 2008 when most of them were originally developed – ten years ago already! Most importantly, Microchip have released a… Read more »