Holy Bot

Bedroom music production, gaming and random shit


analog synth

Entering the Matrix

I got a reasonably priced Oberheim Matrix-1000, originally released 1987. It’s a polyphonic synth with six voices, two DCOs per voice, fully analog signal path and extensive modulation routing options – and its sound is beautiful.

But yeah, it’s a rack module and without editing options via the front panel, and it has a thousand presets and only 200 of them are editable remotely via MIDI.

The trouble with this particular item was that the fifth voice chip was broken (which I found out after buying). Moreover, the firmware running the synth was slow and contained bugs.

Fortunately someone on the internet has updated the code and they have made it available on a EPROM chip, so I ordered that. I also found a replacement voice chip and got that as well. Installing the new firmware and voice chip into the old machine was easy enough – the chips are just sitting in sockets. The voice chips counts from right to left (one to six) and are marked U101-U601.


Small Sawtooths and Low-Pass Filters

I got a few small analog synths that I put next to each other for comparison. The test pattern is defined as follows:

  1. The raw sawtooth waveform of the synth, 100% open frequency cutoff and resonance at null.
  2. Manual filter cutoff sweep, resonance at 0%.
  3. Manual filter cutoff sweep, resonance at 50%.
  4. Manual filter cutoff sweep, resonance at 100%.

The input levels are adjusted to roughly peak at -6 dB on each audio clip (maybe that was a bad decision). All synths were connected to a Mackie 1202VLZ4 mixer before being recorded using high-grade Cirrus Logic converters. No normalizing was added in post.

First is the Korg volca keys. When resonance is added, the volume is intensely boosted. The filter section uses the circuitry of the Korg miniKORG700S (which used dual 12 dB per octave low-pass and high-pass filters that were combined). Given the 128 steps that can be controlled via MIDI, the filter sounds very steppy on high resonance (peak).

Next is the Korg volca bass with the second and third VCOs muted. I’d say it has a little buzzier tone than the volca keys. Its filter is also much smoother, especially on high resonance. It’s a fine-tuned analog filter with a bright and crisp sound, with the resonance going from a clean peak to an increasingly distorted sound. As for the volca keys, the volume jumps with resonance.

The toyish Gakken SX-150 Mark II has a quite nice thick tone, with low resonance that is. Slightly less bottom end content than the volca modules perhaps. Unfortunately the pitch slides some due to me messing up operating the stylus pen. Raising the resonance seems to lower the overall volume. With filter cutoff set to fully open and resonance at 100%, the filter is making a loud noise (hiss). I think the synth has a voltage-controlled filter, Sallen-Key low-pass type, 12 dB per octave.

As a bonus the Yamaha CS01 from 1982 is included. The oscillator (labeled VCO, but is in fact a digital tone generator) lacks of woof and weight compared to the others. The first audio clip is the sawtooth 100% open frequency cutoff and resonance set to low (this model is equipped only with two resonance settings). The high setting follows after. The filter is a 12 dB resonant voltage-controlled filter.

Not sure what conclusion could be drawn from this, if any. However, there are some discussions about which of the volca modules are the best sounding et cetera, and maybe this could help deciding. Although this is just a comparison of their isolated sound engines and filters. Interface, voicing options and such have not been regarded.

P.S. You might be interested in a low-pass filter test I made, running a SH-101 trough the filters of a MiniBrute, a Minitaur and an Analog Four,

Many Mini-Keys

I’ve always fantasized about some small toy-like Casiotone with lots of sliders with good and usable sound, well at least in my younger days. (Actually, I think there’s a Casio SA series ToneBank keyboard laying around somewhere at my parent’s house.)

Anyway, now I’ve found one – the great sounding Yamaha CS01. It looks good too, it fits perfectly next to the SH-101.

The CS01 is an analog monosynth from 1982. The sound is much bigger than its tiny frame would suggest. The PWM is just great. It might not be the best synth for bass, but it would definitely produce competitive lead sounds.

The CS01 has an uncommon feature, a breath control, which is an optional mouthpiece controlling the VCF and VCA. I reckon it’s mostly a gimmick, but I don’t have it, so I shouldn’t really judge. Moreover, the synth has a built-in amplifier and speaker, it runs on batteries (or external power). There’s also pins to attach a shoulder strap like on the SH-101.

If I could decide, I’d trade the breath control and speaker for other features, like MIDI or CV gate, or the ability to mix the noise with any of the waves, or sample and hold on the LFO. I would also change the step-wise glissando to a regular portamento (however, it is nearly continuous with a short setting).

Some say the mark II of the CS01 is superior with its 24 db voltage-controlled filter and adjustable slider control over resonance, but I think the original version is good enough, and I usually don’t modulate peak level that much anyway.

I got it pretty cheap, although I had to repair the pitch lever (the pot was broken). Vintage analog synths on eBay can be overpriced, but this should be one of the less expensive.

My Favorite Synth

I bought another synth, a real classic, I got the monophonic Roland SH-101 sent to me from Japan. Now my rig is full (or is it ever?).

I think the SH-101 is my favorite synth, at least right now. It’s easy to lose hours messing around, and it’s almost hard to render a bad sound with it. I really like the noise modulation, which produce a warm, gritty tone.

The step sequencer is great for a scratch pad and the arpeggiator serves well by looping notes while tweaking parameters and testing different settings.

The SH-101 doesn’t have MIDI but there’s a few workarounds in a common modern rig, e.g. using the MiniBrute, one can convert MIDI (from the DAW) to CV. And by doing this, one can play and even send the MiniBrute’s sequencer/arpeggiator to the SH-101. Also, it’s possible to simply sync the clock from any volca module or drum machine with CV gate out or trigger out like the old TR-606.

On the downside, the LFO rate is shared with the sequencer/arpeggiator speed, although by connection an external clock, internal connections of built-in clocks are cut and detaches the LFO rate from clock speed.

Anyway, it’s a really fun synth to play – instant gratification and all.


I’ve come to prefer several gear, specialized (but limited) with their own characteristics, to my sound palette. I also value analog stuff above digital signal processing (DSP), because the omnipotent DAW and the versatile softsynths can handle digital just fine. And analog needs to be hardware by definition.

The idea is not to expand my rig too much, I wanna push the equipment as far as possible, not just solving the problem by getting a new device. But when the time comes, I will change gear, replace it, one at a time. I think that upgrading and rearranging gear can be inspiring.

Thought I’d finish this track, but I didn’t and I won’t.

It’s a half-baked attempt with some analog hardware (Moog Music Minitaur versus Arturia MiniBrute versus Gakken SX-150 Mark II) and sampled drums.

It’s less than a minute.

Japanese Synthesizer

So I got this package in the mail today. Really just a toy. Maybe not so musical but still a true analog synthesis that’s up to no-good-lush-creamy-noise. Who doesn’t need that? It also features a stylus controller and built-in speaker. And check out the price tag. It fit quite nice next to the volca range (but sounds very different and is more chaotic). Yes it’s the Gakken SX-150 Mark II.

Seq / Arp

Another post about the mighty MiniBrute. Here’s a tip how to hack the arpeggiator to act as the sequencer like on the newer SE model.

Just send the SysEx command: F0 00 20 6B 04 01 75 01 3E 01 F7  to your MiniBrute to enable the sequencer. And if you what the arp back, or if you have a SE version, then send F0 00 20 6B 04 01 46 01 3E 00 F7.

This information was published on one of the developer Yves Usson’s personal sites. You may also wanna visit for more information about how you can send SysEx et cetera.

Speaking of the MiniBrute. Right now I’m in the beginner’s phase, that is, messing around and making lots of noise, but not any songs. I experiment and come up with many sounds that are good enough, but there’s no saving patches on the MiniBrute. (I could take pictures of the knob settings, but I know I would never look at them.)

So it’s a different approach and workflow from what I’m used to, it’s more about improvising and jamming. Now I need to find a way to capture ideas and process them into compositions. I guess it has to do with some kind of multitracking. 

Anyway, it’s fun and I’ve hooked up the MiniBrute to my volcas (sample, bass and keys). The whole band is playing, I don’t even have to start any DAW.

P.S. About the image, well I had no printer at home, just my mad skillz.

Et tu, Brute?


So I finally got an Arturia MiniBrute Mk I today. (I actually got both the MiniBrute and the MicroBrute for what it’s worth, but I’ll return the latter to the store tomorrow.)

It wasn’t easy to decide which one to pick, the Micro, the Mini or any of the SEs. But I looked around, checked Gearslutz, reddit and other forums and came to the conclusion that the MiniBrute seems to be the best choice, at least for me. Perhaps the SE would fit better – because I’d rather have a sequencer than an arpeggiator, but when it all comes down, I need neither of them.

The Micro

While I prefer the size of the MicroBrute, I think the MiniBrute feels sturdier, more heavy duty. The keys are nice, but I don’t mind mini-keys, and I really don’t need another full-size keybed portion (I’m obviously not in the target group for this synth).

Other advantage the MicroBrute might have over the MiniBrute – besides the price – is the patch bay. Although you’re able to do most things on the MiniBrute with its extra encoders; except CV Out LFO and envelope and such, but I don’t have, and I’m not planning to get, any modular system.) Actually, I think the MiniBrute has more modulation options and flexibility than the MicroBrute.

Okay, the overtone control that allows pitch changing and that could be modulated via the mod matrix, would of course be nice. But I’m good with the sub oscillator of the MiniBrute – and it does cover another octave and offer both sinus and square wave.

The Mini

So the reasons to choose MiniBrute wasn’t the semi-weighted keyboard with aftertouch. No, what appealed to me were: separate ADSR envelopes for filter and amplification, an extra filter type (notch), white noise, three additional LFO waveforms, an extra LFO and maybe MIDI Out. I think these things make the MiniBrute a greater, and more versatile synth.

I chose a Brute synth from Arturia because I’ve heard that they have a distinctive voice and filter character, and this purchase was supposed to complement my other gear. Also, I wanted an analog synthesis that couldn’t be found anywhere digital roams.

Faux Step Recording

The volca keys lacks a real step recording such as the bass module, but it’s still possible to program keys in a similar fashion. Activate one step and record note(s) and pot movements, then turn it off and do the same thing on the next step. Here’s the workaround:

  1. Clear sequence, press FUNC + CLEAR ALL.
  2. Enter active step mode, press FUNC + ACTIVE STEP.
  3. Turn off all steps but the first.
  4. Turn on motion sequencing, press FUNC + ON/OFF
  5. Turn off flux if necessary, press FUNC + FLUX.
  6. Leave active step mode, press FUNC.
  7. Press PLAY + REC and choose note(s) for this step. You can also set the filter et cetera if you like. You might have to hit REC a couple of times to get it right.
  8. Turn off recording, press REC, and enter active step mode again, FUNC + ACTIVE STEP.
  9. Turn on the next step and turn off the step you just edited.
  10. Repeat step 6-9 for as many steps as you like the sequence to loop.
  11. When all steps are edited, turn them on, press FUNC + ACTIVE STEP + all steps.
  12. Exit active step mode, press FUNC, and then press PLAY.

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