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  • Writer's pictureOSC

The OSC Toy-Box - Yamaha DX21

Updated: Sep 13, 2021

Preface note:

The "OSC Toy-box" articles look at some of the instruments and equipment I use when making my own music. My ethos regards equipment is always to avoid getting the latest product, or whatever is fashionable at any given time. Instead, aim to get something that's more of a long term investment and/or a little bit quirky and unusual. Learn this equipment like the back of your hand and really exploit its every potential.

Whatever you do, don't break the bank or get in to debt. You can make very cool music that's distinctive and uniquely your own sound without spending a fortune on the latest hardware or software. As you read these articles, please remember, this collection of instruments and equipment has been amassed over the course of 15+ years, and wherever possible, I've avoided paying full retail prices, instead opting for second hand, ex-demo, or in some cases even rescuing from the trash!

Yamaha DX21

Before we get into the whole FM Synthesis thing; if you're unsure of what FM synthesis is and/or how it differs from subtractive synthesis I’d recommend reading this article by Cymatics. FM synthesis is an essay in itself, and maybe one day I'll write a piece about how it works and what it means to me creatively (in terms of sound design and nostalgia), but there are plenty of articles and videos out there already to help you better understand it. I will however say two things about FM synthesis:

Firstly; I've read and heard people refer to it as unpleasant, harsh, glassy, thin, metallic etc... It can be those things, but only as much as subtractive synthesis can be a-tonal distorted noise void of any musical qualities whatsoever. I believe FM synthesis to be a powerful and unique form of synthesis that (on its release) enabled sound design in electronic and pop music go to places it didn't know existed. It revolutionised the music production industry and by extension therefore, it revolutionised the music industry as a whole (for both producer and consumers). Music lovers and music makers alike perhaps owe more to FM synthesis than they realise. For those of us born in the late 1970s and early 1980s, it's also the background noise to our childhood, transcending pop music entirely, which is something I'll discuss a little more below.

Secondly; I’ve heard people criticise it for being hard to program. I don’t buy this! Like anything, it’s only hard if you don’t understand it. I’d recommend making an effort to understand the principles and then just try building tones from the ground up. Start with a linear algorithm and one sine wave. Slowly add frequency modulation to it and introduce subsequent operators one at a time. You quickly get a sense of tone crafting and you'll develop very interesting and expressive sounds; not least when you start applying different envelope settings to each operator. Tones can be made to be very detailed and evolving.

Anyway, setting my defence of FM synthesis to one side, let's get into the DX21...

You've probably heard of the Yamaha DX7. The DX7 was the flagship FM synthesiser of the 1980s. Yamaha patented on the technology so none of the other manufacturers got a look in and every band in the land had a DX7 in their itinerary. I don't own a Yamaha DX7; I own a Yamaha DX21.

The DX21 is a streamlined (polite word for "budget") variant of the DX7. It's essentially inferior in every way. Let's compare the DX21 to the DX7's specifications (crudely speaking - we won't get bogged down in every little difference).


  • 6x Operators

  • 32x Algorithms

  • 16 Note Polyphony

  • Velocity Sensitive Keyboard

  • Aftertouch

  • No Effects (yeah, no effects seems a bit lame, right!)


  • 4x Operators

  • 8x Algorithms

  • 8 Note Polyphony

  • Fixed Velocity Keyboard (no touch sensitivity)

  • No Aftertouch

  • Chorus (take that DX7, the DX21 has one effect, where you have none!)

So, the DX21 is essentially the poor little sibling of the DX7 (the runt of the DX litter so to speak), with its only trump card being that it has one in-built effect in the form of chorus (and it's a laughably subtle chorus at that, not thick and lush like a Roland chorus). Let's face it, one in-built effect is hardly anything to write home about in this situation.

I bought my DX21 in 2016 for about £100 after a month or so of studying various DX synthesisers' selling patterns and typical prices on eBay. Sold as "working", it arrived without a plug on the power chord and it stank! It had obviously lived in a heavy smoker’s house and the keys were filthy too. I completely dismantled it down to every screw and spring in the keyboard mechanism. I soaked the keys overnight in a bicarbonate of soda solution and scrubbed the metal chassis in the bath tub. I used circuit cleaner on all of the electronics, potentiometers and contacts and it worked ok after that... for one day.

In its first day of use it blew its power supply circuit. A friend helped me diagnose the main transformer on the circuit being at fault (the large, black, square component with the grey sticker across the top in the picture to the left) and it was such an old thing, sourcing a replacement was proving impossible.

After much internet research, I found a UK based company that sold open chassis power supplies for various industrial uses and after finding schematic diagrams online I was able to tell them exactly what I needed. £30 later I had a new power supply with the correct voltage and amp rating.

Whilst I had it apart I replaced the memory battery, upgraded the LCD display with an illuminated version (from eBay) and I replaced some missing knobs and the dirty, scratched modulation and pitch wheels with some new ones (in lime green) that I got off a chap on eBay who 3D prints replacement DX parts in different colours (this is actually the same chap who sells the illuminated OLED screens for DX synthesisers). After about two months of cleaning, restoration, much research, soldering and a total spend of about £200, it was finally ready to use. At this point, I was really hoping it would live up to my expectation as I'd now paid over what I wanted to get it all working properly.

"Why go to all this trouble for a DX21? Why not just get a DX7?"

To put it simply, I wanted a DX21. If you’ve followed me for a while, you’ll know I’m a massive fanboy of SEGA video game music from the 16-bit era.

(Read this next bit slowly and let it sink in!)

The synthesis chipset in the SEGA Mega Drive (or Genesis if you’re in North America) is a Yamaha chipset called the YM2612. The DX21 also uses the YM2612 chipset.

(Has that registered and sunk in yet? Because when I first discovered this, it blew my mind for several hours! I mean, it's a SEGA Mega Drive Synthesiser, right? It must be able to play synthesiser patches from SEGA games, surely?!)

The DX21’s chipset is technically a slight variant to the SEGA chipset, which had the capacity to play one audio sample (at a time) from the game cartridge memory (this was often used for speech such as: "SAY-GAAAAA" - see what they did there?!). But putting that aside, the DX21 as it turns out is essentially a SEGA Mega Drive Sound Synthesiser. The operators, envelopes and algorithms are identically configured across both the DX21 and SEGA Mega Drive. With a little internet research and file conversion trickery, I managed to acquire hundreds of SEGA game audio patches, which via the antiquated protocol of MIDI Sysex data dumps could be loaded (one at a time) onto the DX21.

In other words, I was able to play on my keyboard, synthesiser sounds from games like Sonic The Hedgehog. If you'd have told eight years old Steve that one day he'd be able to play Sonic The Hedgehog sounds on his keyboard, he'd have spin-dashed around the room in disbelief!

Ignoring the ability to load old SEGA Mega Drive game sound patches, even when designing your own patches on the DX21, they often have that classic 16-bit video game feel to them (which for me equates to warm and fuzzy feelings of nostalgia).

But it doesn't stop at SEGA. The YM2612 was used across many chipsets in old arcade games by manufacturers such as Namco, Konami and even the legendary Capcom CPS-1 boards that were used for games like Final Fight and Street Fighter II. So by virtue, the DX21 can theoretically create/playback sounds used in the original Street Fighter II soundtrack. Again, pretty, darn cool!

Today, relations and descendants of the YM2612 chipset can be found in all kinds of things from early/mid 1990s Soundblaster sound-cards (remember those?!), early 2000s mobile phones, small electronic children's toys and budget, beginner keyboards. Yamaha really understood the power of what they had in their YM chipsets and truly maximised their revenue potential, keeping the legacy of FM synthesis alive and kicking throughout all kinds of commonplace consumer products in ways that Roland and Korg could only dream of doing.

Another variant of the DX7 was the DX100, which is largely the same as the DX21 but with mini keys and a smaller overall construction. The DX100 is the synthesiser of choice for P-Thugg (Patrick Gemayel) of the band Chromeo who uses it with his Talkbox (see the picture on the left - you can make out the DX100 in shot with the unmistakable DX-green horizontal button layout).

He's one of the coolest, and most talented dudes in the history of electro-funk and also one of the most proficient and knowledgeable synthesiser collectors in all of pop music, so if a 4-OP FM synthesiser is good enough for him, it's good enough for me! There's honestly a lot of charm and legacy in these budget 4-OP FM synthesisers.

As for my DX21, it's been all over my work ever since I got it, providing bass, poly synths, tuned percussive sounds like marimbas and more. It's a cornerstone to the whole Girls On Bikes Production Palette that I discussed in my earlier articles about genre characteristics and the production of Boys On Boards. The bright, zappy, squelchy poly-synth sound that forms the bulk of the synthesiser parts on the song "Girls On Bikes"; it's all DX21.

I don't wish to seem like I'm shamelessly self-promoting here, but if you're a producer and interested in getting your hands on some of these DX21 bass sounds, you'll find samples of the exact sounds I used on Girls On Bikes on the Girls On Bikes Drum & Bass Sample Pack available on The Patchbay.

The DX21's outputs are filthy (lots of electrical noise as they’re unbalanced - and cheaply made!) and depending on the sound I sometimes have to run the audio through a noise reduction plugin. This is something I need to look into in the future as it has proved problematic at times. Even the DX7 was known to have noisy outputs and as this is a cheap knock-off, things are only going to be worse!

As mentioned above, it doesn’t have a touch sensitive keyboard, however it will receive touch sensitivity via MIDI, so I tend to control it from my other keyboards. It’s limited to 8 note polyphony (or four-note polyphony if you stack the 4-OPs twice over in "Performance Play" mode), so I have to be selective with how I use it, but it’s not really been a problem as I'm usually using it in "Single Play" mode with bass lines or simple chordal phrasings.

Oh, and after three years in my studio, the stale cigarette smoke smell is almost gone. You have press your nose against it to still smell stale cigarettes. Maybe in another three years it won't smell of cigarettes at all.

If you are interested in picking up a DX that isn't a DX7, there are a few options and they're pretty reasonably priced, all things considered. Do a little research and dive in on whatever your budget will allow, you won't be disappointed. There's also a very friendly and wonderfully knowledgeable Yamaha synthesiser community online who were super helpful to me when I popped up on their forums asking about DX21 power supplies.

All things considered, these keyboards may be long discontinued, but there's a lot of life left in them yet.


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