Yamaha DX-21 Synthesizer

Yamaha DX-21
Yamaha DX-21

Last weekend I landed another free synth from the local used music shop I frequent. I found a case that I need for another one of my synths and stumbled upon this Yamaha DX-21 that had a $10 price tag on it. The tag said the DX-21 was broken with no sound coming out. I asked the clerk about it and he said that the power worked but that it then freezes with the “Yamaha DX-21 Synthesizer” message on the LCD screen. Plus there is no sound. As a result of buying a case, he decided to throw in the Yamaha DX-21 for free as he didn’t think he could sell it broken. He asked if I wanted it and I said sure thing! I didn’t know a whole lot about the Yamaha DX-21 but I thought it would be fun to try and fix it.

When I got home I anxiously cracked open the Yamaha DX-21 and notice right away that the battery needed to be replaced. In fact, the battery was already starting to leak but nothing had reached the PCB board yet. I desoldered the battery and then soldered in a new battery holder as a replacement. I then did some quick cleaning of the contact areas and some parts of the PCB board that looked a little dirty. I finally put everything back together and fired up the Yamaha DX-21. Sure enough it turn on by using the reset procedure which is holding down buttons 1 and 2 while powering on the synth. The Yamaha DX-21 entered test mode and then I could proceed to load the internal ROM patches back into the 32 Ram voice slots. Everything worked perfectly and so I was excited to basically get a fully working Yamaha DX-21 for free.

The Yamaha DX-21 surprisingly is a great little 4-OP FM synth. It has single and dual modes which allows you to layer or split the keyboard. There is LFO editing, portamento, and a nice sounding chorus effect built in. The body is is very strong and the keys play nicely. It can be a tad bit noisy, but I really feel it adds to the character of the DX-21 and so I welcome the noise it makes. In fact there are some internal presets that really sound cool with a little noise mixed in. It’s all about one’s preference, but I actually like having noise mixed in with FM sounds rather than having them perfectly clean. The Lo-Fi sound of the Yamaha DX-21 is really cool and it’s been fun jamming with it today. The Yamaha DX-21 is a great find I think and definitely a keeper.

Here’s a demo of the Yamaha DX-21 in action found on Youtube.

6 thoughts on “Yamaha DX-21 Synthesizer

  1. It took me a long time to find this Yamaha DX-21 patch info so I thought I would post it here to help others.

    Let’s sum up the categories:
    1- DX7 / TX7: 6-op, sine wave
    2- DX21 / DX27 / DX100: 4-op, sine wave
    3- DX11 / TX81Z: 4-op, 8 waveforms

    — (2) uses VCED sysex format for single patches, (3) uses VCED+ACED
    sysex format, so:
    — (3) can load patches from (2) (except “chorus” parameter)
    — (2) can load patches from (3), but loses all ACED data (waveform,
    fine control of frequency, …)

    The compatibility between (2) and (3) works only for single patches, not
    for bulk dump of whole banks.

    — I heard about converters from (1) to (2) (and thus (1) to (3)), but
    you lose 2 operators — I don’t know how the converter chose which
    operators to delete, nor how the algorithms are mapped…

    — There are converters from (2) to (1) — and thus (3) to (1), but you
    lose the waveform information (all waveforms become sines).

    Please correct me if I am wrong. I don’t know in which category I should
    put the DX9.

  2. Interesting comment I found about removing the two extra blue capacitors (C20 & C19) in the Yamaha DX-21.

    The Dual & split mode are awesome and pure joy.

    And the Chorus!!:D My God! What a Chorus! Much better than the Chorus on my Juno 106!!! I’d go so far as to say this is equally as fun to play as the Juno 106 if not a little more!!!!

    I opened it up and its very well made and even has the odd Carbon Composite resistor & the famouse JRC4558D Chips used in the Vintage TS808’s.


    I did by two. The 2nd sucked big time!!! I tried reloading all the sounds it still sucked. By sucked I mean I did not get that Blues Brothers,”I’ve Seen the light!” moment when playing it!

    I compared the two and the one that sucked had 2 extra blue capacitors (C20 & C19)on the power supply section. I took a chance and removed them, & prayed they were nothing more than filter caps! I turned it on and man!:) Boy! Oh Boy! That DX21 was more righteous than James Brown!!

  3. Kenneth

    My name is Kenny. I just bought a DX21 from a yard sale 14 bucks!!! anyway i turned it on and when i press any of the green program buttons it shows weird symbols and different languages and I know its peculiar. Is there anything you can suggest that I do to change the symbols back to plain English??? thank you and I will send you a pic of the wacky screen symbols if you’d like.

    1. Hi Kenneth,

      The garbled language you are seeing is an indication that the battery need to be changed. This will require desoldering the original battery. Then you need to replace it with a CR2032 and a battery holder which you can find on Ebay or at an electronics store. Once you replace the battery, the DX21 should work great for you.


  4. Ian

    Can you help me I have aYamaha DX-11 Synthesizer. I have just changed the battery and need to know what button to press to reload the factory sounds.
    Many thanks.

  5. Hey Jim!
    After having a TX81Z I just bought a DX21. It has somehow two “ultra-sensitive” key (they can re-trigger the notes quite easily), that goes a bit deeper physically when I push em down. May be they are a bit worn or just some contact issues?

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