Sunday, September 14, 2014

Bypassing the Valves on the Korg ESX and EMX

Needles to say there has been much debate on the sound quality of the valves contained in these machines - which, incidentaly, are made by Electro Harmonix. This tutorial will show you how to bypass the valves permenantly, which gives a much cleaner sound (even with the valves on the lowest volume they add noise!).

Put simply the valves colour the sound at all times. The first picture is a kick sound (with 0% valve). Picture 2 is the same sound with 100% valve. The third picture is the same kick one the valves have been bypassed.

Some stuff you will need:
  • Screwdrivers 
  • Hex keys
  • Soldering iron + solder
  • Wire cutters
  • Needlenose pliers 
  • Multimeter
  • Sharp knife

I would highly recommend looking over the service manual for the ESX/EMX:

Fundamentally, all we are going to do is route the stereo signal that goes to the valves, to the place where the vavles send their stereo signal. therefore bypassing the valve PCB completely.

** Disclaimer - This has worked for me on numerous occasions, but I will not take any responsibility for any damage caused by this mod - if you are not confident about electronics I would advise you to find a qualified technician **

1) First, use your hex key to take off all of the front panel screws

2) Now take off all the caps for the potentiometers (keep them in the same formation as you take them off)

Take off the faceplate - the naked machine will look like this:

3) Unscrew the silver screws near the valves. There is no need to unscrew the black ones! 

Now open up the secondary panel and you should see something like this:

4) Now you need to start removing the connections between the various PCBs.  Most of them have a small section to push in to enable you to remove it easily. Don`t use (mini)brute strength! 

Right, you`ve done very well to get this far. But now for the higher level...I think you`re  ready!!

5) On the main PCB you need to identify two resistors: R54 and R62

6) Similarly, identify the two capacitors: C43 and C50 - they are next to each other.

7) Now, it is essential to identify these exact components on the REVERSE of the board.

The capacitors have been circled in organge and the resistors in green.

8) Now for the `Balls out of the bath` moment. We are going to cut the connection between these components using a sharp knife. Make sure you cut where they are joined - after this there is no going back!

If you`re a seasoned professional like me, you too
can test the connection with a multi-meter.

So now with the lines cut, the Korg will output nothing! We don`t want that so the signal that originally went to the valves will come back in here where we made the cuts.

Below are the stereo inputs the tubes receive: 

On the other end of this cable remove the pins by wedging them with a small flat edge screwdriver.

The main connection will now look like this.

9) So now the signal is not physically going anywhere. We need to make these two points connect to the capacitors we disconnected earlier. This is best done on the reverse of the PCB:

Remember you are soldering points 4 and 6 from the valve ouput board to the outer capacitor points.

That is it! Now make sure the connections, screws, hex keys and caps are put back in the same way as they were removed. Take a deep breath and fire up the beast!


  1. Thanks a lot!!! Going to do this soon.

    But i guess you messed up the pics of the waves, the first one is the without valves i guess and so on. (the file name on the pic "new kick", "original" etc) also tells me they are in the wrong rankig!

    But nice, NICE tutorial! You rock!!
    I will fkn LOVE the clean sound! :)

  2. I've wanted to do this for years.
    I've tried different valves but the noise flaw and distortion was still driving me crazy.
    thankyou so much.

  3. can I take the valves out and sell them when I am dun?

  4. I have just finished this mod in my ESX. It sounds much better. Literally no noise flaw and clear as day. the output is quieter but still plenty. If you have had trouble with mixes getting mushy, I recommend this mod.
    thanks MIDI/Error!!

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  7. I'm not an electronics expert by any means, but I decided to give this mod a try.
    Oh god, did I get a heart attack when there was no sound on the right channel anymore, after
    I closed the unit! Little did I know, that I had to make another cut on the PCB, oh lord!
    Thanks for the mod, the noise is completely gone, and I am glad these damn tubes are bypassed now.
    What a badly implemented marketing gag those are.

  8. I'm about to give this a go. I might put a switch on mine so you have the option of using the tubes or bypassing them.

    1. Did you ever put a switch? Do you have schematics or a tutorial on this? I Where did you mount the switch, for example? Thanks!

  9. I've seen schematics and it seems there's a easier way by connecting in/out directly in the tube socket, replacing hte connector and keeping the valves out. Isn't it possible?

  10. Ok, great but .... After that can i use 3/4 output yet?

  11. All these types are manufactured to regulate or turn on and off the flow of the liquids or gases. In fact, materials including the plastic, metal or an exotic alloy are widely applied to manufacture various industrial valves on different service conditions. To be frank, selection of the proper valve is an important task for following performance. At this moment, a brief introduction to the various industrial valves is given as follows.

  12. Yeah, a second cut on the PCB is necessary, severing the connection between C43 and R54. It's mentioned but not pictured in the photographs. For someone wondering where to cut: it's the very short connection between the orange circle and the green circle to its right (in the picture captioned "The capacitors have been circled in organge and the resistors in green.")

    I hoped this mod would lower the noise floor enough for my taste. I didn't expect it go away entirely! Wow!

  13. I recomend this mod, that is exactly what im looking for, very easy, just check others pictures also.

  14. I did this mod and WOW! This made my ESX usable. Hiss is now gone. Your instructions are great.

    1. Can you confirm if the mod removes the Electribe's low humming/buzzing noise as well, or just the white noise hiss and tube distortion? Cheers!

  15. Fuck shit bitch! I brocken my EMX because open second time and have some electric circuit short, and this is because I'm fool and because you don't have a cut between C43 and R54 on your photo. Please, make some correct photo for next generations of hackers!!!

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  17. Everything went well, thanks for the mod recipe!
    Noise as unprecedented! )
    But the output really got quieter ...
    Any ideas how to increase the output level?

    1. Can you confirm if the mod removes the Electribe's low humming/buzzing noise as well, or just the white noise and tube distortion? Cheers!

    2. No, the low-frequency rumble is still a little audible on some headphones, quite a bit, but audible. But the white noise goes away.

  18. Thanks Midierror for this tip!

    I just finished doing this mod on both my EMX and my ESX. Noise is gone; it's awesome. The mod has breathed new life into my production with these machines.

    I have no background in electronics and I generally feel clumsy doing this type of work, but I went slowly and carefully, and everything turned out fine.

    I would like to say, respectfully, that even though it's a great description with pictures, there's a few pointers that could be included in the instructions for those who are total novices in electronics like me:
    First, I would highly recommend a large table magnifying glass because the electronics are surprisingly small once you open the machine. Personally, I found the soldering the hardest part because you have three parts but only two hands: the solder, the wire you're going to solder, and the soldering iron. Because I had no experience soldering, it took quite a while to do this part (I watched a couple of beginner videos before, just to make sure I made no huge mistake). One video suggested using a wire clip to hold it in place. Since I didn't have a wire clip, I just laid down the wire and carefully soldered it in place, although it does move around a bit.
    Two, the wire you will use is the wire you are cutting from the PCB, so there is no need to buy wire.
    Another tip that may not be clear from the instructions is that you should use the pliers to pull out the connections. Just grab on to the white plastic bit and jiggle it out softly, rather than pull straight out.
    The first mod took me about 4 hours (no experience and going carefully). The second mod took me about 1.5 hours.
    I did make one mistake that required me to open the machine up a second time: On my second mod, once I put everything back together, the machine was only outputting a signal on the right. I opened up the EMX again and tested the connection with the multimeter, and there was still a signal, so I cut a little more and sure enough, it worked fine.

    1. Thanks for this additional info, very helpful! Can you confirm if the mod removes the Electribe's low humming/buzzing noise as well, or just the white noise and tube distortion? Cheers!

  19. I really like adding functionality to gear but I'm not a fan of removing features intended in the original design, so with that in mind I revised your post and found (on paper) that a switch can be added to bypass the tubes completely or to use them if needed. It goes something like this:

    Using a 4 pole switch
    Pole 1 Signal Input L / (Throw 1 Tube Input L) / (Throw 2-Capacitor L in)
    Pole 2 Input from Resistor L / (Throw 1-Capacitor L in) / (Throw 2-Disconnected)
    Pole 3 Signal Input R / (Throw 1 Tube Input R) / (Throw 2-Capacitor R in)
    Pole 2 Input from Resistor R / (Throw 1-Capacitor R in) / (Throw 2-Disconnected)

    If the Switch is at position 1: Signal -> Tube Input -> Resistor -> To Capacitor.
    If the Switch is at position 2: Signal -> Capacitor / (Resistor to Capacitor gets cut).

    I think this might work. Do you? MIDI ERROR?