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.
I would highly recommend looking over the service manual for the ESX/EMX: http://electribe-forum.com/public/EMX1_Svc_man.pdf
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.
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!
