Juno 106 sensitive pitch bend


#1

My Juno 106’s pitch bend is very sensitive when it’s at the center. It starts changing pitch with the lightest touch. Additionally, often times if the pitch bend is at the center and I start bring up the DCO slider on the little modulation board, then the pitch of the synth is affected. Again, this happens without touching the pitch bend itself.

I noticed that the pitch bend pot doesn’t have a center detent, but I don’t know if that’s normal for this Juno (it’s an early serial). Other possible issues I could think of are the spring being worn, or that the pot itself is worn out by the allen screw that hold the plastic bender to the pot.

Any insight into what might cause this? I’m hesitant to buy a new pitch bend pot because of the price but also in case it doesn’t fix the issue.


#2

I am pretty sure there is an ‘electronic detent’ in the pitch bend - in other words, a dead spot is built in electronically so that a few degrees of motion don’t affect the pitch. What I suspect is that the pitch bend lever is not correctly positioned on the pot itself. What will confirm this is if you set the upward pitch bend to an octave at full travel of the lever, then see if the downward pitch bend is exactly an octave also. I’m betting that you will see that it is not.

The solution is to loosen the set screw on the underside of the lever, and use a flat screwdriver in the slot of the potentiometer shaft to adjust its position relative to the lever. This can be pretty delicate - you probably won’t need to turn it much at all. But once you find the sweet spot, the pitch bend will be the same amount both up and down, and you should have that dead spot in the center.


#3

Thank you! I didn’t realize that’s how it works, and you are right, the pitch bend is not set correctly so the range isn’t equally 1 octave up/down. However, in trying to calibrate it to that sweet spot I must have knocked a solder joint cold and now the pitch bend isn’t affecting the pitch at all. Turning the DCO slider up shifts the pitch a full octave down.


#4

If moving the bender doesn’t change the pitch at all, but moving the DCO slider on the bender panel fully upward causes the pitch to bend down an octave, then it sounds like the bender is ‘stuck’ in the fully down position. If this is the case, then moving the DCO slider up and down will cause the pitch to change from in tune (all the way down) to an octave lower (all the way up) - is this what is happening?

If so, it could be that the adjustment of the pot is just way off now (that flat-screwdriver adjustment of the pot shaft in the bender lever). With that DCO slider all the way up, try loosening the bender lever set screw, and turning the pot itself through it’s full rotation to see if that causes the pitch to change. If so, then it just needs to be set correctly. Find the mid-point of the pot’s rotation, by observing the position of the screwdriver slot as you turn it through full rotation, then set it at the midpoint and use that as a starting point.


#5

Of course, you were right again, Sam! The pot was turned all the way down so the lever did nothing. I was able to center the pitch bend so I get a full octave up and down. Here’s what I learned doing this:

The center detent is relatively wide. I can reach it by turning the pot by hand quite easily. However, the sweet spot within the detent is very narrow and easy to miss. Even when I had the pot centered so that little touches to the level didn’t change the pitch, I’d still get an uneven response up and down. In my case, something that contributed to that is that the pot has a really deep divot on its shaft. So I would get the pot centered, then start tightening the screw, but the pot would go out of the sweet spot because the screw kept sliding into that divot. I was able to fix that with a thin paper shim and a lot of patience.

Thanks again for the help!!


#6

Lovin’ the happy ending!