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"How it works" The bass automatic register mechanism.

Author: Julian ibiza
Date: 2023-03-29 15:26

Hi bass players .

For those of you out there who tend to regard the automatic register mechanism as a somewhat mysterious and potentially temperamental gizmo , I would like to offer a couple of very simple exercises you can do which should go a long way to offering insight into how this works. Something which may in turn mean that you can fix it yourself if it malfunctions, rather that having to take it to a tech .

Excercise 1) . Take your bass and hold down the register and A key . Now using a finger, press closed the throat vent and release it a few times observing how your finger pressure is delivered through the rocker to opening the neck vent . Note that the neck vent's little closing spring also acts to hold the throat vent open. Hence when the neck vent is in its open position something needs to keep the throat vent firmly closed . Something that essentially does the job you are now doing with your finger . That something is a linkage up to the rocker mechanisms that's activated when either the A or RH3 keys are released , engaging I little arm upon the rocker . So if you now release the A key ,the throat vent should remain firmly shut when you take your finger off it . If it opens even the tiniest bit ,then that linkage needs seeing to .

Excercise 2). Now remove the neck from the instrument or just swivel it sideways to disengage the linkage . If you once again hold down the A and register and observe the rocker, you will see that it's gone all floppy and without any resolution one way or another . It now has no forces being applied to it and by rocking it with the fingers you can sensitively feel for any binding or catching in the movement .

Conclusions :

If the throat vent is opening somewhat when the neck vent is supposed to be open , this is because the linkage to prevent the throat opening from A and RH 3 keys is out of regulation . When the neck vent is open the throat will always open if it is allowed to .

If the problem is the reverse , namely that the neck vent is trying to open when only the throat is supposed to be , then this is because there is some binding or catching in the rocker movement that is exerting enough force to depress the neck vent's little spring . Before resorting to solving this by increasing the neck closing spring tension , always first establish that the rocker mechanism is truly moving freely .

I'm not going to attempt to go into great detail regarding all points of adjustment for the rocker and it's A-RH3 linkage , but hope that these simple exercises help to point you in the right direction for troubleshooting. All I would add is that before making any adjustments, it's important to carefully study how that will effect all related linkages . The culprit that suggests itself is frequently not in fact the guilty party , so unless you can really get it clear, best seek the advice of a repair person .

Julian Griffiths
Tel. 34 696 798 853

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