Author Topic: [Veroboard] - MXR Phase 45 (Univibed)  (Read 15593 times)

RicF

[Veroboard] - MXR Phase 45 (Univibed)
« Reply #40 on: August 11, 2005, 04:44:33 PM »
Thanks for resurrecting this thread. It's just what I've been looking for.

Eb7+9

[Veroboard] - MXR Phase 45 (Univibed)
« Reply #41 on: August 11, 2005, 10:38:11 PM »
Quote from: RCZ53
... the mix control seems to only bring in the effected signal some where around the middle of the pots rotation (I used a 25k). Also the bias only works at full off (counterclockwise) Is this normal? I sorted through twelve 5458's to find two pair that sounded good ... very quiet, subtle effect. If there is anything to be done I would like to have a bit more intensity


yeah, it's normal that the mix brings in the (phase) effect at 1/2 rotation with a linear pot - this is the stock position where the mixing resistors between dry and wet outputs are equal ... you could wire a resistance of same value as the pot in series at the opposite end of the pot so that the rotation would do what I think you want it to - namely go evenly between phase and vibrato with no dead zone ...  that knob won't get played with much unless you want to bring out the vibrato side - a switch instead of a pot might work better/simpler/cheaper actually ... though it's nice to be able to set it exactly ...

Note: if the bias only works at full rotation then you either need a different Zener or a different pair of jFET's ... a quick fix is adding a 1n4148 signal diode or two in series  with the Zener to bring the reference voltage up by around .6 or .7 volts for each diode added ... use Ge diodes if the increment of one Si diode is too much ... if that leads you in the wrong direction then you need a lower voltage Zener for your jFET's ...

Ideally you want the bias to kick in somewhere near half-rotation so you can have a bit of play on either side allowing you to make the phase "average" go towards the bright or dark side ... again - that control allows to adjust the phase quality in a subtle way ... it just sets the vertical average of the cycling voltage ... if your bias adjustment took you to edge of your adjustment range it's possible that your jFET's won't go as deep as if the bias "peak" lies more in the middle of the bias sweep ...

~jc