Artec Vintage Phase Shifter - Depth problem

[cla2002]

Hi everyone! I just bought an Artec Phaser (SE-VPH), used and for 20 euros.



The pedal sounds great, the only problem is that it seems that the depth works but not as you expect, like if the effect it's there but it is not so present in terms of sound. I opened it up and it has two trimmers, should I have to regulate those two trimmers (which are MAX-RESO and RANGE) to give more volume to the phaser effect?

[Mark Hammer]

Many commercial phasers use a trimmer to set the maximum amount of resonance/feedback.  It is adjusted by maxing the Resonance control and adjusting the trimmer so that it comes just shy of oscillation.  That way, the panel control can be set wherever you like without fear of "howling".

For FET-based phasers (and this seems to be one), the bias voltage has to be set appropriately for the JFETs, such that they have enough usable sweep range, once that bias is summed with whatever the LFO provides.  I imagine more sophisticated and precise methods are used at factory setup, but the home user can probably tweak it by setting Depth to max, adjusting Speed to maybe medium fast, such that  changes in bias are more audible, and then adjusting the bias trimmer.  Note that, much like the pot on a normal wah, the entirety of usable sweep range is generally not used.  This means the "colour"/"flavour" of phasing can usually be tinkered with a bit, by means of the trimmer, making it a little more swirly (moving upwards) or gurgly (moving downwards).

The trimmers can be used to optimize the phasing effect so that it is more pronounced, but neither will have an effect on how loud the pedal is (though I suspect what you really meant was "more pronounced").

[cla2002]

Many commercial phasers use a trimmer to set the maximum amount of resonance/feedback.  It is adjusted by maxing the Resonance control and adjusting the trimmer so that it comes just shy of oscillation.  That way, the panel control can be set wherever you like without fear of "howling".

For FET-based phasers (and this seems to be one), the bias voltage has to be set appropriately for the JFETs, such that they have enough usable sweep range, once that bias is summed with whatever the LFO provides.  I imagine more sophisticated and precise methods are used at factory setup, but the home user can probably tweak it by setting Depth to max, adjusting Speed to maybe medium fast, such that  changes in bias are more audible, and then adjusting the bias trimmer.  Note that, much like the pot on a normal wah, the entirety of usable sweep range is generally not used.  This means the "colour"/"flavour" of phasing can usually be tinkered with a bit, by means of the trimmer, making it a little more swirly (moving upwards) or gurgly (moving downwards).

The trimmers can be used to optimize the phasing effect so that it is more pronounced, but neither will have an effect on how loud the pedal is (though I suspect what you really meant was "more pronounced").

Yes, I meant more pronounced, I'm not a native english so from time to time I'm not able to explain the right things with the right words  So it is a jfet phaser, I was thinking about it but I wasn't sure because i searched for the board's smd transistors code and I can't seem to find them. Maybe the bias trimmer in this circuit is the "range" VR5 trimmer in the upper right of the board?

[Mark Hammer]

Yes, the Range trimmer is for setting the bias.  And, as I noted, since only part of the whole possible usable range*** IS used, feel free to play with the Range trimmer to find a sound you like.

Whenever I make myself a FET-based phaser, I always include what I label as an "Offset" control.  Once I have identified the bias voltage that gives the most usable range, I use this Offset to move the sweep a bit higher or a bit lower, depending on the mood I want.

(*** The trimmer sets the lowest/smallest possible bias voltage that will result in a usable range of sweep; but once that minimum has been identified, it does not impose any specific maximum, so you are free to use whatever part of the entire range appeals to you.  Manufacturers will use a specific bias voltage and "offset" to consistently reproduce a particular distinctive sound for every single pedal made in that product.)

[cla2002]

Yes, the Range trimmer is for setting the bias.  And, as I noted, since only part of the whole possible usable range*** IS used, feel free to play with the Range trimmer to find a sound you like.

Whenever I make myself a FET-based phaser, I always include what I label as an "Offset" control.  Once I have identified the bias voltage that gives the most usable range, I use this Offset to move the sweep a bit higher or a bit lower, depending on the mood I want.

(*** The trimmer sets the lowest/smallest possible bias voltage that will result in a usable range of sweep; but once that minimum has been identified, it does not impose any specific maximum, so you are free to use whatever part of the entire range appeals to you.  Manufacturers will use a specific bias voltage and "offset" to consistently reproduce a particular distinctive sound for every single pedal made in that product.)

Ok, I did set the trimmer and now it sounds better to my ears. I even emailed artec to know how to do some mods and here's the answer:



Do you think it's ok to do the R25 mod? Maybe this resistor it's linked to the depth control on the front face of the pedal

[Rob Strand]

Do you think it's ok to do the R25 mod? Maybe this resistor it's linked to the depth control on the front face of the pedal

My reading of it is the two resistors form part of the output mixer.   A phaser has two signal paths: the dry signal path and the phase-shifted/modulated part.   Normally you would make both paths the same gain, so that's why the resistor values are the same value.  In this case the cancellation notches are deep as possible.  The next issue is the signal level of the bypassed signal vs the effect signal.  You want these to be the same level.  So those two resistors would be decreased to make the effect louder over all and increased to make the effect softer overall.

The "Depth" relates to the modulation.   You might see this called Sweep or Width.  It sets how much the filter characteristics shift in frequency.   It also sets the amount of pitch-shifting present.

Having said that if you reduce the level of only the phase-shifted signal using the mixer resistor that will decrease the depth of the notches and make the phasing effect weaker.   Playing around with the mixer levels is like when you play around with the Dry and Delay levels on a chorus or delay unit.

[Mark Hammer]

I agree with Rob that R24/25 form part of the output mixer.  Having said that, if R24 is lifted, then you'll get phase-only, which will produce a medium-strength vibrato effect.  The usefulness of that will depend on the Speed range of the pedal.  In general, vibrato requires a faster modulation speed to be reasonably audible; not unless the pitch-change undergoes wild swings....which it won't do in a 4-stage phaser.  So if the only usable speeds for vibrato are in the 4:30 to 5:00 zone of the Speed control, then perhaps it wouldn't be worth doing any dry-lift mod.