PCB Guitar Mania Master Phaser (Maestro Stage Phaser) Odd Issue

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rundgrenrules
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Post by rundgrenrules »

I built the Master Phaser from PCB Guitar Mania and the functionality seems to be all there. However, the switch (which I believe switches between 5 and 6 stages) also causes a pretty big bass cut - like a high pass filter - when switched to the DOWN position. I don't know what number of stages is UP switch and DOWN switch as this is not in the documentation. Surely this isn't normal?

I know it might be a more obscure build and maybe I am unsure of the nature of 5 and 6 stage phasing and perhaps this is just how one of those types of phasing sounds.

Any help is greatly appreciated!

Thank you!

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Fender3D
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Post by Fender3D »

any link to schematic?

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Lani
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Post by Lani »


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kreisky
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Post by kreisky »

Hello, I was planning to build this phaser but there is not many information about it so... Did you solve your issue? How does it sound? Do you like it?

Thanks!

K

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stolen
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Post by stolen »

Hi,

this is "intended behavior". At least it's not a build error, but just what the topology does. A phaser consists of allpass stages, and these don't change frequency response, but only the phase depending on the frequency between 0 and 180 degrees. You can build them in versions that leave the phase of low frequencies intact or the other way around, the latter is what we're dealing with here. After a certain amount of stages a phaser mixes this phase shifted signal with the dry input, so that phase cancellation around the 180 deg phase shift occurs, which is why usually an even amount of stages is employed so that very high and very low frequencies never get cancelled. A 5 stage phaser however either kills bass or treble, and here we have the probably less useful implementation of a high pass.

Phasers usually have resonance so that implementing a resonant low pass with a uneven-staged phaser is possible and could yield interesting sounds. If you want to go for this board we'd recommend modding it so that you switch between 4 and 6 stages, or add another inversion stage to get a resonant low pass. However, at first glance we see nothing special about this phaser project, and if you don't feel confident implementing those changes you might just want to go for one with a feature set that suits you more.

Univibe mods are possible with all phasers, it's simply a matter of spreading out the corner frequencies of the allpass stages (vibe) or keeping them close together (phaser).

All the best,
stolen

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kreisky
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Post by kreisky »

Hello,

I've built this pedal yesterday, it's nice but I confirm that 5 stages are quite bright sounding, without bass. In the building documents they say that the original Master phaser was 5 stages... Maybe the original was without high-pass filter?
I would like to try to do 4/6 stages switch but it seems to be necessary to cut a track in the PCB board so it's risky, I will try if I find a document with PCB track layout.

The phaser depth is controlled by 10k trimpot, I don't know if it's correct but I have replaced it by 5k resistor + 5k external pot and it allows to set depth from light to higher.
Also add a switch to set phaser/univibe... nice!

Kreisky

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