MXR - Phase 100  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
Professor SourTone
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Post by Professor SourTone »

Script, Block/no LED, Block with LED

Is the Block/no LED the good value option, or does it really have to be script?

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Post by analogguru »

That´s an really interesting question...
First time I heard about differences with this unit, so I looked through my guts and indeed, there was indeed even a change in the pcb layout. But this change already occured during the script era.

So I think between the late script-era and the block-era will not be a big difference. I have to check that out sometime...

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Post by analogguru »

So after a short analysis I came to the following results:

version 1: early script version (7632)
pcb: version 1
caps in audio path: tropical fish
op-amp-cap in LFO: 10n tropical fish
Resistor in phase stages: 22k
transistors: probably 2SC types
feedback resistor: probably 15k

version 2: later script version (????)
pcb: version 2
caps in audio path: white film
op-amp-cap in LFO: 10n ceramic
Resistor in phase stages: 20k
transistors: probably ZTX types
feedback resistor: probably 15k

version 3: early block version (7745)
pcb: version 2
caps in audio path: white film
op-amp-cap in LFO: 10n ceramic
Resistor in phase stages: 20k
transistors: probably ZTX types
feedback resistor: probably 15k

version 4: block version (7840, 7949)
pcb: version 2
caps in audio path: white film
op-amp-cap in LFO: 10n ceramic
Resistor in phase stages: 20k
transistors: probably 2SC types
feedback resistor: definitely 18k

The only difference in the audio section are the tropical fish caps and the 22k resistors instead of the white film and 20k resistors. I don´t believe that the difference between 22k and 20k will have a big influence, since this can also result from capacitor tolerances (10% - 20 %).

The feedback resistor (intensity) of 15k seems to have been changed in 1978, maybe earlier.

Alltogether it appears that the - not real significant -change has occured earlier in the script era and not together with the script/block change.

The old ones can be recognized on the tropical fish and that the wire holes are symmetrical in the middle of the pcb-edge.

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Post by Bernardduur »

Awesome!

Now on the sound side; how do they differ? It is still one project of me on the shelf :)
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Post by Dirk_Hendrik »

Start naggin me throug mail tomorrow Rogier. I've got some PCB layout files you definitely want ;)

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Post by Bernardduur »

Dirk_Hendrik wrote:Start naggin me throug mail tomorrow Rogier. I've got some PCB layout files you definitely want ;)
Cool :)
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Post by Professor SourTone »

Wow - that is good info - thanks.

I have a script Phase 45 that's just arrived that I really like, but I'd also like a 100 for more variety. I don't want to play in the script 90 playground much - that has to be overdone.

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Post by Professor SourTone »

This is the one I'm looking at

Image

Here is a script version (not great pic, I know)

Image

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Post by analogguru »

Both units shown are version 2 pcb´s and should be identical - maximum except of one resistor (18k vs. 15k).

Here:
http://www.modezero.com/images0000/mxr-phase-100-Bx.jpg
you can see a version 1 pcb.
Note especially the difference in component placement (10n cap) in the right back corner, de different position of the protection diode and the different placement of the jumper-wires.

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Post by analogguru »

Now you´ve got your chance for your personally tailored Phase 100:
https://cgi.ebay.com/MXR-Phase-100-phase ... 0039066944

and if you need a case you can buy this from the same seller:
https://cgi.ebay.com/MXR-Flanger-pedal-V ... dZViewItem

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Post by Bernardduur »

So the script version and the later ones ARE different!!

Got one in for repair and traced it! Main differences are the clean mixing circuit, some small resistor changes in the LFO and the resistor value in the Vref
Phase 100.JPG
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Post by blackbunny »

So the script version and the later ones ARE different!!
Got one in for repair and traced it! Main differences are the clean mixing circuit, some small resistor changes in the LFO and the resistor value in the Vref
Is this traced from a script Phase 100? The one with the "tropical fish" coloured capacitors? :scratch:

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Post by Bernardduur »

blackbunny wrote:
So the script version and the later ones ARE different!!
Got one in for repair and traced it! Main differences are the clean mixing circuit, some small resistor changes in the LFO and the resistor value in the Vref
Is this traced from a script Phase 100? The one with the "tropical fish" coloured capacitors? :scratch:
Yep! Tropical fish caps (10n) all over the place
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Post by zaphod »

I've just bought a fairly old block logo Phase 100, which has clearly seen better days. I plan to get it back to full working order and maybe do some small mods as well. Looking at the schematic, I really don't get why there are four extra stages which aren't modulated by the LFO, as these will not contribute anything to the phasing effect. I even wonder if they did it pourely as a marketing gimmik, to advertose it as a 10-stage phaser, when in reality it's only a six-stage. I would be interested if anyone has any thoughts or insite on this.

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Post by armdnrdy1 »

zaphod wrote:Looking at the schematic, I really don't get why there are four extra stages which aren't modulated by the LFO, as these will not contribute anything to the phasing effect. I even wonder if they did it pourely as a marketing gimmik, to advertose it as a 10-stage phaser, when in reality it's only a six-stage.
The Phase 100 is a 10 stage phaser.
Pedal manufacturers are not in the market to include components in their designs that serve no purpose.

The stages you are referring to are "fixed" stages. Fixed stages do contribute to the overall phasing effect.

This is not an uncommon design.

The ADA Final Phase has 6 swept stages and two fixed stages.

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Post by uncleboko »

armdnrdy1 wrote:
zaphod wrote:Looking at the schematic, I really don't get why there are four extra stages which aren't modulated by the LFO, as these will not contribute anything to the phasing effect. I even wonder if they did it pourely as a marketing gimmik, to advertose it as a 10-stage phaser, when in reality it's only a six-stage.
The Phase 100 is a 10 stage phaser.
Pedal manufacturers are not in the market to include components in their designs that serve no purpose.

The stages you are referring to are "fixed" stages. Fixed stages do contribute to the overall phasing effect.

This is not an uncommon design.

The ADA Final Phase has 6 swept stages and two fixed stages.
And the Eventide Instant Phaser..............

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Post by Fender3D »

TC XII too...

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Post by zaphod »

I still don't see the point, since there's no modulation being applied to the phase shift. So yes, while I agree a phase shift is happening in those stage, the shift is still not being swept in any way, and it's that sweep which the human ear detect.

Disclaimer: I'm an EE with severe OCD, so I like to dig into what's really going on inside FX pedals. So please feel free to set me straight on what I just said, and I realy won't mind. :)

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Post by armdnrdy1 »


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Post by zaphod »

That article has a pretty good summary of textbook flanger and phaser theory. R.G. Keen writes some great articles. What's interesting is that he seems to be agree with me on some important points.
It turns out that the human ear is not too sensitive to phase shifts...
The most common commercial phase shifters stop with four stages (such as the MXR Phase 90, Univibe) or six stages (MXR phase 100).
...although the effect is noticeable, it's much better if the notches move up and down in frequency.
So while I might gree that maybe there's some benefit in having some extra fixed phase shift stages, it's really not clear how much of a benfit that really is. Maybe it becomes more useful when feedback is switched on...? :hmmm: Even then, wouldn't it make more sense if different RC values were used in each of the fixed stages to enhance the effect...?

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