Phase 100 with mods

[armdnrdy]

After Stephen Giles emailed a copy of the Phase 100 that was modified to run on 15 volts, I started looking into this circuit a bit. I was very curious about the fixed phase stages incorporated with the swept stages.

I came across a seller on eBay that was offering an original NOS Phase 100 circuit board with factory documentation such as the schematic, and items not available on the net, parts lists, and component placement sheet.
For only $7.00......I was in.
My first thought was to build a stock Phase 100 but....that thought soon passed!

I researched the Phase 100 a bit more and came to the conclusion that a lot could be done to this circuit to make it more versatile.
I had some ideas of what I wanted to accomplish so I took to the net to search for mods.
Low and behold....someone else had thought of my ideas before I did!  

So... after reading through Mark Hammer's writings on the subject, (Thanks Mark!) I bread boarded the LFO to see what I could come up with.
I tried different configurations and placements for the Depth control but found with the Phase 100s LFO, the idea that Mark had outlined worked the best.
I tried different values for the Depth control until I arrived at 100K. While viewing on my scope the 100K fully clockwise emulates the original rotary switch being open for max depth. When the control is turned counter clockwise it emulates closing the rotary switch for less depth.
I tried a linear pot first but found that there wasn't much "action" in the last 25% of the rotation. A log pot fixed that issue.

I had read about lifting the dry signal (R12 factory schematic) to create a vibrato effect and I came up with a few ideas on that mod.
I thought that it would be useful to change from phaser to vibrato on the fly but....there would be a few issues to overcome.
Mark mentioned that the pitch bend depends on the number of phase shifted stages and a 10 stage phaser (4 fixed, 6 swept) such as the Phase 100 used for vibrato would sound exaggerated compared to a Univibe or other 4 stage phaser. So...to combat this issue I came up with an idea.

I had the thought to incorporate a switch to choose between phaser and vibrato by lifting the dry signal, switching to a different depth control, switching to a different speed control, and switching between two LEDs (vibrato rate & phaser rate located under appropriate controls) using a 4PDT footswitch.
With this configuration the vibrato mode controls can be preset with less Depth, and more Speed. This allows you to switch from a slow phaser setting to a fast vibrato effect with the Depth "tamed" down as to not sound "exaggerated." I went with a 50KC pot for the vibrato speed control which allows a range that I found acceptable for vibrato.

I also added a proper, garden variety feedback control. A 10K pot, 20K trimmer, and a couple of .1µf caps now replace the rotary control and R34. (Factory schematic)

Next...I thought to make the phase stages switchable. I worked the switching out using 3 poles of a 4P3T rotary switch. (It wouldn't be a Phase 100 without some sort of rotary switch!)

According to my schematic,

Position 1: the output of the first two swept stages (1) connects with the input of the last two fixed stages (Z) for 4 fixed and 2 swept stages.
Position 2: the first pole now connects the first four stages at (1) and (X) the second pole connects the output of these four stages (2) to the input of the last two fixed stages (Z) for 4 fixed and 4 swept stages.
Position 3: connects the all of the stages and outputs together to make it as the original. (4 fixed and 6 swept stages)

I was thinking to add 5-10MΩ resistors on the rotary switch between the stage poles to keep any popping at bay while selecting between stages. (Between 1 & X, 2 & Y, and 3 & Z)
Any thoughts on this?

I was originally going to hack on the NOS MXR PHASE 100 board but...with all of these mods, and the age of the board, (late 70s – early 80s) I decided probably better just to route the board.

As I stated earlier, I worked some of this out on a bread board but the whole build is not verified yet. I'm just looking for some input if I'm on the right path.



Clearer image PDF:
https://dl.dropboxusercontent.com/u/53299166/DIYstompboxes/MXR%20Phase%20100.pdf

[Govmnt_Lacky]

At it again huh Larry?   

One of my first "challenging" builds EVER was an etched GGG Phase 100. That was just before the price of Vactrols went through the roof! 

I always liked the sound of it but never thought it was a very "deep" phase. Hopefully, you will find some hidden secrets! 

Eyes and ears open on this one! Good Luck!

[armdnrdy]

Hey Greg,

Yeah, I saw that you weren't that impressed with the depth of phase in this thread:
http://www.diystompboxes.com/smfforum/index.php?topic=68604.20

The YouTube clips of the factory MXR Phase 100 seem to have adequate depth.

One thing that I noticed in the factory parts list is that the Vactrols are matched. if I recall correctly, Mutron matched their Vactrols for the Bi-Phase as well. If you throw in three random Vactrols...the phasing won't be as intense, just like unmatched JFETs.

I have quite a few VTL5C3/2s in stock, so while I still have the LFO on the breadboard, I'll find similar min/max resistances with the Vactrols connected to the LFO.

[Govmnt_Lacky]

Yep. I just threw in 3 of the 5C3/2 vactrols that I bought.

I would try some value matching BUT.... too damn costly right now!   

Maybe in the future. So until then, I will make notes of what happens here 

[armdnrdy]

This is page two of the parts list. Vactrol matching under "Special Note"

[Fender3D]

Hey Larry,
it's nice when mates have the same effect in mind or on breadboard... 
Watch out, I think your SW3 A2 should be connected to the other R9 pin


Since you have it on breadboard, try this selection/mixer:
http://www.aronnelson.com/DIYFiles/up/Phaser_output_mixer.pdf
and see if it works for you...
It might save you the space wasted by the rotary and a lot of wiring...

Just leave all 10 stages in series and get the connections at filters outputs.
I would add an inverting op-amp mixer at output, so you won't have impedance issues with following pedals or stuff... and you may add the ADA noise gate too, there...
Again, it might be interesting get the feedback path as suggested, since it will change according with stages selection

PS
could you please post the other factory documents?

[armdnrdy]

Hey Federico,

I'll have to take a look at your drawing and sugestions. Thanks for the reply.

Here is page 1 of the parts list:



My scan of the same schematic that is available on the net:



and last but not least.....the component placement:

[Fender3D]

Thank you so much

[armdnrdy]

Federico,

I took a quick glance at your drawing.

Since all of the stages are still connected in series, the signal would still pass through all of the stages to the output. It seems like the tapped stage would be reinforced more than the other stages.

Wouldn't your mixer be more of a feedback tap/select?

The rotary switch that I had in mind connects two additional swept stages with each position....a stage selector.

Maybe I'm looking at this wrong.  

[armdnrdy]

Just found the mixing resistor problem that you mentioned. Good catch Federico!

Fixed and reposted above.

It actually worked out better....I was able to move switch pad S3A2 to the top of the board! 

[Govmnt_Lacky]

Hey Larry...

Any idea or info on HOW the Vactrols are matched? Is it by On resistance, Off resistance, etc.?

[armdnrdy]

Hey Larry...

Any idea or info on HOW the Vactrols are matched? Is it by On resistance, Off resistance, etc.?

I'm working on that right now. I'm taking min/max resistance readings with the vactrols connected to the LFO.

I'll report my finding and thoughts later today. So far...it looks like these things are all over the place!

[Fender3D]

Federico,

I took a quick glance at your drawing.

Since all of the stages are still connected in series, the signal would still pass through all of the stages to the output. It seems like the tapped stage would be reinforced more than the other stages.

Wouldn't your mixer be more of a feedback tap/select?

The rotary switch that I had in mind connects two additional swept stages with each position....a stage selector.

Maybe I'm looking at this wrong. 

Look at it this way:
your circuit is a "true" stages number selection,
mine is a "clinton" (as R.G. would say  ) stages selection...

Phaser effect arise from a paralleled mixing, and R30 on my schem. just mixes either 4 and 6 stages, 6 only, or 6 and 10...

Sorry if it looks cryptic...
just woken up...

[armdnrdy]

So was I correct in thinking that the mixer circuit would strengthen the stage that it's being tapped from?

I wonder what the noticeable difference between the two would be .

I don't have the whole circuit bread boarded at the moment....waiting on some parts....I just have the LFO on the breadboard right now.

[armdnrdy]

Vactrol matching thread started here:

http://www.diystompboxes.com/smfforum/index.php?topic=106920.0

[Fender3D]

So was I correct in thinking that the mixer circuit would strengthen the stage that it's being tapped from?

I wonder what the noticeable difference between the two would be .

Sorry for my late reply, Larry

I'll be away from my workbench for a while...
but just simulated it with ltSpice:

actually it changes the number of "holes" when changing stages number
with slight difference in "hole depth" (-42.1dB for "clinton" mode instead of -43.8dB for true mode)

[armdnrdy]

Hi Federico,

Thanks for the reply.

By holes....do you mean notches?

Also...a few more questions about your circuit.

SW2 is labeled as a SP3T. Is it ON/OFF/ON?

If I were to connect this circuit into my schematic, I would reconnect 1&X, 2&Y 3&Z and connect your circuit "to 4 stages" to 1&X,
"to 6 stages" to 2&Y, and "to 10 stages" to 3&Z. Is this correct?

I would imagine that the single op amp depicted in your drawing can be replaced with a TL071, or any other single op amp.

A couple more things....Does your R37 take place of my R9? ("wet mixing resistor")

Since I included a feedback trimmer, a couple of caps, and a feedback control, is R4 needed? (Depicted on my schematic)

[Fender3D]

Yeah notches...
I was struggling for the right term, then quotation marks sped up the process 

SW2 is labeled as a SP3T. Is it ON/OFF/ON?

Yes SW2 is on-off-on

If I were to connect this circuit into my schematic, I would reconnect 1&X, 2&Y 3&Z and connect your circuit "to 4 stages" to 1&X,
"to 6 stages" to 2&Y, and "to 10 stages" to 3&Z. Is this correct?

Yes

I would imagine that the single op amp depicted in your drawing can be replaced with a TL071, or any other single op amp.

I would use a 072 adding a further op-amp for wet/dry mixing...

A couple more things....Does your R37 take place of my R9? ("wet mixing resistor")

No, it decouples the stages mixing

Since I included a feedback trimmer, a couple of caps, and a feedback control, is R4 needed? (Depicted on my schematic)

No R4 is a leftover from my schematic

[armdnrdy]

Gotcha!

Thanks for the info.

[njkmonty]

would it be possible to make your own vatrocols for this project??   but  using 2 leds instead of 1 and connecting 2 legs of the 2 ldr?  if so any led and ldr recommendations?
its just i have heaps of both ldrs and leds, from other phaser projects.

is it possible to use 2 vtl5c1's? to make a makeshift VTL5C3/2 as i have heaps?