depth control pot added to MXR Phase 90 ???

[decadentdesign]

I have instruction that I bought from Indyguitarist and there's info on modding the MXR Phase 90 in there, some of what I want to try.

In particular I'd like to try the depth control. It says to use a 47k or 100k pot attache to r28. I tried both a 50k and 100k linear pot and I'm having problems... When I turn the knob there' a point where I get a high pitch shrill. Now, I haven't wired this to the case since I don't want to drill a hole that I can't later use so I'm just testing it open and loose on the floor without the case. Without the pot it works but I'm wondering if maybe there's a ground missing that the case would make? Or, I'm wondering if maybe the r28. Resistor should still be in there parralel to the pot? In the image the book provides it's not there, but then I,m. Thinking since it doesn't say anything about it maybe it should be there???

My goal is to add a switch to go between 'script' mode and depth control mode. Then I want t add a switch to add trem mode.

For anyone trying to make room inside of one of these you might try pulling out some caps or transistors and flipping them to the other side - as long as everything is connected right it works well... Or at least it did for me.

Any othe suggestions for mods on the Phase 90? I noticed some mention of replacing some caps for script mode too, but can't seem to find details on which ones to replace.

Thanks in advance for your input!

[decadentdesign]

I want to apologize for my bad grammar in advance - using the cell instead of the computer has it's downside...

[paulyy]

I modded mine and did try some of the mods your asking. I didnt care much for the tremolo mod. Just didnt sound good to me.
I try putting a pot in for the depth and I would get some siren noises when the pot was half way up so I just put a on off switch with a 24K resister. Works great. I added some other mods as well and when I get time I'll post some pics but I have to go to work.

[decadentdesign]

Do you mean you put the on/off switch with the resistor in place of the pot?

I read on here somewhere about someone not liking the trem which I think they said is more of a vibrato and they pointed out that it would need a depth control, hence I want to try and get this working before I experiment with that one...

[flintstoned]

Check out tonepads build reports also. There's an intensity mod there (plus many others) that worked out pretty good for me. Make sure you do the pulsing led mod too!

[decadentdesign]

Check out tonepads build reports also. There's an intensity mod there (plus many others) that worked out pretty good for me. Make sure you do the pulsing led mod too!

Any chance I can get you to get me the direct link.  This is the second time I've come across this site within the last 24 hours and I'm just not figuring it out.  It looks to me like I can find a list of clones that you can build but I'm not able to find any info on mods of existing pedals.

What's the pulsing led mod?

Thanks!
David

[paulyy]

I thought i had some gut shots but hears a pic of the outside.

The top switch is in place of C11. Stock is .01. It switches from .01 to off to .022.
Higher the value adds more highs and slight volume boost.
The lower switch just turns R28/24K on and off. Both switches turned off will give the Script mod.
The knob changes the wave form. I dont remember what resister it was. I'll look into it. I know it was a 470K.
I'll try to get some gut shots soon. Hope i was some help.

[decadentdesign]

That's awesome! 470k on that pot? Huh... How does that effect the sound?

Well, at least I have a back-up plan in case I can't get the depth control working. And yeah, if you can get some pic's of the innards of that pedal it would be great - no worries if you can't though. Ithink I know basically what you did.

[zombiwoof]

R28 is the feedback resistor (the one that is removed as part of the "script" mod).  I don't see how that is going to give you a depth control, I think it will only vary the amount of feedback (which is responsible for the extra "swoosh" that the later block logo pedals have).

The complete Script mods are here, I did all of the regular script mods listed at the lower left.  According to this, a pot in place of R20, not R28, is the depth control mod.

http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/MXR_Phase_90_to_Script.gif.html?g2_imageViewsIndex=1

Al

[decadentdesign]

Thanks Al! That really helps. Offhand, would you have any idea of what the mods on the right are for? When I get home I'll look it over closer, but it doesn't seem to say.

I thought there should be more to the script mod than a couple of removed bits!

Guess I'll be ordering some more parts too - this project might just take a bit longer than I was planning but I'm excited about the possibilities!

[zombiwoof]

Thanks Al! That really helps. Offhand, would you have any idea of what the mods on the right are for? When I get home I'll look it over closer, but it doesn't seem to say.

I thought there should be more to the script mod than a couple of removed bits!

Guess I'll be ordering some more parts too - this project might just take a bit longer than I was planning but I'm excited about the possibilities!

I'm not sure what the other mods do, if you look at the schematic they involve changes to those two trimmers and the resistors surrounding them, so probably give more control to those functions (whatever they are!).  I didn't do those, I left it at the Script mods.

Al

[decadentdesign]

I'm thinking that one of those is the wave adjustment that was mentioned in a previous post...

Quick question though...  Is there an easy way to find an image of the PCB without the Resistors, caps, etc.?  Or a Diagram identifying c2, r20, etc.?  On my board most of the caps are so close to the board that I can't identify them.  I'd hate to have to unattach each one just to locate the ones I need.  I have the schematic, but I'm not that versed in reading those things (yet) and it might end up being easier to just go through them one by one if necessary...

Thanks again for all your help!

[zombiwoof]

I'm thinking that one of those is the wave adjustment that was mentioned in a previous post...

Quick question though...  Is there an easy way to find an image of the PCB without the Resistors, caps, etc.?  Or a Diagram identifying c2, r20, etc.?  On my board most of the caps are so close to the board that I can't identify them.  I'd hate to have to unattach each one just to locate the ones I need.  I have the schematic, but I'm not that versed in reading those things (yet) and it might end up being easier to just go through them one by one if necessary...

Thanks again for all your help!

If you open the link I posted, and go to the next listing in the Gallery (at the left it is #7), it shows the version of the board with the board-mounted jacks, switch, and pot.  If that is the one you have it shows some of the components.  I actually had an early Dunlop that has case-mounted jacks, pot, and switch like the original MXR's, so I had to find the layout of my board elsewhere.  There may be more layout pics in the Gallery if you look around.

Al

[decadentdesign]

Thanks again Al.  Guess I should really get better versed with how these sites are set up! 

My plan is to do the Script mode and then...  Well, with this script mode I don't think there's a realistic option to add a switch to go between script and stock, but that's probably ok.  Then I want to try the Wave form pot mod and add a switch for the Trem mod (which is apparently really vibrato I've read but that's still cool too).

I need to get paid before I can order the caps and pots I'll need so I won't probably be able to get this going until late next week... 

Oh, a question about caps if anyone happens to know...  I know not all caps have polarity, but it seems that some do and don't even with the same value.  What I'm wondering is, as long as you wire it in the right direction, can you use them interchangeably?  Or do you have to use one or the other for specific needs?  And also, how do you determine which kind you are buying?  That's been the most difficult part of this whole project, trying to decipher all those bits and pieces at Mouser and the like.  I know Small Bear makes it a lot easier, but part of me still wants to get things elsewhere and understand enough so that I can...

[paulyy]

I never got a chance to open mine up but I think R21 would be your wave pot. I remember I used a 500 log pot. I would of posted sooner but just been busy.

[decadentdesign]

I never got a chance to open mine up but I think R21 would be your wave pot. I remember I used a 500 log pot. I would of posted sooner but just been busy.

No worries and thanks... I'm going to ask a stupid question here though since I'm still learning - what do you mean by log pot? I'm familiar with linear and audio, but haven't noticed 'log' when ordering and researching them.

[Govmnt_Lacky]

Log = Audio (or Taper A)
Linear (or Taper B)
Rev. Log = Rev. Audio (or Taper C)
EQ (or Taper W)

Hope that helps

[decadentdesign]

Log = Audio (or Taper A)
Linear (or Taper B)
Rev. Log = Rev. Audio (or Taper C)
EQ (or Taper W)

Hope that helps

Definitely! Thanks!

[decadentdesign]

So... I've been working on modding this pedal for a little while - got the additional caps I needed to finish the script mod and everything seemed to be working well. Added a pot to adjust the wave form aand another to effect the depth and everything was working as far as I could tell.  Then while making room to add a switch so I could try that trem/vib mode and something went wrong...  I moved a couple of caps from top to beneath and the one that was +/- I was careful to match the polarity... but now it's not working.

When the pedal is off everything sounds fine. When it's on it sounds a bit louder or maybe the tone has changed a tad but there's no phase effect now.  I even switched out some of the parts that I thought might be the problem!

Obviously I've done something wrong but I'm not sure what...  I have a couple of questions if anyone can help out...  First, how easy is it to damage or over heat a cap/resistor/etc.?  While removing C10 (15uF) I had to mess around a lot with desoldering it - it just didn't want to let go. If I messed that up might it explain my problem or wouldn't I be getting any sound at all?

Second question is, just to test this out I tried a cap of another value (I thiink I had a 22uF cap which was as close as I have) but had the same results - sound comes through but no obvious effect.

Third... I'm testing the pedal without the case - is it very likely (or not) that I could've damaged the pedal by touching the wrong parts and making a connection or short of some kind?

I've gone over the board again and again and even switched one of the pots back to a resistor which worked sort of but then the rhthym of the effect was not right and still it wasn't working right.  I'd swear that if I jiggle the pedal I'll briefly get a subtle phase effect, but it doesn't work quite right and I just don't know...

Any help or suggestions would be appreciated! I really just need to figure out how likely and easy it is to ruin parts and if the results would be similar to my experience thus far...

Thanks in advance!
David