Phase 90 mini-toggle

[The_Philth]

Greetings Tweakists,

I just scoured the Forum for anything close to this question but came up short! Hopefully this inquiry will benefit others as well as myself so here goes.

How can I ad a mini toggle switch to my Phase 90 reissue to switch between the R28 (10k) resistor (script mod) and stock? I imagine that’s the option the new *cough*-[overpriced] Van Halen Phase 90 offers.

Okay, I'm pretty good with a soldering iron as well as following instructions with a diagram. I’ve read somewhere that this type of addition is fairly simple, even to the novice.

Does this seem like a viable modification that a tech-in-training can tackle or is it far too complicated a task? Either way, I’d still love to see someone post the process albeit, it’s not as complicated as I hope!

Cheers!

[vanhansen]

This topic was brought up before.  I was involved in it.  Can't remember the exact subject but "phase 90" or "script mod" should bring it up.

Lift the leg of the resistor, you can get the exact location of it from my site in the DIY Effects and Mods section.  I have a picture of a reissue board.  With one leg lifted, use a SPST switch.  Wire the lifted leg to one lug and run a wire from the other lug to the board where you lifted the leg from.  Use a desoldering braid and don't apply too much heat.  You want to avoid lifting the solder pads.

EDIT 4/18/05:  Better to use a DPDT on-on switch.  Wire it up similar to true bypass.  Resister across two outside lugs, wires from R28 PCB holes to each middle lug, leave other outside lugs open.

I just clipped the resistor out completely (it's 24k BTW, not 10k).

The fun part next is drilling a hole in the enclosure for the switch.  I didn't want to do that with mine, reason why I just clipped the resistor out.

Hope this helps.

[Alex C]

http://diystompboxes.com/sboxforum/viewtopic.php?t=26093&start=0&postdays=0&postorder=asc&highlight=

[The_Philth]

Thanks vanhansen,

You da man!

Your help is icredibly appreciated here!

[The_Philth]

http://diystompboxes.com/sboxforum/viewtopic.php?t=26093

Thanks Alex! I read that (et al) thread thru-and-thru but offered no answer for my question.

[Mark Hammer]

RG Keen's solution is actually better than what the EVH pedal has to offer, and that is continuous control via a pot.  Indeed, most *real* phasers have this.  The P90 is a holdover from the days of "one knob wonders" that continues to enjoy sales in its original form because too many people tend to equate "vintage" with the 11th commandment "Thou shalt not disturb anything, not even the garbage on the floor nor dust on the counter".

The original had a small amount of feedback introduced in the regen loop.  The other issues change the amount via the value of that resistor, but they all do it with fixed components.  The maximum regeneration produced should not be any higher than what comes through a 10k resistor.  Additional resistance in series with that will reduce the regeneration.  If you stick a 50k to 100k pot, wired as a variable resistor, in series with a 10k resistor, in place of R28, you will have the Script, the post-script and all sorts of other pleasing variations to boot.  Beats the pants off the original by a long shot.

[vanhansen]

Cool idea Mark.  I didn't see that in RG's article.  I'll have to check that out sometime.

[vanhansen]

I know this is an old thread but trying to keep the info all together with this one.

How would the pot (variable resistor) be wired?  Would the resistor go:

1. From the board to lug 3 and the wiper. Lug 1 to the board

-or-

2. From the board to lug 3.  Wiper and lug 1 to the board

-or-

3.  Just use two lugs.  If so, which ones?

[Mark Hammer]

Here is what is probably the smartest way to do it.

1) Score yourself a 100k pot.  I have no oreference for lin vs log in this case.  They will both "work" though whether one suits your taste more than the other is up to you.

2) Score yourself a 12k 1/4W resistor.

3) Remove the R28 from the existing board, and solder in two wire leads to the pads formerly occupied by R28.

4)  Solder the 12k resistor between the wiper and the side lug usually reserved for ground on the pot.  That would be the one on the left if you were staring at the shaft of the pot with the lugs pointing downward.

5) Solder one of the wires to one outside lug, and the other wire to the other outside lug.

Done.

How does it "work"?

The 12k resistor is in parallel with whatever resistance lies between the two lugs it is soldered to.  In conjunction with the resistance of the other leg of the pot, it forms an overall resistance to replace R28.

When the pot is turned all the way counterclockwise, the 12k is in parallel with zero ohms, but added to the full resistance of the pot, yielding a total resistance of about 100k (pots are rarely EXACTLY the value stated).  Turned the complete other way, the "other leg" of the pot is now zero ohms, and the fixed resistor is placed in parallel with the full value of the pot.  If the pot was *precisely* 100k, that would yield a combined parallel resistance of about 10.7k.

The reason I prefer this is because it keeps the max regen slightly away from the point of oscillation (one hopes), and uses the pot itself to secure the extra resistor.  That's a more structurally secure arrangement than, say, lifting one end of the on-board resistor and running a wire from the free end to the pot.

The values indicated here are simply suggested values.  It may be that 12k gets you too close to oscillation, and a value like 15k or even 18k is better for "audio safety".  A parallel 18k resistor results in a resistance of 15.25k when in parallel with a 100k pot.

It may also be the case that yoiu look the way the pedal sounds with even LESS regen, in which case consider using a 250k pot rather than 100k.  Naturally, parallel resistances will be subject to change.

Finally, let us know how you like it.

[vanhansen]

Mark, your knowledge is worth more than you know.  This is great.  I appreciate you chiming in.

Once I get it all checked out, I'll most likely add it to my Phase 90 mods page.

Thanks, again.

[Mark Hammer]

Thanks.

By all means, dicker aqround with minimum and maximum amounts of regen, and give us a sense of what resistance range is most useful.  Hell, for all I know, a 50k pot may be more than enough.

[sidewinder]

i have a device which has all resistor settings in it. i used it on my phase 90 and the range i slocated between 24k and 10 k, under 10 k i get a "short" screeching sound. also, i dont know if my ear is bad or what, but setting it on 24k and then taking it off, i hea rno difference, im wondering if there is really a difference between the r28 mod and the stock mode.

[Fret Wire]

RG Keen's solution is actually better than what the EVH pedal has to offer, and that is continuous control via a pot.  Indeed, most *real* phasers have this.  The P90 is a holdover from the days of "one knob wonders" that continues to enjoy sales in its original form because too many people tend to equate "vintage" with the 11th commandment "Thou shalt not disturb anything, not even the garbage on the floor nor dust on the counter".

I don't know about that Mark, in regards to it's long lived popularity. Most of the Phase 90's popularity (script version) is simply because it sounds good with any setting. Plenty of phaser's do have additional pots for depth and regen, and are somewhat more versatile, but don't really sound much better. MXR set fixed parameters for everything but the rate. They took the knob-itis option away from the user. With a lot of phasers, many settings will produce good sounds, with the 90, every setting produces a good sound IMHO. Sometimes, less is more.

The feedback pot mod is a neat idea, but isn't it a kind of a one trick pony? The 24k feedback resistor is what makes the later issues so horrid sounding with a clean tone or acoustics. The more you turn up the pot, the more you get that distorted mid heavy sound. If you like that.

Replacing the 150k output resistor with a pot is useful, because the 90's output, like most phasers, varies depending on where it is in the signal chain, and what's before or after it. The ability to get slightly below, unity gain, or slightly above, is a nice option regardless of the phaser settings.

I guess a three knob 90 would be usefull to some people.

[vanhansen]

Replacing the 150k output resistor with a pot is useful, because the 90's output, like most phasers, varies depending on where it is in the signal chain, and what's before or after it. The ability to get slightly below, unity gain, or slightly above, is a nice option regardless of the phaser settings.

Not a bad idea. I never thought about that. I sometimes wondered why it didn't have an output level pot to begin with but like you said, it sounds good with everything so one knob was all it ever had.  What value pot would you recommend?

[TheBigMan]

Just a couple of things seeing as I just did a toggle switched R28 mod.  There isn't much space in this pedal, so a DPDT toggle may not be possible.  I used an SPDT cos I've run out of SPSTs and mounted R28 on a small piece of veroboard attatched to the casing by a standoff.  It's to the right of the pedal just above the input jack, but it's a pretty tight fit.

[vanhansen]

Just a couple of things seeing as I just did a toggle switched R28 mod.  There isn't much space in this pedal, so a DPDT toggle may not be possible.  I used an SPDT cos I've run out of SPSTs and mounted R28 on a small piece of veroboard attatched to the casing by a standoff.  It's to the right of the pedal just above the input jack, but it's a pretty tight fit.

Do you have a pic of it?  Any issues with squealing when you switch to the resistor being out of circuit?

[Dai H.]

fwiw, script spec conversion needs more than the fdbk. resistor removal. (Let me find some info I've got by "cerrem") :

There are a lot of small difference between script circuit and later circuit...
First, the phase shift sections, 4 of them, use .05 caps on the script while the later block circuit uses .01, also the same phse shift sections, the scipt uses four 22K as opposed to 24K resistors.... The R28 feedback resistor 24K is not in the script circuit...
The key difference is in drive at the op-amp input circuit...The script uses the input satge as a buffer "follower"....ie..no gain.
The later circuit uses that op-amp with some gain since it uses a 10K in the feedback with a 2.2K to ground through a .01 cap...You need to remove the 2.2K and cap and then use a bypas wire for the 10K to convert that stage to a buffer..
Also the script circuit uses a 470K resistor input load resistor, after the 10K series resistor, while the block circuit uses a 1Meg instead of 470K...
Also..the output stage transistor, 2N4126, on the block ciruict uses a fedback network of 150K and 680pF from collector to base...the script ciruit does not use the 680pF but does use the 150K..
The last section to change is the DC BIAS control pot...The script circuit used a 200K trimpot with 24K to ground on one leg and 27K on the other leg that goes to B+ rail....The resistor for the center wiper on the script is 1Meg....
The later block logo used 25K trim-pot with 56K on one leg and 68K on the other leg with 750K for the center wiper...
The script circuit used 6 OP-AMPS all are single op-amps... The block logo uses DUAL OP-AMPS and therefore uses only 3 OP-AMPS...
Thats about it..
Regards
Chris

iirc, there was also a 10k? in series w/the output, 1M from hot to ground at input (my TL062x3 Dunlop which I think is equivalent to block-logo models), 25k? trimmer and maybe some other things. And look at the Tonepad project schemo. Should help to figure it out.

[TheBigMan]

Just a couple of things seeing as I just did a toggle switched R28 mod.  There isn't much space in this pedal, so a DPDT toggle may not be possible.  I used an SPDT cos I've run out of SPSTs and mounted R28 on a small piece of veroboard attatched to the casing by a standoff.  It's to the right of the pedal just above the input jack, but it's a pretty tight fit.

Do you have a pic of it?  Any issues with squealing when you switch to the resistor being out of circuit?

I'll take a pic and post it.  No squealing that I noticed when I tested it.  Sounds pretty good too.

[vanhansen]

Just a couple of things seeing as I just did a toggle switched R28 mod.  There isn't much space in this pedal, so a DPDT toggle may not be possible.  I used an SPDT cos I've run out of SPSTs and mounted R28 on a small piece of veroboard attatched to the casing by a standoff.  It's to the right of the pedal just above the input jack, but it's a pretty tight fit.

Do you have a pic of it?  Any issues with squealing when you switch to the resistor being out of circuit?

I'll take a pic and post it.  No squealing that I noticed when I tested it.  Sounds pretty good too.

You da man, Big Man.

I've had so many hits to my Phase 90 Mods page that I've decided to expand it and include adding the switch or even a series resistor/pot combo option.  Right now I have a diagram using a DPDT switch.  One guy that emailed me hooked it up with a SPST 2 lug but it squealed when he switched out the resistor.  The same thing happened with the 3 lug I think.  And it even happened with the DPDT when wired with the resistor across two outside lugs, wires from PCB to middle lugs and jumpered other outside lugs.  Leaving the other outside lugs open stopped the squeal.  Go figure.  I'm pretty sure it would work with a SPST switch though.  Maybe the wiring was wrong or something.

[sidewinder]

yo Erik, it sme vince. the spst 2 legs worked, i just had a hard time seeing the difference. spdt 3 legs squeeked though. dpdt worked  but not with the legs soldered together, that squeaked as well. leaving the leg sunsoldered works great. i also tried the dpdt with different resistors on each end, and it works great. the switch wont accept no resistance thats why you either put another resistor there or leave the legs unsoldered together. btw, i managed to ground the volume box. i soldered lug 3 to the ring of the input jack (where the male jack goes into) this grounded my box because the lug 1 to pot and sleeve to sleeve wasnt enough.