Phasers on stun!!

[Mark Hammer]

I was graciously sent a schematic for the Boss PH-2 Phaser today by one of your colleagues here who shall remain nameless for the moment.  I've posted it here: http://img.photobucket.com/albums/v474/mhammer/PH-2_2.png

For comparison purposes, I've also posted the schematic for the "table-top" half-rack RPH-10 (in two parts): http://img.photobucket.com/albums/v474/mhammer/rph10-a.gif
http://img.photobucket.com/albums/v474/mhammer/rph10-b.gif

You'll note a couple of distinctive things:

• The PH-2 is NOT a simple pedal.  There is as much stuff in here as in a Dimension C.  Lotsa op-amps, a compander, and a pair of 16-pin proprietary chips.  The IR3109 is a chip made specially for Roland/Boss.  It is essentially in the same class as the venerable SSM2040, though not as good from what I hear.  That means it is 4 linked, but nondedicated filter cells that can be in allpass, lowpass, highpass, etc mode.  Here it is used as 4 allpass stages.  Think of it as a Small Stone on a chip.  It is to some extent mimicked by a pair of LM13600s/13700s or 4 CA3094s, but not easily and occupying a bigger footprint than an IR3109.  Bad news: you can't buy them.
• There are 12 stages of phase shift organized into two sets of 6.  Both the PH-2 and the RPH-10 stick a pair of fixed (unswept) allpass/phaseshift stages after the quartet of swept ones.  This is similar to the MXR Phase 100 which has 6 swept stages, preceded and followed by two fixed stages.  In the PH-2, there are two modes: 6 and 12 stages.
• Where the PH-2 does not have manual phase shift, the RPH-10 does.  It is implemented in pretty much the same way that speed/depth/manual are in a number of Boss pedals.
• The PH-2 has no means for adjusting the polarity of the phasing, but the RPH-10 does.(Addendum: This is wrong.  When I stitched the two image halves together, I realized that the "Polarity" switch on the RPH-10 has nothing to do with the positive/negative phasing aspect.  Rather, there is a control-voltage input called the M-bus, for controlling it by external means and syncing it to other swept devices.  The polarity switch allows you to change the direction of sweep in the event that you need to.  Note that it would be a fairly trivial mod to have 6 stages sweping in one direction and the other 6 going opposite.)
• The PH-2 routes the output of stage 6 back to the first stage for feedback purposes.  It goes through an inverting stage on the way.  This extra stage of inversion is the reason why the usual recommendation is to have a regeneration path that goes back an odd number of stages.  In the RPH-10, they do something a little novel, and run TWO feedback paths from the end of a series of 6 stages to the first of that set.  Because the two sets of 6 stages can be configured in series, what you're getting in the RPH-10 is an input signal to the second set of 6 stages that has already undergone regeneration before you add even more.  Weird, and perhaps something worth checking out if you have a P100 or clone thereof, *or* a PH-2.  Note that the two feedback pots are ganged, if you own an RPH-10, it might be worth unganging them for a little broader sonic palette. (ATTENTION SEAN COSTELLO  )

Thanks again, mystery donator, and enjoy folks!

[Joe Kramer]

Thanks very much for posting these Mark!

I find the LFO circuit in both these interesting.  Sine or blunted triangle do you think?

Joe

[frequencycentral]

Thanks Mark, just what I was looking for. I've had a IR3109 in my parts drawer for 5 years, salvaged from a friends MC202 that he managed to drop a car battery on at an illegal rave, cracking the PCB in a number of places. Just put it on the breadboard today to test it.......now it's time to use it. Though I'll have to simplify that schematic a little. Phasers on stun!

[frequencycentral]

For those interested, I've hacked together a schematic using the PH2 LFO and phase core, together with the inny outy bits from the Ross OTA Phaser, in the middle of breadboarding it now, so it's a work in progess with some bits missing and some spare bits. The LFO works nicely with half a LM324, as do the inny outy bits. So I hope to end up with a 4 stage OTA phaser using only a IR3109 and an LM324.

http://dl.getdropbox.com/u/967492/IR3109%2520%252B%2520LFO%5B1%5D.JPG

[Mark Hammer]

Nice work.  You may want to raise the value of the 27k resistor going to the regeneration insert point to 56k or higher to match the value used by the original circuit.

Note, as well, that the LFO used has the design tweaked to be "clickless".  C50 and R84 are inserted to the LFO so that it starts out with a sort of slightly trapezoidal waveform, which is then converted to triangle by IC8b.  Simply slowing down the rise time of that initial square wave a bit to spreads the current draw out over a longer period of time, removes the audible click.

Finally, if my intuition is correct, the 470pf caps fulfill the same function as the 3300pf caps on the Ross.  Which means that if you reroute the end of the 470pf cap that connects to each of the 68k input resistors, so that it is tied to ground, you convert that stage from an allpass to a lowpass section.  That's the long way of saying that the IR3109 is also amenable to the phasefilter mod.  And if you're going to do that, then I recommend installing a dry-lift switch to cancel the clean signal.

[frequencycentral]

Thanks for that Mark, I'm about there but with one major flaw. It would seem that the third OTA of my IR3109 may be dead. Shame, I might have applied too much heat desoldering it from the MC202. I've re-checked my wiring twice, and also completely bypassed that stage, just using stages 1, 2 and 4. So I may end up with a three stage phaser  . I'll test the 3rd OTA in isolation, but I'm pretty sure it's not passing signal. I hope it's just one of those breadboarding errors, because the IR3109/LM324 concept seems so sweet. As for the vref, it doesn't work just using the voltage divider from the Ross, so I've buffered it with a unity gain opamp - that would make 5 opamps in total, unless I use a 78L05 for vref, which seems like a good idea.

[frequencycentral]

Yup, I can confirm that the 3rd stage is sadly deceased. Bummer. I don't think it's worth continuing this idea with just three stages. Oh well, now I know at least. I'll use it in my modular synth instead as an 18db/oct multimode filter. Back to the LM13700's then......or should I dig out my stash of metal can 3094s and 3080s to cheer me up?

[Paul Marossy]

Wow, that's a complex looking schematic. That little PCB must be packed full of components. 

[Mark Hammer]

It's packed, alright, but keep in mind how many of the chips are SIP type, and the resistors are vertically mounted.

If you've never tried a build using SIP chips, you owe it to yourself to try it at least once.  You'll be hooked, I promise.

[ayayay!]

If you've never tried a build using SIP chips, you owe it to yourself to try it at least once.  You'll be hooked, I promise.

That's funny you say that Mark.  Just today I mapped out my first "SIP Powered" pedal thinking, "This is gonna be hard."  Turned out to be a lot of fun and much easier than I thought.  Still, phasers and SIPs... Oy! 

[Mark Hammer]

In this community, dual op-amps are, if not king, then certainly crown prince.  But the thing with dual op-amps is that they goad you into sticking parts over here and over here, because the pins are on that side of the chip.  With SIPs, both sides of the chip are fair game.  I can stick a feedback cap on one side and the feedback resistor on the other if it suits me.  Lets you make traces nice and short.

[Joe Kramer]

Hey Guys,

A bit OT, but I just did a chorus with a SIP LFO.  Very breadboard friendly, as Mark said.  Trouble was finding my go-to TL062 in a SIP.  I ended up posing as a "Prototype Engineer" to get hold of some samples from a well-known chip manufacturer.   

That said, I wish I had seen this sooner:

http://cimarrontechnology.com/so8dip8tosiladapterpn060301.aspx

Not too pricey if you absolutely must have the preferred SIP.  And check out their RC4136 adapters for upgrading those old Anderton PCBs.   I'm eventually going to pimp-out my Tapco 4400 spring reverb with some high-end op amps.

Regards,
Joe

[Earthscum]

Hey, Mark... you may know the answer to this one. I'm not too familiar with phaser layouts, but I have a KMD phaser that is getting pretty old. Nobody I know has ever even seen one before (KMD, not a phaser itself, lol). Would you happen to know if it's a variation of the Boss pedals? I know for sure it sues the same flip-flop switching as alot of the Ibanez and boss pedals, and the case is almost complete Boss ripoff (or clone, to be nice).

If you want when I have time I could post some pics of the guts. Just figured I'd ask here, since the boss phaser reminded me to ask.

[Mark Hammer]

I don't "know" the answer, but I'll surmise a bit, and you can take it for what it's worth.  KMD is Kaman, which are the people who brought you Ovation Guitars and the Breadwinner (now cloned by Eastwood).  They also brought you a bunch of solid-state amps endorsed by then up-and-coming band Bon Jovi.  Kaman's modus operandi was to make products that could be produced efficiently.  Kind of a music company masterminded by MBAs.  That's not to say that they made crap, but rather they were NOT going to go too far out on what they believed to be a limb, even if it was (as illustrated by the Breadwinner).  In the case of the Ovation roundback, as much as it may have looked like a freakish detour in the world of guitars, the motivation behind it was that suitable wood would likely be in short supply so fibreglass was explored as a dependable replacement that could ensure long-term product viability.

This is the long way of saying that you should VERY much expect KMD pedals to be very standard in what they aspire to.  That includes using flip-flop-based FET switching (and Boss aren't unique there either), and FET-based phasing.  There are links to info and images of some KMD pedals here: http://filters.muziq.be/model/kmd/coron

I'm just speculating, but my guess is that if you pop the hood, you're gonna see a bunch of k#) JFETs and some 4558s.  If not, I'd be very interested in what IS in there.

[Earthscum]

I'll crack it back open (had it open to check for leaky caps before I used it again... sat in storage for many years) and take some pics just for the reference and post them in a new thread so I don't muck up this one. That's more than I've EVER known about KMD. Awesome stuff (I dig on history stuff like that). Thanks a bunch.

[nelson]

I don't "know" the answer, but I'll surmise a bit, and you can take it for what it's worth.  KMD is Kaman, which are the people who brought you Ovation Guitars and the Breadwinner (now cloned by Eastwood).  They also brought you a bunch of solid-state amps endorsed by then up-and-coming band Bon Jovi.  Kaman's modus operandi was to make products that could be produced efficiently.  Kind of a music company masterminded by MBAs.  That's not to say that they made crap, but rather they were NOT going to go too far out on what they believed to be a limb, even if it was (as illustrated by the Breadwinner).  In the case of the Ovation roundback, as much as it may have looked like a freakish detour in the world of guitars, the motivation behind it was that suitable wood would likely be in short supply so fibreglass was explored as a dependable replacement that could ensure long-term product viability.

This is the long way of saying that you should VERY much expect KMD pedals to be very standard in what they aspire to.  That includes using flip-flop-based FET switching (and Boss aren't unique there either), and FET-based phasing.  There are links to info and images of some KMD pedals here: http://filters.muziq.be/model/kmd/coron

I'm just speculating, but my guess is that if you pop the hood, you're gonna see a bunch of k#) JFETs and some 4558s.  If not, I'd be very interested in what IS in there.

My first thought was a Jfet based phaser as well.

I would be interested in seeing the schematic when someone traces it.

You never know, those MBA's might have invested in some real R+D.

[MikeH]

salvaged from a friends MC202 that he managed to drop a car battery on at an illegal rave

How the hell... nevermind; I don't want to know.  I'll just use my imagination.

[frequencycentral]

salvaged from a friends MC202 that he managed to drop a car battery on at an illegal rave

How the hell... nevermind; I don't want to know.  I'll just use my imagination.

He was powering a cool combo of MC202/TR606/SH101 from a car battery at a gathering deep in the woods.............insane really!

[SeanCostello]

Note that the two feedback pots are ganged, if you own an RPH-10, it might be worth unganging them for a little broader sonic palette. (ATTENTION SEAN COSTELLO  )

I just bought an RPH-10, and was looking for a schematic. I found this post, 10 years after you called this to my attention. So, here's a super belated thanks to Mark Hammer for posting this!

Sean Costello

[Mark Hammer]

You're most welcome.
Do look into how you might use that M-Bus.  The RPH-10 is easily converted to a voltage-controlled phaser.