Boss PH-1r schematic

[R.G.]

The Boss PH-1r schematic is now up at GEO (http://www.geofex.com).

Many thanks to those who helped and offered help in extracting this one. In the end it was a combination of top/bottom shots from the net and the gracious assistance of Ry Hoffman that got this done.

[Geoff Hunter]

Thanks for all the hard work!  I'll confess I've got a PH-1r sitting on my desk waiting to be fixed, but I never seem to get started (happens a lot on all my projects.)

You've given me an excuse to get started now 

[R.G.]

It's kinda funny. They broken unit showed up here and I dove right in, full of the certainty that I could fix anything it had wrong.

It turned out to be a broken power wire.   

But boy, I'm ready for the next one... 

[stm]

Thanks, RG.

Another Boss schem for the collection!

[Gus]

R.G.  I wonder how fast a "improved" clone of this will be marketed?

   maybe in a forum or more, questions will be asked about how to select the Fets and stuff like that.

Then a clone appears improved with "true bypass" selected fets etc.

Did you time the time between the treble boost ampage posts and  PDF and all the RM types?

[Mark Hammer]

R.G.  I wonder how fast a "improved" clone of this will be marketed?

   maybe in a forum or more, questions will be asked about how to select the Fets and stuff like that.

Quite honestly, there is nothing in the PH1-R we haven't seen before in a hundred other places.  The JFET chosen is commonly used.  It's a 3-knob 4-stager, and uses a switching FET to lift the wet path from the mixing stage.  Finally, it uses a 100n/330k drain-gate network to reduce distortion.  A slight improvement over the P-90, which was its chief competition at the time (assuming the Small Stone was in a separate class).  But not much more than that, and most assuredly NOT a Bi-Phase or A/DA Final Phase.

Nah.  Repairing one you have, I can see value in that.  But cloning one in pursuit of something special will be met with resounding disappointment because it is nothing that special.

Looking at the schem for the PH-1, it may even have a few advantages over the R version.

The first difference is the absence of the 100n/330k drain-gate network.  Although this is known to reduce distortion in FETs used in this manner, apparently it essentially holds off distortion until a higher signal amplitude, at which point the distortion that does occur is uuuuuuuuug-LEEE (beaten soundly with an ugly stick,that is).  That changeover point may or may not be material, depending on what sorts of levels you tend to use.

The other difference I find clever is the presence of Q6.  Q5 does the usual job of lifting/making the contact to feed the wet path to the mixing stage.  Q6 is there to compensate volume levels and achieve level balance between effect and bypass modes.  It does this by changing the resistance of the ground leg from pin 2 of IC2.  Neat.

Finally, you will note that where the PH-1R uses a discrete input buffer followed by an op-amp stage, the PH-1 skips the discrete buffer.  That may or may not yield some noise and/or input improvements over the PH-1 (which uses a so-so RC3403 quad op-amp).  The key thing to note is that because it employs regeneration, the PH-1R needs to have a mixing node after the input buffer (for input+regen) that the PH-1 does not require.

[Gus]

Mark

  I guess you are not getting the humor I see in the web forums and clones.
   

[Karmasound]

I have one of these and was wondering about some mods that could be made to it. Anyone have any?

What about "univibing" it?

[Mark Hammer]

Mark

  I guess you are not getting the humor I see in the web forums and clones.
   

Oh I'm getting, all right, Gus.  It may only be humorous to a few of us here, there.  When "This is Spinal Tap" first came out, my wife and I went to see it in the theatre.  When Tap's manager, played by Tony Hendra, tried to convince the band to shrug off the cancellation of their Boston gig, he noted "Well, Boston's not much of a college town anyway."  My wife and I were killing ourselves laughing.  The rest of the theatre, that had on a great deal of black leather, did not seem to see the humour in that statement.  I guess some humour has a VERY limited audience.

[George Giblet]

Thanks for the schematic.   It *is* very similar to the PH-1.  Small amount of juggling to get the Regen in and some distortion lowering networks around the JFETs.

A few questions come up:

Based on the PH-1 the bias zener is almost certainly a 5.1V 0.5W zener (NEC RD5.1EB); if it's not 5.1V it will be 4.7V.

The regen pot value is missing, perhaps 10kC?

Looking at the PH-1:  Is there a cap (100n?) from the 330k gate resistors to ground, just after the 2.2M and 1M?

[R.G.]

I have one of these and was wondering about some mods that could be made to it. Anyone have any?
What about "univibing" it?

Sigh. The sixth reply was a fulminating case of BUMS.

Why exactly do you want to mod it? Is it that the sound is not very exciting and you think it could be turned into a new monster sound? That won't be the case in general.

"Univibing" a phaser can be done to any phaser. Whether you want to or not is subject go some question. The whole issue of how the univibe does phase stage location versus the rest of the phasing world has finally gotten settled. It was actually settled in the mid 70's, but I didn't get to read the paper until almost 30 years later.

What JC calls "univibing" is staggering the values of the phase caps to spread the phase shift range over the middle of the audio spectrum. What this does in the univibe is to give a better vibrato sound by making the apparent frequency shift be spread around over the audio spectrum instead of concentrated in one place. This is a big deal when one of the switch positions is marked "vibrato". It's less of a big deal when what you want is phasing. It moves the phase notches out to ideosyncratic positions that may or may not be pleasing and diffuses the phase sound. There were a couple of papers on this in the JAES in the mid 70's, and the upshot is that the best phasing sound comes from identical time constants in the phase stages. But as I'm fond of saying "What exactly do you mean by 'best'?" There can be no "best".

Sorry - you pushed my button. 

No, I don't have any mods for it.

The other difference I find clever is the presence of Q6.  Q5 does the usual job of lifting/making the contact to feed the wet path to the mixing stage.  Q6 is there to compensate volume levels and achieve level balance between effect and bypass modes.  It does this by changing the resistance of the ground leg from pin 2 of IC2.  Neat.

Yeah, I did like that one. Once you go to cold switching, it's good to remember that you can switch ANYTHING when you switch operational modes. It's well worth remembering.

I think if I was designing a phaser, I'd go for a few fixed phase shift stages before the variable phase line, maybe a few fixed stages in parallel, and probably two phase lines in parallel, but driven from synchronized but not identical LFOs. Something like a 3 to 4 relationship maybe. And allow much of the assemblage to be switched in or out with signal routing on the board.

OK, I guess what I'm really doing now is modding. Busted.

So my mod for the PH-1r goes like this: Take four of them. Neuter the LFO on two of them. Disconnect the internal feedback on all of them. Run one in series with one of the non-neutered ones, and another in parallel into the final mixer, which you will also need. Run the output of the two live phase stages back through a pot to the input of that section. Now put switching in/out on all of them, and add synchronized LFOs on the two active phase lines. Or, to taste, just leave the LFOs non-synched and let the human do it.

[LOTUS]

 I beg to differ on this pedal not being that special. After upgrading the opamps and leaving 1 alone, and upgrading some caps and input resistor, and adding 2 toggle-switch activated mods, this pedal  super  :icon_mrgreen:rocks.