Ross Phaser built...

[Fp-www.Tonepad.com]

Ok, so I finally did the offboard wiring of my Ross Phaser. I had all the components soldered in for weeks!

And it works. It's nice, I've built it stock but I plan on adding the phase filter switch to hear what that's about.

Now, I have a question:
The RATE pot is definitely a reverse log (I ordered a few from Small Bear ) it works nicely in all it's rotation.

BUT the REGEN pot is kind of 'weird' in it's behavior (I used reverse log on this one too): First, it's wired like a volume pot, so it makes rev-log kind of odd in that position. Then it's effect on the sound is subtle but noticeble (I'm talking both 'ends' of the pot travel).

I have only tried the pedal by itself connected to the soundcard.

Can someone take a look at the REGEN portion of the circuit and help me figure it out? (I mean how the pot works and what taper should be best)

Thanks!
Fp

[dubs]

I have an original ross phaser I could take a look but don't know how to pull the knobs off, they are fixed on tight!!

[Samuel]

There's an article bout that at www.runoffgroove.com

[Fp-www.Tonepad.com]

Thanks!

Keep in mind I'm talking about the one that uses LM13600 ICs (schematic is found at runoffgrove, and tonepad)

Any info on actual unit's pot taper would be great!

It's more a 'small stone' kind of circuit... I haven't studied it enough to figure it out, but I did the redraw and layout... Damn, it's been a while.

Fp

[Boofhead]

The original schematic for the Smallstone like Ross phaser is on the runoffgroove site.  It shows two 500k R/A (Reverse Audio) pots, based on that it matches your build.

[Fp-www.Tonepad.com]

Yes, I know it says two 500 reverse audio pots. It just doesn't feel right...

I'll figure this one out myself.

Fp

[J. Luja]

with that 27k tapering resistor it looks like it should be a linear pot for regen. otherwise you'll have an extreme taper like what you're describing

-Jeremy

[Mark Hammer]

A standard audio taper should be fine for regeneration, and the taper of the speed/rate pot really depends on what speeds you tend to use it at most.  Remember, the taper has no bearing on whether it *works* or not; it just helps you to be able to dial in the settings you want with greater or lesser resolution (i.e., amount of change per unit rotation).  Some folks prefer to have fine degrees of control over the slowest speeds and rarely use the more "bubbly" settings.  Others use only variations of bubbly and hardly ever use the slowest sweep speeds.  Still others simply go back and forth between slowest and fastest.  Ideal taper will depend on which you are.  

Since rate is set by the pot acting as variable resistor and a fixed resistor to set a minimum resistance. those wishing to dial in speeds with greater precision might want to consider using a 250k pot and 270k fixed resistor to replace the original pot.  Shunt the resistor and you get one end of the sweep range (but with more degrees of pot rotation to adjust with).  Engage the resistor and you get the other end of the speed range.

Fundamentally, the "problem" of pot taper is a question of having too much change cramped into too little pot rotation.  With the exception of wahs, where you need specific tapers because you have to cover the whole range, pot rotation/taper issues can often be handily sidestepped by splitting up the whole control range into a few chunks, using fixed resistors and toggle switches.

Personally, I haven't gotten mine working yet.  I think I'm going to have to make another board and use only *new* components this time.

[mattv]

I really like the LFO on that Phaser. With the speed knob all the way down, you can actually still hear phasing. With my DOD, the phasing all but disappears.
I'm trying to figure out why that is.. :?

[Fp-www.Tonepad.com]

Thanks for the replies,

Jeremy, I thought about that also, but that's the way it's shown on the original schematic. The taper IS indeed extreme, more like a 'switch' than a transition... then again, the effect of the regen pot is not that noticeable at low speeds.

Mark, I thought about the audio taper for regeneration, but I wanted to follow the original schem (a mistake obviously). Now imagine what I got when I put the reverse audio instead of the audio pot in there!... a very useless taper. I will try linear and log to see which one does the job best... That 27k resistor across pins3&2 is still bothering me.

The rate pot is perfect for me as Rev-Log, it changes nicely all over it's rotation, but I think that a linear pot could also be used and still have acceptable results.

Matt, I like the LFO also, I'll be releasing a pdf with the 'lfo only' part of the ckt one of these days.

Fp

ps: I just noticed I hadn't uploaded the very latest version of the pdf, please download it here http://www.tonepad.com/getFileInfo.asp?id=47