From:
        
        Leo Bloom
   Date:
        4/27/2001 12:06 AM
 Subject:
        Who understands the Anderton phaser (Help me tweak/fix?)



O.K, I finally accumulated enough "floor sweeping" components to try the phase shifter project from the old EPFM book by Craig Anderton.

I built it, and it works. To use Microsoft Windows terminology, no "Catasrophic Errors."

Anyway, it's not as intense as I expected. I'm gettings some cool swooshiness, but it's much less pronounced than my ol' Phase 90 -- it sounds more
like a mild Phase 45 (NOTE: Anderton writes that this is pretty much a 180 degree phase shifter.) Also, both the Vibrato and the Subtract (a.k.a.
auto-wah) modes are really weak when engaged. 

Is it because I used VTL5C3's instead of CLM600's (or '6000's)? I've seen in several places that the VTL5C3 is a direct replacement, but after
looking at the spec sheets myself the 40ma "on" resistance of the VTL5C3 is 1,500 ohms (off: 10M), and the 20ma "on" resistance of the CLM600
is reported as being only 500 ohms (off: 500k). Clearly, there are some differences.

Any suggestions on how to juice this phaser up? I was thinking that I should lower the four 470K resistors in parallel with the LDR portion of the
vactrols to make up for the difference in the on resistances of the CLM vs. VTL. Does that make sense? 


  From:
        
        ETH
   Date:
        4/27/2001 3:44 AM
 Subject:
        Re: Who understands the Anderton phaser (Help me tweak/fix?)



If you know what the resistance range difference is between the clm600 and the vtl that you used... You might want to start there. Try this

(on resistance of CLM600)* .01 = (on resistance of vtl)* X

X is the new cap value

that may work for ya.

Lowering the value of the 470k paralell resistor will only limit the range more as the combination will make the ldr less effective. This resistor keeps
things quiet(Blocking). 


  From:
        
        Gino   (giorfida@drifteramps.com)
   Date:
        4/27/2001 9:21 AM
 Subject:
        Re: Who understands the Anderton phaser (Help me tweak/fix?)



After a few of the parts I orderd and are on backorder arrive, I'm going to tackle one of these. Someone toled me, when set up right, you can get
amazingly close to a UniVibe with one of these (which when you compare the schematics, they really aint much different, except the use of
opamps vs discrete transistors. I"ll post my results when I'm done., though, as well as some tweaks I"m sure I'll ahve to do. I"m going to use
discrete LDR's and going to try both LED and incandescant lights as drivers for the LDR's to see if I can hear any difference (technically, I
SHOULDNT hear any difference, however from the way I understand it, LED"s turn on in pretty much a linear fashion, while the intensity of an
incandescant bulb provides more of a logarithmic transition.. so we'll see... 


  From:
        
        Mark Hammer   (mhammer@ccs.carleton.ca)
   Date:
        4/28/2001 3:48 PM
 Subject:
        Re: Who understands the Anderton phaser (Help me tweak/fix?)



Both the CLM6000 and VTL5C3 contains LED's which: 
a) need to be oriented correctly to conduct and shine on the LDR,
b) can burn out if overheated during soldering.

The phase may be milder than expected because the identifying dot on the LED/LDR unit was misidentified, or perhaps you burnt one or more out
when installing them. Not likely, but possible.

A good strategy is to set the LFO for a very slow sweep and measure the change in resistance of each of the LDR sections with a meter. If some
of the LDR's are swinging over a much wider resistance range than others, that may be your problem.

Another factor is that maximum notch depth is helped along by having the caps and resistors that determine the frequency at which phase shift is
occurring well-matched. Some folks think that maximum notch depth is not essential to what makes a phaser sound interesting (that one is for you
Mike), but it is worth considering. Are the caps you used reasonably well-matched?

Finally, no one has said anything about the power supply in all of this. Do you have enough juice to produce sufficient current for the LED's? If you
are trying to run it off 2 nine-volt batteries, that may well be your problem. 


  From:
        
        Leo Bloom
   Date:
        4/29/2001 4:06 PM
 Subject:
        Why this forum is great - I'm now swirlin' and twirlin'



ETH's cap switching trick seems to have done it, although I may tinker some more (FYI, Mark--right now I'm running it with a dual 12-volt power
supply, 8 AA's per side; I already checked the resistance changes using a meter, and the four LDR's behaved in a surprisingly consistant manner).

The CLM and VTL data sheets don't provide for straight-ahead comparison of on-resistances (they used differing currents to generate spec sheet
data). So, I had to do some work. I even plotted some current vs. on-resistance charts, used some nasty math to play connect-the-dots, etc. 

Anyway, I used my crude charts and ETH's algebra lesson and figured that the new caps should be roughly between 0.0017 - 0.0025 uF. 

I dropped in four 0.0022's, and it now seems to be doing it's thing the way it's supposed to.

I'm going to tinker some more, and I'll report back with recommendations for using VTL's in this project when I'm 100% convinced it's howlin' like
it should.

*But*, I'm quite impressed so far. I built it because I wanted a nice versatile phaser -- and it is! The auto-wah function, however, is really solid (and
I don't usually like auto-wahs). The Resonance control lets you dial in some throaty nastiness -- and nastiness is usually missing in auto-wahs I've
tried. I haven't tinkered enough with the Vibrato option, which seems to be a little harder to dial in to an effective setting (could be the VTL
discrepancy again?). It is giving an audible, true vibrato (e.g. not tremolo), though. 

Thanks guys! I can't believe how much time this forum has saved me -- with this project and with others. 


  From:
        
        Steve A.   (steve_ahola@yahoo.com)
   Date:
        4/29/2001 5:35 PM
 Subject:
        Re: Why this forum is great - I'm now swirlin' and twirlin'



Leo:

The auto-wah function, however, is really solid (and I don't usually like auto-wahs). 

    Are you referring to the LFO function or the envelope follower? This project is way cool when you wire it up to his EF... Having the phasing
effect triggered by your playing dynamics is refreshingly different from the Mutron/EF filter effects...

--Thanks for your notes on converting the circuit over to VTL's!

Steve Ahola