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Vintage threads from the first ten years

Pearl Phaser

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4/25/2000 4:11 PM
GFR	Pearl Phaser http://www.mif.pg.gda.pl/tmp/tom/files/PH-03.gif Any idea on what's inside IC4 ? Also what's the circuitry from IC4 pins 8-9 to IC4 pin 14 ? And what about the "lambda diode" D4?

4/25/2000 4:43 PM
peter	at least part of IC4 is providing the varying resistance that gives you the phase shift, where it is connected to the RC and op-amp stages in the signal chain. the rest of this looks pretty mysterious!

4/25/2000 5:04 PM
Mike I.	Checked my CMOS manual and the CD4069 hex inverter chip has the same connections as the mystery IC4. The CD4069 was used in the Aria PS-10 phaser as a hex voltage-controlled resistor. Apparently the CD4049 was used in the Electroharmonix Bad Stone phaser in a similar manner. Try it out! Mike I.

4/25/2000 7:14 PM

My first guess was a CMOS hex inverter but

1) pin 7 goes to the LFO and
2) pin 14 goes to a comparator + transistor inverter + capacitor load from pins 8&9.
3) No pin to ground or Vcc.

On the Bad stone pin 8 goes to ground and pin 16 goes to B+ plus LFO, together with some other pins.

4) The controlled resistance pins go to a "B1" voltage through some very big resistors (220K) and
5) also have some very big resistors in parallel (680K).

On the bad stone there's a smaller resistor (27K) going to ground.

On the bad stone it looks like the "bottom" mosfet of each inverter is used as a variable resistance (Rds) by varying each Vgs while the "top" mosfet is off.

Maybe it's cmos inverters, but then they're working differently from the Bad Stone. I'll also take a look at the ETI cmos phaser (it only uses cmos inverters) to see if it's similar.

4/25/2000 11:38 PM

Just took a look at the ETI schematic (CD4049) and my partial Aria PS-10 6-stage phaser (CD4069) schematic. The PS-10 looks like this: 470K resistors on each inverter input going to V+/2 reference. Vdd (pin 14) also goes to V+/2. 470K in series with 0.001 uF from output to input of each inverter. The inverter outputs go to corresponding allpass op amp (+) inputs. There is a bias trimpot which is adjusted to +2.66V on the unit I opened up. There is a 1M resistor connected to the trimpot wiper. The output of each inverter also has a 470K resistor going to the other end of this 1M resistor. Pin 7 (Vss) also goes to this point. There is a 0.1 uF bypass capacitor attached here as well. The triangle LFO circuit oscillates between +4V and +7V . The wiper of the LFO depth pot is connected through a 2M2 resistor to the same end of the 1M resistor where all the 470K resistors are connected. The voltage at this point oscillates between +2.9V to +3.4V with the depth at max.

The Pearl circuit has some resemblance to this, but certainly does look different than the other units too. What is very curious is the function of op amp IC5 and transistor Q2. I am guessing that this is what is going on: IC4 pins 8,9 (inverter input and output shorted - if it is a CD4069) are connected to the (+) input of the op amp. The transistor inverts the signal coming out of the op amp and adjusts the pin 14 voltage (Vdd) so the voltage at IC4 pins 8,9 equals the B1 voltage. The LFO and manual control voltages are applied to IC4 pin 7 (Vss) after being summed in another op amp (the other half of the IC5 dual). Another mystery: are IC4 pins 5, 6 left unconnected? If this was a CD4069, that would not be a good thing to do... By the way, is this a good-sounding phaser? Mike

4/26/2000 10:08 AM
Jered	Does this phaser sound good? I'm kind of curious because I've got a Pearl Flanger that sounds terrible. I could have the bottom of the line though. Take care, Jered

4/26/2000 12:16 PM

quote:
"By the way, is this a good-sounding phaser?"

I don't know - I'm mostly curious.

Z Vex has posted this on Aron's forum:

quote:
"... pearl ph-44 (coolest phaser ever made... copy that, somebody), ..."

Maybe the PH-03 has some of this "coolness"

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