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Vintage threads from the first ten years

Re: Pearl Phaser

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4/30/2000 11:06 AM
peer b	Re: Pearl Phaser I have a Ph 44 phaser -and I would not say its the best ever -there's MXR 90 and The Biphase-and these are classics. But the 44 is absolutely killer: very silent and extremely tweaklable- very cool sounds! Unfortunately the ph 03 is nothing like it, in sound nor tweakability...

5/8/2000 9:58 AM

I've got a pearl phaser,the PH-03 one.I think its a really good sounding phaser,the manual control is a good idea on the phaser,I wonder why more manufacturers dont put one on.

The only thing I dont like about it is that it sounds a bit too muddy.Is there any way to tweak it to make it a bit brighter.I put this question up a few months ago but got no reply.

I'd love to get hold of the PH-44 phaser,what extra controls does it have?

Matt

5/8/2000 6:00 PM

After talking with Mike Irwin about his recent experiments (this is a guy that LOVES phasers, and probably has more of them than Aron Nelson has fuzzes), it occurs to me that Pearl may have made a conscious choice to tame the high end of the PH-03 as a way of removing some of the distortion. The 4049, or any inverter or FET for that matter, tends to introduce a little bit of unsavoury distortion, because it can't handle a lot of signal.

Alternatively, they may just have made some poor choices with respect to op-amp choice. What's in there?

5/10/2000 12:34 PM
matt	Thanks for replying Mark, Had a look inside my Pearl phaser and it has the following: 2 x TL022 2 x TL062 (these are all Texas inst.) JRC 4558 The main IC has been scrubbed out, but only with black texta,holding it to sunlight I could see what was written: Motorola IC MC14069U(?)B CP J8132 As a start,For the TL062 maybe swapping for the TL072,am I right in saying these are better ICs Matt

5/10/2000 5:23 PM

To the best of my knowledge (which is VERY limited), the chip choices made by Pearl in this case seem to be driven more by current consumption than by noise. The 062 and 022 are low current versions. While they certainly extend battery life, they tend to be noisier than their 072 cousins. Of course, subbing 072's for 062's will reduce battery life. The more knowledgeable types here could probably tell you if the 072 would present any unique difficulties in this context, but in general, the 072<->062 tradeoff is one of current vs noise.

The Motorola chip is an unbuffered hex inverter, similar to a 4049. It is being used here as a voltage-controlled resistor. Given the number of op-amps listed, it seems like there are enough for 6 stages of phase shift - what the 4069 is capable of assisting.

Between the inherent tendency for distortion and noise provided by the 4069 (they can't take signals levels like an LDR can, but in their defense they come already matched, which is more than one can say for LDR's and individual FET's), and the extra hiss provided by the low power chips, my hunch - unsubstantiated, mind you - is that Pearl probably has some grit-n'-hiss-taming capacitors strategically positioned in the design, resulting in less high end, as per your perceptions.

"Fixing" this would likely mean identifying those caps where the value seems especially high, then swapping op-amps and changing the caps for smaller values. Likely places to look would be the last phase-shift stage before the mixer stage, and the mixer stage itself, since these are pivot points where a single cap can exercise a lot of control. For example, if the mixer stage used a 100k feedback resistor, in parallel with a 500pf cap, you'd have a rolloff at a little over 3khz. No hiss, but very little "air".

5/14/2000 12:28 PM
matt	After talking to one of my friends who knows a lot more on than I do,we came to the conclusion that maybe c21(1nf) maybe the culprit,and possibly r22(56k),coming out of one of the op-amps.Going to play around with it tomorrow,and I'll post the results up. Matt

4/26/2000 12:42 PM

quote:
"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."

I've thought of the following:

IC5 is wired as a comparator, then to a transistor inverter with a big capacitive load - so maybe a portion of IC4, IC5, Q2 and C11 work as an oscillator, with the pulse width modulated by the LFO, so varying the "average" resistance at the all-pass stages. ???

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