How to increase the volume of a phase 90?

[haveyouseenhim]

I built a phase 90 from the tonepad layout for a friend of mine and he says that when engaged there is a volume drop. I looked at the schematic to see if there was a fixed voltage divider and saw this.



I wouldn't even know where to start.   Should I try a buffer at the end? Or even a boost after the phase 90?

[wavley]

This is a good place to start, it's PRR's answer for the Phase 45, worked great on mine.

The P-45 opamps have some grunt to spare. Change some 10K to 1K-2K. This gives a good near-600-ohm output. Change-up the output cap to be sure of driving heavy loads well.

[Mark Hammer]

How much of a volume drop?

Keep in mind that the P90 attempts to be unity gain, but most folks are going to build them with 5% resistors, so it is quite possible for there to be small volume differences because some parts are under-spec and others are over.

Also keep in mind that if one attempts to produce notches in what tries to be a unity-gain signal, what comes out is going to be a bit quieter than what went in.

One way to "fix" it is to insert a tinybit of gain in the inpt stage instead of it being a unity-gain buffer.  This can result in easy distortion of the JFETs, though, depending on the amplitude of the signal your friend feeds into the pedal (if the input signal to the P90 is already boosted in some manner, this change is contraindicated).

All of the above said, however, I'm assuming that someone better informed about transistors than I can suggestone or two resistor changes in the transistor mixer/output stage that might add a little gain.

[Mark Hammer]

This is a good place to start, it's PRR's answer for the Phase 45, worked great on mine.

The P-45 opamps have some grunt to spare. Change some 10K to 1K-2K. This gives a good near-600-ohm output. Change-up the output cap to be sure of driving heavy loads well.

The P45 has a network around each JFET that raises the threshold for distortion, so they can afford inserting a little gain.  The P90 has no such protection.  I would be reluctant to port the "fix" for the one over to the other.

[haveyouseenhim]

I'm a huge dummy! (as most of you know)     Right on the tonepad page it tells you how.

''The resistor to change the level is the 150k which connects between the collector and base of the PNP transistor: 120k to reduce gain, 180k to increase it."

[Govmnt_Lacky]

I small a 250K pot going into a pedal...... 

[sugonidamaso]

I small a 250K pot going into a pedal...... 

Sorry, noob here. How do I put the 250k pot? Thank you!

[Mark Hammer]

In the "back" of the 2N4125 (or whatever PNP you are using for your output stage) you will see a 150k resistor that also makes contact with one end of a 56k resistor and .05 (.047) cap.

Remove that resistor.  Run a wire out from each of the solder pads where it used to be.

Although a 250k pot is not unreasonable, it is also kind of overkill.  What we'll do is solder a 100k fixed resistor to one lug of a 100k pot.  One of the wires coming from the board will go to the free end of that 100k resistor.  The other wire will go to the next lug over on the pot.  This will let you adjust the gain of that stage from a usable amount less than the stock gain  (100k resistor + zero ohms from pot) to a usable amount more than the stock gain (100k + 100k).  The pedal will then be useful for phased soloing ( combined resistance > 150k), or for background phased rhythm strumming (combined resistance < 150k).

[Govmnt_Lacky]

Good idea Mark!

Or.. if you have one.... you could go with a 200KB pot with no resistor 

More people would have the items that Mark suggests though 

[sugonidamaso]

In the "back" of the 2N4125 (or whatever PNP you are using for your output stage) you will see a 150k resistor that also makes contact with one end of a 56k resistor and .05 (.047) cap.

Remove that resistor.  Run a wire out from each of the solder pads where it used to be.

Although a 250k pot is not unreasonable, it is also kind of overkill.  What we'll do is solder a 100k fixed resistor to one lug of a 100k pot.  One of the wires coming from the board will go to the free end of that 100k resistor.  The other wire will go to the next lug over on the pot.  This will let you adjust the gain of that stage from a usable amount less than the stock gain  (100k resistor + zero ohms from pot) to a usable amount more than the stock gain (100k + 100k).  The pedal will then be useful for phased soloing ( combined resistance > 150k), or for background phased rhythm strumming (combined resistance < 150k).

WOW! Thank you so much Mr. Hammer! And to Mr Lacky