P90 Question (R28 mod)

[jayab]

Hi guys, I have a regular 2012 MXR P90 Phaser pedal and the high mid boost is irritating to me.  I will be doing the R28 mod where you break the feedback circuit but keeping my warranty would be nice too, so I don't really want to desolder the resistor from the board.  Couldn't I just short the circuit to ground with a wire after the resistor?  I asked this question somewhere else and a supposed "electronics tech" said it would be okay, but I want to be sure I don't fry anything.  So again I would be shorting the feedback circuit so that the extra signal boost would go to ground instead of back to the input amplifier.

Is this okay?

And if so, would it noticeably lower the amp input impedance?

Pics and more info (I hope links are okay here):
http://www.erikhansen.net/mxrphase90mods.php

Thanks.

[Mark Hammer]

Lift one end of R28 (assuming its through-hole parts).  You don't need to remove the whole thing.

[jayab]

Lift one end of R28 (assuming its through-hole parts).  You don't need to remove the whole thing.

I understand this is an option, but I'm wondering if shorting the feedback loop to ground before the amp would provide the same effect, so that I don't have to void my warranty.

Edit: in other words I want to avoid turning on the soldering iron.

[jayab]

I am going to try and describe the circuit I'm looking at on the board right now.

It begins at the amp (TL064CN) [U2], output 3 (pin eight). It runs up and connects to a 47nF capacitor [C9]; the circuit splits here.  

Continuing down the series after the capacitor (not through it) it goes to a 10k resistor. Then this resistor goes to another 10k resistor. From there it goes to meet a 24k resistor (R28, the one you normally snip). The other end of R28 goes to a 20k resistor. At the other end of that resistor there's another 47nF capacitor [C3]. After the capacitor is a 24k resistor [R25]... the circuit splits here too. It goes past the resistor into pin 3 (drain) of a 2N5952 transistor [Q3]. But going through the resistor instead goes to pin 2 (source) of another identical transistor [Q4].

Going through the capacitor instead after the amp, this goes to pin 10 of the amp [U2] (inputs 3).

I hope that helps. I'm not that great with this stuff - just took a couple classes in high school - so I don't know how much use that is to you.

Sorry maybe I should've drawn a schematic...
The link I gave above has some good pictures of the board. Here you can see some more (Ignore the fact that some are green and some are red, they are the same): http://stinkfoot.se/archives/975

TL064CN datasheet: http://www.futurlec.com/Linear/TL064CN.shtml

[Seljer]

Lift one end of R28 (assuming its through-hole parts).  You don't need to remove the whole thing.

I understand this is an option, but I'm wondering if shorting the feedback loop to ground before the amp would provide the same effect, so that I don't have to void my warranty.

Edit: in other words I want to avoid turning on the soldering iron.

You can always solder it back in.

Shorting R23 at either end would silence the wet signal chain, leaving you only with your dry phaser-less sound

[jayab]

Lift one end of R28 (assuming its through-hole parts).  You don't need to remove the whole thing.

I understand this is an option, but I'm wondering if shorting the feedback loop to ground before the amp would provide the same effect, so that I don't have to void my warranty.

Edit: in other words I want to avoid turning on the soldering iron.

You can always solder it back in.

Shorting R23 at either end would silence the wet signal chain, leaving you only with your dry phaser-less sound

Ah, darn. I guess I'll just try to be as neat as possible and hope it's not noticeable if I end up needing to put it back.
Thanks.

P.S. I assume you meant R28?

[Seljer]

Ah, darn. I guess I'll just try to be as neat as possible and hope it's not noticeable if I end up needing to put it back.
Thanks.

P.S. I assume you meant R28?

yeah, R28, my typing is awful when it's late

get a desoldering pump if you don't have one and actually desolder one end, no cutting, no nothing