Introduction: Phaser Guitar Pedal

Picture of Phaser Guitar Pedal

A phaser guitar pedal is a guitar effect that splits a signal, send one path through the circuit cleanly and shifts the phase of the second. The two signals are then mixed back together and when out of phase, cancel each other out. This creates a sound somewhat akin to a flanger or an auto-wah.

This effect pedal first hit the scene very hard in the 1970s and added a special brand of outerspaciness to a pretty funky decade. Looking to revive this original vintage sound, I have built a classic 4-stage phaser. This particular pedal is pretty basic and allows you to adjust depth and the rate of the phasing. While the controls are rather bare, you can still dial it in to produce a subtle fullness to the guitar, or crank the dials all the way up for full-on slippery sounding funk.

Step 1: Materials

Picture of Materials

(x5) LM741 (RadioShack #276-007)
(x4) 2N5457 FET (RadioShack #55050922 - online only)
(x3) 2N3904 transistor (RadioShack #276-2016)
(x1) 100K trim potentiometer (RadioShack #271-0284)
(x1) General purpose PCB (RadioShack #276-150)
(x1) ON/OFF pushbutton (RadioShack #55050535 - online only)
(x2) Aluminum knobs (RadioShack #55048882 - online only)
(x2) 50K potentiometers (RadioShack #271-1716)
(x2) 510K resistors (RadioShack #55049227 -online only)
(x1) 390K resistor (RadioShack #55049555 - online only)
(x2) 150K resistors (RadioShack #55049550 - online only)
(x11) 100K resistors (RadioShack #271-1347)
(x1) 47K resistors (RadioShack #271-1342)
(x1) 43K resistor (RadioShack #55050326 - online only)
(x4) 22K resistors (RadioShack #271-1128)
(x2) 10K resistors (RadioShack #271-006)
(x1) 5.1K resistor (RadioShack #55048038 - online only)
(x2) 2.2K resistors (RadioShack #271-1325)
(x1) 220uF capacitor (RadioShack #272-1029)
(x1) 22uF capacitor (RadioShack #55047796 - online only)
(x1) 10uF capacitor (RadioShack #55047762 - online only)
(x1) 0.33uF capacitor (RadioShack #55047258 - online only)
(x3) 0.15uF capacitors (RadioShack #55047730 - online only)
(x1) 0.022uF capacitor (RadioShack #272-1066)
(x4) 0.01uF capacitors (RadioShack #272-131)
(x1) 0.001uF capacitor (RadioShack #55046626 - online only)
(x1) 7.5V Zener Diode (RadioShack #55051160 - online only)
(x2) Stereo audio jacks (RadioShack #274-312)
(x1) 9V battery snap (RadioShack #270-324)
(x1) 9V battery (RadioShack #23-2211)
(x1) BB-sized enclosure

Step 2: Phaser Schematic

Picture of Phaser Schematic

Build the circuit as specified in the schematic. Do not worry about the potentiometers, audio jacks, or toggle switch for the time being. These will be installed later.

Keep in mind that you are squeezing a lot of components into a small space, so lay the parts out and plan carefully before you begin soldering.

About the Circuit

While this may seem like a very large mess of analog electronics, the circuit is somewhat simple.

The guitar signal first enters through a preamp stage. It is then split such that the clean signal goes straight to the output jack and the signal to be phase shifted goes to a series of 4 LM741 op-amps that form an all-pass filter. This filter is essentially what shifts the phase based on the signal from the LFO (low frequency oscillator).

The LFO is comprised of the 5th LM741 op-amp in the circuit (and surrounding circuitry). The rate of the LFO is controlled by a 50K potentiometer. The LFO then provides a CV (control voltage) to the all-pass filter by way of the 2N5457 FETs. This modulation then causes the signal in the filter to shift phase at the rate of the LFO.

The audio signal from the all-pass filter then goes to the foot switch. If the switch is open, only the clean signal makes it to the output jack. If the switch is closed the phase shifted signal is allowed to pass through to the output and get mixed with the clean signal. However, before the altered signal gets mixed in with the clean signal it passes through a 50K potentiometer which determines how much of the signals get mixed together.

From there, it goes out to the amp and the rest is history.

Step 3: Attach Wire

Picture of Attach Wire

Attach 6" wires for the two potentiometer connections to the circuit board.

Also, connect 6" wires to the circuit board for the audio jacks.

Finally, connect the red power wire from the power jack to the appropriate place on the circuit board.

Step 4: Guitar Pedal Template

Picture of Guitar Pedal Template

Print out and afix the attached template to the the outside of the guitar pedal closure in preperation for drilling.

Step 5: Drill

Picture of Drill

Drill 9/32" holes for each of the potentiometers.

Drill a 1/2" hole to house the foto switch.

Drill a 3/8" hole for each audio jack.

Step 6: Insulate the Case

Picture of Insulate the Case

Cut out a 1/8" sheet of cork using the attached template.

Apply spray adhesive to one side of the cork and stick it to the inside of the enclosure's lid.

Step 7: Rubber

Picture of Rubber

Cut a rubber spacer out of 1/8" thick adhesive rubber sheeting using the attached template.

Attach the rubber spacer to the inside of the enclosure where the potentiometer mounting holes are.

Step 8: Install

Picture of Install

Mount the potentiometers and foot switch in their respective mounting holes.

Step 9: Wire It Up

Picture of Wire It Up

Wire the circuit board to the audio jacks, potentiometers, foot switch and the 9V battery snap as defined in the schematic.

Step 10: Audio

Picture of Audio

Mount the audio jacks into the body of the case.

Step 11: Power

Picture of Power

Connect the battery to the 9V battery snap.

Step 12: Close the Case

Picture of Close the Case

Close the enclosure using the appropriate hardware.

Step 13: Knobs

Picture of Knobs

Press the knobs onto the potentiometer shaft.

Step 14: Plug and Play

Picture of Plug and Play

Plug the guitar into the audio-in jack and the amp into the audio out jack.

You should now be ready to rock out.

Comments

Irbis777 (author)2017-10-04

Hello!

I am about to built this pedal and your tutorial is very helpful. Thank you so much!! I was wondering why do we put a 100K pot rather than just a usual resistor? We are not going to change this setting anyway. Also, what setting are we meant to put it on?

Thanks!

herikkkkk (author)2017-09-06

Hey buddy. i'm builded the circuit exactly like your schematic says, however, the phaser effect didn't work. The voltage on the capacitors (lm741)are around in milivolts, instead 9v or higher. Can you tell me what can i do to fix this problem?

Sorry for my english.

Thanks.

herikkkkk made it! (author)herikkkkk2017-09-06

here

randofo (author)herikkkkk2017-09-13

The schematic is a bit labeled wrong.

From an earlier comment:

I think
I found the potential culprit. The "154" caps are labeled 0.01uF. They
should be 0.15uF. Try changing those and see if it fixes things.

herikkkkk (author)randofo2017-09-14

I switched the capacitors and still doesn't work. The voltage on the capacitors are around 3-5 V. By the way, which is the voltage on the LFO ?

randofo (author)herikkkkk2017-09-09

Maybe you mixed up the polarity or forgot to ground a capacitor? It is hard to tell just be looking at a picture. Have you double and triple checked all of your connections? there could be a bad solder joint.

Did you try building the circuit on a breadboard first to make sure it works?

herikkkkk (author)randofo2017-09-13

I built the circuit in the breadboard and it's having the same problem, the output signal that passes through is the original one, either if the pushbuttom is open or close. The delayed phase signal isn't mixed up with the original.

iann245 (author)2017-03-30

The output jack has only one wire conected??

MartijnS9 (author)iann2452017-04-10

No, the tip should be connected to the wire as mentioned, the sleeve should be wired to ground.

espguitarist33 (author)2017-03-22

What is the recommended wattage on the 7.5v zener diode? I'm having issues sourcing one through radioshack (likely due to their restructure sale), and am turning to amazon (they are also not common on any of the component sites I've been looking at)

randofo (author)espguitarist332017-03-22

What ratings are you finding? It probably does not to be very much.

espguitarist33 (author)randofo2017-03-26

Additionally, I don't think I see any instructions for adjusting the trimpot. Am I missing them?

espguitarist33 (author)randofo2017-03-22

Thanks for the reply! I found a 7.5V .5w Zener for about $1.75 and free shipping, so I'm going to order a handful of those if they are stout enough for this application.

prsteve27 (author)2017-03-18

What do you use to create the graphical schematic? I really like the look and readability of it, and would like to be able to make my own. Thanks!

randofo (author)prsteve272017-03-19

I custom draw each one in Adobe Illustrator. It's not exactly the fastest way, but at this point I have generated a lot of different component graphics I can copy and paste from one to the next.

prsteve27 (author)randofo2017-03-20

Luckily illustrator is something I already know how to use... ??

prsteve27 (author)randofo2017-03-20

Good to know - thank you!

MartijnS9 (author)2017-01-01

Just a quick question: the 5th op-amp, in the bottom right, is connected with some green wires in the schedule. Some greens cross each other but it seems odd to have them connected with each other, am I right?

RodB1 (author)2015-09-25

It didn't work. I was never able to get the 510k Res. And, what's with
the video? It doesn't even show the pedal working. It'd be nice if there
was a detailed explanation on the schematic.

gary909 (author)2015-08-29

BOM

x1 9v Battery Holder

x2 Audio Jack

x2 50k Pot

x1 100k Trim Pot

x1 SPST Switch

x2 2.2k Res

x1 5.1k Res

x2 10k Res

x4 22k Res

x1 43k Res

x1 47k Res

x11 100k Res

x2 150k Res

x1 390k Res

x2 510k Res

x7 .01uF Cap

x1 .001uF Cap

x1 .22uF Cap

x1 .33uF Cap

x1 10uF Cap

x1 22uF Cap

x1 220uF Cap

x1 7.5v Zener Diode

x3 2N3904 Trans

x4 2N5457 Trans

x5 LM741 Op-Amp

RodB1 (author)gary9092015-09-22

the .22uF Cap is actually .022uF

gary909 (author)2015-08-29

Any idea what I could use for the Zener Diode?

glayvin34 (author)2015-03-15

I'm not an engineer but I've been messing with this circuit on a breadboard for several Sundays now and though I've set it up according to the diagram above (except for those slightly mislabled capacitors), it doesn't seem to work for me. Currently I'm trying to just test the preamp stage (ignoring the filter and oscillator stages for now) because it doesn't pass a signal from my guitar to the amp even when the SPST is open. I tried passing a prerecorded song through the preamp and still got nothing, but if I disconnected the 100k Resistor between base and ground and the .001 uF capacitor between base and ground some drums came through.

I looked at other NPN amps that use a 2N3904 around the web and I found this one:

http://hackaweek.com/hacks/?p=327

It's set up completely different from the one above but I connected it on my breadboard and it works great to make the guitar signal louder on its way to the amp, using the same 2N3904 that barely passed drums with the preamp above, so I'm pretty sure I set everything up correctly.

Also, why is the output jack not grounded? My amp picks up local radio stations and buzzes like it's going to explode unless I ground the output jack on any effects between the amp and guitar.

Like I said, I'm not an engineer so I have no idea what I could be doing wrong, if anyone has any pointers or sees anything obvious from my description please give a shout. Has anyone else built this circuit? Had any issues?

randofo (author)glayvin342015-05-04

The output should be grounded. The case is metal, so it makes the ground connection without a wire, so I didn't draw it in.

I am not able to tell what is wrong based on your description. Do you have any pictures?

randofo (author)randofo2015-05-04

I think I found the potential culprit. The "154" caps are labeled 0.01uF. They should be 0.15uF. Try changing those and see if it fixes things.

glayvin34 (author)randofo2015-05-10

Awesome, thanks so much for getting back to me!

I replaced those caps and now signal is definitely getting through (and some Spanish radio stations), the guitar comes through undistorted. However, the phaser effect isn't working, the guitar sounds the same in both positions of the switch.

I'll keep looking for shorts, but if you can make any sense out of these pics that would be awesome, I understand if it's too hard to tell what's going on. The colored rails test at the appropriate voltages (or within 0.2V) compared to ground, I'm not really sure how else to test or analyze to circuit to figure out what's wrong.

Svennibus (author)glayvin342015-05-04

I am having the same issue as you. I cannot get my guitar signal to come through the output. Have you figured it out?

gprimbo (author)2015-05-07

will it work with the UA741 opamp instead of lm741? (what ua means?)

tmackabuto231 (author)2015-03-20

Around what frequency is the LFO producing?

johnh27 (author)2015-01-18

Could someone tell me about the voltage of every capacitor or doen't matter?

glayvin34 (author)johnh272015-03-15

You want capacitors with a voltage rating greater than that of the circuit. I'm not terribly knowledgeable in these matters but this circuit is powered by 9 volts, so you'll want capacitors with a voltage rating greater than that.

Most capacitors have a rating greater than 25V so you should be good with what you have for a 9V circuit.

More knowledge:

http://www.learningaboutelectronics.com/Articles/What-does-the-voltage-rating-on-a-capacitor-mean

djfrizz (author)2014-12-01

In regards to the parts, when people list the pots for projects and link them to RS's site, the ones on the Shack have long shafts. Are you (and/or others) just showing the general specs for the pots? The shafts would be too long to use in the case, or at least it looks that way. I used to think that people were cutting down the shafts, or am I missing something on the RS site?

Kevin_Minckler (author)2014-06-19

The LM747 isn't the best choiceof an op-amp for audio applications. A much lower noise alternative would be an OP27. http://www.analog.com/static/imported-files/data_sheets/OP27.pdf

ckgarside (author)Kevin_Minckler2014-09-29

Can you swap the LM747's for OP27's without any other modifications to the circuit?

Kevin_Minckler (author)ckgarside2014-09-30

Well, first of all I meant LM741 not LM747. The LM741 is a single amp vs the LM747 which is a dual. The OP27 is a single vs a OP270 which is a dual. The trim or offset null pins are not the same, but the rest of the pins are for the single amp parts. You would want to download the spec sheets. and match up the pins appropriately. You could switch to the dual to reduce chip count from 4 to 2. Even better would be to use an OP470 quad op amp and you could do all it with one chip. See http://www.analog.com/en/all-operational-amplifiers-op-amps/operational-amplifiers-op-amps/op470/products/product.html

LucaC2 (author)2014-09-10

May I have a video in which I can hear this pedal working? And, also, a schematic "on board"?

wkopacz (author)2014-07-14

Will this work with tube amps?

nursetom61 (author)2014-06-22

In your instructable you say to print out template. I have looked everywhere in this instructable but can not find any template. Is it on a different page or web site? Thanks in advance for your help

jefferdomd (author)2014-06-22

Buddy!! can i use an DC Line to power up this thing!! :)

BTW Nice Work!!! And I love your demonstration videos too!! ;)

Wingloader (author)2014-06-20

I am going to build this baby! Not because I need it, but because it will look so cool when I enclose it in clear acrylic! And say to my buddies, Yea, I made this up on a napkin when I was drunk one night... NOT.

Are you an engineer?

randofo (author)Wingloader2014-06-20

No. Not an engineer. I have just been messing around with this stuff for a while.

Gerard50 (author)2014-06-19

Hi,

Do you have a schematic diagram for this project?

Regards

Gerard

gavinjackson (author)Gerard502014-06-20

Theres a diagram shown in Stage 2
If you can't see the bottom of it, click on it and it shows a fuller complete diagram.

GJ

randofo (author)Gerard502014-06-19

See Step 2

anetprophet (author)2014-06-19

Great project... what was the total cost of goods on the components you used to make this? Thanks!

randofo (author)anetprophet2014-06-19

Not sure. I would say it could be made for around $50.

NEIN (author)2014-06-19

Good parts list, and nice schematic, but it would be ideal to have:

1) Better photos (top down) of each step of building the board for those that can not follow schematics.

2) A sample of what the effect sounds like.

Great work though. I'll be building one shortly, and if all goes well, I might run a class at my local hackspace.

Momo4895 (author)2014-06-18

where do you buy your enclosures, do you paint them yourself?

randofo (author)Momo48952014-06-19
sonicase (author)2014-06-18

:/ it's not true bypass,..i don't think it would be too hard to make it true bypass though, and you could add an LED to tell when it's on too

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