please check, correct and upgrade my DIY parallel looper schematic

[Max999]

Hi guys, I have made a schematic for a parallel loop pedal. No level adjusts, just unity gain. The loop will be between R4 and R6.
R3/5/9 are to stop oscillations due to cable capacitance.

Please check, correct and upgrade my schematic. Any parts that I can omit ( possibly u4, the first buffer?)

Thank you!

[blackieNYC]

You could, really, drop U2 and U3. And just split the output of U4 with two 1 K resistors.

[Max999]

Thanks blackieNYC. The reason for me to put U2 and U3 there is to insure that when the pedal in the loop has a different input resistor than R7 the split will not be uneven. The inverting topology of U1 lso makes R7 the input impedance.
I always think of resistors as holes that the signal has to go through, and that it likes to take the easiest route ( biggest hole) when possible .. wrong?

[GGBB]

I would make U4 inverting, so that overall phase is maintained.

[Max999]

Thanks GGBB, but wouldn't that make the pedal have more resistor noise by putting a 1Meg in series with the input and one in the feedback loop?
Is there an improvement in sound by keeping things in overall phase in your experience?
The funny thing is that I am using a jmp2203( which inverts), so having an inverting pedal would actually put things in phase

[GGBB]

Thanks GGBB, but wouldn't that make the pedal have more resistor noise by putting a 1Meg in series with the input and one in the feedback loop?

If you use noisy resistors, maybe a little.

Is there an improvement in sound by keeping things in overall phase in your experience?
The funny thing is that I am using a jmp2203( which inverts), so having an inverting pedal would actually put things in phase

Potentially, yes. Some people can 'hear' phase. I can't. However, if you ever have to combine this signal in parallel with another, you'll wish it didn't invert phase. There are always ways to fix those problems, but if you can easily build it without phase inversion, why not.

[blackieNYC]

You might be right about the two buffers - without level trims you're trying to maintain balance. I'm not sure if that will really be a factor or not.


There's absolute phase (one audio channel), and there's relative phase (between two or more channels), which is the concern here. If you mix a pedal that inverts polarity with a straight signal that does not invert, you will cancel some audio starting with the bass. And vice versa.  The polarity reverser at Geofex will give you a switch.
Absolute phase of a pedal isn't really significant (okay, I'll say very significant so the thread doesn't derail) until you start mixing pedals together.  Then you are in relative phase territory.

There is a list of pedals that invert phase, and unfortunately it is surprisingly long. I did not compile this, its from the Gear Page:

in a parallel or stereo setup pedals that invert phase can be a real menace.
(depending on which side of the camp you populate it may or may not be an issue in a mono setup/rig)

either way, i thought it would be handy to list phase inverting pedals here as a reference.


i'll update this list as people add to it.............


note: i made a decision not to list pedals with wet/dry or stereo outs where the secondary output flips polarity while the primary output remains in phase.

why?....that list would be too long.

i WILL however list the pedals if the primary output flips polarity.




<<<<<<(all pedals invert signal only when engaged unless noted in red, blue, pink, purple, orange, green, gray, aqua, maroon)>>>>>>


boosts/overdrives/distortions/pre-amps:
Analogman KOT (each channel inverts independently)
Bad Bob Booster
Badger Badgerplex Vintage Pre (The Badgerplex Plural does NOT invert)
Boss DS-1
Boss OD-1
Catalinbread Super Chili Picoso
Cmatmods Super Signa Drive (each channel inverts independently)
Colorsound Overdriver/Power Boost (and clones of)
Danelectro Daddy-O Overdrive
Devi Ever Dark Boost
Devi Ever Karaoke Party
Electra Distortion
Electro Harmonix LPB
Fuchs Plush Pure Gain
Fulltone Fat Boost1 (FatB2 and FatB3 do NOT invert)
Henretta Engineering Choad Blaster
Ibanez SML Super Metal
Infanem STEP: (inversion depends on settings)
- 0 up = inverted phase
- 1+4 up = inverted phase
- 1+3 up = inverted phase
- 3+4 up = inverted phase
- (octave switch 3 likely inverts)
Kingsley Jester Overdrive/Boost (each channel inverts independently)
Legendary Tones (pre-Keeley) Time Machine Boost: Vintage channel inverts when engaged regardless of '66 or '73 setting. (Modern channel does NOT invert)
Lizard Legs Flying Dragon Boost
Lovepedal Amp Eleven (each channel inverts independently)
Lovepedal COT
Lovepedal Les Lius
Marshall Bluesbreaker OD
Menatone Dirty Blonde (6 knob knob version)
Menatone Fish Factory (each channel inverts independently)
Menatone Foxy Brown (4 knob jacks on top battery on side version)
Manatone Howie (6 knob version)
Menatone Red Snapper (4 knob red box, jacks on top version)
Menatone Shut Up And Drive
MI Audio Boost n Buff v1 and v2 (always inverted. inverts engaged AND bypassed)
MI Audio Tube Zone
OceanFX Pearl Drive
Seymour Duncan Twin Tube Classic (channel 1 inverted. channel 2 flips signal back to non-inverted when engaged)
Smallsound/Bigsound F**k Overdrive
Smallsound/Bigsound Mini
Smallsound/Bigsound Sparkle Motion
Skreddy Screw Driver
Soulsonicfx Hunny Bunny OD
Telenordia Treble Boost
Xotic BB plus (each channel inverts independently)
Xotic EP Booster
Zvex Super Hard On (and clones of)

ANY single transistor boost....


(general):
ANYTHING that has 1,3 (or any other odd number) inverting gain stage(s).....for example: Spencer Subzombie fuzz


compressors:
Earthquaker Devices The Warden Compressor
Mad Professor Forest Green Compressor
MXR Dynacomp
Okko Coca Comp

all Ross compressors,clones and variants invert: some examples.....
Analogman Bi-comp (only one channel inverts) (Ross side of the Bi-Comp inverts. Orange Squeezer side does NOT invert) (REV4 with blue circuit board does NOT invert)
Analogman CompRossor
BYOC 5 knob compressor
GoudieFX Compressor
Keeley Compressor
Retro-Sonic Compressor
Wampler Ego Compressor (compression signal inverts. clean blend does NOT invert)

delays:
Biyang AD-10 (only dry signal inverted, repeats are non-inverted)
Blackbox/Ooh La La Quicksilver
Danelectro Dan Echo (always inverted. inverts engaged AND bypassed)
Danelectro Fab Echo (always inverted. inverts engaged AND bypassed)
DLS Echo-Tap
DMB Lunar Echo
Electro Harmonix Deluxe Memory Man
Empress Super Delay / Vintage Modified
Ibanez AD-80 (always inverted. inverts engaged AND bypassed)
Lovepedal Echo Baby
Seymour Duncan Deja Vu (when true bypass: inverts when engaged / when buffered bypass: always inverted. inverts engaged AND bypassed)
SIB Blue Echodrive
TC Electronic Nova Delay


fuzz pedals:
Blackout Effectors Musket Fuzz (from Kyle @ blackout: "5 inverting gain stages, which results in flipped polarity")
Bluebird Fuzz
Colorsound Tonebender (and clones of)
Electronix MessDrive Hybrid
Fender Blender
Gretsch Controfuzz
Infanem STEP: (inversion depends on settings)
- 0 up = inverted phase
- 1+4 up = inverted phase
- 1+3 up = inverted phase
- 3+4 up = inverted phase
- (octave switch 3 likely inverts)
Maestro Brassmaster / Malekko B:Assmaster
MI Audio Pollyanna
Mosrite Fuzz Rite (and clones of)
Skreddy Lunar Module and Dlx
Soulsonicfx Shizzle fuzz
Spencer Mixmuff
Spencer Subzombie (stage #1 and stage #3 invert)
Spencer Suprazombie
Zvex Fuzz Factory

(general):
most octave up fuzz's

Infanem STEP: (see above) (inversion depends on settings)
Fulltone Ultimate Octave

looping pedals:
Zvex Lo-Fi Loop Junky

modulation pedals:
chorus:
Catalinbread Callisto Chorus (inverts phase when mix full dry, in phase when fully wet) (inversion depends on settings)
MXR Micro Chorus
TC Electronics Chorus

flangers:
MXR Micro Flanger
Ross Flanger (ac powered)

phasers:
Blackout Effectors Whetstone Phaser
MXR Phase 90 (original)
Red Witch Moon Phase
Subdecay Baby Quasar
Subdecay Quasar DLX
Subdecay Quasar Quantum

tremolos:
Amptweaker Swirlpool (inverts phase with the 'surf' switch set to the left ONLY) (inversion depends on settings)
Danelectro Cool Cat Tremolo
Danelectro Tuna Melt Tremolo (always inverted. inverts engaged AND bypassed)
Effectrode Delta Trem Tremolo
Toadworks Pipeline

vibe pedals:
Effectrode Tube Vibe
Retroman Ubervibe (main output inverts, other output does not)

vibrato pedals:
Behringer UV300: inverts in "latch" and "unlatch" mode / does NOT invert in "bypass" mode (inverts in some modes but not in others)

multi fx:
Digitech RP-155 (always inverted. inverts engaged AND bypassed)


noise reduction:
Behringer NR300


reverb:
Zcat Stereo Big Reverb TI

PEDALS THAT INVERT PURPOSEFULLY(to correct out of phase pedals etc.)

- Barge Concepts VB-jr
- Badger Schism
- GigRig Humdinger
- GigRig Wet Box
- One Control Mesquite Blender

any others?..................

[Max999]

@blackieNYC

Yes relative phase with parallel circuits is very important. I should have clarified that I will be building the parallel loop especially for use with a Boss DSD-2 ( basically a DD-2), which is modded for kill-dry.
I do not like the headroom and the pre-emphasis and de-emphasis circuit ( that the dry signal also goes through) in the DSD-2, so I am building this to avoid these problems for the dry signal. I tried modding the DSD-2 for 18v, but this did not work out unfortunately.

So phase issues are not a problem, and I kind of like the idea that the loop pedal flips the phase becasue I use an inverting Marshall 2203.