A...

 A&M Custom Effects

 A.G.M.

 A.Y.A

 A/DA (Analog/Digital Associates)

 AAT

 AbbyTone

 Able Electronics

 AboveGroundFX

 Abraxas Sound

 Absolutely Analog

 AC Efectos

 Ace Custom Effects

 Ace Tone

 Acid Fuzz

 Acoustic Imaginearing

 Acoustyx

 ACRfx

 Add+ Pedals

 Addrock Musical Products

 ADM / Europa

 ADtech

 Advance Tube Technology

 AED

 Aethan Electronics

 Affectronix

 Aguilar Amplification

 AJ Custom FX

 Akai

 Akbay Electronics

 Alairex

 Alber

 Albit

 Alcove

 Alctron Electronics

 Alden

 Aleatorik

 Alen Geere

 Alesis

 Alex Companion

 Alien Amplification

 Alien Pick

 Alien Rabbit

 Alien Systems

 All-Test Devices (ATD)

 Allen & Heath

 Allen Amplification

 Allied Electronics

 Allsound

 Alpha Omega effects

 Altai

 Alter Ego Effectors

 Alvin Youngblood Hart

 Amdek

 Amiko

 Amorim Custom Effects

 AMP - Associated Musical Products

 AMPedals

 Ampeg

 Amplifier Corporation of America (ACA)

 Amptweaker

 Amsterdam Cream

 AMT Electronics

 AMtech Handwired

 Amtron

 amukaT

 Analog Alien

 Analog King

 Analog Man

 Analog Metropolis

 Analog Musical Products (AMP)

 Analog Sound

 Analog Sound Lab / AXDXA (by Terry Tsutsumi?)

 Analog-Lab

 AnalogPro

 Analogue Solutions

 Analogue Systems

 Anarchy Audio Australia

 Anderson

 Andre

 Andrew Ross Pedals

 Andy Effects

 Animal

 Ansom

 Antech Handcrafted Pedals

 Antelope Effects

 Anthology Of Sound

 Anthony Regan Effects Pedals

 Antoria

 Anyware Instruments

 Apezila

 Aphek

 Aphex

 Apollo

 Apollo (China)

 Applause

 Applied

 Aramat Effects

 Arbee

 Arbiter

 ARC Electronics

 Archangel Electronics

 Area 51

 Arger FX

 Argie Amps

 Aria

 ArielFX

 Aries

 Arion

 Ark

 Aroma

 ARP

 ART - Applied Research and Technology

 Art of 59

 Artec

 Arteffect

 ArtFX

 ARTNT

 Artroy

 Asama

 Ashbass

 Ashdown Engineering

 Ashland (by Crafter)

 Ashton

 Asonix

 Aspect Design Labs

 Asselton

 aSTa Crazy Pedal Clone

 Aston Electronics

 AStone

 Astro Amp

 Atelier Audio

 Atelier Z (by Day's Corporation)

 Atlantic

 Atomic Amps

 Atomic Audio

 Atwater Kent

 Audible Disease

 Audigoa

 Audio Matrix

 Audio Monk

 Audio Rakitan

 Audio Squared

 Audio Storm

 Audio Tecnico ATX

 Audio-Phonic

 Audio-Technica

 Audiobox

 Audiolex

 Audiotech

 Audioworks

 Auralux

 Austin

 Austin Retro

 Austone Electronics

 Auto Labor

 Auxiliary Workshop

 Aviation Effects

 Avon

 Avondale

 Avora

 Award-Session

 Awenda Music

 Axcess by Giannini

 Axe

 Axis Guitar Effects

 Axis Research

 AXL

 AXS Effects

 Axtar

 Axtron

 Ayan Enterprises

 D'Amico FXS

 Elise (Элиз)

 Kent Armstrong

 Larry Alan Guitars

 Sam Ash