Guest Feature – Warm Audio WA76 Stereo Link DIY: Phase 1


By Author:  Matthew Blue

If you are reading this, you must be as excited as I am about the new Warm Audio WA 76 Comp/Limiter.  There is a lot of information about the WA76 at the Warm Audio site and sound clips and video of it in use. (  wa76.png The WA 76 is an awesome piece of gear.  It is modelled after the original 1176, so, of course, the WA 76 is mono, but there is a way to modify two WA76s so that they can pass a stereo signal, great for tracking stereo sources or for strapping across your mix buss.

Hairball Audio

This article demonstrates how to use the Hairball Audio MNATS DIY kit to link the FET circuitry of the WA76 circuitry in order to create a stereo link in two units.  Hairball Audio (HBA) is a very respected company providing a variety of DIY kits. They can be ordered directly from the HBA website ( Here is pic of the completed board from the HBA site:


*Note: Phase I includes the build of the two stereo link boards.  Phase II, to follow ASAP, but at a later date, will review the installation into the WA76s and power up.


Please go to the HBA site, to read about the design of the stereo link circuit.  The build guide from the HBA site and to find a reference to another DIY thread for information about the stereo link build.  I followed the Hairball Audio information for my build. *Disclaimer: IMPORTANT NOTE:   Phase 1 of this project, building the stereo boards, does not entail opening up the WA76 unit.  However, Phase II of this DIY project involves working with circuits that carry LETHAL voltages.  The processes and build procedures demonstrated in this thread are for educational purposes only.  All work should only be performed by qualified technicians.  While the parts count in this project is low and build procedures outlined in this project straight-forward, information provided in this post and any subsequent ones should be studied to ensure a thorough knowledge of all connections and components is clarified prior to attempting this build. Before beginning this project, a few strong recommendations: 1.  If you are new to DIY electronics and do not have the confidence and technical knowledge to troubleshoot the circuitry when problems arise, make sure you have a solid fall-back plan.  Before purchasing parts, find someone  local (friend or professional) who can assist in person, if you get stuck! (If you decide DIY, is not for you, ZENN Audio is doing a stereo link mod for a fee.  I would certainly suggest that you contact them directly to find out if that is your preferred route to Wa76 stereo compression nirvana and/or bliss: ohmmmmm 😉 !) 2.  Get a temperature controlled soldering iron.  Delicate electronic components can easily become damaged with even low-wattage, non-regulated soldering irons.  Weller, Hakko, and other name-brand tools are also good. For example: Or, a cheaper 45 watt regulated alternative. 3.  Hakko 808 de-soldering tool.  This expensive tool can save you from hours of frustration and damaging the traces on your PCB if you need to remove components after they have been soldered in. * This is a paraphrase of information from the Group diy C-12 project but applies to this project as well.

Engaging the Dilythium Crystals

OK, with a full understanding of the inherent risks involved in working with DIY electronics, the first step in this project is checking your materials against the build list. After you order your kit, you will receive a well packaged container with the following parts, as described on the the HBA audio site: Stereo Link Kit Includes:

  • 2 Stereo Link PCBs
  • 2 TL072CP OP-AMPS
  • 2 TL071 CP OP-AMPS
  • 10 22uf Panasonic FM Series Capacitors
  • 12 25K (24.9K) Xicon 1% Metal Film Resistors
  • 4 10K Xicon 1% Metal Film Resistors
  • 2 100K Xicon 1% Metal Film Resistors
  • 2 1K Xicon 1% Metal Film Resistors
  • 2 22R Xicon 1% Metal Film Resistors



Please note when you review the build guide, the kit does not include the 2 switches, 2 female TRS plugs (picture at end of thread), the internal wiring (board-to-board and some shielded), nor a male-to-male TRS cable that you will need to complete the build, and for the two units to be fully functional in stereo mode. You can check the HBA site for these parts.  I ordered my switches and TRS plugs from Mouser. To prepare myself for the build, I simply laid everything out on paper and grouped the like parts together.


To confirm and double check the resisters values, I went to the following interactive site  ( to enter the color bands in sequence to confirm the resister value (isn’t the internet great?!)


I confirmed all the parts were received  (yes,they were, yea, Mike!)



Then, I organized everything into two separate bags, one for each build.


Note: Gold bars on black capacitors indicating polarity.

Final Prep: Ready, Set, Stop ! 🙂

Before you fire up your iron, please take some time to review the actual board and to note the position of the parts, in particular the polarity orientation of the capacitors, marked as round circles with a + label (9 o’clock) and the Op-amps A201 and A302, marked with a white circle, bottom left hand side. You will note that the capacitors are also marked clearly with a negative sign in relief against gold markings (pic later) and that their long leg aligns with the positive polarity.  Getting this wrong may give you the opportunity to hear the capacitors pop like firecrackers when you power up; fun, ya!!! (but not the intended purpose).



Please don’t resist using use the following table to confirm the colour code of your resisters, because your build just won’t have the capacity to deal with this error.

Type Part Number PCB Position Colour code
Op-amp TLO72CP 2 A201 Black (white circle polarity)
Op-amp TLO71CP 2 A202 Black (white circle polarity)
Capacitor 22uf Pan. FM 10 C201-03, C301-02 Black and gold
Resisters 25K  Xicon 1% MF 12 R201-02,  R205-08 R,Gr,W,R,Br
Resisters 10K  Xicon 1% MF 4 R316-17 Br,Bl,Bl,R,Br
Resisters 100K Xicon 1% MF 2 R203 Br, Bl,Bl,O,Br
Resisters 1K     Xicon 1% MF 2 R204 Br,Bl,Bl,Br,Br
Resisters 22R 2 R209 Br,G,Bl,R,R

Board Games: Getting Stuffed

Please ensure you use sensible ventilation (small fan) when soldering and use good technique, clean the tip regularly, use good solder, heat the board/trace, and let that draw the liquified solder.  If you watch carefully, you will note that the trace takes on a different appearance as it approaches the melting point of solder.  If you touch the solder to the trace at this point, it should liquify, flow and draw.  Resist the temptation to rush and touch the solder to the iron tip; it will just make things worse, trust me :). You will be stuffing the parts, meaning putting the legs through the boards and flipping the board over to solder from the bottom. It it is common practice to start with the shortest parts first and proceed to the tallest parts last (resistors, op amps, capacitors).  I did one board starting with the resistors and one with the op amps; the resistors seemed a little easier.


In placing the resisters, remember to follow the R values which are noted on the board and which you confirmed from the Digisite.  Also, normally you bend the leg of the resistors around a small diameter screwdriver to achieve a right angle bend to ease their fit through the holes in the board.  I also reviewed the photo from the HB site and oriented my resisters identically, just check the colour sequence to see what I mean. Please note with the Op-amp polarity white dot, you will see a corresponding black circle etched into the top surface of the op-amp.  Ensure that you overlap them when installing on board.  


Its a good idea to raise the board above the height of the legs which will protrude from its bottom. An almost completed Board, no caps yet. (Note: The black circles indicating polarity on bottom left hand side of each Op-amp.)  


It may have occurred to you that when you flip the board over for soldering, that the parts may fall out or shift.  So, it is common practice to splay and or to bend the legs out away from each other underneath the board, 30 degrees or so should suffice.  Remember to be gentle, the legs are very pliable, so will bend easily – easy does it!!


Once you turn the board upside down, check that you have good clearance and access at each solder point.  If not, complete the solders that are most accessible and then snip away, as close to the board as possible, the excess leg, beyond the solder point. This will allow access to the remaining solder points.


Soldering will leave residue on your board and this is conductive, so have some new, clean isopropyl, a toothbrush, and a small dish, so that you can clean off the board after your soldering and let it air dry.



Now it’s time to install the caps.  If you recall, I mentioned earlier that the caps are polarity marked. Here you can clearly see the negative rectangle in relief against the gold vertical bar running the length of the capacitor top to bottom.  Ensure you align the polarity with the markings on the pcb itself.  They are clearly marked in white against the red, but two are immediately adjacent (C201 and C202), so ensure you do one cap, (no ninja bla soldering guys or gals allowed!) at a time and double check before soldering.  Remember to splay the legs before turning over and prior to soldering, tighten the bend up against the bottom of the bcp board as the caps tend to lift away from the board.  Placing them upside down with top of caps to a flat surface should ensure they are uniformly seated but best to check before you solder.


Completed Board

All done! Feels good, I assure you!


And when both are done, why it feels 100% better; would I lie to you?!


Phase I to Phase  II

So, that is the end of the Phase I build.  I will post the remainder of the build as Phase II, when I have completed it. Essentially, we will end up with a linked arrangement that looks something like this, (diagram from HBA DIY thread):

stereo linking3

Here are the two switches and the trs female  jack that will be fitted into the WA76’s !


From Mouser Electronics part numbers: Switch 611-t101stdcbe on/on and  Chassis-jack 568-nj3fp6C The build in the WA 76 look like this  like this:


You will install a red PCB in each WA76 with the wires and TRS cable doing the actual connection between the two units. Please note the black shielded cable from Stereo link (red) board to Output controller and to TRS female plug of the unit (Note: This is a picture of the hairball audio compressor, also from its DIY thread.) Stay tuned: same bat time, same bat channel!!!


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