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In July 2020 we released an updated version of the ACA called the ACA V1.8.

List of all differences between V1.6 and V1.8:

  1. Rear switch is a 3 position DPDT instead of 2 position, necessitating a change in wiring
  2. Rear panel is printed with a connection diagram
  3. Chassis rails are improved using weld nuts and secured by bolts
  4. Blade terminals are included for the front power switch
  5. Longer wire
  6. LED resistors have been changed from 10k to 33.2k to reduce LED brightness

Please note that the PCB did not change whatsoever between 1.6 and 1.8, and so the PCB included in all 1.8 kits says "V1.6". That's the correct version of the PCB.

To build V1.8:

  1. Print out and use the ACA V1.8 wiring diagram.
  2. Follow the ACA V1.6 build guide, but follow the V1.8 wiring diagram
  3. Review the comparison of the V1.6 and V1.8 wiring shown below

The build guide shows how to solder your power switch. Some early kits may include female spade connectors - if your kit has them we don't recommend you use them as they can be so tight as to be problematic. Just follow the instructions for soldering noting not to linger and overheat the switch.

Work has begun on new photographs and information to make a dedicated V1.8 build guide. It will be available here in the coming weeks.

If you have any questions please post them in the ACA Kit 1.6/1.8 Discussion Thread where you will get swift and comprehensive answers.


PS V1.5/V1.6 owners: In October will be offering V1.5/V1.6 to V1.8 make-up kits for builders who have already built a V1.6 (or earlier) and want to bring it up to V1.8 specification (or build matching monos). We'll email you when they are available.

  1. ACA V1.6 wiring vs ACA V1.8 wiring
    • ACA V1.6 wiring vs ACA V1.8 wiring

  2. Here are two photos of the rear panel wired the 1.8 configuration. Photo 2 shows the detail of the switch.
    • Here are two photos of the rear panel wired the 1.8 configuration.

    • Photo 2 shows the detail of the switch.

    • Note the red power wires from the center of the barrel connector are not shown.

Finish Line

12 other people completed this guide.


Member since: 12/09/2013

1 Guide authored


Watts Up Member of Watts Up


1 Member

1 Guide authored


To do the 1.8 wiring you need to use a DPDT On-Off-On switch on the rear panel. That means that the lever has a center position.

1.6 kits came with DPDT switches but they are just On-Off with no center detent so they need to be replaced.

Here’s one:

Variac - Reply

Wiring diagram shows positive output from the circuit boards tied to ground.

stlhifibob - Reply

That’s correct Bob. Positive out from the boards to ground. From the Amp Camp Amp article:

We will note that Common-Source operation intrinsically inverts the phase of the amplified signal, and so we have reversed the polarity of the output terminals to account for that.

Jason -

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