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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 ACA V1.8 kit includes blade terminals so you can attach wires to the power switch without soldering the power switch. Some builders of the V1.6 kit applied too much heat to the power switch terminals (which is easy to do), resulting in melting the switch assembly and causing switch failure. The included terminals can be crimped or soldered onto the wires going to the main power switch. These connectors will slide onto the switch spade pins. They are the correct size, but are stiff to push on.

You have three options:

  1. Carefully push the connectors onto the switch without breaking anything
  2. Pry the connectors open a bit with a small screwdriver and push them on
  3. Don’t use the terminals at all, and carefully solder the wires to the switch without overheating the switch

The choice is yours, and you should use whichever technique you feel is the best match for you.

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.

We will be offering 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).

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.

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

Finish Line

6 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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