10 in stock (can be backordered)
Power supply upgrade kit for Adcom GFA-555, MK1 and MK2. (Not for recent “SE” models)
Kit arrives mostly assembled, as seen in the first picture. You’ll install the big capacitors in a later step.
*Please allow up to 7 days for shipping. They are hand-built to exacting standards, and I don’t always have one ready on the shelf.
Installation requires the amplifier to be fully torn down to the bare chassis and re-wired. It’s a sizable project with a rewarding result!
- WAGO Cage-Clamp terminal blocks provide a spring-loaded, gas-tight connection that will never come loose.
- Designed to cope with fault conditions such as a brown-out. Soft-start circuit will operate correctly down to 75VAC without relay chattering.
- This kit may be used with other amplifiers, besides the Adcom GFA-555, but it is up to you to figure out if it will work.
The soft-start circuit consists of a 10-ohm NTC thermistor in series with the incoming AC. After 1/2 second, a high-current relay shorts across the thermistor.
There are no cost-saving shortcuts in this design. The GFA-555 is a famously reliable amplifier. Many examples are still working basically fine after 33 years, so the soft-start relay driver circuitry must also be this reliable. Thus, the board features a traditional transformer power supply, feeding a 12V linear regulator, instead of a cheap off-the-shelf switch-mode power supply module. The relay is driven by a good-old NE555 timer IC, and the drive current of the 555 is isolated from the relay load by an open-collector switching transistor. This circuit should out-live the amplifier, and probably yours truly.
Please read these assembly instructions before you order, so that you are comfortable with the scope of the project. This involves working with AC mains voltages, so please know what you’re doing, and be safe!
Specifically, you’ll need:
|Dimensions||13 x 9 x 9 in|