Author Topic: Jiro Kasuga (Accuphase) DIY 55+55watt power amplifier  (Read 4202 times)


  • Guest
Jiro Kasuga (Accuphase) DIY 55+55watt power amplifier
« on: April 06, 2011, 02:04:06 PM »
Got this amp coming. Will see how it goes powering the 15" woofers :)

Some info and photos:

A beautiful home-made power amplifier. It's based on a module designed by one of my heroes, audio genius Jiro Kasuga (founder and chief designer of Accuphase Laboratory Inc, director of Japan's Audio Engineering Society), published in a Japanese audio magazine from the late 1960s.  This unit has been converted to 240volt, rather than the original spec 110v.
It's ClassAB (although I would guess that bias in Class A) and delivers 55watts + 55watts into 8ohms and 100w + 100w into 4ohms.  Dual monoblock construction means no crosstalk between channels and each discrete power supply gives +/- 40 volts at 2 amps.  Frequency response is terrific at 10Hz-100kHz (+/-2dB) and signal to noise ratio is better than 100dB (ref: 0.7V RMS input).
Distortion was rated at .02% in the original design but has been further reduced with the omission of the current limiting feature - in its place a separate electronic fault detection and dethump module has been added.
It's been thoroghly overbuilt with many components "overspec", namely the 2 BIG transformers in a shielded section, the braced, rigid alloy chassis, the lovely front heatsinks (which would easily accommodate 120watt), a thick copper earthplate, 4 lovely big Nichicon 8000uF filter caps, gold-plated binging posts and inputs etc.  Includes a standard 3-pin power cable.

It's built into an old Tasmanian Blackwood scientific instrument case which has been restored and polished to a smooth gloss. Beautiful boxjoints on all four sides and it has a little glass window on the top (to peep at the hotrod).  The whole chassis can be removed/slid out by undoing two large bolts underneath.  Cosmetically it's, well, magnificent.  Sound reproduction is exceptionally good and more than a match for most commercially manufactured power amps. Fast, authoratative bass and lovely, even "unspooling" power. It's extremely smooth and exhibits none of the "graininess" of lots of solid-state offerings (to clarify, I know this is due to topology and componentry rather than inherent defects with solid-state as a system - I like solid state amps). Ahem, anyway it's a beaut, it runs nice and warm and with the help of your favourite preamp, will reliably feed out gorgeous tunes. What more could you want?  39cm long x 21 cm wide x 19cm high and weighs 10kg.


  • Guest
Re: Jiro Kasuga (Accuphase) DIY 55+55watt power amplifier
« Reply #1 on: November 01, 2012, 07:57:40 PM »

Could you please post more details of this amp? I'd like to know if the PCB is available anywhere and if I could get any more information if possible. For some reason, I was not able to find more information on this on the web. Thank you for your time.



  • Guest
Re: Jiro Kasuga (Accuphase) DIY 55+55watt power amplifier
« Reply #2 on: November 01, 2012, 10:54:07 PM »
Hi Gruby,

Pcbs were custom so don't think they are available anywhere. I do have circuit diagram which I will post below.  Hope it helps.