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November 6, 2013 / billo44

EL34 ultra linear single ended amp. Designed by Iwamura Yasuo

This amp caught my eye when I was looking for my next project late 2012.


I have been buying parts little by little since January 2013.

This amp was one of four amps designed by well known Japanese designers, sponsored by the transformer maker Noguchi.  The contest was to make the best EL34 amp for under 400 USD.   The four amps were featured in the audio magazine MJ.  I picked this one based on looks and the performance curves (since I can’t read Japanese).

For a time they were offering a kit with the four transformers and an aluminium box pre-cut… but they were out of stock by the time I got around to ordering.

This is my study build in a nasty plain aluminum box.  Next I hope move it into a nicer (and bigger) case with a wooden front and sides and maybe a brass top.


Here is a dry build without everything hooked up underneath.

I am using Russian made electro harmonix EL34/6CA7 EH tubes.

I was lucky to find Matsushita 6SJ7GT (glass tube) on auction, and I had an old Matsuhita rectifier tube (nice flat top).


Here is the case with all the holes cut out as per the plan.


Showing the first problem , there isn’t enough room for the alps blue pot, I want to use, and the second problem…


It’s all very crowded near the transformer terminals.

Lesson learned is that I need a case at least 50 mm deeper front to back… Never mind, for now I will move the pot over to the right…


The large knob (Ooh err) covers up the original holes.






Local 100v AC supply has an un-polarised plug  although myself I will use a polarised three pin plug with safety earth.


11-06-2013 Getting closer to ‘smoke test’ time.  One heater wire still adrift, the input wires and the lug boards to finish….IMG_7075

Here are the remaining parts of the circuit mounted on lug boards.

Note the lug boards screwed to special tool #14, a grubby bit of plank, to secure them for soldering (special tools 1~13 are all various types of special stick).


Getting ready for the Smoke Test… 8Ω 200W dummy load, variac, bulb tester, safety glasses….

Got some knackered old speakers to try if the first test goes OK.

Also have an old signal generator, 2 channel audio voltmeter, oscilloscope ready but don’t really know how to use them yet.  Planning to learn!  Any advice or links?


Here we are with all the dots joined up at last….

This was a first for me since it has been my first point to point build from a schematic without the support of a forum and without build instructions (that I could read).


Smoke test was negative…  the amp is now running in on the bench… Sounds good!

Ahhh!  Need to find a way to contact Mr. Iwamura. the designer to say thanks, it really sounds nice!



Leave a Comment
  1. Dave / Nov 14 2013 8:25 am

    Here you go Bill:
    メールアドレス ********

    • billo44 / Nov 14 2013 10:57 am

      Thanks Dave, I made a note of the address and then edited it… I’ll write to him.. thanks again.

  2. David Townsend / Nov 22 2013 7:46 pm

    It worries me that I find your blog so soothing Bill.

    • billo44 / Nov 23 2013 9:02 pm

      It worries me too David…. Is it the soporific writing style?

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