Sunday, December 8, 2013

Sansui AU-101 Solid State Stereo Amplifier

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Although the AU-101 was the 'budget' amplifier for Sansui back in 1973, it is not to be underrated. Power output is at a conservative 1970's 15 watts per channel. Its pedigree comes from the popular Sansui AU-555A which is quite a respectable amplifier itself.

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This amplifier was part of a job lot. Although working, it did have the usual symptoms of a 40 year old amplifier. Scratchy potentiometers, the volume was particularly bad and the capacitors were showing their age with quite some distortion when bringing the volume up and adjusting the tone. Cosmetically, it had some oxidation from age but was otherwise complete. Below you can see it's original condition.


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 On the bench ready for its service. The knobs were removed to be ultrasonically cleaned- A new method I'm using as I have recently acquired a dental grade ultrasonic cleaner.

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First up is the tone board, for this, the whole front faceplate needs to be removed as the tone board is fixed to the front internal chassis via the potentiometers.

Tone board before recapping:
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Remember I mentioned that the the AU-101 pedigree came from the popular AU-555A? Well the tone board is a direct descendant of the AU-555A. So if they sound familiar, now you know why.

Even now I still have a good chuckle at how modern technology has come, below on the left we have the original compononent removed, in this case a 470uF 35v capacitor, next to the replacement, a 470uF 50v capacitor which is only 1/3 the volume of the original! As always, Panasonic AM series capacitors are being used. These are specifically made for sensitive equipment such as medical devices and computers and always sound wonderful in any audio gear I use.

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Tone board rebuilt:
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The power amplifier section is pretty simple, the circuit board also includes the AC>DC circuit which can be seen to the right. Here it can be seen after being restored.

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And another great example of miniaturisation. Below is one of two filter capacitors on the power amplifier circuit. The original component on the right, is rated at 1000uF at 35 volts. The replacement, I've upgraded to a 2200uF capacitor which is 1/2 the height and about 1/4 the volume of the original component.
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There really wasn't all that much to this restoration, total time was about two hours of which most of the time ended up being the cleaning of the faceplate to make it look like new again. It calibrated almost perfectly without any adjustments and overall was a very smooth process.

All the capacitors replaced can be seen below:
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How does it sound? Pretty damn nice. Remember that you are probably not going to get the best out of a set of floor standing JBL speakers out of these, but paired with a nice efficient set of bookshelf speakers, or as a headphone amplifier this amplifier will surpass expectations within the normal realm of human hearing! The bass-mid-treble controls give a range of adjustment to refine the sound to what you like, and the range is excellent.

Its limitations are really set around the market it was designed for- the low budget line. But this is 1970's low budget for a reputable brand of its time. It only has one set of speaker outputs and basic inputs of Aux, Phono, Microphone and Tape. But it does have plenty of power in its 15 watts per channel more than any headphone or set of bookshelf speakers will ever need. If you have a small space and want a cool running, great sounding vintage amp, this is one to consider.

Enjoy the finished pictures below, if you would like to see a couple of more photos, have a look at the the Flickr Gallery.

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3 comments:

  1. Love your work and this amp. Thank you for this write up, I owned a 101 once and sold it and bought a 555A since then I have been looking for another 101!

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  2. Fascinating to read this but I thought you might be interested to know that I purchased my 101 new in 1972/3 and I am still using it everyday. Apart from a slight crackle from the volume pot when first turned on (but not thereafter) everything seems to be working fine and although it took me over 30 years to find and be able to afford a really good pair of speakers to to match it I now have a good working system* which I hope will see me (listen me.....?) out. (* AU101 - Musical Technology PM15 monitors - Technics SL1200 MkII - Cambridge Tuner & CD player.)

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