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Old 1st April 2007, 04:00 PM   #1
Heiney9 is offline Heiney9  United States
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Default Yamaha AX-900U

I have been looking for a decent older integrated to run a computer/office system. I aquired a pair of classic Polk Monitor 5b's and I needed something to run them. A friend had an old Yamaha AX-900U integrated just stitting around (5 years in the box of no use) so I snagged it.

Upon firing it up all the controls except the volume control were very noisy and actually caused the unit to cut out in spots. So I tore it apart and used Caig products on all the controls. This gave me a chance to remove alot of dust, etc. and see the innards.

Normally I've never been a big fan of Yamaha. Typically they tend to over complicate things and have all kinds of useless (to me) bells and whistles. This seems like a very rugged well built unit. Nice and clean inside as well as a lot of space to get at things. The internal board is marked right and left and has actuall copper power rails running down the center of the board for power distribution rather than pcb traces. Huge Nichicon 22,000 uF (x2) powers supply caps as well as a huge encapsulated transformer. Completely seperate pre-out and main-in to use as a pre or power amp only. Weigh in at a heafty 39 lbs.

It seems to sound real nice and is a powerhouse at quoted 130 wpc. Kind of renews a little faith in Yamaha and since this was built in 1987 I'm guessing the very last of the beefy Yammy's. It can't really hold a candle sonically to my Nak/Adcom seperates but it does alright.

My only concern is that after about an hour of use, idiling or light use the transformer case gets extremely hot to the touch. Is this normal? The PS caps are within centimeters of the heat and I wonder if it will shorten their life span. The output tranny's are only slightly warm. Any ideas? Should I be concerned? Any other comments on this series of amps good, bad or indifferent.

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Old 2nd April 2007, 06:41 AM   #2
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Join Date: Jan 2006
Location: central Iowa
I wouldn't worry to much about the transformer heat unless its hotter than 185F and the caps are 85C temp.rated or 221F and the caps are 105C temp.rated. Just allow ample space for cooling vents to get air.
If your really concerned you can always use a small fan.

Ret. USAF... AKA- Avionic *** Solder slinger for hire...***
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Old 17th October 2012, 10:54 AM   #3
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very good find! I have one of this bestie it is good for real., probably one of the best amplifier by Yamaha. Btw, about the hotter, what impedance & power is your speakers? Recomandation: try to connect omly minimal 8ohm impedance speakers, and somewhat equal wattage with your amplifier. Anyway, don't worry, this amplifier is very resistive and had protection.
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Old 17th October 2012, 03:56 PM   #4
jitter is offline jitter  Netherlands
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Location: Eindhoven, The Netherlands
Originally Posted by Heiney9 View Post
My only concern is that after about an hour of use, idiling or light use the transformer case gets extremely hot to the touch. Is this normal?
If you mean by "extremely hot", too hot to keep your fingers on, then I would say no, it is not, expecially when idling.
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