Sanyo P55

for more information and beyond the classic problems for this machine , and that will be terrible soldering courtesy of standing pcb , and missadjustments , and high temperature , all small and big electrolytics , often some of the resistors rolls to a higher value ...

be aware now cause these are rolling with symmetry same for both rails and that will mean that is easy not to see the trouble

resistors are R 819,808 719,708 5K6 and R925 ,926 4K7

kind regards sakis


2009-11-20 8:57 pm
Can you elaborate on that voltage thing a little please?

Technically that does not make a huge difference as long as you adjust bias properly for the voltage you have. (If it even is voltage dependent)

I changed most caps in mine but only the smallest ones were bad when I measured. The 10000uF I left untouched as they measured almost as new values.

In the 80s Finland had 220V/380V nominal and then they increased to 230V/400V
They say e.g. lightbulbs died quite soon after the voltage increase. I would not have imagined that a 4-5% change would have been so bad for lightbulbs either but of course it has some effect on them.
Verify mains in your area , verify secondary rail voltage , if you ever manage to adjust the bias properly let me know

Primary is strictly 220V the few extra volts in an already compact case with limited heatsink cause excessive heat stress to the amp

DO NOT forget to replace mains switch is about to fail ...if it fails with a spark the result might be huge catastrophe...

My 2 cents


2009-11-20 8:57 pm
It is somewhere between 230 and 232V at home, varies a little with load.
Also I think some transformer is changing tap pretty close to us...enough dip to see a blink on led lamps, but not enough to hear on audio equipment.

At work I get 233,6 to 233,7V at the moment. Used a fluke 87, crappy meter that costs almost a grand, but I guess it is rather accurate.
My Metra hit 29s is 10x better at the same price.

I'll check the secondary voltages at in the P55, but BIAS is very stable.
But keep in mind that I biased it too high too. 100mA per FET.
I think 50mA may be too low for low dist.

The mains switch has been sparking like a maniac, all black inside.
I just sanded the metal parts and it works ok for now.

A new switch of the same type costs like 25-50euros shipped to Finland so do you have any replacement suggestion? If I find one that can easily be made to fit I could buy one. Say, if it is under 10 bucks.

Unfortunately Finns often hate DIY, if power switch is non-original I may not be able to sell it and will get questions like:
-Did you replace the switch your self? I do not think you are allowed to do that.
-Is it the original Sanyo switch? I do not think you can replace it with some other brand, it may not work right.
-I do not want an amp that has had switch problems...what if the problem comes back in a year?
-How do you know what the switch does? Only the manufacturer can know that!

Sorry, you see that I am a bit fed up with some people :)

Now that I do evening and weekend work as a repair guy I finally start getting some credit.
well voltage difference is not that much at 15 volts above rated while combined with more bias will have issues in terms of long time stability ....In total 800 ma of idle for this type of enclosure and style of heatsink is pretty hot ..

we change the switch with ones for Sony CRT tv we have plenty new screws knob fit exactly feeling is the same bit heavier and the small pcb inside we remove totally We have been doing so for more than 30 p55 amplifiers with no problems ...

Things you write about the Finns i don't bother to consider, i expect second thoughts when they find their P55 burned beyond repair ( outputs are almost no where to be found in a reasonable cost and original condition ) after a good switch spark ...

Image for triac switch


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Yes but the second thoughts come after the amp has burned :)

I was exaggerating a little. Or maybe citing the 10 most stupid audiophiles.

Will you sell me a switch?
I could still put a little time and money on it and then maybe keep it.

Reason I bought it for 70euros is the Hitachi fets.
Was a bargain until I found out how much needs to be done. It was sold in "working condition"

Maybe I should just have stripped it for parts...but I am beyond that point now :)