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Nakamichi PA 5E class A Stasis amplifier hum problem
Nakamichi PA 5E class A Stasis amplifier hum problem
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Old 9th February 2018, 06:21 PM   #31
classAchap is offline classAchap  United Kingdom
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Quote:
Originally Posted by Sixtron View Post
c401 136v AC opposit 0v AC
c402 135v AC opposit 0v AC
The a.c. voltage is problematic but the reverse readings of 0V is makes no sense at all.

Can you confirm your measurements with a scope or another meter?

Failing that I suggest you check your meter by measuring the rectifier a.c. terminals in both directions - as a test. It should read the same a.c. in both directions.
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Old 9th February 2018, 06:45 PM   #32
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It's the multimeter. I made a test and measured a 1,3v rechargeable battery in AC and it shows 2.1v.
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Old 9th February 2018, 06:50 PM   #33
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Nakamichi PA 5E class A Stasis amplifier hum problem
maybe it's not just multimeter

you can't measure battery , which is DC , with AC meter
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Old 9th February 2018, 06:56 PM   #34
classAchap is offline classAchap  United Kingdom
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Quote:
Originally Posted by Sixtron View Post
It's the multimeter. I made a test and measured a 1,3v rechargeable battery in AC and it shows 2.1v.
Good - thatís progress.
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Old 9th February 2018, 06:57 PM   #35
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Of course not. But it should show 0v. Very irritating.
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Old 13th February 2018, 04:28 PM   #36
Sixtron is offline Sixtron
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Today i had installed a 5, 10 and 20 ohm resistor from the input ground to the main ground.

The Result:

The hum is gone completely with the 20 ohm resistor. With the 5 and 10 ohm resistor there is a little bit hum remaining, but so few that i don't hear it from sitting on my couch.

The sound changes in this form that if the resistance is higher it's loosing more - i will call it - precision and dynamic for my ears. So i let 5 ohms. See photo.

There is also some kind of few sough from my Tv that is connected to my amp remaining.
It's not the antenna.

Next days i will change the small capacitors and i could order a matched pair of mylar capacitors 10uf 250V from the US made in Taiwan that i will exchange also.
It's part c102 and it's in the input line from the 2SK240.
Btw. before i had changed this capacitor just for testing the sound like some one recommend here in this forum with a bipolar Mundorf capacitor 220uf 63V.
This sounds terrible. The high tones let explode your head so i can not recommend this.
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Last edited by Sixtron; 13th February 2018 at 04:45 PM.
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Old 13th February 2018, 05:43 PM   #37
Mooly is offline Mooly  United Kingdom
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Nakamichi PA 5E class A Stasis amplifier hum problem
Much reduced hum Well that's good

Be careful if you start swapping a lot of parts. Always fit like for like values and check your work carefully before switching on. Any little solder blob or short could be disastrous.
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Old 14th February 2018, 04:27 PM   #38
Sixtron is offline Sixtron
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Thanks all for help.
Today i had changed the small capacitors.
Two are looking inflated a little.
For testing i removed the hum braking resistors.
There was the same hum like before.
So it had nothing to do with the capacitors.
I installed the resistors again. This time 3.3 ohm.
This works also. No more hum.
But really i don't understand why in earlier time there was no hum and why today there is hum without the resistors.
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Old 14th February 2018, 05:12 PM   #39
Nelson Pass is offline Nelson Pass  United States
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Nakamichi PA 5E class A Stasis amplifier hum problem
Yay for DIY....

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Old 14th February 2018, 05:20 PM   #40
Mooly is offline Mooly  United Kingdom
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Nakamichi PA 5E class A Stasis amplifier hum problem
Perhaps you had a different configuration of equipment and source components using a different combination of mains grounding.

It is always hard to tell from pictures whether a part is OK or not but those caps actually look fine as far as visuals go.

In circuit locations that see a high ripple current it is often the other end of the cap that distorts (where the vent is) as the cap ages and deteriorates.

Do a Bing or Google image search for 'failed electrolytic' to see examples.
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