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Old 29th January 2013, 07:14 PM   #1
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Default Hiraga 30Watt DC offset

Hi all,

I'm trying to adjust the DC offset of a Hiraga 30W design amp. I can't seem to get it "steady".

Anyone any ideas on what could be wrong?

Kind regards,
Sjoerd Smits
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Old 29th January 2013, 10:08 PM   #2
amptech is offline amptech  Scotland
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post the schematic...some amp circuit's can be say 10mv to as high as 100mv..
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Old 31st January 2013, 03:51 PM   #3
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Hi,

Here's the schematic.... I'm thinking maybee I used wrong parts.....

I used MKP instead of Silver/Mica condensators.....

Thanks for any help!

Kind regards, Sjoerd Smits
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Old 31st January 2013, 04:12 PM   #4
Mooly is online now Mooly  United Kingdom
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How "not steady" ? How much is it varying and how quickly.

Have you tried with the input shorted. The cap type shouldn't make any difference. I'm wondering if its oscillating or unstable in some way. A scope check would show any problems.
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Old 4th February 2013, 07:15 AM   #5
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what complementary for ztx753 and ztx653?this for avondale amp
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Old 4th February 2013, 04:00 PM   #6
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Hi Mooly,

I'm thinking maybee a defective transistor.... It goes up to +80mv. Then I trim the pot back to "zero" and it just keeps going up....

I Agree, I need someone with an oscilloscope to check what's wrong....
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Old 4th February 2013, 04:00 PM   #7
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PS: Yes I shorted the input and measured the DC offset of my preamp witch was "zero"
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Old 4th February 2013, 04:08 PM   #8
alex mm is offline alex mm  Europe
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.... can you ,tell us , rail supply voltage and please post a picture of your amplifier ...... maybe I will see something
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Old 4th February 2013, 04:17 PM   #9
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Difficult to diagnose without actually working on it. I'm not so sure about a faulty transistor tbh, That would tend to cause a huge offset. Are any of the transistors running very hot ?

Is it worth slapping a zobel network on the output just to see if it alters anything. Something like a 0.1uf and 10 ohm in series to ground.
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Old 4th February 2013, 04:18 PM   #10
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Hi,

Voltage +-33VDC on the amps. Nice and steady.
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