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AB100 Class AB Power Amplifier
AB100 Class AB Power Amplifier
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Old 13th August 2019, 06:07 AM   #641
osscar is online now osscar  Latvia
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Good news! I'll wait for feedback on the sound.
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My DIY so far: two Leach amps,two Pass AB100, Pass F5, B1 buffer, Hiraga le monstre, two LM3875, LM1875, OPA549, 6C33C SE, GU32 PP, 6p3c-e PP, Marsh headphone amp.Phono - OBH-8se, Pacific RIAA, inDiscreet Phono, MF A1 Clone, Whammy headphone amp.
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Old 13th August 2019, 05:49 PM   #642
manniraj is offline manniraj  India
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I am yet to receive the boards and hopefully it lands up after waiting for more than 40 days now
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Old 14th August 2019, 01:41 AM   #643
Freecrowder is offline Freecrowder  United States
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AB100 Class AB Power Amplifier
So noticing some things during testing. First +/- 40vdc rails. Gain is 46dB(not sure why it's so high), Bias is 40ma per trannie. When I do a sweep from 20-20khz bias is stable up to right around 10khz. From 10kHZ-20khz the bias rises to just above 60ma/per and you can smell it warming up somewhere. Is this just because gain is too high? What resistor do I adjust for overall gain? Does it need a comp cap added? do I raise or lower gain resistor to lower gain. This of course testing using sine wave from signal generator set at .1vac
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Old 14th August 2019, 05:21 AM   #644
osscar is online now osscar  Latvia
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Hi, I reduce gain with R3 - my value = 1K ( 1st post original schematic R3).
I don't have any instability in both of the my AB 100's without C9 - maybe you have an oscillation somewhere? Is there any soldering mistake in resistor values ?
Have you checked the output waveform with the oscilloscope?
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My DIY so far: two Leach amps,two Pass AB100, Pass F5, B1 buffer, Hiraga le monstre, two LM3875, LM1875, OPA549, 6C33C SE, GU32 PP, 6p3c-e PP, Marsh headphone amp.Phono - OBH-8se, Pacific RIAA, inDiscreet Phono, MF A1 Clone, Whammy headphone amp.
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Old 14th August 2019, 06:13 AM   #645
carsten.witt is offline carsten.witt  Germany
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@manniraj,
I cannot change it unfortunately that so far with you nothing arrived and it also nothing came back.
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Old 14th August 2019, 12:26 PM   #646
manniraj is offline manniraj  India
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Quote:
Originally Posted by carsten.witt View Post
@manniraj,
I cannot change it unfortunately that so far with you nothing arrived and it also nothing came back.
Yes I understand and I should have gone with tracked shipment at least to see where exactly its held up. With no tracking its just a guessing game now

Thanks
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Old 14th August 2019, 01:16 PM   #647
Freecrowder is offline Freecrowder  United States
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AB100 Class AB Power Amplifier
So to be more clear. I'm looking at scope images and they look great. I see no signs of oscillation. Is it perhaps that I'm testing with 10-20khz sinewaves at just under clipping? Also there is no load on the output, open circuit. With music signals the levels at those frequencies would be drastically lower. Have you ever tested yours like this and monitored the voltage drop across the emitter resistors?
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Old 15th August 2019, 01:47 AM   #648
Freecrowder is offline Freecrowder  United States
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AB100 Class AB Power Amplifier
Ok the latest. I adjusted my overall gain to 26db by raising the feedback resistor from 100 to 1000. The bias is stable up to 100khz and beyond now. Actually have it rigged up on the bench with Epos speaker and sounds pretty good! I'm happy with it so far. What supply rails are people using? This is running on +/- 40vdc
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Old 15th August 2019, 05:05 AM   #649
osscar is online now osscar  Latvia
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Glad to hear good news!
i use is 43V rails on first one and 37V for second amp - because I had such transformers on the shelf.
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My DIY so far: two Leach amps,two Pass AB100, Pass F5, B1 buffer, Hiraga le monstre, two LM3875, LM1875, OPA549, 6C33C SE, GU32 PP, 6p3c-e PP, Marsh headphone amp.Phono - OBH-8se, Pacific RIAA, inDiscreet Phono, MF A1 Clone, Whammy headphone amp.
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Old 15th August 2019, 01:00 PM   #650
Freecrowder is offline Freecrowder  United States
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AB100 Class AB Power Amplifier
I'm running maggies rated at 4ohm. Would like to push the rails to 50-53ish and get a real 200 watts out of this amp. Anybody think that would be an issue? I'm mounting to a heatsink that could be used for Class A to 25-35 watts. What about input electrolytic cap. I would like to change to polymer film type. How big does it have to be to get descent low frequency.
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