300 watt Hi-fi power amp project.

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hydrovac
Neuling

#1 erstellt: 19. Jul 2013, 17:55

Hi all DIYers,

Building a 300 watt Hi-fi power amp, which we designed and prototyped few years ago.
Please follow the links for details.

http://www.diyaudio....power-amplifier.html

http://www.diyaudio....r-4.html#post1330047

PCBs have been fabricated and gathering all components on hand.
Few pictures of the same.

IMG_4459 by

hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

hydrovac
Neuling

#2 erstellt: 22. Jul 2013, 17:15

Holes for output devices drilled on heat sinks using a TO3 jig. Input and speaker binding posts holes done and connectors mounted.

IMG_4448 by

hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

This is the den for our hobby & passion, and where all our classics come to life.

IMG_4399 by

hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

Power transistors mounting process and progress.

IMG_4420 by

hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

hydrovac
Neuling

#3 erstellt: 02. Aug 2013, 11:20

Hi friends,

Sorry for the long gap in my post as I was preoccupied with other commitments. In continuation to my earlier posts, here is progress in amp build.
Checking the DC rail voltages: Left channel, Right channel, both channels

IMG_4645 by

hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

Checking full rail voltages: Left channel, Right channel, - Ve and +Ve rails

IMG_4652 by

hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

I am supposed to get around +62 and -62 volts DC on rails. The increase in reading is because of the mains input voltage (250 volts AC). Toroidal transformer winding is rated for 230 volts primary.

IMG_4682 by

hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

Setting the quiescent bias current for output stage:
Fabricated a 10 ohm 5 watt wire wound resistor suitable for the fuse holder.

IMG_4671 by

hydrovac, on Flickr

IMG_4674 by

hydrovac, on Flickr

Inserted in +Ve side holder and switched on the power. Adjusted the trim pot to get, 1.0 volt across the resistor.

IMG_4658 by

hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

You can see the thermal sensing bias transistors mounted mid way between the power transistors on the heat sink. Good going so far.

IMG_4678 by

hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

Now, looking at output side. Measuring the speaker output terminals for DC.

IMG_4669 by

hydrovac, on Flickr

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hydrovac, on Flickr

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hydrovac, on Flickr

Left channel looks clean without any DC. But right channel is showing 0.04 volts. There seems to be a hitch somewhere. I will get back with updates after trouble shooting.
Thanks for looking and following the post.

hydrovac
Neuling

#4 erstellt: 13. Aug 2013, 03:46

Actually 40mv dc offset isn’t that bad. I traced it to a slightly leaky cap. Replaced it and now it reads 1.5mv on right channel and 2.8mv on left channel, in 200mv range of multi meter.
My Dc offset is excellent and will not damage the speakers, but many say as high as 50mv is still OK.
I connected a source and performed an extensive listening session. Must confess the amp has an amazing sonic quality.