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Little Big Amp - page 2

Posted 5th August 2013 at 04:34 AM by homeskillet (Journey to the Center of the Circuits of Homeskillet)
Updated 5th August 2013 at 06:49 AM by homeskillet (added a bit of plate to plate feedback)

Continued after some listening and more tinkering from here:
http://www.diyaudio.com/forums/blogs...e-big-amp.html

It seemed lacking in the high end so I added a bit more capacitance to the bypass cap on the cathode resistor on V1.

This picked the high end up nicely. I then hooked the speaker up to the 16 ohm tap and used the 8 ohm tap as the feedback center tap. This resulted in a bit more output and I like the sound just fine.

The volume seems to increase after it's turned on a while. Also, it needs a B+ fuse in the event that V1 doesn't draw then V2 will have no bias and will draw tons of current and then will dump tons of current into it's cathode resistor.

The schematic posted here is updated with voltages and values done to the best of my ability and it sounds very nice. It's not a finished design but great for experimenting.

I will be setting this aside as my curiosity is leading...
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Old

Passive fiilters - musings on inductors and topologies

Posted 5th August 2013 at 12:58 AM by abraxalito
Updated 5th August 2013 at 01:02 AM by abraxalito

I've spent many hours recently poring over webpages and catalogues of inductors, looking for the best bang-for-the-buck in relation to anti-imaging filter inductors.

The gold standard, where performance is uppermost and cost and size are subsidiary, looks to be still the gapped ferrite pot cores I started out using. Their disadvantages are they need to be custom wound, not being available off-the-shelf, and their consequent higher cost. They also produce relatively bulky filters when a dozen or more are called for in a design. I've found nothing to beat them in performance, particularly accuracy and repeatability of their value and in terms of achievable Q (I've seen 500-plus in some cases on my meter).

I do hanker after a more portable and easier to replicate design though hence my investigations into cheaper alternatives.

Right down the bottom of the pile are the bobbin-wound coils, available in a wide variety of values here, at stunningly affordable...
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