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wildcopper

Posted Thu Aug 20, 2020 8:13 pm

I love my newly acquired Amiga 1000. But I've always much preferred the sound of the Amiga with the low pass audio filter disabled. Unlike the software switchable filter on later Amiga models the filter on the Amiga 1000 is always on. Fortunately there's this simple hack to disable it - either making it switchable as in the original hack description or permanently off (what I chose). Probably this hack isn't news to anyone familiar with the Amiga 1000 - but I figured I'd share some photos of the end result.

I found the hack itself on Tom-D-Tek's AMIGA Hack Page. I noticed a minor error where the labeling of pins 6 and 7 of the LF347 were swapped. Here's the corrected version:

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The section of interest on the original board looks like this (daughterboard has been removed):

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The op-amp chip (U5G) on this motherboard is actually an LF347 equivalent (µPC4084C).

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In order to interrupt the original filter output path the positive lead of C66 and C64 electrolytic capacitors are lifted and connected to the filter inputs at TP2 and TP3 respectively. No permanent modifications are necessary (no traces cut) - only a bit of soldering (and desoldering). You'll want to use good quality temperature-controlled, ESD safe soldering and desoldering irons to minimize the chance of damaging anything.

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Here it is mostly buttoned back up. I turned it on and heard a beautiful (unfiltered) kickstart boot chime. :)

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finrock
Cupertino, California

Posted Thu Aug 20, 2020 10:29 pm

Thanks for posting this. I may have done the mod incorrectly, I will verify using this information.

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intric8
Seattle, WA, USA
Website

Posted Sat Aug 22, 2020 12:18 pm

I asked a friend of mine who is an Amiga/hardware guru if he had ever seen this hack before.

Christian:
Not with that one. Only the more elaborate one which controls the filters with the CIA (dark LED -> low pass filters off) just like all later Amigas.

I like [this] simple one. Less modifications.
That's high praise right there, I can guarantee.

You've also inspired a few folks over on Reddit to follow your path, Wildcopper. Super cool!

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Christian

Posted Wed Aug 26, 2020 9:07 pm

As Eric cited me - this is really great.

P.S.: I can‘t believe that I wrote “less modifications” - I must have been tired. Fewer modifications is the correct way to say it :-)





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