I recently come into possession of a DC-300A that allegedly works and doesn't seem to have any scorch marks on anything. I've read a bunch of threads here and there. I've just finished replacing all of the electrolytic caps, special emphasis on the 10uf 160v cap and upgraded big can caps. Also replaced the zeners with new 1w parts, and replaced the bridge rectifier with a new 50A part.
Haven't bench tested it yet.
Since this is the old DC-300A, it's built around that super old, crummy opamp that was cutting edge tech at the time and has no modern equivalent.
The Series II has clipping detection of course, and the late version of it was based around a pair of LF357H that we can presumably replace with a modern ultra-low-noise part.
I see where the idea of making DC-300A Series II clone boards was brought up before, by someone who seriously knows what they're doing, in this thread:
http://www.diyaudio.com/forums/group-buys/91796-crown-amcron-dc-300-serie-ii-clone.html
A few component changes allegedly received from Crown in this post:
http://www.diyaudio.com/forums/solid-state/89975-dc300a-ii-tweaks.html#post1056200
(The LM339 is of course not an opamp in the usual sense but a comparator and it only does clipping detection duty)
It's suggested in various threads that a lot of the other transistors are not really selection-critical and may comfortably be replaced with current production parts with similar specs.
There are threads around the various forums with discussion of current production output transistors, but right now i am under the impression that all or most of my original output transistors work, so I'd like to keep them if possible. I understand that the compensation network will have to change from what's in the Series II schematic to make that stable.
I sort of know my way around kicad and I have a good toner-transfer etching process at home.
The general idea, then, is to make a board that bolts and solders into my DC-300A, using the original chassis, power supply, and output transistors but adding the feature set of the Series II and with a cleaner opamp.
I can make and drill small numbers of boards myself. I even have an electroless tin plating process i can use.
Since it's not like i'd own the IP anyway, I figure I'd offer up the kicad files. The board layout, I sort of feel like I'd kind of feel ownership of, but i'd be cribbing from the datasheet there too, and it's not like there aren't people who would gladly distil board artwork from a photograph so maybe transfer art would be posted too. But maybe not the pcbnew files. I don't want to be "in business" but it wold be a kick in the pants to see someone take the project and run it into a business, and I've seen that happen to community projects.
Any interest? Warnings? Jeering from the peanut gallery?
I've got about a third of the main board schematic transcribed already.
Haven't bench tested it yet.
Since this is the old DC-300A, it's built around that super old, crummy opamp that was cutting edge tech at the time and has no modern equivalent.
The Series II has clipping detection of course, and the late version of it was based around a pair of LF357H that we can presumably replace with a modern ultra-low-noise part.
I see where the idea of making DC-300A Series II clone boards was brought up before, by someone who seriously knows what they're doing, in this thread:
http://www.diyaudio.com/forums/group-buys/91796-crown-amcron-dc-300-serie-ii-clone.html
A few component changes allegedly received from Crown in this post:
http://www.diyaudio.com/forums/solid-state/89975-dc300a-ii-tweaks.html#post1056200
(The LM339 is of course not an opamp in the usual sense but a comparator and it only does clipping detection duty)
It's suggested in various threads that a lot of the other transistors are not really selection-critical and may comfortably be replaced with current production parts with similar specs.
There are threads around the various forums with discussion of current production output transistors, but right now i am under the impression that all or most of my original output transistors work, so I'd like to keep them if possible. I understand that the compensation network will have to change from what's in the Series II schematic to make that stable.
I sort of know my way around kicad and I have a good toner-transfer etching process at home.
The general idea, then, is to make a board that bolts and solders into my DC-300A, using the original chassis, power supply, and output transistors but adding the feature set of the Series II and with a cleaner opamp.
I can make and drill small numbers of boards myself. I even have an electroless tin plating process i can use.
Since it's not like i'd own the IP anyway, I figure I'd offer up the kicad files. The board layout, I sort of feel like I'd kind of feel ownership of, but i'd be cribbing from the datasheet there too, and it's not like there aren't people who would gladly distil board artwork from a photograph so maybe transfer art would be posted too. But maybe not the pcbnew files. I don't want to be "in business" but it wold be a kick in the pants to see someone take the project and run it into a business, and I've seen that happen to community projects.
Any interest? Warnings? Jeering from the peanut gallery?
I've got about a third of the main board schematic transcribed already.
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