Demian:
Thanks for sharing this.
I'm curious - I didn't think those old Supertex VN1306 were Depletion Mode MOSFETs. Assuming they really are not, how does the front-end diff amp in the "DMA-50 driver revised" bias up properly? I would have expected some high IDSS JFET like a pair of J111 as cascodes instead for this kind of cascode configuration ...
Thanks for sharing this.
I'm curious - I didn't think those old Supertex VN1306 were Depletion Mode MOSFETs. Assuming they really are not, how does the front-end diff amp in the "DMA-50 driver revised" bias up properly? I would have expected some high IDSS JFET like a pair of J111 as cascodes instead for this kind of cascode configuration ...
Sorry about the oversight. I am using depleation mod gets now. I just sailed past that detail. I have not looked at this stuff closely since the 1990's. Fortunately my amp has been working fine since then.
You have the full Crosby mod. There are possibly other areas to tweak but not many and not much ROI for huge effort.
The Crosby mod started with the active regulator for the input/driver circuit. I believe there was also a seperate always on supply for the regulator. (There is in the DMA 50 mod) Then additional caps and component tweaks on the modules. Since it used very premium parts initially there is not a lot to upgrade.
The backlight is an electrolumincent panel. An LED backlight for a display would be the best modern option. This may be a "direct fit" option: https://www.adafruit.com/product/625
The Crosby mod started with the active regulator for the input/driver circuit. I believe there was also a seperate always on supply for the regulator. (There is in the DMA 50 mod) Then additional caps and component tweaks on the modules. Since it used very premium parts initially there is not a lot to upgrade.
The backlight is an electrolumincent panel. An LED backlight for a display would be the best modern option. This may be a "direct fit" option: https://www.adafruit.com/product/625