Hi stretchneck
Indeed 50W (and even more) does not require 2 pairs. I call it Turbo version instead of Twin Turbo with 2 pairs. Remember that a single double die pair is already like 2 single pairs!
you simply has to reduce bias depending on heatsink size. However I would not go below 500ma of bias current to keep distorsion low enough, highest current is best.
Of course this is for USSA-5 versions only since USSA-3 versions have maximum PSU voltage because of input jfet.
good luck
p.s. I do have a more simple extended board than the one from nfsgame is developing that I had done as a prototype but it was never tested so far…
Fab
Indeed 50W (and even more) does not require 2 pairs. I call it Turbo version instead of Twin Turbo with 2 pairs. Remember that a single double die pair is already like 2 single pairs!
you simply has to reduce bias depending on heatsink size. However I would not go below 500ma of bias current to keep distorsion low enough, highest current is best.
Of course this is for USSA-5 versions only since USSA-3 versions have maximum PSU voltage because of input jfet.
good luck
p.s. I do have a more simple extended board than the one from nfsgame is developing that I had done as a prototype but it was never tested so far…
Fab
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stretchneck
Well…assuming +/-36 VDC that makes 86 to 108W steady dissipation per heatsink…
1.5A gives already min 36Wrms in full class A ( more in reality) into 8 ohms and then class AB up to maybe 60Wrms into 8 ohms in class AB (with +/-36VDC). For 4 ohms, >18W class A and about double power ( >100W) in class AB. I assume you have a big PSU.
Higher voltage gives more class AB but then less bias thus less class A…your choice.
Soundwise the USSA performs better in class A than class AB…. Higher class AB would benefit more going Twin Turbo…
My own USSA-5.2 Twin Turbo is 75Wrms / 8 ohms And about > 7Wrms in full class A / 8 ohms.
But, from reported experience, USSA 20Wrms/8 ohms class A can drive any speaker tried so far (example: kEF Reference 5 Meta) and even to high sound level in a normal size room…
Fab
Well…assuming +/-36 VDC that makes 86 to 108W steady dissipation per heatsink…
1.5A gives already min 36Wrms in full class A ( more in reality) into 8 ohms and then class AB up to maybe 60Wrms into 8 ohms in class AB (with +/-36VDC). For 4 ohms, >18W class A and about double power ( >100W) in class AB. I assume you have a big PSU.
Higher voltage gives more class AB but then less bias thus less class A…your choice.
Soundwise the USSA performs better in class A than class AB…. Higher class AB would benefit more going Twin Turbo…
My own USSA-5.2 Twin Turbo is 75Wrms / 8 ohms And about > 7Wrms in full class A / 8 ohms.
But, from reported experience, USSA 20Wrms/8 ohms class A can drive any speaker tried so far (example: kEF Reference 5 Meta) and even to high sound level in a normal size room…
Fab
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If you can stomach to build your own enclosure, this should get you further than a modushop case. Their heat sinks are large so heat cannot be spread effectively, and only 40mm thick. The eBay ones are higher, narrower and 75mm thick. Much more suitable for high dissipation from four transistors mounted from a small pcb.
Cheers - Vunce uses something similar, heat sinks from PV inverters.
I’m going with the clean look of modushop however - but which I might do is mount the USSA PCB on a copper bar/time to extend the useful heatsink area… also potentially easier for mounting.
a usefully sized copper plate sounds expensive. Heat pipes + Alu clamps from Ali might be cheaper, and if you simply use that to spread the heat, while still mounting the actives to the heatsink directly, you can add it easily later if you find you need it.