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USSA-5 PCB GB

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#921
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
 
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#922
Yes single-Turbo does seem easier than waiting for the helper PCB and the added complexity. I just don't want to have regret of not having built twin-turbo 🙂

USSA 5.0 then, 36v CLC dual mono power supply, 1.2 to 1.5A bias, 4U modushop.

Or should I consider higher voltage for more class A/B?
 
#923
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
 
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#925
Way to go man!
You can always change Turbo to Twin Turbo later ( a few added drilled and tapped holes). You can buy the number of Exicon mosfet for 2 Turbo amps which can be used for 1 Twin Turbo amp. This way they should be rekat well matched by Profusion (same buy normally same lot).

Fab
 
#926
stretchneck said:
pretty much on the edge of what is practical in terms of heatsinking
Click to expand...
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.
 
#927
maximax77 said:
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.
Click to expand...
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.
 
#930

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#933
Hello Elias
thanks for your interest in the FSSA amplifier. See this thread for more info: https://www.diyaudio.com/community/...-build-thread-with-review.350238/post-6097777
USSA type is mainly class A amplifier
FSSA is class AB amplifier
Both use different PCB.

I do not know that specific quasi complimentary amplifier you refer to. The FSSA design is quite different than this quasi design in many aspects. Both amps should sound very different in my opinion….

“huge“ mean bigger than big 😉, so wide and deep sound stage for example. This has no relation with mono or dual mono PSU which is more related to left and right channels separation. Soundstage is much more than channel separation and related to instruments separation (isolated) and position in space…. example : like a band playing in front of you where each instrument has its position and is clearly defined as opposed to a “blended” sound coming from nowhere in particular…. Some people’s report this type of sound as holographic.

Fab
 
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#934
fab said:
“huge“ mean bigger than big 😉, so wide and deep sound stage for example.
Click to expand...
thanks for the link.
This is my obsession with stereo sound. Since '76 when I made my first amplifier (nothing sophisticated, just 30W AB-class) I found experimentally that using a transformer (160VA that I had) with a double secondary and then 4 rectifier bridges with the corresponding capacitors (8 x 22000µF - capacitance COUNTS - as well as the power "isolation" between the channels), I had the "optimal" results, regarding the stage presentation.

Elias
 
#935
Good that you have experienced that and especially with a better power supply for a same amplifier.

However power isolation is only a contributor to sound stage but the main one is the amplifier topology. The sound stage character of the USSA or FSSA should not be driven that much by power isolation if using the same overall power supply capacity (power and filtering).

Fab
 
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