This amplifier deserves because its sound is sumptuous if everything is respected on the manual.
The only thing wrong is the difficulty in finding the mosfet drivers.
The only thing wrong is the difficulty in finding the mosfet drivers.
I think Fab has recently been experimenting with a darlington driver stage that will give an alternative to the hard to find mosfet driver stage.
Vunce has 26vdc *1.3A * 2= 67,8W dissipated. For sure that is too much for your heatsink size. Based on my 150mm height heatsink with +/-24vdc and 1.25A giving less than 50C with about 22C ambient, then we can extrapolate that 110/150* 48*1.25= 44W. This is only a rough estimation because our heatsink could have slightly different thermal coefficient property too. 44W/48vdc= 0.92A. If you reduce voltage by a few volts you can get more than 0.92A. 1A would give plenty of class A power into 8 ohms. Otherwise it switches into class AB at highest power demand.
Fab
Hi
I am not sure where your shown sheet comes from but surely not from me.😕
Ussa5 has 4.7uf and 22 kohms for high Pass filter to prevent DC to reach your speaker in case you have issue with your preamplifier and also shifting bias operating point of the amplifier input stage. In the past this filter was also filtering the low frequency generated by turntable (rumble) and I think phono player are still used today... the cutoff frequency is based also on feedback cutoff frequency amongst other parameters choice...some builders have decided to not install the input cap.
Fab
Yes that is correct. However, it is tested electrically but not in a system with speakers since I only had one pcb left of ussa5. Based on USSPA 1 & 2 and FSSA 1 & 2, I can suppose that the selected darlington bjt would also give excellent results. I think some members have proposed to build the ussa v 5.1 (darlington bjt drivers) provided they can get their hands on new USSA5 pcb....a small group buy is started but only 2 committed buyers since then...
Fab
Hi Nikosokey,
Ambient room temperature was 23°C when the hottest spot on the heatsink reached 42°C. The size is 300mm x 300mm x 75mm.
I have a couple of built Project16/Prasi CRC psu boards that I can compare to the SLB psu when I get both channels powered up and dialed in.
Thanks for the kind words 🙂
-Vunce
Hi Fab,
Success!! A single channel USSA5 is singing away 😀
Here are some of the vitals: Antek AN-2222 trafo, SLB psu, 26vdc @ 1.2A bias. The heatsinks are massive, there is margin to increase bias if needed. After 60 minutes the HS reaches 42°C
I’m happy to report there is an absolutely silent background at idle with this combination, also no power up/down thumps or noises. And if you look closely, it’s driven by a USSPA2 pre 😉
Next step will be to get the second heatsink prepped for mounting the USSA5 board. Final build will have a single SLB and Antek AS-4222 transformer.
Thanks for all your help!
Best,
Vunce
Vunce,
Great job! I would highly recommend a second SLB and trafo (if you have the chassis room) for a dual mono setup.
Even with no voltage sag and excellent current delivery, you just have to hear the difference between single vs. dual mono. Therefore, I build all of my preamp and amps as dual mono.
Cheers,
Greg
Thanks Greg!
I have been going back and forth with this decision 🙄
The chassis will be totally DIY in order to use these heatsinks, so I can make the room needed for a dual mono setup. In this case, Antek transformers have 200va and 300va sizes, nothing in between. I’d probably go for the larger of the two.
While I’m at it, I should make a wheelie cart for it also, this amplifier will be heavy!!!😀
Best,
Vunce
Vunce,
For dual mono, 2 x 200VA should be enough? IIRC Fab's minimum recommendation is 160VA per channel?
However, price difference isn't that much for Antek 200VA vs 300VA. Assuming you are going to order Antek, as with the SLB power supply you will need ~22VAC on the secondaries.
For dual mono, 2 x 200VA should be enough? IIRC Fab's minimum recommendation is 160VA per channel?
However, price difference isn't that much for Antek 200VA vs 300VA. Assuming you are going to order Antek, as with the SLB power supply you will need ~22VAC on the secondaries.
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Long story short.
A scrap metal yard was closing down to make way for a free way. I offered them $70 for copper off cuts, that they had thrown in a box. They agreed thinking that I would not be able to lift everything that was in the box. The copper was in my car before they could blink. 😀😀😀
A scrap metal yard was closing down to make way for a free way. I offered them $70 for copper off cuts, that they had thrown in a box. They agreed thinking that I would not be able to lift everything that was in the box. The copper was in my car before they could blink. 😀😀😀
