The darlington are not suitable for the USSA in that position since it would reduce to much the gain of input stage then open loop gain, then damping factor compared to Mosfet. The reason being the lower vbe of bjt compared to higher vgs of Mosfet. For the FSSA, since the overall open loop gain is much higher than the USSA then it is not a problem to switch to darlington bjt in lieu of the Mosfet.
Meanie
If you can’t locate genuine Mosfet driver you can send me a personal message to see what we can do...
Fab
Meanie
If you can’t locate genuine Mosfet driver you can send me a personal message to see what we can do...
Fab
Reading thru Fab's building manual, the power supply stated it can take +/- 32Vdc rail.
Very tempting to customed wind the transformer for 22-0-22.
Has anyone running any voltages other than +/- 24Vdc ?
Am i pushing the limits ?
Many thanks.
Very tempting to customed wind the transformer for 22-0-22.
Has anyone running any voltages other than +/- 24Vdc ?
Am i pushing the limits ?
Many thanks.
Hi meanie
You can go with +/-32vdc PSU but we aware that you will have to reduce the bias current accordingly compared to using +/-24vdc for the same heatsink temperature. If you increase voltage you will have higher class AB power but since you reduce bias current then you will have lower class A power. And if your speaker are only 4 ohms then not that much power in class A anymore... since this is a low feedback design the THD is not that low in class AB....
Fab
You can go with +/-32vdc PSU but we aware that you will have to reduce the bias current accordingly compared to using +/-24vdc for the same heatsink temperature. If you increase voltage you will have higher class AB power but since you reduce bias current then you will have lower class A power. And if your speaker are only 4 ohms then not that much power in class A anymore... since this is a low feedback design the THD is not that low in class AB....
Fab
Great Asanden. I just sent you a build manual of the USSPA. Thanks to Tomtest for his comments on the first version of the manual. For H2 adjustment I will eventually provides more info but in the mean time you can just use the preamp as-is as the other builders including myself.
Fab
Last edited:
I think that the trim POTs need to be turned 180 degrees. The silk screening is correct.
Actually the trimmer does not match the silkscreen which is correct but I think that it will not pose any problem if it is a reverse rotation.
You're right. All he has to do is turn the pot in the opposite direction, when he is doing the setup.
I mentioned it because the manual needs to be updated and that many builders look at photos for guidance.
I mentioned it because the manual needs to be updated and that many builders look at photos for guidance.
For clarification the trimmers orientation shown in build pictures of the manual is correct. It was only versions 0.1 and 0.2 of the pcbs that had not the proper silkscreen for P3 and P4 screw indication. Version 0.4 has the proper screw position shown on the silkscreen.
This means that meanie has reversed the P1 to P4 orientation but he only has to turn the pot in reverse direction as pointed out here.
Fab
This means that meanie has reversed the P1 to P4 orientation but he only has to turn the pot in reverse direction as pointed out here.
Fab
Hello Fab,
I got the USSPA PCBs, thanks a lot. It seems that the Dutch post is faster then the German one. 😉
Sadly I am not at home this weekend, so I will start in the next week.😀
It is my pleasure if I can help, feel free to send it to me any time you want, I will have a look again.
A nice weekend to everybody and good progress.
André
I got the USSPA PCBs, thanks a lot. It seems that the Dutch post is faster then the German one. 😉
Sadly I am not at home this weekend, so I will start in the next week.😀
It is my pleasure if I can help, feel free to send it to me any time you want, I will have a look again.
A nice weekend to everybody and good progress.
André
USSPA PSU
Good afternoon Fab,
I think about a PSU for my USSPA build. What I have in my drawer, ist an unpopulated Sigma22 pcb and cap multiplier pcbs. Sigma22, a regulated PSU for premaps would be common for both channels, cap multiplier I 'd have one for each channel. Or I could easily make a CRCRC plus 7815 PSU, as Wayne did for the Whammy HPA. Would you recommend one of them?
Cheers
Ernst
Good afternoon Fab,
I think about a PSU for my USSPA build. What I have in my drawer, ist an unpopulated Sigma22 pcb and cap multiplier pcbs. Sigma22, a regulated PSU for premaps would be common for both channels, cap multiplier I 'd have one for each channel. Or I could easily make a CRCRC plus 7815 PSU, as Wayne did for the Whammy HPA. Would you recommend one of them?
Cheers
Ernst
Hi Ernst,
I have two USSPA preamplifiers and both uses a single Sigma 22. It is totally quiet, very dynamic and well separated. All my builds are usually dual mono but I can honestly say that I love them as is with the single Sigma 22, which i believe has a cap multiplier built in.
All the best!
Do
I have two USSPA preamplifiers and both uses a single Sigma 22. It is totally quiet, very dynamic and well separated. All my builds are usually dual mono but I can honestly say that I love them as is with the single Sigma 22, which i believe has a cap multiplier built in.
All the best!
Do
USSPA
Regulation Power dissipation may not be a major criteria here...unless you want to go full green...😛
Unfortunately I have not made comparison experiments to provide a specific recommendation for USSPA psu....however a very good regulated supply is needed because the PSRR of the preamp circuit is not high. Personally I use the very low noise series psu from DIYIHK because because they are convenient. I know that some builders have used a different approach with simple shunt regulators from Salas and they report good sound results.
Fab
Regulation Power dissipation may not be a major criteria here...unless you want to go full green...😛
Unfortunately I have not made comparison experiments to provide a specific recommendation for USSPA psu....however a very good regulated supply is needed because the PSRR of the preamp circuit is not high. Personally I use the very low noise series psu from DIYIHK because because they are convenient. I know that some builders have used a different approach with simple shunt regulators from Salas and they report good sound results.
Fab
Last edited:
I have a lot of inputs at this Audiocircle thread:
< or = $700 Linear Power Supply Comparisons
Sigma22, DIYIHK and much more.
< or = $700 Linear Power Supply Comparisons
Sigma22, DIYIHK and much more.