Great news !Good Sunday afternoon, I've just finished my PSU for my USSA-5 build, and completed and measured both channels. So I need just a few resistors in order to correct the drivers current to 20ma.And I need a new R27 on one channel, because I fried it while taking off the crocodile clamps in an unproper way.
Beside that everything seems to be OK and I have to wait for the resistors. In the meantime the amp will move into its future chassis.
More to come.
Have a great Sunday!
Remember that 20ma driver current is for adjustment purpose at 1A output bias assuming that your final output bias will be more than 1,2 A . You can also target a little higher driver current such as 23ma for example.
Fab
Not with this amp. Fab has another version which uses similar 2SK1530 & 2SJ201 Toshiba power mosfet. Be careful with those mosfets are rated only for medium (less) power.
Yes that is right. Using vertical mosfet (even if these are good vertical mosfet for audio) instead of lateral MOSFETs would need design changes...
USSA1 and 2 use the mosfet you indicate. Even F5-USSA amp is a good candidate for your mosfet.
I can entertain an USSA5 type schematic with the 2SK1530 & 2SJ201 but that would be another thread subject and the sound result would be different too.
Fab
I was lucky enough to buy a USSA-5 kit in November that was a left over from the earlier QuebecDIY forum group buy (thanks Do).
I promised Fab that I would update as I made progress, so here is the first. These are the version 0.1 boards in glowing red. Most of the small resistors are in (though I made a mistake on my last order and shorted myself a couple of 220R, so testing will have to wait until I can get more)). Some of the larger resistors, small diodes and jfets are in too.
Question for Fab: capacitor C1 (220 pF mica in the kit). The mica leads are too big and would have to be soldered to the top of the pads, per Do's suggestion. I have some extra 240 pF polystyrene that would go through hole and wondering if these would be appropriate in this position?
Thanks!
I promised Fab that I would update as I made progress, so here is the first. These are the version 0.1 boards in glowing red. Most of the small resistors are in (though I made a mistake on my last order and shorted myself a couple of 220R, so testing will have to wait until I can get more)). Some of the larger resistors, small diodes and jfets are in too.
Question for Fab: capacitor C1 (220 pF mica in the kit). The mica leads are too big and would have to be soldered to the top of the pads, per Do's suggestion. I have some extra 240 pF polystyrene that would go through hole and wondering if these would be appropriate in this position?
Thanks!
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12V offset
Hi Fab,
meanwhile I have I have changed the reisistors R13/R14 on both channels in order to have about 26ma drivercurrent.
One channel is working very well, I could set bias to 1A, offset ist below 2mV
The second channel shows 12V offset after resistorchange and I have no idea, why that could be. This offset cannot be reduced under about 9V by adjustment of P1/P2.
Any idea, what this could be?
Cheers Ernst
Hi Fab,
meanwhile I have I have changed the reisistors R13/R14 on both channels in order to have about 26ma drivercurrent.
One channel is working very well, I could set bias to 1A, offset ist below 2mV
The second channel shows 12V offset after resistorchange and I have no idea, why that could be. This offset cannot be reduced under about 9V by adjustment of P1/P2.
Any idea, what this could be?
Cheers Ernst
Hi ErnstHi Fab,
meanwhile I have I have changed the reisistors R13/R14 on both channels in order to have about 26ma drivercurrent.
One channel is working very well, I could set bias to 1A, offset ist below 2mV
The second channel shows 12V offset after resistorchange and I have no idea, why that could be. This offset cannot be reduced under about 9V by adjustment of P1/P2.
Any idea, what this could be?
Cheers Ernst
I am glad you have one channel fine.
For the other channel, you can redo the test sections (8.7, 8.8.5, 8.14, 8.17, 8.18) of the manual with pcb fully populated and provide results for each. I need more info. Ensure you have both ground terminals of the pcb connected to PSU. Check for any solder bridge or cold solder joints. Check for shorted diodes close to mosfet gate. Check driver VGS which should be about 2 to 2.4 volts.
Fab
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