Thanks for the encouragement Fellas! I was able to make some more progress today 🙂
All previous measurements checked out fine, now my test bed is set up and ready for full power to set Mosfet bias and VGS measurements.
Question: Should the USSA5 PGND and GND tabs tie together at the psu GND tab?
Thanks,
Vunce
All previous measurements checked out fine, now my test bed is set up and ready for full power to set Mosfet bias and VGS measurements.
Question: Should the USSA5 PGND and GND tabs tie together at the psu GND tab?
Thanks,
Vunce
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Hi Vunce
Yes both PGND (power) and GND (small signal) should be connected to PSU ground.
You are progressing well!
Just a note I do not see any RVx resistors installed....
Fab
Yes both PGND (power) and GND (small signal) should be connected to PSU ground.
You are progressing well!
Just a note I do not see any RVx resistors installed....
Fab
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Hi Fab,
Powered up!
Running approximately 2mV offset and 60mV bias after 30 minutes.
RV1B = 100R
RV2B = 47R
These are mounted on the backside of the pcb.
Powered up!
Running approximately 2mV offset and 60mV bias after 30 minutes.
RV1B = 100R
RV2B = 47R
These are mounted on the backside of the pcb.
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Be careful with the thermistors on the heatsink surfaces, i had mine singing happily then suddenly smoke out, because one the thermistor's insulation broke and shorted to gnd thru the heatsink.
I recorded the voltages at the TP’s,
but haven’t done the calculations yet.
VGSN = 1.068V
VGSP = 1.680V
I did some calculations (hopefully correctly) and here is what I came up with.
Positive Side: 1.68v
RM3 = 84R
RV1 = 37R
RV1A = 33R (closest value in parts bin)
Driver current = 23.3mA
Negative Side: 1.07v
RM4 = 53.5R
RV2 = 6.5R
RV2A = 0R
RV2B = 0R (jumper)
Driver current = 22.8mA
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
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
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Hi Vunce
Congratulations and you are welcome!
With the SLB you should have a clean PSU. Also, the AS transformer is quite good for the buck.You have quite a huge heatsink 😛 if you have 4 ohms speakers you can increase bias a little furthermore to increase the class A power envelope.
For the calculations, IM3= VGSP / (47+ RV1A ll RV1B) and similarly for IM4.
Good luck for the second channel.
Fab
Congratulations and you are welcome!
With the SLB you should have a clean PSU. Also, the AS transformer is quite good for the buck.You have quite a huge heatsink 😛 if you have 4 ohms speakers you can increase bias a little furthermore to increase the class A power envelope.
For the calculations, IM3= VGSP / (47+ RV1A ll RV1B) and similarly for IM4.
Good luck for the second channel.
Fab
Yasou Niko. I hope you inspire Thimios to build this amp.
My amp is on hold because my wife has made me renovate
Yasou Harry !!!🙂🙂
I'm talking always with Thimios but i know he hasn't started-finished this amplifier....yet ...
i hope finish yours.... Harry.
I would like to thanks my friends Project16 ,Pinnocchio , Fab that helped me start this amplifier....
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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,
Very nice work !
I hope you write us your impressions of this amplifier and acoustic differences if present... between classic PSU vs SLB if you have that opportunity...
Τhanks .
What is the room temperature you had?
Very large Heatsink ... and reaches 42°C ? !!
Dimensions?
Input section
hello i am planing to direcly feeding ussa from a preamplifier, i think (C2 R1) at the input section is high pass filter. Cut of frequency is around 1.5 Hz i guess. I saw simillar topology in different amplifiers (exp jlh2003) before but i do not know what they used for and what if we do not used it?
hello i am planing to direcly feeding ussa from a preamplifier, i think (C2 R1) at the input section is high pass filter. Cut of frequency is around 1.5 Hz i guess. I saw simillar topology in different amplifiers (exp jlh2003) before but i do not know what they used for and what if we do not used it?
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