USSA-5 Build with Review

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Project16

Project16

Member
Joined 2012
e_fortier said:
Hi Fab

What type of chassis would you recommend ? Is a 3U, 300mm deep ok ?

Thanks
Eric
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Hello Eric

My USSA-5 is in a box 3U - 300mm and no particular problem of heat for 1.1A on the mosfets, the temperature of the heatsinks does not exceed 47 ° with an ambient temperature not exceeding 25 °. The only problem with a model 3U - 30mm is the space available inside for the power supply which is quite limited and a model 3U - 400mm would be more suitable.

;)
 

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e_fortier

e_fortier

Member
Joined 2001
Project16 said:
Hello Eric

My USSA-5 is in a box 3U - 300mm and no particular problem of heat for 1.1A on the mosfets, the temperature of the heatsinks does not exceed 47 ° with an ambient temperature not exceeding 25 °. The only problem with a model 3U - 30mm is the space available inside for the power supply which is quite limited and a model 3U - 400mm would be more suitable.

;)
Click to expand...

Thanks guys, I’ll go w 3U but aim for 400mm.

Amazing work Project16
 
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fab

fab

Member
Joined 2004
fabaudio.online
Paid Member
taccodude said:
Would it be ok to use 0,25W Resistor instead of 0,5W, got a lot of those.
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It depends on the quality of the resistors you have. First drift of nominal value is based on temperature of the resistor and its Temperature Coefficient of Resistance. The TCR of the part number indicated in BOM is 100ppm (or lower).
Lower power resistor means higher temperature in operation. Therefore, you must at least verify the TCR of your 0,25W resistors. The most critical resistors (0,5W ones) in that regard are the M3/M4 at source and the "low" feed-back resistors (75 ohms for USSA-3). In USSA-3 this feed-back resistors value of 15 ohms is even more critical. As for the effect on sound it has not been evaluated but if you want optimised results do not deviate from BOM parts characteristics...
Metal film vs carbon material has been found to have different sonic signature by peoples. I do not have much experience in that regards but technically metal film is good for me.

Fab
 
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fab

fab

Member
Joined 2004
fabaudio.online
Paid Member
To give you an idea my USSA-5 with 25Wrms full class A (into 8 ohms) has about 300mm x 140mm x 40mm heatsinks (standard vertical fins) for about a little less than 50C (20C ambient).
Smaller heatsink will allow less bias thus less power in class A for the same temperature.
Fab
 
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