USSA-5 Build with Review

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#2,043
It’s Time…. Release the Beast!!🔥

Cooler weather is here and Fab’s USSA5 is first in rotation. Almost 5 years old and still one of my Favs.😉
 

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#2,046
Turns out the Source is connected to the back plate of ECW20n20 and ECW20p20 's , even though the Exicon data sheet doesn't state this .
https://www.exicon.info/PDFs/ecw20n20.pdf
Fortunately when testing the amp , I had 5 Amp fast blow fuses between the power supply rails and the USSA Amp board .

Can someone recommend which thermal pads to use for a TO-264 package ?
Or should I buy a sheet ?
I usually buy from mouser because shipping is free for amounts over $100 .
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#2,050
anatech said:
lol!
You aren't the first to find this out the hard way.
Non-standard package, it should have clear warnings.
Click to expand...

That's the 3rd time fuses have saved by back side when prototyping or setting up a Power Amp .
So highly recommend having fast blow fuses between the power supply and Amp board , when setting up an Amp .

If the ripple and noise on the +Ve and -Ve supply rails is equal , but opposite in phase ,
then theoretically ripple and noise should cancel out at Vout ... theoretically .
There is voltage drop across the fuses .
As such , recommend using the same value of fuse for both the +Ve and -Ve rail .
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#2,052
Brijac said:
One more thing to note, they have changed manufacturing process - well improved it - and new ones have slightly different name. ECW20N20-W6S ECW20P20-W6S. Should be in stock in a few days.
Click to expand...

As I recall , Profusion usually ships by DHL , which can get a bit pricey .
With my order last year for just 8 MOSFET's , I phoned them and asked if they would ship by Royal Mail - they were good with that .
It was $9 US from the UK to Canada , and there was no brokerage fee .
Royal Mail is slower than DHL , and I paid over the phone with a VISA .

Note that the phone number for Southend Sea , Essex only has 6 digits ... refer to post No. 2,033
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#2,053
Yep, they are really nice and communicative, willing to help out. Royal mail suits me too, so they also do me a solid with it as well. But told me to wait, as newly manufactured are on the way to get stocked.

"Starting wafer size changed from 4” to 6”.
6” wafers fabricated on a more modern fab with improved clean room
specification, improved wafer cleaning equipment, and higher precision
lithographic equipment."
 
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#2,054
With all the good audio transistors going EOL, several weeks ago I panicked when I checked Profusion's LatFet stock and all parts were showing zero stock!!
Communicated with them and they calmed me down, LatFet stock is safe for new projects to come.
 
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#2,055
Amadeus00 said:
In my case, for USSA-5 (EXICON) I was using AOS 218 247 1 from Fischer Elektronik.
Click to expand...


Thanks for this reference . I've already soldered on the MOSFET's and the Fischer pads are 1.5 mm thick .
Plus , I usually buy from mouser because shipping is free over $100 ... with No brokerage fee .
https://www.fischerelektronik.de/web_fischer/en_GB/heatsinks/E01.06/Aluminium oxide wafers/$catalogue/fischerData/PR/AOS2182471_/search.xhtml

I don't believe this is such a difficult item to source . You'd think I was asking for the meaning of life . Its just a thermal pad .

Here is a discussion on the topic of thermal pads for a TO-264 package .
N

Thread 'Currently available TO-264 insulators?'

I am planning an amp build using a pair of TO-264 devices on the output of each channel, but am having trouble finding a matching thermal pad which is not electrically conductive. Datasheets for Bergquist suggest there should be Sil-Pads of appropriate size, but I cannot seem to find them in-stock at my usual suppliers (Arrow, Mouser). It looks like the DIY Audio Store's Keratherm pads will work, but the price is rather steep.

Does anyone know of thermal pads of sufficient size and affordable price? Is it possible to make these work with careful orientation?

https://www.digikey.ca/en/products/detail/bergquist/SP900S-0.009-00-104/307800

I don't know anything about this topic , are there any other recommendations ?
The pad size needed is approx 24 mm x 20 mm

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#2,056
Amadeus00 said:
In my case, for USSA-5 (EXICON) I was using AOS 218 247 1 from Fischer Elektronik.
Click to expand...

Now its clear why you recommended these .... because Aluminum Oxide Ceramic pads have a high coefficient of thermal conductivity ,
and at a relatively reasonable price . Unfortunately , like everything else in life , there is a trade off .
Aluminum Oxide pads are quite thick .

These Aavid 4180G pads are 2.0 mm ( 0.079" ) thick
https://4donline.ihs.com/images/Vip...6-1.pdf?hkey=CECEF36DEECDED6468708AAF2E19C0C6

So I'd have to run the risk of moving the solder joints on the Exicon MOSFET's . It can be done , but I don't want to risk it .

These Bergquist SPA2000-0.015-00-104 pads have a thermal conductivity rating of 3.0 W (m-k )
https://www.mouser.ca/ProductDetail/951-SPA2000-01500104

They are 0.015" thick . Other than the silly price , before I order them , anyone see any issues with these ?

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