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Old 30th January 2013, 07:05 PM   #61
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Quote:
Originally Posted by Nelson Pass View Post
Here's a story for you. We were buying BJT output devices from a major semi
manufacturer (you can guess who, but they no longer make transistors and
it was forty years ago). We paid a premium to have all devices tested for
secondary breakdown as we had seen some problems with that, and we also
tested them in-house. We found a significant percentage breaking down
at voltages way below spec, so clearly they were either not testing them or
shipping them anyway. We called in the factory rep who was a real d**k
and after much discussion they agreed to replace them. We shipped the
bad parts back.

Later we received a batch of replacements, and found that they had our
felt pen test marks on them.

Thats awesome. at least they didnt erase the marks
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Old 30th January 2013, 07:31 PM   #62
amp_guy is offline amp_guy  United States
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Been there and done that too. I have made it a policy whenever the need arises to return product, I make a small mark or note some small cosmetic defect that will provide positive identification. Surprising how often I have that deja vue sensation.
A co-worker once had a inexplicable habit of placing components that he had replaced back in the supply cabinets, I suppose they were magic healing boxes. Maybe that bizarre notion is more widespread than we know.

I just found that ROHM is into SIC as well, if there are some alternatives to the unobtainium please share and the race will be on to hoard them as well!
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Old 30th January 2013, 07:33 PM   #63
amp_guy is offline amp_guy  United States
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On second thought
manufacturers BEWARE EXPOSURE ON DIYAUDIO seems to be the kiss of death for your product!
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Old 30th January 2013, 07:34 PM   #64
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Cree has lower comparable gain to the SS. Haven't seen the ROHM.
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Old 30th January 2013, 09:42 PM   #65
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Quote:
Originally Posted by Nelson Pass View Post
Here's a story for you. We were buying BJT output devices from a major semi
manufacturer (you can guess who, but they no longer make transistors and
it was forty years ago). We paid a premium to have all devices tested for
secondary breakdown as we had seen some problems with that, and we also
tested them in-house. We found a significant percentage breaking down
at voltages way below spec, so clearly they were either not testing them or
shipping them anyway. We called in the factory rep who was a real d**k
and after much discussion they agreed to replace them. We shipped the
bad parts back.

Later we received a batch of replacements, and found that they had our
felt pen test marks on them.

Prudent business practices by you at THRESHOLD. It pre-empted a quagmire of failed and returned amps plus possible ill reputation. Your scientific and business reputation is pristine clean due to all that.
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Old 31st January 2013, 04:01 PM   #66
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Thanks, amp-guy. Too kind for sure, but

I have wondered about the Cree MOSFET from an audio perspective myself. Attached is a LTSpice model of the CMF20120 MOSFET distributed by Cree and evaluated by one of my students in the second attachment for validity against the data sheet. The capacitance and transfer characteristics match up well which are of first order importance to linearity and performance. The output curves computed by the model are less valid which, while not so important to the intended customers of the MOSFET, definitely plays a role in the compensation of the square law dependence of the transfer curve. Hence the model may not tell you all you want to know about using it for audiophile work in lieu of a SemiSouth JFET. Getting a Cree MOSFET is easy so I assume folks here have already checked them out. Love to hear about experiences.

On another note, I'm putting the finishing touches on an article containing my thoughts on spotting SemiSouth fakes. I'm going to post the PDF in a new thread, which I'm planning to call the "SemiSouth boiler room." I expect to make the first post any day now. I look forward to feedback from the community and ideas for new topics.


Quote:
Originally Posted by amp-guy View Post
first of all I feel safe in expressing a hearty thanks from all of us fanatics here at DIY to Mike Mazzola for providing his first hand knowledge.
One of the great things about DIYAudio is that the real great contributors to the art are willing to share knowledge and experience freely here.

As one who stood on the sidelines and have not obtained a single SIC device, where does that leave those who are looking.
Are the devices from CREE at all suitable?
Attached Files
File Type: txt CMF20120.txt (4.4 KB, 33 views)
File Type: pdf CMF20120D_sim_vs_datasheet.pdf (410.9 KB, 53 views)
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Old 31st January 2013, 05:33 PM   #67
amp_guy is offline amp_guy  United States
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Maybe the illegitimate parts should be labeled "somewhat-south"
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Old 31st January 2013, 05:41 PM   #68
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The CMF10120 is $16 and they are in stock at Digikey.

The only potential issue I note is that the Crss increases quite a bit at Vds
below 30V. This means that you either want to drive it with a low capacitance
or keep the Vds high.

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Old 31st January 2013, 06:30 PM   #69
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Quote:
Originally Posted by Nelson Pass View Post
The CMF10120 is $16 and they are in stock at Digikey.

The only potential issue I note is that the Crss increases quite a bit at Vds
below 30V. This means that you either want to drive it with a low capacitance
or keep the Vds high.

Nelson brings up a good point that power switching folks and audiophiles can agree on. The SiC MOSFET is more capacitance heavy than the SiC trench JFET. This is a result of the fact that the SemiSouth JFET has better figures of merit on specific on-resistance than is possible with current lateral channel SiC MOSFETs. This applies to the Rohm MOSFET too. A trench MOSFET by Rohm which is not commercially released yet should (eventually) benchmark better with the trench JFET.
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Old 7th February 2013, 12:42 PM   #70
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Quote:
Originally Posted by Blink_PT View Post
China has destroyed the trade in almost all over the world, counterfeiters are in almost everything, have contributed to the crisis World.

If paid by Paypal, make a complaint to paypal and get your money.

Both Tranton Shenzhen Electronic Technology Co., Ltd. as the Elcodis.com are companies that sell fake stuff.

I received emails from two.

I asked to the two photos, one said he sent the photo with the product, not the other responds, the Tranton sold each to $ 10, the Elcodis sells $ 37.5 each.

Photos true.

Click the image to open in full size.


Mail to me...
--------------------------------------
Hello dear

Thank you for the request. I have a quotation for you.

Item: (SJEP120R100A )
Quantity requested:4
Quantity available: 4
Price per item: 37,5 USD
I can send you the order in 3-5 days after payment.

I will also need your shipping address to calculate shipping cost. Please let me know if you have any shipping account.

We accept payment by:
1.Wiretransfer (30 USD fee)
2.PayPal (5% from the total amount of the order)

If you need more details for this quotation don't hesitate to ask me.

Regards,
Marina
Does your photo show genuine parts or fakes?
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