John Curl's Blowtorch preamplifier part II - Page 2072 - diyAudio
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Old 22nd February 2012, 02:42 PM   #20711
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Originally Posted by john curl View Post
We prefer not to use a nickel interface if we can avoid it. Our best connectors, for example, are direct gold on copper.
You're not avoiding the nickel. The alloy used to directly plate over copper or brass is a mixture of gold and nickel (or sometimes cobalt).

se
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Old 22nd February 2012, 03:42 PM   #20712
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Originally Posted by hitsware View Post
>Replacing all of the Supertex mosfets essentially
>fixed the amp up to new-like performance.

I at one time revamped a preamp circuit from ua709
(in cans) to DIP LF356. After a year the preamps
started sounding sorta muted. The Signetics guys
said it was leakage in the plastic. I assume the plastic
is better now ?
There have been significant advances in the plastics. Lower ionic contamination is one, better TCE another, better glob top material evolved.

The manu's became more technical with regard to the molding design, providing better physical catches on the leadframe for the plastic to grab.

Passivation techniques and concerns also changed.. better oxide layers, sometimes silicon nitride, getting rid of lateral pnp's, better guard rings on the silicon.. I've had problems with ionic contamination creeping in and compromising chips back in the day..twas when I larned about Scanning Ion Microscopy.

The wirebonding guys also got better..you've no idea how many times the silicon under the bonding pad ended up cratering, but some manu's just did a second bond next to the crater and shipped it.....

Soldering process control also helped.

Cheers, jn
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Old 22nd February 2012, 10:10 PM   #20713
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I never knew Signetics did the LF356. I thought that was National. I also used them in my first preamps. They were ok for the price, but by the early '80's there some other really better options, one them the NE5532/4 but of course these were bipolar inputs with high Ib.

Molding compounds are a very specialist area and there have been significant improvements over the last 20 years. One of the reasons metal and ceramic packages are no longer needed.
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Old 22nd February 2012, 10:18 PM   #20714
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Passivation techniques and concerns also changed.. better oxide layers, sometimes silicon nitride
A polyamid layer has become standard on many parts.
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Old 22nd February 2012, 10:26 PM   #20715
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Talkin to them physicists again Scott? Haven't you larned?

No, in 1982 I tried in vain to find anyone who understood the implications of thin metalizations on the Seebeck effect. I was trying to verify my empirical numbers for aluminum to gold plated Kovar.

John - We're making and offer tomorrow on a place in Bayview SF so I won't be far, Berkeley didn't work out this time around.
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Last edited by scott wurcer; 22nd February 2012 at 10:31 PM.
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Old 22nd February 2012, 10:43 PM   #20716
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Originally Posted by Bonsai View Post
I never knew Signetics did the LF356. I thought that was National. I also used them in my first preamps. They were ok for the price, but by the early '80's there some other really better options, one them the NE5532/4 but of course these were bipolar inputs with high Ib.

Molding compounds are a very specialist area and there have been significant improvements over the last 20 years. One of the reasons metal and ceramic packages are no longer needed.
http://home.earthlink.net/~dimlay/si...iesiiopamp.pdf

We were hooked up with Signetics some way.
Probably habit.
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Old 22nd February 2012, 11:39 PM   #20717
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Originally Posted by scott wurcer View Post
A polyamid layer has become standard on many parts.
Polyamide or polyimide? The latter has much higher temperature range.
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Old 23rd February 2012, 01:08 AM   #20718
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John - We're making and offer tomorrow on a place in Bayview SF so I won't be far, Berkeley didn't work out this time around.
Bayview? good long term investment. You must be in great health.

Good luck on your offer
-Antonio
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Old 23rd February 2012, 04:36 AM   #20719
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Bayview? good long term investment. You must be in great health.

Good luck on your offer
-Antonio
Great health, great wealth, or a thick skin? Take your pick.
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Old 23rd February 2012, 04:40 AM   #20720
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Polyamide or polyimide? The latter has much higher temperature range.
It's for mechanical reasons I might have failed on the spelling soory.
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