Preamp with features!

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fotios

fotios

Member
Joined 2007
SQLGuy said:


Magnetic contacts would, in most cases, be non-stainless ferrous metals. That means they would be prone to oxidation, especially if being repeatedly heated, cooled, and exposed to arcs.

Also, magentic materials lose magnetism when heated. High current relay contacts that rely on the magnetism of the contacts themselves might become bad connections under high current.
Click to expand...

Thanks for the explanation, and yes it makes sense.

Fotios
 
jean-paul

jean-paul

Disabled Account
Joined 2002
+ and - 9V for the analog section seems a little low. Why not use dual 15 V supplies for more headroom ?

At the risk of being accused to be too precise: 39 uf is a value that is hard to get. 47 uf is a more common value. Please adjust the layout to accomodate for 47 uF or even 100 uf.
 
jwb

jwb

Member
Joined 2002
+/-9V is the most the CS3318 can handle.

The 39µF part is a specific part if you'll refer to the bill of materials. It's chosen to reduce power supply impedance in the band of interest (< 100kHz). Also I like using those polymer caps for their high reliability.
 
jwb

jwb

Member
Joined 2002
And so it begins.
 

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jwb

jwb

Member
Joined 2002
That transformer I specified is useless. Digi-key says it's 16VAC in parallel, but it's not. It's 16VAC on one secondary, and 35VAC on the other. The correct transformer is Tamura 3FD-416. Sorry for the error.

Here are the manufacturing images for the board, in a 1MB PDF file. The pages, in order, are the outline, the silkscreen, the top solder mask, metal layers 1 through 6, and the bottom solder mask.

http://octothorpe.barelyconnected.net/~jwb/preamp/gerber.pdf
 
jwb

jwb

Member
Joined 2002
I had 10 boards made, although I only plan to build two units myself. I will sell the boards to forum members for the low, low, insanely low price of $125, shipped in the USA or Canada, if anyone is interested. That's my cost. Anyway I'll post it over on the market forum later after I prove that the boards are error-free.
 
jwb

jwb

Member
Joined 2002
One design note: I found that you can't allow the -9V regulator to operate when the +9V regulator is disabled. The CS3318 draws infinite current in this state. Luckily my negative shunt regulators are inherently limited to 200mA of current, so I don't think the chips were damaged or destroyed in my testing.

The good news is all four regulators work great, and nothing smokes when the unit is powered on.

The only real construction difficulty was mounting those Jensen transformers. Their #30 stranded leads are very difficult to strip properly, and sticking a #30 stranded wire in a #30 drill hole is painful.
 
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