John Curl's Blowtorch preamplifier part II

[kgrlee]

Originally Posted by john curl

I was a fool, who still believed in Scott Wurcer. '-)

JC, if you believed in him, you should have read his datasheet.

The best OPA or even Golden Pinnae stuff, hand carved from solid Unobtainium by virgins, won't stop poor design from losing 10dB of signal noise .. or introducing distortion and instability with poor decoupling and layout.

Mostly explained in the AD797 datasheet.

[mikelm]

So do most people here believe everything they read in data sheets ?

[SY]

They're not always 100% accurate, but one would be foolish to not use them as a starting point. The 797 datasheet is a particularly good one.

[jan.didden]

@ RM: Wel if I stay with the total current through the device below the stated dissipation, than that's taken care of I guess.
Like a 5k pot in mid position, with 7 mA entering at each end terminal, and the wiper sinking the total. Dissipation is just 250mW, but the wiper current is 14mA. That OK you figure?

jan

[stormsonic]

Originally Posted by jan.didden

I have a project using some Bourns series 3296 25-turn trimmers. I've been trying to find a spec for the max wiper current but it's not on the Bourns data sheet; it only lists max dissipation. An email to tech support was met with deafening silence. Google couldn't help either.
Anybody has any info on that?

jan

http://www.digikey.com/Web%20Export/...f?redirected=1

http://www.bourns.com/pdfs/OnlinePot...erHandbook.pdf

too big files to be attached

[jan.didden]

Many thanks! The first doc gives me what I was looking for. Seems I am in the clear, which is good since I already ordered the boards

jan

[Esperado]

Originally Posted by jan.didden

I have a project using some Bourns series 3296 25-turn trimmers. I've been trying to find a spec for the max wiper current but it's not on the Bourns data sheet;

It depend of the value. I would use max 10mA for a 1/25 W of 1K, but 3ma for 10k, 1mA for 100k etc and this, for the long run
If you are in concern with noise for DC and distortion for signal , better divide those value by 3. Just my two cents.

[edit] Oh, I don't saw the previous, hope it correlate.

[john curl]

It's only a schematic, guys! At first I could not understand what you were referring too. Then I realized that you meant the 500 ohms that gets paralleled with 50 ohms to get the higher gain for MC input. I consider it a good compromise, so that I don't load the OPA.

[jan.didden]

Not bad:

Rtrim 0.25W 0.5W 1W
10 OHMS 100 MA 100 MA 100 MA
100 OHMS 50 MA 71 MA 100 MA
1 K OHMS 16 MA 22 MA 32 MA
10K OHMS 5.0 MA 7.1 MA 10 MA
100K OHMS 1.5 MA 2.2 MA 3.2 MA
1 M OHMS 0.5 MA 0.7 MA 1.0 MA

jan

[john curl]

The photo that I put up was: Me arguing with Saul Marantz in 1982, with Noel Lee looking on. I guess that I will argue with just anybody. '-)
3 Years later, I was hired by Saul as VP of Engineering for Lineage.