John Curl's Blowtorch preamplifier part II

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#33,121
john curl said:
JC-3 phono preamp measurements from STEREOPHILE.
Please note: No complaints about S/N
By the way, I did NOT use the AD797 in the final design.
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Wanna explain what possessed you to use AD797 in the evil JC2 original?

YOUR poor design and YOUR inappropriate choices are NOT reasons to dismiss excellent devices (wrongly used) and claim they are mid-range, evil, must have unacceptable 7th harmonic distortion .. bla bla

Wanna show us the poor reviews of the original JC2?
 
#33,124
PMA said:
I do, I have my own measurements of dozens of opamps under normal conditions, with standard load like 2k - 10k, 2Vrms, gain 1 - 10. None of the good opamps (OPA627, AD797, OPA134 ...) has any residual 7th above -120dB. They do not sound same, but the 7th is not the reason. John's fairy tales about the 7th are marketing claims. We can easily find the 7th above -120dB in many so called High End products, as I have linked earlier.
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Hello to Pavel and all others here, and not the least hello to you JC 😎.
As a long time looker and listener to this thread, I and I am sure most others here have gained very much valuable and insightful knowledge....the value of a true collective.
Recently there has been much debate about the deleteriousness of presence of 7th harmonic production, at what would seem to be close to infinitesimal levels.

Pavel, could you please elaborate on your above statement (my bolding) in objective and/or subjective terms ?.

Thanks, Dan.
 
#33,125
john curl said:
JC-3 phono preamp measurements from STEREOPHILE.
Please note: No complaints about S/N
By the way, I did NOT use the AD797 in the final design.
Click to expand...

But Atkinson wrote
As with John Curl's legendary Vendetta phono preamplifier, the Halo JC 3 was superbly quiet. The wideband, unweighted signal/noise ratio, measured with the input short-circuited, was 78dB (MM) ref. 1kHz at 5mV, and 67dB (MC) ref. 1kHz at 500µV.
Click to expand...

78dB ref. 1kHz at 5mV with input shorted is a high noise. With proper design, you can get near 90dB under these conditions. As Richard has said, you have lost some 10dB due to your circuit design.
 
#33,127
test2:
 

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#33,128
Is that a slide rule you're holding John? Great pic.

Now that I'm here, can I interrupt the great entertainment with a tech question to the assembled intellect here:

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
 
#33,130
The wipers can take quit a bit of current as they are metal. Its the resistive material that cant take as much current.

However, for distortion, the contact point in the presence of dc current thru it can be a source of distortion. The design of the contact wiper will determine to a large extent the distortion from that point contact. -RNMarsh
 
#33,131
john curl said:
I was a fool, who still believed in Scott Wurcer. '-)
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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.
 
#33,135
jan.didden said:
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
Click to expand...

http://www.digikey.com/Web%20Export/Supplier%20Content/Bourns_118/PDF/Bourns_TrimmerPrimer.pdf?redirected=1

http://www.bourns.com/pdfs/OnlinePotentiometerHandbook.pdf

too big files to be attached
 
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#33,137
jan.didden said:
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;
Click to expand...
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.
 
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