John Curl's Blowtorch preamplifier part II

[john curl]

I was going to introduce the somewhat more complex circuit later, once the CORE of the design was well discussed, but I can't fight 'city hall'. '-)

 

[john curl]

less tilted

 

[john curl]

Now together, side by side. Note similarity.

 

[john curl]

together

 

[Wavebourn]

Resistors in tails of transistors turn outputs to kind of LTPs as well.

 

[john curl]

OK, first question, what sets the (approximate) current limit of each jfet on the CORE schematic?

 

[elektroj]

Well, to me the main difference is inclusion of multiple feedback loops in the later design, although it's difficult to analyze it exactly without knowing the ratios of all resistors that are connected to all four Fet sources.

Best,

 

[hitsware]

But isn't the ground (0V) in the middle implied ?
But yet if hardwired turns the whole thing class B

 

[johnferrier]

the resistor in the middle ?

 

[john curl]

It does NOT need a ground reference, except at the inputs.

 

[hitsware]

the resistor in the middle ?

Yea ....... Center tap it to ground (0V)

 

[hitsware]

It does NOT need a ground reference, except at the inputs.

If you split the resistor in the middle in half
and put a test probe in the middle .........
What should you see ?

 

[johnferrier]

the middle resistor sets the operating current of the four JFETs

one of feedback resistors will reference the JFETs to ground

.

 

[Wavebourn]

If you split the resistor in the middle in half
and put a test probe in the middle .........
What should you see ?

Distortions of input ignal.

More questions? 😉

 

[john curl]

Not ground, except by exceptional luck.

 

[johnferrier]

“I wake up and I see the face of the devil and I ask him, 'What time is it?' And he says, How much time do you want?”

"Never speak with strangers."

Mikhail Bulgakov


.

 

[jan.didden]

Hi JC,
What is it?

Erno Borbely's articles in Audio Amateur in the 70-ies. Only he managed to do it with all FETs. ;-)

jan

 

[stinius]

Parasound JC-2 simpified


The link should bring you to post #1515

Add the output buffer's (LED's, resistors (trimpot's) and MOSFET's shown in previous post by John) and feedback resistors.

Two of the components are wrong in the schematic I posted.

Cheers
Stein

http://www.diyaudio.com/forums/analog-line-level/146693-john-curls-blowtorch-preamplifier-part-ii-152.html#post1931584

 

[ThorstenL]

Hi,

So, small change is "gelding"? Sorry, couldn't resist....

For you, probably. For me it is "kleingeld" (small money).

Ciao T

 

[godfrey]

less tilted

Hi John

What's the connection in the center of the diagram for? (aside from "NOT GROUND, DAMMIT!" 😀)
Is it just a test point?

p.s. Looking at it again, it seems that common mode voltage at the input will be transferred to the output, albeit not amplified. Is that not a concern? IIRC, one of Nelson's topologies does the same thing.