John Curl's Blowtorch preamplifier part II

[gpapag]

Yes. It was one of Jim Williams creations.

http://cds.linear.com/docs/en/application-note/an120f.pdf

At 120-25 to 120-28 there is a full technical (i.e. rational) justification for the positioning of components and routing of wiring.
This does not subtract a iota from it artistic value

George

 

[31697B]

FYI -- to critically damp a high quality film cap (1 mfd) takes about 0.22 ohms.


THx-RNMarsh

 

[simon7000]

Question!

In a BJT input stage does Vce change NF?

ES

 

[Max Headroom]

FYI -- to critically damp a high quality film cap (1 mfd) takes about 0.22 ohms.
THx-RNMarsh

I'm not clear on what you mean here...could you please elaborate.

Thx-Dan.

 

[rayma]

I'm not clear on what you mean here...could you please elaborate.

In a series RLC circuit the damping factor is R/2 x (C/L)^0.5 where L is the parasitic series inductance and R is any series resistance present.

For critical damping, this expression equals 1, so rearranging we have R= 2 x (L/C)^0.5

If C = 1uF and L =50nH (for example), then: R= 2 x (50nH/1uF)^0.5 = 0.45 Ohms

 

[Bonsai]

Yes. It was one of Jim Williams creations.

http://cds.linear.com/docs/en/application-note/an120f.pdf

At 120-25 to 120-28 there is a full technical (i.e. rational) justification for the positioning of components and routing of wiring.
This does not subtract a iota from it artistic value

George

I've downloaded it - some reading for next time I take a flight!

 

[Max Headroom]

In a series RLC circuit the damping factor is R/2 x (C/L)^0.5 where L is the parasitic series inductance and R is any series resistance present.

For critical damping, this expression equals 1, so rearranging we have R= 2 x (L/C)^0.5

If C = 1uF and L =50nH (for example), then: R= 2 x (50nH/1uF)^0.5 = 0.45 Ohms

So typical 1uF film cap should have 0.22R in series to prevent uncontrolled resonance behaviour ?.
What applications ?....crossovers, filters etc ?.

Dan.

 

[john curl]

This is the sort of thing that we often address in quality audio design. Matti Otala turned me on to it back in 1978. Darned inconvenient isn't it? Or do you just ignore it?

 

[john curl]

test

 

[rayma]

So typical 1uF film cap should have 0.22R in series to prevent uncontrolled resonance behaviour ?.
What applications ?....crossovers, filters etc ?.

It depends on the circuit. For example, if the film cap is in parallel with an electrolytic capacitor in a power supply, that cap's ESR
could serve as the damping resistance for the film cap. Likewise for coupling capacitors.

If the film capacitor is at the output of a regulator, the stability of the regulator can be improved.

There are lots of parasitic inductances in audio circuits, and these can interact with circuit capacitances. If a wire or pcb trace connects a
power supply to a grounded bypass capacitor at an op amp, the parasitic inductance will cause a resonance under some signal conditions
at the op amp's supply terminal. A small series resistor can be added in the supply connection near the op amp to damp this resonance.
This is one reason why low inductance pcb design is important.

 

[Max Headroom]

This is the sort of thing that we often address in quality audio design. Matti Otala turned me on to it back in 1978. Darned inconvenient isn't it? Or do you just ignore it?

Inconvenient, yes, ignore it, no.
Thanks to RNM for heads up on typical/ballpark values.

Dan.

 

[fas42]

Hmmm .... a summary: accurate measurements with 60dB dynamic range is easy; accurate measurements with 120dB dynamic range is hard, very hard ... and unfortunately the sensitivity of people's hearing dances around in the middle of those "extremes" ...

 

[Esperado]

FYI -- to critically damp a high quality film cap (1 mfd) takes about 0.22 ohms.

It makes-me remember some nice inputs in a French military book from 1914, at destination of soldiers.
It was presented under a questions/answers form.

Q- How long it takes for the barrel of the gun to cool down ?
A- Quite a while.

and, the best ones:
Q- In what did we dig the toilets ?
A- In the quarter of hour after the arrival of the troup in the camp.

Q- Of what are the feet ?
A- Subject to constant care from the infantryman.

 

[IO390]

Yes. It was one of Jim Williams creations.

http://cds.linear.com/docs/en/application-note/an120f.pdf

At 120-25 to 120-28 there is a full technical (i.e. rational) justification for the positioning of components and routing of wiring.
This does not subtract a iota from it artistic value

George

All the Jim Williams app notes are available from the LT website. Most of them from App note 25 and onwards have a cartoon at the end.

I have a book of some of the early LT app notes. I found this in the index (written by Williams):

 

[Bonsai]

Hilarious!

I remember in one of his very early app notes (pre LT) he referred to digital circuit designers as 'TTL Jockeys'

 

[31697B]

.22 - .27 ohm

So typical 1uF film cap should have 0.22R in series to prevent uncontrolled resonance behaviour ?.
What applications ?....crossovers, filters etc ?.

Dan.

I used the term 'critically' damped. More Rs will over damp the circuit thru the cap and less will be under-damped (ringing). For accuracy in impulse response, you want critically damped circuit. Over-damped is usually what I see... that means an impulse will be compressed and time smeared... would be one way to describe it.

THx-RNMarsh

 

[IO390]

Hilarious!

I remember in one of his very early app notes (pre LT) he referred to digital circuit designers as 'TTL Jockeys'

Another of the great engineers, Mr. Widlar:

 

[scott wurcer]

Another of the great engineers, Mr. Widlar:

That summarizes what Bob Pease and Jim Williams though about most audiophile ramblings.

 

[Triodethom]

To me the funny part of their view was that their approach to design solved problems. Bob P. favorite simulation software was solder works for DIYers. Guess the psychological part of the audiophile equation was over loading the understanding of what audiophiles where rambling about.

 

[wayne]

Just got my new Absolute sound with the product awards in it. John really unfair that your phono stages won in both price categories. Congratulations!