John Curl's Blowtorch preamplifier

[EUVL]

Enough excursion to my layout.
Let's get back to circuits.

I want to refer to Richard's schematics.

Would it not be better to use a voltage reference or LED's (to replace e.g. R5) in combination with a CCS diode like J511 (to replace R1) to bias the MOSFETs ?

I expect at least better PSRR ??

Patrick

[Upupa Epops]

What do you can extend, Patrick ? Do you know correlation between " on paper's parametres " and sound quality ?

[bogdan_borko]

can someone give me the lik to the schematic of blowtorch preamp???

[jacco vermeulen]

Patrick,

sticking the elektrolytics through the heatsink is funny.
I recollect that EB seems to favor fast regulation for his EB-116 lineamp too instead of CCS's. Is it me, or does it seem that CCS diodes are not in much use ?
Bogdan is even funnier, lets give him a lik.

[anatech]

Hi Bogdan,
John Curl, who designed the preamp, is selling it commercially. He has stated he has no intentions of releasing the schematic. I'm sure there are unit to unit variations to compensate for component variables. I fully support John's decision to not release the diagrams for those reasons.

If you read the entire thread, there are many clues. This is more of a gift as you can apply these lessions to your own low level designs.

Read and learn.

-Chris

[uli]

Releasing the Original would make this thread boring and senseless

Uli



BTW: did anybody ever try the LSK389 type C as the 2SK389 fades away?

[PMA]

How about this one?

[jacco vermeulen]

Originally posted by uli
ever try the LSK389

Uli,

i'm sorry, i seem to be dyslectic. Can you show the link to the LSJ109 ?
I always have that problem with P-channel fets.

[Upupa Epops]

Be calm, Jacco, and use some " normal " one... By line level preamp, with 3-5 gain isn't noise so critical - is free, if SNR is " only " 120 dB and not 126-130 dB.....

[plep]

I’m trying to put the ideas gathered here to work (serie reg + CCS + shut reg).
I still use the basic Curl follower running under switchercad. I think this circuit is both less sensitive to the psu and “harder” to the psu than the symmetric folded cascode we are talking about here. Sorry If I’m lagging ideas by Richard and allied…

How can I improve the line regulation provided by the simple shunt reg ? I imagine that higher gm transistors would help (which ones?). At about 100ma the gm of the irf640 and irf9540 are just a bit above 1S. Regulation is quite similar to the one provided by a .85ohm internal resistance voltage source.

I can obtain a slightly more linear regulation in high frequency with a small (about 470nf) in // with the reg. It also helps to eliminate the overshot one can see with square waves (I think that Richard published them a while back). Funny, John says “no cap” and he must have good reasons.

A “massive” approach to passive filtering, 3 cells composed by a 10ohm resistor and a 47000µf 1nH ESL and 3mohm ESR cap (I hope these values are realistic), provides a much higher attenuation in most of the audio frequencies and above, but this attenuation is changing with frequency and there is a severe bump at very high frequency (due to very low esr ?). I know that only the last cell is useful in term of regulation.

The active reg shines in terms of line rejection. I probably obtain one more time meaningless results because real live noise masks the simulated behaviour that lies at impossibly low levels. Anyhow, I think that the curves are interesting. For instance, you have a less acute peak in HF using 3 different caps in the passive way and you can see the interest of multiple cells.

Any help and comment gratefully welcomed.

Philippe (who as difficulties to explain himself in English and whose mail is broken :-/).