John Curl's Blowtorch preamplifier

[jbaudiophile]

Hephaistos

Hi, all "Blowtorchers",

From the grave, perhaps that I can help......

Here is a link to download the papers of any interest... You have 7 days from now... Please remember !

Really hope this helps...

http://www.yousendit.com/transfer.php?action=download&ufid=3A8B34A461B96D42&rcpt=jblemaire@free.fr

 

[CheffDeGaar]

Hi jbaudiophile

THX A LOT !!! 😀 😀 😀

(It's a pdf file, just in case 😉 )

You're great

😎

 

[Justcallmedad]

I am playing around a circuit near the one proposed in Post #1429, and carry out some measures with 2 sets of MOSFETS: 2SJ79/2SK216 and 2SJ313/2SK2013, but I face a problem with some SK2013! I get around -105 dB noise instead of 120 dB. Is this a known problem with them? Otherwise the Toshiba pairs shows ten times less THD. Once I solve the noise problem I will post measures graphs.

 

[PMA]

Hi,

you have to display the FFT parameters, for us to tell you if you have reached the FFT floor.

Cheers,

Pavel

 

[courage]

Richard,

A quick question regarding your earlier posted schematics and simulation plots.

Why have you chosen to create a sort of local feedback connection between the output Mosfets Drain and Gate?
Can this still be considered an open loop design as such?

Regards.

 

[Justcallmedad]

Hi PMA,

My FFT floor is -140 dB (AM700 Tektro). I must specify that one side is -120 db the other one is 105 dB (with the Toshiba pairs), the problem is one SK2013 (I inverted with the other side. I tested too with the Hitachi pairs apart that THD is ten times higher (0.1% instead of 0.01 at 1V RMS for the Toshiba pair) the output noise floor is ok.

Hi Courage,

It’s just a small amount of local feedback around the mosfets, it linearizes the output stage and the parasitic output capacitance, but for more J.C. must enlighten us. The design is open loop.

 

[courage]

Richard,

Thanks for your reply. As John stated the bandwidth is a bit of a concern as it will change with attenuator positions. However my simulations point out that a shunt capacitor at the outputs sets the bandwith at the 350 kHz with a 1st order rolloff. Not sure though if this is the best way to do this. There may be a better/easier way to do this and if John or others are willing to share their insights or experiences it would be nice.

The other thing that puzzles me is how you manage to set the gain of the line stage. Since the JFets sources are tied together this may be a bit of a problem.

Regards

 

[Justcallmedad]

Noise problem must be oscillations problems, but the fact is that I can’t see them on my Tek 745 Scope… Never mind here 2 graphs 1V RMS output 3V RMS Output in S.E. I will try to solve these oscillations problems this w.e.

Jfet sources are tied together by side P and N pair but not to esch side (differential I use 150R.

THD Harmonic distribution:

1V RMS_SE

3V RMS_SE

 

[PMA]

Anything new, John? The Solid State forum is becoming a bit uniform, let us go divergent 😉

 

[Gopher]

Definitive Circuits

I'm not going to trawl through153 pages of endless guesses at endless vaiants of Blowtorch circuits.
Does anyone actually know, or are pretty sure, what the psu and amp schematics for the Blowtorch are?

Thanks

 

[R-K Rønningstad]

Re: Definitive Circuits

I'm not going to trawl through153 pages of endless guesses at endless vaiants of Blowtorch circuits.
Does anyone actually know, or are pretty sure, what the psu and amp schematics for the Blowtorch are?

Thanks

I believe one John Curl knows! 🙂

 

[john curl]

Only John Curl knows, and he isn't telling.

 

[R-K Rønningstad]

But after all you have shared much of your knowledge and thoughts and for that a great "thank you".

RK

 

[PMA]

I would probably build a sample if I had not moved to active speakers. For them the BT use makes no sense.

 

[aparatusonitus]

Only John Curl knows, and he isn't telling.

...Yet...Time works for us😀

 

[B Cullingford]

Sometimes the journey is more interesting than the destination.

 

[jacco vermeulen]

Shoot, it's fortune cookie season again ?

If you don't have the cash to buy Mr Curl's limo, have the patience to let him teach you how to build a better one instead of at gunpoint stealing his.

 

[anatech]

Hi B Cullingford,

Sometimes the journey is more interesting than the destination.

Exactly!

If you don't have the cash to buy Mr Curl's limo, have the patience to let him teach you how to build a better one instead of at gunpoint stealing his.

How can anyone disagree with that statement?? Using the basics to guide your own topology is more valuable. The world does not need a bunch of clones.

-Chris

 

[Stefano]

PS regulation

Hi John Curl,

about suplly regulation, have you ever tried to use a LC filter?
I think that it would really make the difference making more simple the work of the post-regulator.
I hope it would renew the discussion....

 

[jbaudiophile]

Blowtorch

Hello, Stefano,

John tried it in earlier PSU stages (just see the very first Darry's posts), but perhaps that the "passive" assembly is just quite uneffective (my own conclusions) for him.

All of John's posts are GREAT, but let us have a time to understand them fully (my own experience). Please be patient and read them a bunch of times. All is in.

Best regards,

Jbaudiophile