John Curl's Blowtorch preamplifier

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#521
Sorry, I was interrrupted !

The point is now seen by me as unimportant for the forum that just want to have "gurus" benediction for most points... Not me !

But I think that I am different... Still to live with that !!!! Academics are wrong at most times... I know what I am saying : I am with this stuff and guys all the time !!

But, anyway, thanks to your sincere explanations, Forr !

Jbaudiophile
 
#522
Hi, JustCallMeDad,


The data for 2SA1349 wasn't confimed by the manufacturer, so I can't be sure on it... But as they are compliment parts to te 2SC3381, here are the required data for the last ones :

VCBO : 100 V
VEBO : 5 V
IC max : 1 A
PC : 800 mW
ICBO : 1 uA
Beta : 70... 240
VCE : 2V
VCB : 2V
F : 50 Mhz
Cob : 20 pF
Rbb' (= Hie real) : 10 Ohms

All data taken from a Japanese 1981 data book...

Hope these helps !

Jbaudiophile
 
#526
2SA1349

Hi,

I still have the Toshiba Databook which includes the 2SA1349.

If there is anything you wish to know from this, just ask, and I will happily oblige.

You are quite right and the 2SC3381 is definitely its complement, by the way.

Regards,🙂
 
#528
Low Rbb'

Justcallmedad said:
Since nobody here answer to the questions about low Rbb' devices (recent), how to choose BJT's in consequence knowing that this parameter doesn’t appear on datasheets (or exceptionally) and even the semiconductors headquarters are not informed at least in France?

In other words, can some people here please, share some small signal devices references like 2SA1349/2SC3381 I think, and for medium power (drivers) or medium power output BJT’s.
Click to expand...

I haven't read the complete thread, so I'm not sure how relevant this is, but in general medium power and HF transistors tend to be useful for low noise preamp designs with a focus on low voltage noise (rather than current noise), needing transistors with a low Rbb'.

In April 1980, Nordholt published an MC preamp in the JAES, based on the BFW16A. This NPN transistor has a repectable 4 Ohm Rbb'. Elekor published in July/August 1980 the same design. In the article some transistros are mentioned that have a low Rbb':



TIP30A - 13 Ohm
BFY90 - 21 Ohm
BFW92 - 16 Ohm
BF181 - 12 Ohm
BFW16A - 4 Ohm

Steven
 
#530
HI JBAUDIOPHILE

---Academics are wrong at most times... ---
Academics may be full of theories but they ask proofs for them. The importance of spectral content of amplifiers is a pure theory which nobody has ever tried to prove in neutral tests, rather easy to conduct by the way. Too unconfortable for "non-academics" ?

~~~~ Forr

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#531
Hello everyone,
looks like low Rbb transistors have high Ft, as the ones Steven indicated.
Now my question: is it wise to use an high Ft semiconductor as input transistor?
Some years ago I showed a cascode preamplifier, in this forum, that was using a BF245C jfet in the lower cascode part: the BF245C is suggested in LF-HF amplifiers, and has a Ft=700MHz; everyone participating at this thread suggested not to use HF jfet as input stage.

Regards,

Claudio
 
#532
agreed 100%

forr said:
HI JBAUDIOPHILE

---Academics are wrong at most times... ---
Academics may be full of theories but they ask proofs for them. The importance of spectral content of amplifiers is a pure theory which nobody has ever tried to prove in neutral tests, rather easy to conduct by the way. Too unconfortable for "non-academics" ?

~~~~ Forr

§§§
Click to expand...
Agreed one hundred percent Forr! (100%)

😎
 
#533
forr said:
HI JBAUDIOPHILE
---Academics are wrong at most times... ---
Academics may be full of theories but they ask proofs for them. The importance of spectral content of amplifiers is a pure theory which nobody has ever tried to prove in neutral tests, rather easy to conduct by the way.
Too unconfortable for "non-academics" ?
~~~~ Forr
§§§
Click to expand...

Please excuse me Sir, what is a "spectral content" ?
Do you refer to distortion spectrum?
If you had to choose some instrumental tests to ***** the quality of a unit what would be your tests of choice ?
I am trying to understand if instrumental measurements can be of any help to assess the quality of an audio equipment.
After all any reviews give some sort of technical data.

Thank you so much.
Kind regards,

beppe
 
#535
HI BEPPE61

Sorry, I was a bit unlcear, you guess correctly. The spectral content I refered is effectively the distorsion spectrum.

One of the tests which I think of, would be to pick up a very low distorsion amplifier, to introduce some nice distorsion using some special circuit ahead of it, and then to compare the results with the beloved amps designed with consideration to the spectrum of harmonics they generate. This is what should have been done by Cheever at the very beginning of his thesis, and what examinators should have asked him to do, prior to any further reading.

~~~~~~ Forr

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#538
 
#539
forr said:
HI BEPPE61
Sorry, I was a bit unlcear, you guess correctly.
1) The spectral content I refered is effectively the distorsion spectrum.
2) One of the tests which I think of, would be to pick up a very low distorsion amplifier, to introduce some nice distorsion using some special circuit ahead of it, and then to compare the results with the beloved amps designed with consideration to the spectrum of harmonics they generate.
This is what should have been done by Cheever at the very beginning of his thesis, and what examinators should have asked him to do, prior to any further reading.
~~~~~~ Forr
§§§
Click to expand...

Thank you very much Sir for your kind and valuable reply.
1) All right. Thank you.
2) Very interesting methodology.
Do you have any link explaining Cheever's approach to audio equipment evaluation ?

Kind regards,

beppe
 
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