Hi Jacco,
Actually I did not recommend anything specifically, but, as Pavel says, 2SC3955 is fine and dandy, though I believe now obsolete.
I try not to give actual types or values. I prefer the idea of 'teach a man to fish, and he eats for a lifetime' as my background was education.......
Cheers,
Hugh
Actually I did not recommend anything specifically, but, as Pavel says, 2SC3955 is fine and dandy, though I believe now obsolete.
I try not to give actual types or values. I prefer the idea of 'teach a man to fish, and he eats for a lifetime' as my background was education.......
Cheers,
Hugh
to VAF, or not to VAF...
Hi,
sorry for being a bit OT but are we talking "Spice" language here?
VAF, is it used else where?
What does the abbreviation stand for?
I guess Early Effect is the right kind of abbreviation!
Cheers Michael
Hi,
sorry for being a bit OT but are we talking "Spice" language here?
VAF, is it used else where?
What does the abbreviation stand for?
Code:
A brief guide to the effect of each Spice model element :-
IS and NE control Icbo and where hFE falls with high Ic.
ISE and NE control the fall in hFE that occurs at low Ic.
BF controls peak forward hFE.
BR controls peak reverse hFE i.e. collector and emitter reversed.
IKF controls where hFE falls at high collector currents.
IKR controls where reverse hFE falls at high emitter currents.
ISC and NC controls the fall of reverse hFE at low currents.
RC, RB and RE add series resistance to these device terminals.
[COLOR=crimson][u]VAF controls the variation of collector current
with voltage when the transistor is operated in its linear region.[/u][/COLOR]
VAR is the reverse version of VAF.
CJC, VJC and MJC control Ccb and how it varies with Vcb.
CJE controls Cbe.
TF controls Ft and switching speeds.
TR controls switching storage times.I guess Early Effect is the right kind of abbreviation!
Cheers Michael
ChocoHolic said:
Rather the other way around. Although the Early effect is considered a second-order effect it is caused by the effective base width being modulated by Vbc. hfe varies as a consequence of this. I think, but am not sure, that this also affects Cob and Cbe. (Cob definitely varies with Vcb, but I am not 100% sure if that is because the effective base width changes).
As for the the notation VAF, that is a Spice parameter. However, at least my book in semiconductor physics uses Va as a notation for the Early Voltage, so presumably that is if not a universal so at least a common notation. As for why it is denoted VA/VAF I can oly guess. The V is obviously because it is a voltage, and the F is because VAF means the Forward Early Voltage (in contrast to the Reverse Early Voltage VAR). So why A? Probably because the obvious choices would be B, for base-width modulation, or E, for Early, but both B and E are reserved for voltages somehow related to the base and emitter nodes. Probably they just took the first unused letter in the alphabet, which happened to be A.
AKSA said:
Yes you did, or at least half ;
01-31-2003:
A very good one to use is the Sanyo 2SC3955, a 300MHz beast with impeccable specs and collector capacitance of just 1.8pF.
02-03-2003:
Sanyo has a proprietary manufacturing process which reduces collector capacitance, and frankly this makes them very desirable as VA devices.
01-26-2004:
I have used 2SC1819 and 2SC3955 with good results, but both these devices are now obsolete.
Problem with this forum is that anything you post can be used against you.
Just like JCX i enjoy searching and reading old threads, especially for posts of gents as you and Mr Jonathan Carr when it comes to 2SA/2Sc devices as you are close to the source.
I'd like to eat while i'm tought.
One more :
02-13-2003:
Ft for the VAS is crucial. You make it as fast as possible. 30MHz of the 1943 is a doddle, and will sound slow and leaden. Go to at least 100MHz and preferably 200MHz, or more.
Jacco,
Ho ho ho!!! There is no feeling quite like having the egg you have just eaten thrown back in your face...... (I still remember it well from my adolescence, after drinking too much port.)
What you did not say here is that audio, like any other technology, is a journey, and over all those years my beliefs, experience and philosophies change.
Even I don't agree with myself three years on!!
What was that Moorcock stuff about the multiverse, and the myriad of parallel universes?
Yours in good humor,
Hugh
Ho ho ho!!! There is no feeling quite like having the egg you have just eaten thrown back in your face...... (I still remember it well from my adolescence, after drinking too much port.)
What you did not say here is that audio, like any other technology, is a journey, and over all those years my beliefs, experience and philosophies change.
Even I don't agree with myself three years on!!
What was that Moorcock stuff about the multiverse, and the myriad of parallel universes?
Yours in good humor,
Hugh
Mr Dean,
sorry about the egg, no backwash intended.
The absolute truth i am not looking for, the general one will do, already figured you are not Dr Who.
That speed is a parameter for the Vas seems to be a general consensus on this thread.
But not the only one, and unlimited speed is a terminator, fine by me.
Audio seems to resemble religion, i have to pick a number of designer brains to get a functional average truth.
sorry about the egg, no backwash intended.
The absolute truth i am not looking for, the general one will do, already figured you are not Dr Who.
That speed is a parameter for the Vas seems to be a general consensus on this thread.
But not the only one, and unlimited speed is a terminator, fine by me.
Audio seems to resemble religion, i have to pick a number of designer brains to get a functional average truth.
You know, Jacco, the absolute truth is probably not the right answer. If it had been, then eighty years of audio technology would have come up with the absolute best possible amp by now. Fact is, these are the indications:
1. There is much more to it than simply low THD.
2. Some distortion sounds, well, acceptable.
3. All audio technology concentrates on delivery, not on perception at the ear canal, labyrinth and nerve interface.
4. People have widely different tastes.
5. There is a market for SE tube, PP SS, switching/PWM amps. All have their place in the sun.
That fashions change, ways of thinking alters, what is hip today is passe tomorrow, is indisputable. It is regrettable in some ways, but even applies to medicine. Look at the cholesterol debate, the cancer debate, the Altzheimer debate - every year there is a different explanation. Where is the absolute truth?
I would humbly suggest that the only absolute truth is the need for fresh explanations, different ways of seeing and saying - in short, marketing....
Cheers,
Hugh
1. There is much more to it than simply low THD.
2. Some distortion sounds, well, acceptable.
3. All audio technology concentrates on delivery, not on perception at the ear canal, labyrinth and nerve interface.
4. People have widely different tastes.
5. There is a market for SE tube, PP SS, switching/PWM amps. All have their place in the sun.
That fashions change, ways of thinking alters, what is hip today is passe tomorrow, is indisputable. It is regrettable in some ways, but even applies to medicine. Look at the cholesterol debate, the cancer debate, the Altzheimer debate - every year there is a different explanation. Where is the absolute truth?
I would humbly suggest that the only absolute truth is the need for fresh explanations, different ways of seeing and saying - in short, marketing....
Cheers,
Hugh
speed!
is the speed of a transistor and the Cbe all shot to you know what when you have to start compensating,..namely slapping a pf cap across the collector-base junction or whatever other methods you choose? this seems like an interesting topic to make a few posts on.... Has anyone built a VAS from a fast tranny without anything else?
is the speed of a transistor and the Cbe all shot to you know what when you have to start compensating,..namely slapping a pf cap across the collector-base junction or whatever other methods you choose? this seems like an interesting topic to make a few posts on...
. Has anyone built a VAS from a fast tranny without anything else?
Does it make ANY sense to look for ft in the GHz range when the max. obtainable ft for the outputs is about 10 - 50 MHz?
The VAS stage has to become as linear as possible in the audio range not lightning fast for ultrasonic frequencies. The VAS suffer from much more than only speed, back reflected crossover distortion from the output stage comes in my mind...
The VAS stage has to become as linear as possible in the audio range not lightning fast for ultrasonic frequencies. The VAS suffer from much more than only speed, back reflected crossover distortion from the output stage comes in my mind...
I used a smallish mosfet (yes, that's right,..a mosfet) a number of years ago and achieved an open loop bandwidth of 300khz from just playing around. Things actually looked pretty boffo until I ran into oscillation problems with the output and the project eventually got scrapped. I don't recall the mosfet's type.
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