Re: thanks
Hi Eric.
I have found my notes now!
At first there is many parameters who is different from BJT to BJT, so i modified a model for a FMMT491A/591A where i raised the "va" around 50%.
The where setup as a buffer like the second one shown at my page. The 2. order harmonic fall of with about 3dB at large voltage swing (4 Vrms). At smaller level only 1dB (700mVrms).
The 3. order does not change at all by raising "va". The only way to get this down is to have one or more highly linear pairs of BJT in the output operating at the "top spot" ie. flat current gain over a wide area.
For the input BJT in the buffer. Use a BJT with a low Ccb. higher Ccb means higher distortion when driving a high impedance load ~ 10K. The flat current gain over a wide area is not as important as a low Ccb at this point.
As a BJT at this point i would use something like BC847BPN or BC850/860 A or B selection at this point. Something with a lower Ccb than 2SC2240/2SA970 (Now i am going to burn in hell!!!!)... Even 2SC1815/2SA1015 shows of a lower distortion than 2SC2240/2SA970 when simulated.
Cbe is not that important ... Because of the very little "vbe" change...
I know!!! All whats count is real world.... How they sound.
Sonny
capslock said:
Hi Eric.
I have found my notes now!
At first there is many parameters who is different from BJT to BJT, so i modified a model for a FMMT491A/591A where i raised the "va" around 50%.
The where setup as a buffer like the second one shown at my page. The 2. order harmonic fall of with about 3dB at large voltage swing (4 Vrms). At smaller level only 1dB (700mVrms).
The 3. order does not change at all by raising "va". The only way to get this down is to have one or more highly linear pairs of BJT in the output operating at the "top spot" ie. flat current gain over a wide area.
For the input BJT in the buffer. Use a BJT with a low Ccb. higher Ccb means higher distortion when driving a high impedance load ~ 10K. The flat current gain over a wide area is not as important as a low Ccb at this point.
As a BJT at this point i would use something like BC847BPN or BC850/860 A or B selection at this point. Something with a lower Ccb than 2SC2240/2SA970 (Now i am going to burn in hell!!!!)... Even 2SC1815/2SA1015 shows of a lower distortion than 2SC2240/2SA970 when simulated.
Cbe is not that important ... Because of the very little "vbe" change...
I know!!! All whats count is real world.... How they sound.
Sonny
Crazy world of Arthur Brown?
Well at least it is not a '3904.
Actually, the much touted Toshiba parts are cheap.........last bunch I bought was less than $0.10 each.
So much for the argument that "cheap is all I can afford".
Jocko
Well at least it is not a '3904.
Actually, the much touted Toshiba parts are cheap.........last bunch I bought was less than $0.10 each.
So much for the argument that "cheap is all I can afford".
Jocko
Maybe i was a bit hard on the 2SC2240/2SA970... In general this pair of BJT is better than the most BJT.
But in this case where a buffer should be able to buffer a high impedance source.. It has to high Ccb. The most parts from Zetex have the same problem and is even worse than 2SC2240/2SA970.
The BJT should be selected with care for a given design to get optimum perfomance...
For Jocko ... I like your humor!! Are you refering to another post!?
😀
Sonny
But in this case where a buffer should be able to buffer a high impedance source.. It has to high Ccb. The most parts from Zetex have the same problem and is even worse than 2SC2240/2SA970.
The BJT should be selected with care for a given design to get optimum perfomance...
For Jocko ... I like your humor!! Are you refering to another post!?
😀
Sonny
Now you are going to get Hairy Holler on your case too!
No, I was refering to "you're gonna burn........!"
Maybe you aren't old enough to remember that one.
Speaking of Hairy, and humor, did you see the link on "balanced DAC makes no sense to me"? Seems I irritated some more people there, but I added some levity at Hairy's expense.
Jocko
No, I was refering to "you're gonna burn........!"
Maybe you aren't old enough to remember that one.
Speaking of Hairy, and humor, did you see the link on "balanced DAC makes no sense to me"? Seems I irritated some more people there, but I added some levity at Hairy's expense.
Jocko
Yes i did see it.. I think you suffer a lot just because of your short and precise replys!?...
Before they judge a person maybe they should read more threads so they can learn a person better before kick him in the face!... I am also a bit to fast on kicking!!
for the "Crazy world of Arthur Brown? " Yes i think i am to young and read to few books....
Maybe i should start reading a bit more!? Do you think so? 😉
Sonny
Before they judge a person maybe they should read more threads so they can learn a person better before kick him in the face!... I am also a bit to fast on kicking!!
for the "Crazy world of Arthur Brown? " Yes i think i am to young and read to few books....
Maybe i should start reading a bit more!? Do you think so? 😉
Sonny
Boy.........you are too young!!!!!!
It was ......ah, shall we say.......a musical act from.......'68 as memory serves (what little is still left).
Some crazy hippy form the UK, sounded like he may have been Welsh, performed it. He died about 6-8 years or so ago.
Might burn you a copy. I don't believe he has any heirs that will be shortchanged. But it is very strange, and very poorly recorded.
Basically, they lowered this nutcase down onto the stage and he proclaimed "I am the god of hellfire......and I bring you fire......!"
Really weird stuff. By weird, I mean funny.
Speaking of funny........some kid in Aussie land thought I was rude. Imagine that.........being accused of rudeness from the land of Fosters.
Now that is conmedy you just can't get everywhere, folks. [joke]
Hmmmm......... looks like I can't spell either. Glad they have this "edit" button
Jocko
It was ......ah, shall we say.......a musical act from.......'68 as memory serves (what little is still left).
Some crazy hippy form the UK, sounded like he may have been Welsh, performed it. He died about 6-8 years or so ago.
Might burn you a copy. I don't believe he has any heirs that will be shortchanged. But it is very strange, and very poorly recorded.
Basically, they lowered this nutcase down onto the stage and he proclaimed "I am the god of hellfire......and I bring you fire......!"
Really weird stuff. By weird, I mean funny.
Speaking of funny........some kid in Aussie land thought I was rude. Imagine that.........being accused of rudeness from the land of Fosters.
Now that is conmedy you just can't get everywhere, folks. [joke]
Hmmmm......... looks like I can't spell either. Glad they have this "edit" button
Jocko
Well apparently, he isn't dead afterall......but it seems he came close.
http://www.godofhellfire.co.uk/sitemap.htm
Jocko
http://www.godofhellfire.co.uk/sitemap.htm
Jocko
The words "Boy.........you are too young!!!!!!" Could you please say them again!!
I turned thirty last year. It sound a bit better than "We thought you where younger!?" or when i go to boxecise and the instructor says "I am not oldest today (Happy sounding)... Sonny is" and so on....
Back to Athur Brown. I have heard the part you described "I am the god of hellfire......and I bring you fire......!"
But i did not know it was him... You have just made my "world wider"... and thanks for the link
I am mostly into late 70 and up to 90's music... I start at Simon and Garfunkel, Gasolin (do you know them? Danish band who tried making a breakthrough in the USA.. Have you heard them .. no? i think so .. They slamed right into the ground with their "breakthrough") ...
Speaking of aussie.. I have some friends who have been living in aussie for som years and there oldest daughter is maried to one.. called Chris...
Every time he meets new people he start of giving them a nickname after some hours. Thats fun! The nickname he come up with is hint to their personality...
Sonny
I turned thirty last year. It sound a bit better than "We thought you where younger!?" or when i go to boxecise and the instructor says "I am not oldest today (Happy sounding)... Sonny is" and so on....
Back to Athur Brown. I have heard the part you described "I am the god of hellfire......and I bring you fire......!"
But i did not know it was him... You have just made my "world wider"... and thanks for the link
I am mostly into late 70 and up to 90's music... I start at Simon and Garfunkel, Gasolin (do you know them? Danish band who tried making a breakthrough in the USA.. Have you heard them .. no? i think so .. They slamed right into the ground with their "breakthrough") ...
Speaking of aussie.. I have some friends who have been living in aussie for som years and there oldest daughter is maried to one.. called Chris...
Every time he meets new people he start of giving them a nickname after some hours. Thats fun! The nickname he come up with is hint to their personality...
Sonny
Toshiba SMD small signal BJTs
Have found SA1162/SC2712 on Toshiba web page. Seem to be the same thing as SA1015/SC1815 with slightly lower power rating due to SMD case. Anybody have SPICE models (I did search).
Found SA1349/SC3381 in Borbely article. Seem to be 80 V monolithic dual transistors with reasonable C_cb (4.2 for the SA, nothing quoted in Tower's for the SC, neither is f_T). Are still available from Reichelt at less than a € each. Unfortunately, no data sheet and SPICE models at Toshiba or the web.
Eric
Have found SA1162/SC2712 on Toshiba web page. Seem to be the same thing as SA1015/SC1815 with slightly lower power rating due to SMD case. Anybody have SPICE models (I did search).
Found SA1349/SC3381 in Borbely article. Seem to be 80 V monolithic dual transistors with reasonable C_cb (4.2 for the SA, nothing quoted in Tower's for the SC, neither is f_T). Are still available from Reichelt at less than a € each. Unfortunately, no data sheet and SPICE models at Toshiba or the web.
Eric
Eric von Deutsche, please DON'T ask Harry about spice models, or heatsinks, ......... or ...............
Eric von Downunder.
Eric von Downunder.
Eric
The datasheets for the dual devices can be found here:
http://site.pcmagazine.com.tw/audio/Files/Parts/2SA1349.pdf
http://site.pcmagazine.com.tw/audio/Files/Parts/2SC3381.pdf
Geoff
The datasheets for the dual devices can be found here:
http://site.pcmagazine.com.tw/audio/Files/Parts/2SA1349.pdf
http://site.pcmagazine.com.tw/audio/Files/Parts/2SC3381.pdf
Geoff
A1349
Thanks Geoff I was looking for those. Does anyone know of a press fit heat heatsink for this part.
H.H.
Thanks Geoff I was looking for those. Does anyone know of a press fit heat heatsink for this part.
H.H.
Thanks Geoff! I wonder why my worldwide search did not find these. Currently, the server does not respond but I will try later.
Eric
Eric
Hi Harry, Do you have a Farnell Catalogue?
There is a heatsink with a clip. Normaly for TO220 but i think it would do the job. It is from Redpoint and is a 13degress/watt.
I do not know the Redpoint number, but i could find it out tomorrow!?
The Farnell number is 175-645.
For Eric, Hi!
It is a nice pair you have found. Look at the 2SC3381 datasheet under "h parameter - VCE" and take a look on the hfe ... nice and flat > High VA ... Low C_cb ... And dual, just perfect!!
Sonny
There is a heatsink with a clip. Normaly for TO220 but i think it would do the job. It is from Redpoint and is a 13degress/watt.
I do not know the Redpoint number, but i could find it out tomorrow!?
The Farnell number is 175-645.
For Eric, Hi!
It is a nice pair you have found. Look at the 2SC3381 datasheet under "h parameter - VCE" and take a look on the hfe ... nice and flat > High VA ... Low C_cb ... And dual, just perfect!!
Sonny
Hi Sonny,
I keep getting a time-out from the Taiwanese server, and I am even on a different computer, connection, OS and browser now....
If it doesn't work tomorrow, I'll ask one of you guys for an e-mail.
Good night,
Eric
I keep getting a time-out from the Taiwanese server, and I am even on a different computer, connection, OS and browser now....
If it doesn't work tomorrow, I'll ask one of you guys for an e-mail.
Good night,
Eric
V_af
Sonny:
Another thought I had while browsing some data sheets: I wonder how accurate the early voltage in spice models is, especially if derived from data sheets rather than more comprehensive measurements.
The SA1015/SC1815 data sheets give I_C(V_CE) at 200 to 2000 µA base current, i.e. ridiculously high for a small signal BJT. The same plot is given for the SC1775/SA872 at 2 t o10 µA. Hard to compare, let alone derive spice models.
On second thought: VAF isn't that important when you cascode which you can always do on input stages as well as voltage gain stages, provided you have sufficient headroom. And I have come across a paper by Nelson Pass outlining how to cascode an emitter follower output by referencing the cascode transistor's base voltage to the output trannie's emitter rather than an AC grounded voltage. I'll have think about that one....
Eric
Sonny:
Another thought I had while browsing some data sheets: I wonder how accurate the early voltage in spice models is, especially if derived from data sheets rather than more comprehensive measurements.
The SA1015/SC1815 data sheets give I_C(V_CE) at 200 to 2000 µA base current, i.e. ridiculously high for a small signal BJT. The same plot is given for the SC1775/SA872 at 2 t o10 µA. Hard to compare, let alone derive spice models.
On second thought: VAF isn't that important when you cascode which you can always do on input stages as well as voltage gain stages, provided you have sufficient headroom. And I have come across a paper by Nelson Pass outlining how to cascode an emitter follower output by referencing the cascode transistor's base voltage to the output trannie's emitter rather than an AC grounded voltage. I'll have think about that one....
Eric
Hi Eric.. you wrote :
"Another thought I had while browsing some data sheets: I wonder how accurate the early voltage in spice models is, especially if derived from data sheets rather than more comprehensive measurements. "
? but i would agree with you to some point. Not that i do not think that it does not give you a good indication off I_C(V_CE) linearity but how precise it is i would agree.. It depends on what basis the spicemodel is done.
"The SA1015/SC1815 data sheets give I_C(V_CE) at 200 to 2000 µA base current, i.e. ridiculously high for a small signal BJT. The same plot is given for the SC1775/SA872 at 2 t o10 µA. Hard to compare, let alone derive spice models. "
You can still calculate the "VA" point to some point. with a IB=200uA and IC=40mA.
In a buffer the double up of "VA" would only give you something like 3dB lower 2.order.
"VAF isn't that important when you cascode which you can always do on input stages as well as voltage gain stages, provided you have sufficient headroom. And I have come across a paper by Nelson Pass outlining how to cascode an emitter follower output by referencing the cascode transistor's base voltage to the output trannie's emitter rather than an AC grounded voltage. I'll have think about that one...."
If you can do the cascode on basis of referencing the cascode transistor to the emitter, then you are right. Then the problem is eliminated. It is same thing they do when cascoding a currentmirror. You can get mirror with a 1/hoe = ~100Meg.
This is done in the AD797 from AD. Take a look.
Hey! IT is nice with some feedback.. You know i could be wrong without knowing it!! Way to go!
You are one the Objective guys around here!
😉
Sonny
"Another thought I had while browsing some data sheets: I wonder how accurate the early voltage in spice models is, especially if derived from data sheets rather than more comprehensive measurements. "
? but i would agree with you to some point. Not that i do not think that it does not give you a good indication off I_C(V_CE) linearity but how precise it is i would agree.. It depends on what basis the spicemodel is done.
"The SA1015/SC1815 data sheets give I_C(V_CE) at 200 to 2000 µA base current, i.e. ridiculously high for a small signal BJT. The same plot is given for the SC1775/SA872 at 2 t o10 µA. Hard to compare, let alone derive spice models. "
You can still calculate the "VA" point to some point. with a IB=200uA and IC=40mA.
In a buffer the double up of "VA" would only give you something like 3dB lower 2.order.
"VAF isn't that important when you cascode which you can always do on input stages as well as voltage gain stages, provided you have sufficient headroom. And I have come across a paper by Nelson Pass outlining how to cascode an emitter follower output by referencing the cascode transistor's base voltage to the output trannie's emitter rather than an AC grounded voltage. I'll have think about that one...."
If you can do the cascode on basis of referencing the cascode transistor to the emitter, then you are right. Then the problem is eliminated. It is same thing they do when cascoding a currentmirror. You can get mirror with a 1/hoe = ~100Meg.
This is done in the AD797 from AD. Take a look.
Hey! IT is nice with some feedback.. You know i could be wrong without knowing it!! Way to go!
You are one the Objective guys around here!
😉
Sonny
Taiwanese server still down
Maybe has to do with the earthquake there. Does anybody have the files who would be willing to e-mail them to me if they are not too big? The account this forum is linked too will accept up to 4 Meg. I have another one which will accept bigger files, but then the question is whether anybody would be willing to send the files.
Thanks in advance,
Eric
Maybe has to do with the earthquake there. Does anybody have the files who would be willing to e-mail them to me if they are not too big? The account this forum is linked too will accept up to 4 Meg. I have another one which will accept bigger files, but then the question is whether anybody would be willing to send the files.
Thanks in advance,
Eric
Eric
The links were working yesterday when I checked them before posting and I had no problems when I tried again a few minutes ago. However, I have the pdf files on disk so if you send me an email I'll copy them to you.
Geoff
The links were working yesterday when I checked them before posting and I had no problems when I tried again a few minutes ago. However, I have the pdf files on disk so if you send me an email I'll copy them to you.
Geoff
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