It's not just the voltage, it's the current. Look at the SOA chart and see where your particular voltage and current intentions lie. Leave plenty of margin.
Note that 60V rails on an Aleph-X would be somewhere in the vicinity of 800W output...and about 2500W of heat dissipation at idle.
Not that you'd want to run an 044 anywhere near that hard.
Grey
Note that 60V rails on an Aleph-X would be somewhere in the vicinity of 800W output...and about 2500W of heat dissipation at idle.
Not that you'd want to run an 044 anywhere near that hard.
Grey
Dennis,
I would not use over + and - 30 volt rails, assumining that the voltage you are talking about is the drain to source voltage.
60 volt rails would exceed the devices limits and probably cause the devices to fail (60volt rails could mean a potential of a 120 volt signal swing) not good.
Jam
I would not use over + and - 30 volt rails, assumining that the voltage you are talking about is the drain to source voltage.
60 volt rails would exceed the devices limits and probably cause the devices to fail (60volt rails could mean a potential of a 120 volt signal swing) not good.
Jam
Ooop...Sorry for not being clear with my question.
I wasn't trying to run a 60V rail Aleph-X; I'd need
my own power generator for that 🙂
I was thinking more of whether +-25V rails
(at 3 amps bias per channel) would be ok for
the 60V IRFP044.
About the SOA: The datasheet shows graphs for
10ms and shorter testing pulses. For example,
at 10ms, 40V @ 8 amps is at the edge of the SOA.
But for what we're interested in, the current
is running continuously. Are there any good
rules of thumb for estimating what is acceptable
in this case?
Thanks,
Dennis
I wasn't trying to run a 60V rail Aleph-X; I'd need
my own power generator for that 🙂
I was thinking more of whether +-25V rails
(at 3 amps bias per channel) would be ok for
the 60V IRFP044.
About the SOA: The datasheet shows graphs for
10ms and shorter testing pulses. For example,
at 10ms, 40V @ 8 amps is at the edge of the SOA.
But for what we're interested in, the current
is running continuously. Are there any good
rules of thumb for estimating what is acceptable
in this case?
Thanks,
Dennis
Dennis,
I would find the minimum requirements and multiply it by four. I think Mr.Pass talks about that in one of his articles. Which means about 8 devices a channel.
Jam
I would find the minimum requirements and multiply it by four. I think Mr.Pass talks about that in one of his articles. Which means about 8 devices a channel.
Jam
Substitute suggestions
Hi!
Me think it would be a good time to make a (long) list for part-substitute, thinking first on mosfets, ....and sort them for best/easiest implementation (based on spec./experience).???
(Warning: it will make this tread much shorter).
Arne K
Hi!
Me think it would be a good time to make a (long) list for part-substitute, thinking first on mosfets, ....and sort them for best/easiest implementation (based on spec./experience).???
(Warning: it will make this tread much shorter).
Arne K
Dennis,
although it's not a likely scenario, it happened to me, I am going to bring this practical example. Say you are testing an AX and you got too much resistance somewhere and your and your CS and gain mosfets are unequally biased Vds are giong to be very different. I have seen maybe 3 or 4 Vds on one mosfet and 26 V on the other. With 25-0-25 you may have as much as 45~48 VDS that's maybe a tad too close for comfort. Something to think about.
although it's not a likely scenario, it happened to me, I am going to bring this practical example. Say you are testing an AX and you got too much resistance somewhere and your and your CS and gain mosfets are unequally biased Vds are giong to be very different. I have seen maybe 3 or 4 Vds on one mosfet and 26 V on the other. With 25-0-25 you may have as much as 45~48 VDS that's maybe a tad too close for comfort. Something to think about.
In desperation, I had considered making a table of comparable MOSFETs to see if I could head off some of the "Will MOSFET X work in the ZEN/SOZ/Aleph/etc." threads. Then I had an attack of sanity. I realized that IRF alone has, what, a hundred MOSFETs? Then add Motorola (aka OnSemi), Hitachi, Toshiba, and whoever else might come to mind. The table would be absolutely enormous.
Worse yet, one of the companies would inevitably do something rude like discontinue a device--you'd be forever updating the confounded thing.
Not to mention the fact that the sheer size of the table would be so intimidating that newbies would be horrified. At which point we'd be faced with a new series of threads saying "Will someone interpret this thing for me? You forgot to include the Rosetta stone..."
So these days I just say,"Check the SOA. If it looks okay there, give it a shot."
Device parameters for an Aleph-X are no more stringent than they are in an Aleph. However, a little extra care in matching will give you an easier time setting the DC offset after assembly.
Grey
Worse yet, one of the companies would inevitably do something rude like discontinue a device--you'd be forever updating the confounded thing.
Not to mention the fact that the sheer size of the table would be so intimidating that newbies would be horrified. At which point we'd be faced with a new series of threads saying "Will someone interpret this thing for me? You forgot to include the Rosetta stone..."
So these days I just say,"Check the SOA. If it looks okay there, give it a shot."
Device parameters for an Aleph-X are no more stringent than they are in an Aleph. However, a little extra care in matching will give you an easier time setting the DC offset after assembly.
Grey
Aleph Mosfet Substitution
1. Interpetation of SOA for a mosfet involves analysis of graphical data that calles for some pretty good engineering skills will be less than useful to most. Picking a mosfet by the Power Rating, Linear Derating Factor, and Thermal Resistance seems a little more straight forward. You want high Power Dissapation and low Linear Derating Factor and Thermal Resistance numbers.
2. The Hitachi, Tosiba, and Exicon mosfet are lateral devices with much different transconductance and turn on voltages and are really not suitable without major circuit redesign.
3. Nelson Pass discusses mosfet fet choice in the Zen articles at www.passdiy.com as well as on this forum.
4. Down load the datasheets for the transistor types in the Zen articles from www.irf.com for baseline numbers for the parameters above as well as transconductance, turnon voltage, and device capacitance numbers. I think you will narrow down your choices to less than a dozen device types pretty easily. International Rectifier or Harris are two of the better vendors.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=828&highlight=mosfet+substitute
1. Interpetation of SOA for a mosfet involves analysis of graphical data that calles for some pretty good engineering skills will be less than useful to most. Picking a mosfet by the Power Rating, Linear Derating Factor, and Thermal Resistance seems a little more straight forward. You want high Power Dissapation and low Linear Derating Factor and Thermal Resistance numbers.
2. The Hitachi, Tosiba, and Exicon mosfet are lateral devices with much different transconductance and turn on voltages and are really not suitable without major circuit redesign.
3. Nelson Pass discusses mosfet fet choice in the Zen articles at www.passdiy.com as well as on this forum.
4. Down load the datasheets for the transistor types in the Zen articles from www.irf.com for baseline numbers for the parameters above as well as transconductance, turnon voltage, and device capacitance numbers. I think you will narrow down your choices to less than a dozen device types pretty easily. International Rectifier or Harris are two of the better vendors.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=828&highlight=mosfet+substitute
GRollins said:
Maybe it would be possible to base the table on figures like Vds, transconductance, capacitance instead whcih could be picked up from datasheets? Say something like this (and thus unrelated to specific FETs):
Amp FETs Min Vds Max Input C Min Idss rating
Aleph2 6+ 100 V 8 nF total for all FETs 15 A
Aleph3 3+ 60 V 2 nF 12 A
Yoda: <i>Always with you, it cannot be done...</i>
Anna,
1--Don't know about Arkansas, but over here they taught us how to read graphs in elementary school. I always thought they were kinda fun, myself.
2--One man's major redesign is another man's idle play. It doesn't take an EE to do one of these things...there are a number of people around these parts who could have put together the Aleph-X circuit. I just kinda got interested in the idea a little sooner and followed through a little quicker. Refiddling the circuit for tubes, bipolars, or even the MOSFET from Mars is well within the capability of some of our members. Even supposing a newbie were to give it a shot and find something unexpected...help is as close as their keyboard.
Grey
Anna,
1--Don't know about Arkansas, but over here they taught us how to read graphs in elementary school. I always thought they were kinda fun, myself.
2--One man's major redesign is another man's idle play. It doesn't take an EE to do one of these things...there are a number of people around these parts who could have put together the Aleph-X circuit. I just kinda got interested in the idea a little sooner and followed through a little quicker. Refiddling the circuit for tubes, bipolars, or even the MOSFET from Mars is well within the capability of some of our members. Even supposing a newbie were to give it a shot and find something unexpected...help is as close as their keyboard.
Grey
Mosfets and Misfits
Dr. Ian Malcolm:
I'll tell you the problem with the scientific power that you're using here: it didn't require any discipline to attain it. You read what others had done and you took the next step. You didn't earn the knowledge for yourselves, so you don't take any responsibility for it.
So you learned electronics in elementary school? Which sheds no light at all to anyone using the SOA graph. Comparison of the parameters from the data sheet I mentioned gives a pretty straight forward benchmark that is of more use than SOA curves. I think the therma data has been dissussed of the forum also. I believe you would need look at them to interpet SOA anyway.
Lateral Mosfets are really not a good substitute for Hexfets which I believe was my point in the context of the Mosfet substituition disscussion. Refiddling is not the same as design, in the same vein as Hemingway's quote about typing not being the same as writing.
I agree that redesign is within the capability of some of the forum's other members. Perhaps me could give me a few of thier names. Thanks for your response. It was more inspirational than informational though I'm afraid.
Anna
Dr. Ian Malcolm:
I'll tell you the problem with the scientific power that you're using here: it didn't require any discipline to attain it. You read what others had done and you took the next step. You didn't earn the knowledge for yourselves, so you don't take any responsibility for it.
So you learned electronics in elementary school? Which sheds no light at all to anyone using the SOA graph. Comparison of the parameters from the data sheet I mentioned gives a pretty straight forward benchmark that is of more use than SOA curves. I think the therma data has been dissussed of the forum also. I believe you would need look at them to interpet SOA anyway.
Lateral Mosfets are really not a good substitute for Hexfets which I believe was my point in the context of the Mosfet substituition disscussion. Refiddling is not the same as design, in the same vein as Hemingway's quote about typing not being the same as writing.
I agree that redesign is within the capability of some of the forum's other members. Perhaps me could give me a few of thier names. Thanks for your response. It was more inspirational than informational though I'm afraid.
Anna
Mosfets and Misfits
Man.........
What a rude women! Will you have my baby Anna? I for one will be happy to offer hopefully substitive audio advice. Ask away!
Man.........
What a rude women! Will you have my baby Anna? I for one will be happy to offer hopefully substitive audio advice. Ask away!
Re: Mosfets and Misfits
Are you turning into an hermaphrodite Fred? All of these new aliases are with the moderator permission I hope. Not that it matters anyway.
SornilltheWhite said:Man.........
What a rude women! Will you have my baby Anna? I for one will be happy to offer hopefully substitive audio advice. Ask away!
Are you turning into an hermaphrodite Fred? All of these new aliases are with the moderator permission I hope. Not that it matters anyway.
I think Fred's appearance as SornilltheWhite in Aleph X thread can only help us to finish our contest earlier. If you looking for his kind of humor, check anna_grahm as well.😉
Anna the kid(der)
I am not sure she was kidding. Can someone fill me in what was funny in her post? She appeared to be loaded for bear. Was there some kind of subtext that I missed? Is every one here a conspiracy nut? I suppose this Fred guy had something to do with the Kennedy assasination. BTW, he wouldn't be a 33rd degree Mason would he?
I am not sure she was kidding. Can someone fill me in what was funny in her post? She appeared to be loaded for bear. Was there some kind of subtext that I missed? Is every one here a conspiracy nut? I suppose this Fred guy had something to do with the Kennedy assasination. BTW, he wouldn't be a 33rd degree Mason would he?
anna_grahm IP: 172.132.233.102
sornillthewhite IP: 172.132.233.102
You know what they say about AOL users...
sornillthewhite IP: 172.132.233.102
You know what they say about AOL users...
Driven by circumstance towards the Cliffs of Sheetrock, the stranger pulled his horse, Aleph, up short. Eyes narrowed, he scanned the path ahead. Something was wrong. He could feel it.
His eyes fell to the ground. Yes. The tell-tale hoof prints of the heavily-laden horse of the EE Kid. Somewhere ahead, the Kid was waiting in ambush.
Though the Kid hadn't known that the stranger would be coming this way--the stranger himself hadn't even known ahead of time--it was widely known that the Kid loved nothing better than to ambush some some greenhorn coming down from Electron Gap with saddlebags full of Possibilities. Stealing Possibilities from pilgrims was about as low as you could get in the stranger's estimation. Once robbed, they left forever, not trusting the sheriff to enforce the law beyond the town limits...and sometimes not even within the town.
The stranger urged Aleph on.
The day would bring what the day would bring.
Grey
His eyes fell to the ground. Yes. The tell-tale hoof prints of the heavily-laden horse of the EE Kid. Somewhere ahead, the Kid was waiting in ambush.
Though the Kid hadn't known that the stranger would be coming this way--the stranger himself hadn't even known ahead of time--it was widely known that the Kid loved nothing better than to ambush some some greenhorn coming down from Electron Gap with saddlebags full of Possibilities. Stealing Possibilities from pilgrims was about as low as you could get in the stranger's estimation. Once robbed, they left forever, not trusting the sheriff to enforce the law beyond the town limits...and sometimes not even within the town.
The stranger urged Aleph on.
The day would bring what the day would bring.
Grey