Re[02]: capacitance of the Mosfet which increases non-linearly
Nelson,
I am not an electronics engineer, not even as hobby. I just know enough to be "dangerous"
.
I have couple questions if I may re your post:
1) Is this mostly related to Class A amps?
2) If no to (1) above, what threads, forms, documents, et al could you suggest one read, even if target audience is electronics engineers, that I could read and see what I can digest out of?
3) Which specs are you referring to as capacitance that is listed on the MOSFET specifications?
I was asking as I have a couple of 225VA 15VAC based toroidal transformers I was thinking I use for small 15W amps.
Regards,
John L. Males
Willowdale, Ontario
Canada
12 December 2004 19:03
Nelson,
I am not an electronics engineer, not even as hobby. I just know enough to be "dangerous"
.I have couple questions if I may re your post:
Nelson Pass said:
1) Is this mostly related to Class A amps?
2) If no to (1) above, what threads, forms, documents, et al could you suggest one read, even if target audience is electronics engineers, that I could read and see what I can digest out of?
3) Which specs are you referring to as capacitance that is listed on the MOSFET specifications?
I was asking as I have a couple of 225VA 15VAC based toroidal transformers I was thinking I use for small 15W amps.
Regards,
John L. Males
Willowdale, Ontario
Canada
12 December 2004 19:03
John,
1-That's basic MOSFET behavior, and will be pretty much the case regardless of operating class of the amplifier.
2-There's nowhere to go to get a "one stop shop" answer for these sorts of things. The de facto standard for books is Horowitz & Hill, The Art of Electronics. There are a zillion other places you can go to get small pieces of the puzzle, but that's as good a reference as you're going to find for anything relating to audio. There have been books written with audio in mind, but they're either hopelessly narrow-minded or too specialized to be a good general reference text for audio use. Face it, we're a very, very small niche market and there's not much money to be made on audio design books.
3-Start with www.irf.com and look up the spec sheets for whatever device you're interested in. They're available as PDF files, so you can print 'em off and wallpaper your kitchen with them. That's not to say that your interior designer will think much of your choice in wallpaper, but it's the latest thing in electro-geek.
Are the transformers 15-0-15 or just a single 15V secondary? You can get things to work either way, but you have to hook them up differently. A 15V secondary will give you roughly 20V rails. That's good for a nearly 20W amp as long as you don't get radical with the bias current. As a matter of fact, I've got a Mini-A in the living room right now that runs under almost exactly those conditions.
Grey
1-That's basic MOSFET behavior, and will be pretty much the case regardless of operating class of the amplifier.
2-There's nowhere to go to get a "one stop shop" answer for these sorts of things. The de facto standard for books is Horowitz & Hill, The Art of Electronics. There are a zillion other places you can go to get small pieces of the puzzle, but that's as good a reference as you're going to find for anything relating to audio. There have been books written with audio in mind, but they're either hopelessly narrow-minded or too specialized to be a good general reference text for audio use. Face it, we're a very, very small niche market and there's not much money to be made on audio design books.
3-Start with www.irf.com and look up the spec sheets for whatever device you're interested in. They're available as PDF files, so you can print 'em off and wallpaper your kitchen with them. That's not to say that your interior designer will think much of your choice in wallpaper, but it's the latest thing in electro-geek.
Are the transformers 15-0-15 or just a single 15V secondary? You can get things to work either way, but you have to hook them up differently. A 15V secondary will give you roughly 20V rails. That's good for a nearly 20W amp as long as you don't get radical with the bias current. As a matter of fact, I've got a Mini-A in the living room right now that runs under almost exactly those conditions.
Grey
Re[04]: capacitance of the Mosfet which increases non-linearly
Hi Grey,
(Hope Grey does not refer to grey hair with all the IT challenges I have seen you comment on odd time from IT real world )
Thanks for your reply and answers.
1) Thanks for answer. I had asked as I am not sure other Class A amp heat issues aside, if I have much power to draw from. I am limited to a sort of 15A circuit can use, unless run couple extensions in from kitch to living room( So I am thinking maybe I build a few to have and enjoy, and also have some low wattage Class AB amps as well, ergo the question.
2) Sorry I was not implying one stop shopping. I am already trying to piece and organize the pieces of information I have read. It will burn up a few DLT tapes and more than few CDs I had feeling this is collection process and cross referencing of raw information. That was the contect of the question, sorry to have not been articulate that was assumption. Expect this collection process will consume about 200 GB of space very easy if not 400GB. Hours to do so, well you have some clue I am sure. Distill the information ... umm ... Time to Distill in hours = size of data in bytes ** 10!
3) Already have lots of the IFP, and many other datasheets in PDF on my system. Lord only knows how many times I have looks at a number of these datasheets. I was asking if I could be enlightened as to what spec item on datasheet "as capacitance". I know tehre are lots of capacitance specs, just not sure which one you may be referring to or what otehr specs one refers to to calculate this "capacitance" you have refered to. My cats are not fussy about the interior design of place. They in fact have their own opinions of interior design anyway
As to the 225VA 15VAC based toroidal transformers I have, each has a primary 117VAC, and 4 seperate (not centered tapped), yes 4, 15VAC secondaries. I have sent in an inquiry to find out what is the rating of each secondary. The rating is for 7.5 amps. I do not know if that is 7.5 amps for ceach secondary or 7.5/4=1.875A a secondary or a "floating" rating in that any sum of the secondaries must not exceed 7.5A. 20W of power is just fine for me based on 15VAC supply. I have a spreadsheet to calculate VAC to rail to rms/peak -+V and A, which suggested about 16W of power. 16W is ok by me as well. The spreadsheet is not slanted to the Aleph design, but at least I get an basic ballpark good enough for my selection needs.
Oh, another question. What is the AC at mains draw for your Mini-Aleph? If you know please advise what transformer, amp bias, amp output driver using and number of Mini-Alephs connected to supply?
Regards,
John L. Males
Willowdale, Ontario
Canada
12 December 2004 22:57
Hi Grey,
(Hope Grey does not refer to grey hair with all the IT challenges I have seen you comment on odd time from IT real world
)Thanks for your reply and answers.
1) Thanks for answer. I had asked as I am not sure other Class A amp heat issues aside, if I have much power to draw from. I am limited to a sort of 15A circuit can use, unless run couple extensions in from kitch to living room
( So I am thinking maybe I build a few to have and enjoy, and also have some low wattage Class AB amps as well, ergo the question.2) Sorry I was not implying one stop shopping. I am already trying to piece and organize the pieces of information I have read. It will burn up a few DLT tapes and more than few CDs
I had feeling this is collection process and cross referencing of raw information. That was the contect of the question, sorry to have not been articulate that was assumption. Expect this collection process will consume about 200 GB of space very easy if not 400GB. Hours to do so, well you have some clue I am sure. Distill the information ... umm ... Time to Distill in hours = size of data in bytes ** 10! 3) Already have lots of the IFP, and many other datasheets in PDF on my system. Lord only knows how many times I have looks at a number of these datasheets. I was asking if I could be enlightened as to what spec item on datasheet "as capacitance". I know tehre are lots of capacitance specs, just not sure which one you may be referring to or what otehr specs one refers to to calculate this "capacitance" you have refered to. My cats are not fussy about the interior design of place. They in fact have their own opinions of interior design anyway
As to the 225VA 15VAC based toroidal transformers I have, each has a primary 117VAC, and 4 seperate (not centered tapped), yes 4, 15VAC secondaries. I have sent in an inquiry to find out what is the rating of each secondary. The rating is for 7.5 amps. I do not know if that is 7.5 amps for ceach secondary or 7.5/4=1.875A a secondary or a "floating" rating in that any sum of the secondaries must not exceed 7.5A. 20W of power is just fine for me based on 15VAC supply. I have a spreadsheet to calculate VAC to rail to rms/peak -+V and A, which suggested about 16W of power. 16W is ok by me as well. The spreadsheet is not slanted to the Aleph design, but at least I get an basic ballpark good enough for my selection needs.
Oh, another question. What is the AC at mains draw for your Mini-Aleph? If you know please advise what transformer, amp bias, amp output driver using and number of Mini-Alephs connected to supply?
Regards,
John L. Males
Willowdale, Ontario
Canada
12 December 2004 22:57
The capacitance in question is the Gate capacitance.
Egad, I use junk-box transformers to build Mini-As. There's no telling what the things are rated at. I just pick it up, heft it, scowl at it...you know, the kinda things that you do when you're doing Science. If it's not too rusty and I want the shelf space where it was sitting for something else, I toss it in a circuit. Did this recently for a headphone amp. The rail voltage was too high for what I intended, so I grubbed around and found some parts and built a CRCRC power supply to rub off a couple of the unnecessary volts. Silver lining to the cloud was that the rail was absolutely quiet after all that massaging--still a clean, flat line on the smallest resolution on my scope.
Grey
Egad, I use junk-box transformers to build Mini-As. There's no telling what the things are rated at. I just pick it up, heft it, scowl at it...you know, the kinda things that you do when you're doing Science. If it's not too rusty and I want the shelf space where it was sitting for something else, I toss it in a circuit. Did this recently for a headphone amp. The rail voltage was too high for what I intended, so I grubbed around and found some parts and built a CRCRC power supply to rub off a couple of the unnecessary volts. Silver lining to the cloud was that the rail was absolutely quiet after all that massaging--still a clean, flat line on the smallest resolution on my scope.
Grey
To me it would seem that if the IRFP240 or IRFP044 are hard to get replacing it by IRFP044N is not the obvious choice.
e.g. :
Three IRFP630 in parallel have a lower Cgs and Cds than a single IRFP044.
Rjs = 0.73 for the IRFP630's and Rjs = 1.54 for the IRFP044N.
A negative difference is Rds which is 0.13 for the 630's and 0.020 Ohm for the 044N.
At 8 amps of bias that reads as a bit more than 1 volt drop instead of 0.16 Volt for the 044N, not that impressive.
As cooling is the prime directive for these components in Aleph circuits cheap 630's that can be had anywhere for a dime are a better choice than 044N's.
Even if they have a TO220 package, three midgets can conquer one giant.
Reichelt sells the 240, even at a very attractive price, i miss the point.
e.g. :
Three IRFP630 in parallel have a lower Cgs and Cds than a single IRFP044.
Rjs = 0.73 for the IRFP630's and Rjs = 1.54 for the IRFP044N.
A negative difference is Rds which is 0.13 for the 630's and 0.020 Ohm for the 044N.
At 8 amps of bias that reads as a bit more than 1 volt drop instead of 0.16 Volt for the 044N, not that impressive.
As cooling is the prime directive for these components in Aleph circuits cheap 630's that can be had anywhere for a dime are a better choice than 044N's.
Even if they have a TO220 package, three midgets can conquer one giant.
Reichelt sells the 240, even at a very attractive price, i miss the point.
Capicitance Question
I have recently finished an Aleph 4 using 8 irfp260s per channel. I did this just to get it finished at the least cost since I already had a bunch of 260s. To me, the amp sounds great, but I now need to decide if I should replace them because of the capacitance issue. Does anyone know from experience what effect on the sound the high capacitance has at high frequency? My amp goes to prettty high frequencies, and I do notice a very faint sssssss sound at the top. This sound is similar but more faint than in many commercial Mosfet amps I have heard that claim very low distortion. Does the capacitance cause roll-off on the high end? In all respects, the amp sounds spectacular, so I may need some convincing that I need to swap out these IRFP260s.
BTW, I want to thank Nelson Pass (The One And Only) and many others on this forum, like GRollins, for making my project possible.
I have recently finished an Aleph 4 using 8 irfp260s per channel. I did this just to get it finished at the least cost since I already had a bunch of 260s. To me, the amp sounds great, but I now need to decide if I should replace them because of the capacitance issue. Does anyone know from experience what effect on the sound the high capacitance has at high frequency? My amp goes to prettty high frequencies, and I do notice a very faint sssssss sound at the top. This sound is similar but more faint than in many commercial Mosfet amps I have heard that claim very low distortion. Does the capacitance cause roll-off on the high end? In all respects, the amp sounds spectacular, so I may need some convincing that I need to swap out these IRFP260s.
BTW, I want to thank Nelson Pass (The One And Only) and many others on this forum, like GRollins, for making my project possible.
Re: Capicitance Question
buglehead,
Interesting observations. I have been labouring over the various spec of many of the popular IRF's used by many of the projects here. Part of my motivation is to have sense if there be any corelation of performance the ears hear to specs. I have been doing some non-engineering evaluation of the specs and some "interesting" math on the specs.
Assuming the issues you have noted are based on the output driver IRFP260, if you have IRFP260N it would be interesting to know what you think of the quality from IFRP260N. Based on my number crunching you might want to try a IRFP264N or IRFP250N as well or instead of the IRFP260N. These suggestions are based purely on non-engineering based math I have done on the specs of the some IRF Mosfets. That said, others far more qualified will be able to suggest any points about bias, part value changes or supply changes specific devices require within the design. It goes without saying being able to keep as many of the parameters the same if one does compare different output devices, this will enable one a more objective manner to evaluate any sound quality differences. I realize what is being evaluated in terms of sound quality is subjective, but at moment you are the same subjective evaluator and I assume that other than the changes you make to the Aleph-X all the otehr items in the audio food chair (speakers, pre-apms, room, material, wires, etc) remain the same.
Regards,
John L. Males
Willowdale, Ontario
Canada
13 December 2004 16:24
buglehead said:
buglehead,
Interesting observations. I have been labouring over the various spec of many of the popular IRF's used by many of the projects here. Part of my motivation is to have sense if there be any corelation of performance the ears hear to specs. I have been doing some non-engineering evaluation of the specs and some "interesting" math on the specs.
Assuming the issues you have noted are based on the output driver IRFP260, if you have IRFP260N it would be interesting to know what you think of the quality from IFRP260N. Based on my number crunching you might want to try a IRFP264N or IRFP250N as well or instead of the IRFP260N. These suggestions are based purely on non-engineering based math I have done on the specs of the some IRF Mosfets. That said, others far more qualified will be able to suggest any points about bias, part value changes or supply changes specific devices require within the design. It goes without saying being able to keep as many of the parameters the same if one does compare different output devices, this will enable one a more objective manner to evaluate any sound quality differences. I realize what is being evaluated in terms of sound quality is subjective, but at moment you are the same subjective evaluator and I assume that other than the changes you make to the Aleph-X all the otehr items in the audio food chair (speakers, pre-apms, room, material, wires, etc) remain the same.
Regards,
John L. Males
Willowdale, Ontario
Canada
13 December 2004 16:24
I don't have the datasheet for the IRFP260s.
IRFP260 has a tremendous high Cgs, more than 5000pF.
Using 8 means Cgs = 40nF.
What is Cgs for the IRFP260s ?
I can imagine that with such high Cgs you'll have slewrate problems at high frequencies, even if the real Cgs for the given output may be significantly smaller.
Your story confirms NP's statement that SR figures are not all that important.
IRFP260 has a tremendous high Cgs, more than 5000pF.
Using 8 means Cgs = 40nF.
What is Cgs for the IRFP260s ?
I can imagine that with such high Cgs you'll have slewrate problems at high frequencies, even if the real Cgs for the given output may be significantly smaller.
Your story confirms NP's statement that SR figures are not all that important.
Thanks for the replies.
I should have been more specific about the chip. It is IRFP260N. I'm sorry but IRFP260s does not exist, it is the plural of IRFP260.
Ciss = 4057. I'm using 4 per rail. I finished the amp about 2 months ago and it has settled in pretty well. Good soundstage and imaging. Great bass. I have used massive heatsinks and can bias it up, which I should probably try in any case. It would be a lot of work to swap out output devices, so I would probably try it once only. I think I would rather spend the energy on a pair of Aleph-X. I would use the "proper" output devices, and would then have something to suitable to compare against.
I should have been more specific about the chip. It is IRFP260N. I'm sorry but IRFP260s does not exist, it is the plural of IRFP260.
Ciss = 4057. I'm using 4 per rail. I finished the amp about 2 months ago and it has settled in pretty well. Good soundstage and imaging. Great bass. I have used massive heatsinks and can bias it up, which I should probably try in any case. It would be a lot of work to swap out output devices, so I would probably try it once only. I think I would rather spend the energy on a pair of Aleph-X. I would use the "proper" output devices, and would then have something to suitable to compare against.
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