I'm a bit of a fan of lateral FETs as well - fast, low capacitance, negative temperature coefficient (above 50-100mA bias anyway). It's easy to make fast slewing power amps with plenty low distortion with them.
My only gripe is that there is a very limited range of parts available - we're essentially stuck with two very discrete lots of devices - the 2SK1058/J162 type parts, with Vds ~ 160-200V and Id(max) ~ 7-10A, and the 2SK216/J79 size, with Id(max) ~ 0.5A.
I've been on a bit of a power consumption kick around the house of late (I've reduced our standby load by ~200W, or ~$260 per annum), and would really like to do a nice 20W lateral power amp, with bias currents of ~10mA or so (this'll allow me to run around a watt or two at idle, rather than the ten watts my amps tend to pull). Alas the available devices just aren't amenable to that sort of use. The larger ones have a slight positive temperature coefficient, so end up pulling ~50mA if you leave them to it on hot days, and the little ones are just basically lacking in SOA.
I reckon the world really needs a 2SK1056 and complement cut in four. ~2A Id, 20W Pd, and 1/4 the capacitance as well. And in a TO-220. Anyone fancy cutting some up for me?
My only gripe is that there is a very limited range of parts available - we're essentially stuck with two very discrete lots of devices - the 2SK1058/J162 type parts, with Vds ~ 160-200V and Id(max) ~ 7-10A, and the 2SK216/J79 size, with Id(max) ~ 0.5A.
I've been on a bit of a power consumption kick around the house of late (I've reduced our standby load by ~200W, or ~$260 per annum), and would really like to do a nice 20W lateral power amp, with bias currents of ~10mA or so (this'll allow me to run around a watt or two at idle, rather than the ten watts my amps tend to pull). Alas the available devices just aren't amenable to that sort of use. The larger ones have a slight positive temperature coefficient, so end up pulling ~50mA if you leave them to it on hot days, and the little ones are just basically lacking in SOA.
I reckon the world really needs a 2SK1056 and complement cut in four. ~2A Id, 20W Pd, and 1/4 the capacitance as well. And in a TO-220. Anyone fancy cutting some up for me?
Mooly said:Do you leave your amp on standby and if so why -- if you don't mind me asking
I'm fairly careful to turn them off when I'm not using them, but I am prone to falling asleep while listening to music.
My big one stayed powered up for four months or so when I first built it, because I hadn't gotten around to building an anti-thump circuit for it. My husband was a little frightened of the thump, so left it running. That was idling around 45-50W, so was quite a load.
But even so, as Andrew said, under normal listening my 100W amp rarely comes out of class-A, so I'm quite happy at the idea of reducing Iq.
Actually, I can work that out. Our normal listening volume is -40dB (I use a PGA2310 as a volume control), so when the music (on CD) goes hard into clipping (2.2V RMS), I'm putting 22mV into my power amp. The amp has a gain of 24dB, so that means just 350mV RMS ends up at the speakers.
So no, I'm not ever going into class-B under normal conditions.
I can turn it up (it clips at around 0dB on the dial with a full-power input), but then the neighbors start yelling (which could be taken to be a form of distortion in itself, now that I think about it).
Hi,
It's just a pet hate of mine unneccessery power consumption. If an amp really does need hours, or even minutes to "warm up" and if it is genuinely better for that warm up then (my personal opinion) there is something fundamental wrong with the design. And it must be readily measurable as well.
However I know many do like to leave them on, so, why not add a standby function that switches the bias generator into a power saving mode.
It's just a pet hate of mine
unneccessery power consumption. If an amp really does need hours, or even minutes to "warm up" and if it is genuinely better for that warm up then (my personal opinion) there is something fundamental wrong with the design. And it must be readily measurable as well. However I know many do like to leave them on, so, why not add a standby function that switches the bias generator into a power saving mode.
I take back what I just said. I've just had a good look at the 2SK213 datasheet, and I can't see a good reason for the 0.5A Id(max) rating. Every other specification would indicate that it's simply a 2SK1056 with a scaled down die (by about a factor of 4-5).
Has anyone here actually used the 2SK213/J76 in a power amp? The data sheet doesn't have any SOA curves at all, and the Id(max) number looks like they've just pulled it out of the air.
If I can ignore the Id(max) number, then these actually look like a very nice transistor for 10-20W amplifiers.
Now for the really hard bit - actually getting my mitts on some.
Code:
2SK1056 2SK213 Factor:
Id(max): 7A 0.5A 14
Vds(max): 120V 120V 1
Pd(max): 100W 30W 3.3
Ciss: 600p 90p 6.6
Crss: 10p 2.2p 4.5
0tc point: ~100mA ~20mA 5
Admittance: ~0.5S ~0.17S 3 (at Id=250mA)Has anyone here actually used the 2SK213/J76 in a power amp? The data sheet doesn't have any SOA curves at all, and the Id(max) number looks like they've just pulled it out of the air.
If I can ignore the Id(max) number, then these actually look like a very nice transistor for 10-20W amplifiers.
Now for the really hard bit - actually getting my mitts on some.
Mooly said:Hi,
It's just a pet hate of mine
However I know many do like to leave them on, so, why not add a standby function that switches the bias generator into a power saving mode.
Agreed. The only warming up an amp should need is time for the filter caps to charge up.
suzyj said:
Yeah, something like the lateral RF MOSFETs in fancy cases that Motorola used to make would be jolly nice to have in N- AND P-channel pairs.
But i'd already be pretty content with new 20-50W semi-lateral versions in a TOP3 case.
There's a stereo power amp set under the floor of my living, with automatic 2-hour delay stand-by bias switching.
As an additional precaution there's an automatic power limiter connected between the power amps and the mains fuse box, old (mechanically operating) electricity company gear which cost a few dollars each at dump stores.
The limiter resets each time the amps are switched to stand-by, if the continuous power consumption setting is reached it disconnects the power lines.
I've used TO-220 Hitachi's for output stages of headphone amp designs, (+ drivers in power amp output stages).
The preamp line stage i'm working on now has 16 of them in the output stages.
Difficult to find nowadays, plus expensive.
suzyj said:
Erno Borbely used them as drivers in a series of articles in Audio Amateur 3/93 and 4/93. They are probably archived on his website. They were also used as drivers in the Grand Mos 2x100W from "Revue du Son et du Cinema" #247 -- December 1999. You might be able to find this on the web.
The devices, or their close cousins, are available in the 'States from MCM.
One interesting property of the laterals is that not only do they have the negative temperature coefficient, there also seems to be some kind of gate clamping when the transistors overtemperature. At about 160 degrees some kind of thyristor fires and shorts the gate to the source, protecting the transistor. I tried to destroy one on a big 50V power supply but didn't succeed.
I did a little experiment some time ago:
http://www.diyaudio.com/forums/showthread.php?threadid=111116
OTOH, as MJ21195/MJ21196 are $2/pc and FJL4215/4315 (Fairchild equivalent to 2SC5200/2SA1943) are $1/pc it's cheaper to build massive overkill output stages instead.
I did a little experiment some time ago:
http://www.diyaudio.com/forums/showthread.php?threadid=111116
OTOH, as MJ21195/MJ21196 are $2/pc and FJL4215/4315 (Fairchild equivalent to 2SC5200/2SA1943) are $1/pc it's cheaper to build massive overkill output stages instead.
megajocke said:
But it's not, really, because to get the same sort of slew rates with lots of vertical fets, you've got to drive the gates really hard, meaning your driver circuit is significantly more complicated, and burns a lot more power. Then there's issues with current sharing due to the positive temperature coefficient, etc.
The cost of the output pair is peanuts compared to the cost of everything else, anyway. It's PCBs and heatsinks and transformers that really cost money.
Peranders: You mean the internal zeners? I don't believe those will be enough to protect the transistors from blowing up except protecting the gate oxide. I've heard of the bond wires failing and this I guess is due to high currents when no external zeners are used. 10V seems like a value commonly used. Do you have any idea where this thyristor action on the gate on overtemperature comes from? It's quite interesting.
suzyj: Those are bipolars Vertical fets seem just like a PITA with their temperature coefficients and gate voltage spread. Some manufacturers (QSC for example) use verticals with each transistor having it's own feedback circuit with an opamp to equalize currents. Bipolars and laterals seem much easier... And some high current FETs actually have second-breakdown-like characteristics!
If you only have one pair I agree it might not be much of the total price but if the amp needs 8 or 10 pairs per channel it starts to get expensive with the laterals! The self-protection might not be as big of an advantage if they are this expensive considering the cost and performance of modern BJTs. Still, maybe one likes the sound of the lateral mosfet amps - then that's a good reason to use them.
suzyj: Those are bipolars
Vertical fets seem just like a PITA with their temperature coefficients and gate voltage spread. Some manufacturers (QSC for example) use verticals with each transistor having it's own feedback circuit with an opamp to equalize currents. Bipolars and laterals seem much easier... And some high current FETs actually have second-breakdown-like characteristics!If you only have one pair I agree it might not be much of the total price but if the amp needs 8 or 10 pairs per channel it starts to get expensive with the laterals! The self-protection might not be as big of an advantage if they are this expensive considering the cost and performance of modern BJTs. Still, maybe one likes the sound of the lateral mosfet amps - then that's a good reason to use them.
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