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Old 10th June 2005, 01:07 PM   #21
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hi quasi ...
and thnx for help ..
but if u remember me ( my subwoofer construction thread ! u helped me so much there ) i have not much experience in electronic ,,, if i want to be honest i really donno what r u talkin bout lol ! .. sorry ...
how can i control the bias current ... ?
u suggest me to build ur amp ,, is ur amp have a pcb layout ? ..
cuz i cant convert the schematic ...
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Old 10th June 2005, 05:36 PM   #22
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Quote:
Originally posted by EUVL
Is it your experience that vertical FETs have in general a more gentle variation in capacitance with frequency than lateral FETs ?
I don't work with Lateral devices very often, but it is my
understanding from Charles Hansen that they have less
non-linearity in the capacitance.

I think that this is an issue when considering their use as
a Common Drain (follower) or as Common Source (having
voltage and current gain) Lateral Mosfets have some
advantage in the former if the driving impedance is high, and
Vertical Mosfets have some advantage as followers

When the impedance driving any of these is low, the problem
tends to go away, and then the issue is more what
transconductance you want - the Verticals being quite a bit
higher. I deal with this issue a lot because I favor 1 and 2
stage designs, and giving the transistors a low impedance
source often means yet another stage, so I have to make
my trade-offs accordingly.
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Old 10th June 2005, 05:56 PM   #23
EUVL is offline EUVL  Europe
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Nelson,

We discussed once about a year ago in a private email communication about 2SK1529, which you suggested could be a lateral FET. I checked the Toshiba website but still could not come to conclusion whether it is one or the other.

According to my measurements (Id vs Vgs using 1 kHz sinewave), the 2SK1529 has, within 10%, the same transconductance as IRFP240 at around 1A (the quoted value is much higher for IRFP240 in the datasheet, but at a much higher current; it drops also proportionally to bias current, so at 1A, it is about the same as the Toshiba), but the 2SK1529 has much lower capacitance. So my conclusion from the measurements was that the 2SK1529 is at least a equal replacement for IRFP240 in e.g. an Aleph-X. Different story for the likes of 2SK1058, that I agree.

Perhaps Charles would care to shed some light on the topic?


Patrick
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Old 10th June 2005, 06:43 PM   #24
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Susan Parker is under the impression that the 2SK1529 is
a lateral part, using it in her Zeus (see the solid state forum),
and I have nothing to contradict that.

If it has the same transconductance as the 240, I imagine it's
a pretty big chip.
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Old 11th June 2005, 12:00 AM   #25
tlf9999 is offline tlf9999  United States
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The datasheet seems to suggest high current beyond which tempco turns negative (a few amps), and high Vgs threashold. But also high Rds.

If I am a betting man, I would say that it is a vertical.
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Old 11th June 2005, 03:16 AM   #26
quasi is offline quasi  Australia
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Quote:
Originally posted by Ahmad_tbp
hi quasi ...
and thnx for help ..
but if u remember me ( my subwoofer construction thread ! u helped me so much there ) i have not much experience in electronic ,,, if i want to be honest i really donno what r u talkin bout lol ! .. sorry ...
how can i control the bias current ... ?
u suggest me to build ur amp ,, is ur amp have a pcb layout ? ..
cuz i cant convert the schematic ...

Of course I remember, hows the box going?

Anyway schematic, layout and tracks are on these links;


http://www.diyaudio.com/forums/attac...mp=1111145851&

http://www.diyaudio.com/forums/attac...amp=1111145980

http://www.diyaudio.com/forums/attac...amp=1111237713

If you decide to build this please contact me so that I can provide a construction guidline (heatsinking, wiring layout etc.)



Cheers
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Old 11th June 2005, 08:04 AM   #27
EUVL is offline EUVL  Europe
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> Susan Parker is under the impression that the 2SK1529 is
a lateral part.

She got the FETs from me. : )

According to a broshure on power FETs from Toshiba, they refer 2SK1529 as pi-MOS. From the picture, it looks more lateral than vertical to me. In any case, it is D-MOs, and has the characteristic "linear" region after the parabolic at low current.

Patrick

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Old 11th June 2005, 08:10 AM   #28
EUVL is offline EUVL  Europe
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And this are the measured Vgs vs Id curves for both IRFP240 and 2SK1529. As one can see, transconductances is practically identical at around 1A.

Measurement was done at Vds = 24V, with the gate driven by a function generator using 1kHz sine wave with appropriate DC offset. Single shot, 1000 measurement points, 16 bit.

Unfortunately I have no equipment to measure distortion or frequency dependent capacitance. If anyone is able and willing, I am more than happy to offer a couple of FETs, for the sake of knowledge for all.


Patrick
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Old 11th June 2005, 07:28 PM   #29
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As far as the SK1529/1530 SJ200/201 being Verticle or Lateral makes no difference with these devices as far as bias tracking is concerned in audio amps. It is my understanding that these devices are Lateral but the negative Tempco doesn't kick in till 6Amps with the 1529 (higher for the 1530). As far as audio is concerned these should be treated more like Verticles. Some even consider them Verticles. I just consider them Fets that need a Vbe Multiplier for bias stability

As for using them in the schematic in the first post, they may work and not have thermal runaway with big enough heat sinking as Nelson suggest, or not. You would be taking a chance with bias tracking using only a Pot for bias. Its not that hard to add a Vbe multiplier, and i personally would.

Another thing that needs considertion is the Vgs on value. For the 1058/1529 162/200 this value for a class AB amp is about 1.5 V. For the IRF devices this is typically ~4 V. What I'm getting at is that the IRF devices need a different bias voltage, and could have very bad cross-over distortion used in the circuit without taking this into consideration. (I'm not sure if the author of the amp posted in post #1 has or not, but I get the feeling that the amp was designed with the 1058/162 devices in mind).

-D.
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Old 11th June 2005, 08:16 PM   #30
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Getting back to post 1 :

The schematics i have seen on Edwin Paij's homepage are not by his hand.
I would have more faith in circuits that were designed and tested by the same person, this one was originally intended for Lateral SJ/SK Mosfets.
And even then it wasnt that great.
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