All Hitachi Lateral Fet amplifier for DIY described by Paul Kemble - Page 4 - diyAudio
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Old 6th October 2012, 08:08 PM   #31
wahab is offline wahab  Algeria
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Quote:
Originally Posted by gaborbela View Post
Hello wahab

Is these acceptable for front end??

Greetings
Cant answer for the whole schematic but for the bipolar part of the cascode
increase the 6.8K resistor to 33K at least as the original value send
way more current than necessary to the zener.

This latter should be reduced to 10V max as it is the value
at wich the excess current start to increase dramaticaly
in most jfets.

Also , the MPSA18 are perhaps undersized in respect of TDP ,
a good replacement would be 2SA1360/2SC3423.

I once simulated this circuit to check its behaviour ,
i ll look at the data that are on an old hard drive ASAP.

Last edited by wahab; 6th October 2012 at 08:11 PM.
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Old 6th October 2012, 10:01 PM   #32
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Quote:
Originally Posted by jackinnj View Post
Very similar circuit was in The Audio Amateur over 20 years ago by Erno. The MOSFETs in the middle are unobtanium, although you sometimes see them on EBay.
Recently there was 3 sets of lateral FETs for the 1980's Maplin mosfet amp on ebay.
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Old 6th October 2012, 11:23 PM   #33
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Quote:
Originally Posted by wahab View Post
Cant answer for the whole schematic but for the bipolar part of the cascode
increase the 6.8K resistor to 33K at least as the original value send
way more current than necessary to the zener.

This latter should be reduced to 10V max as it is the value
at wich the excess current start to increase dramaticaly
in most jfets.

Also , the MPSA18 are perhaps undersized in respect of TDP ,
a good replacement would be 2SA1360/2SC3423.

I once simulated this circuit to check its behaviour ,
i ll look at the data that are on an old hard drive ASAP.
Hello
Thank you wahab!
I made all the mod you advised.
I having second thoughts about the 2SC3423, do we really need that beefy bipolar for cascoding.
But I did changed because want to keep going forward so I can do some real life test.
I changed the resistor and the zener diode to.
When I did the first mod I drew the cascode both BJT reverse.
Hard to wait to see your sim result you have done.
I still believe there is a possibility to bring out a great amplifier from these circuit with some mod.
Thank you one more time.

Zen Mod I did look up the Marantz MA24 schematic I think that to complex.

I like as simple as possible until do not degrade the sound.
Thank you any way!
Greetings Gabor
Attached Images
File Type: jpg All fet Hitachi amplifier modified front 1.JPG (56.0 KB, 595 views)
File Type: gif MA-24-schematic good.gif (76.8 KB, 595 views)
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Old 6th October 2012, 11:37 PM   #34
Zen Mod is offline Zen Mod  Serbia
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matter of taste ....... MA24 is much more elegant , even if looking more complex

besides having too small current through input LTP , and few other small details , it's really neat amp
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Old 7th October 2012, 12:06 AM   #35
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Hello Zen

Yes you right, it is really a nice amp specially seeing the end product.
I would like to build something around these simple circuit. Many amplifier designer got inspiration from the Hitachi circuit.
I think on the WAS (all do I have those fets) probably not the best idea how it is now.
Please keep follow the thread you always have great solution, great idea..

Greetings Gabor
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Old 7th October 2012, 12:28 AM   #36
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I have a similar ciccuit banging around that has never been powered up fully (driver, yes - driver plus outputs, no), based on hot-biased MPF960 for the input stage - maybe I should dredge up that amp and finish it. The circuit was inspired by the original amp schematic in the Hitachi lateral MOSFET data sheet. I suspect that the inspiration for the Kemble circuit came from the same place, as the topology is similar.

Last edited by wrenchone; 7th October 2012 at 12:31 AM. Reason: sp, exposition
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Old 7th October 2012, 12:31 AM   #37
wahab is offline wahab  Algeria
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Quote:
Originally Posted by gaborbela View Post
Hello
Thank you wahab!
I made all the mod you advised.
I having second thoughts about the 2SC3423, do we really need that beefy bipolar for cascoding.
But I did changed because want to keep going forward so I can do some real life test.
I changed the resistor and the zener diode to.
When I did the first mod I drew the cascode both BJT reverse.
Hard to wait to see your sim result you have done.
I still believe there is a possibility to bring out a great amplifier from these circuit with some mod.
Thank you one more time.
I try to give you a few point that will help you understand
some of this amps requirements.

- The LTP total current is defined by the 16K resistor and will amount
to about 4.5mA so this resistor dissipation will be 0.315W , wich
is a lot , surely that it can be reduced without entailing the perfs
but if such a change is made the 3.3K resistors that load the cascode
should be increased in an inverse ratio.
The 16K could eventualy be replaced by a current source using
a 2SC3423 with a little heatsink.

- Each side of the cascode will have 2.25mA , hence the bipolar parts
will dissipate about 0.14W each , that s why i proposed the 2SA/2SC parts
wich can be replaced by their plastic case version 2SA1145/2SC2705
(used in the MA24 !!) although for reliability i would stick with the first ones.

- It is likely that the 2.2K trimmer has too high value for a VAS current
that is in the vicinity of a few mA to 10ma , a 470R would be more cautious ,
at least for the test board.

- If your output transistors are matched enough you can get
rid of the source 0.22R and expand the domain in wich the
output stage has a square law behaviour.

Hope this will be useful to your project.
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Old 7th October 2012, 02:38 AM   #38
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Hello
Yes it help a lot!
I'm so grateful to you and some other guys who came to help not just write these or that bad, or please look for another amp.
About the Source resistors Juma once wrote those does not hurt if they used.
You 100% right if the power mosfet well matched better if the Source resistors left out.
Those are right before the speakers..
So reduce the 2.2K trimmer to 470R.
I'll stick with the transistor you told for cascode. For cascode I need only NPN device, or not???
Do I leave the WAS how it is now? Or let it test how is it and we will see.
If the sound to soft I think it will be better to use BJT..
When you find your sim. result please let us know.
I do have a amplifier to build (I have the stuffed PC boards) use almost the same devices but that is a symmetrical circuit.
Called Grand Mos
I post the basic circuit because that a commercial amp of Jean Marc.
Same lateral power mosfets , same mosfet as a driver and Toshiba J Fet cascoded with BC550/560
Symetrical circuit has a lot of disadvantage to. Can't be matched the P channel to the N channel not even close to 80%
Thank you
Greetings Gabor
Attached Images
File Type: jpg Grand Mos.JPG (48.0 KB, 576 views)

Last edited by gaborbela; 7th October 2012 at 02:42 AM.
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Old 7th October 2012, 02:52 AM   #39
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Hello

Upgraded circuit.
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File Type: jpg All fet Hitachi amplifier modified front 1.JPG (54.8 KB, 567 views)
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Old 7th October 2012, 07:11 AM   #40
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Quote:
Originally Posted by gaborbela View Post
Hello

Upgraded circuit.
Skip the so-called current mirror with MOS-FET from VAS because is not useful. Or does not have the same benefits as one with BJT's. If you do not believe me, then try and convince you.

Then, why use MPSA42? Try my solution where you can use instead of 2N6800 any equivalent Hitachi part or IRF610 from Samsung. And includes some constant current source in the circuit input and VAS as we have done it.
It's much better this way if you want to get some performance, because otherwise, as you drew you amplifier diagram, the results are in performance of BJT's classic. I guess the solution with MOSFET you want to achieve much higher performance variant BJT. Right? If yes, then follow my advice.
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Last edited by donpetru; 7th October 2012 at 07:13 AM.
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