Hitachi mosfet power amplifier

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cs

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#1
Some time ago (1980's I think), Hitachi published an App Note for a power amp using their mosfets. It was unusual in that the VAS was configured as a diff pair, thereby improving the PSRR over the conventional arrangement.

I would like to have a go at this, but using more modern devices. Does anyone have a copy of the original App Note (or schematic) they could post please ?

TIA,
Chris.
 
#4
If you use the search function you will find that this classic amplifier has been discussed in much detail many times already 🙂

The diff pair style voltage amplifier stage is not really a diff pair as we know it, this topology is used to achieve high gain. And actually this amp has worse PSRR than most.
 
#6
Lumba Ogir said:
cs,
or this:
http://www.geocities.jp/mutsu562000/root/amps1/htm/e/hp179e.htm
Click to expand...


This is a quasi-complementary design using UHC mosfet N channel only in the output stage. I wonder how they cost and if easily available?

The 150 ohm resistors, are they photoresistors or else?

Is this one really in a Denon amp and which one?
I wonder how it sounds...

I have already used the same design topology but bjt in input stage and vertical mosfet in output stage.

😎
 
#8
fab said:



This is a quasi-complementary design using UHC mosfet N channel only in the output stage. I wonder how they cost and if easily available?

The 150 ohm resistors, are they photoresistors or else?

Is this one really in a Denon amp and which one?
I wonder how it sounds...

I have already used the same design topology but bjt in input stage and vertical mosfet in output stage.

😎
Click to expand...

From Denon Literature

The UHC-MOS has a gain that is even higher than that of bipolar transistors; with a single element, the UHC-MOS achieves the current linearity of 35 MOS-FETs and 3 bipolars

http://www.alldatasheet.com/datasheet-pdf/pdf/155495/HITACHI/2SK1297.html

To be honest, I do not see what is so special with the UHC MOS fets that they use. Hitachi does not seem to refer to them as UHC MOS only Denon does. They look to have a transconductance of 9 S at 2A @ Tc 75oC. Capacitances are very high also. It's like they have an oversized die for pulse apps without the case to dissipate the power for long periods. Probably better with multiple IRF devices to get the same tranconductance and lower capacitances.

Or am I missing something ?
 
#14
The topology is typical Kaneda. There is also an Xed (Balanced) version published in his book. Just mirror image along the middle of the input diff pair.

The 150 is indeed NTC for thermal compensation. There are very detailed description of the characteristics of UHC-MOSFETs in Kaneda's book, and they have very high tempco.

If you google in google.co.jp, you will find enough examples of DIY amps built with UHC-MOSFETs. The latest generation also has P-devices.

In theory it is possible to get the same transconductance with paralleling IRF or Fairchild MOSFETs, but then if you use say 4 devices at 0.5A bias, you would need a devices which has 2.25S at the said bias current to equal one 2SK1297. I have not found one yet. And of course you need source resistors for current sharing, which does not help your effective transconductance; and the capaitance adds 4x.

I also did not manage to find any suppliers outside Japan.


Patrick
 
#15
Kaneda MOSFET Amplifier

EUVL said:
The topology is typical Kaneda.
There is also an Xed (Balanced) version published in his book.
Just mirror image along the middle of the input diff pair.

The 150 is indeed NTC for thermal compensation.
There are very detailed description of the characteristics of UHC-MOSFETs in Kaneda's book,
and they have very high tempco.
--------------
I also did not manage to find any suppliers outside Japan.

Patrick
Click to expand...

😉

I want to goto Japan.
Can I come and live.
Somebody in Tokyo has got one room for me, Lineup from EU.
😉

Lineup - Is one Kaneda type man for Amplifiers, for sure
Simple but very Good 😎
 
#16
2SA606 needed

Hello

I started to collect the parts for these Japanese amplifier . Mostly all the parts are available only I don't find the driver transistor NEC 2SA606 .
I see in China , Hong Kong and other Asian countries they have a lot but they only ship if I purchase min.$500 vale to N America .
May be someone could help me who live in China or Hong Kong to get 10PC of these transistors ad send it to me .
I can pay via pay pal .
Thanks for any help or any useful info .

Greetings
 
#19
back to the original question, the circuit in this link looks very much like the original from the hitachi databook.

http://www.plexoft.com/SBF/mounted/0tube.html

i have the original databooks in storage in my basement. if i can get to it, i'll post it.
hitachi also included a schematic for an all fet version of the amp. i'll include that as well ...
again, IF i can get my hands on the book.

mlloyd1

cs said:
Some time ago (1980's I think), Hitachi published an App Note for a power amp using their mosfets. It was unusual in that the VAS was configured as a diff pair, thereby improving the PSRR over the conventional arrangement.

I would like to have a go at this, but using more modern devices. Does anyone have a copy of the original App Note (or schematic) they could post please ?

TIA,
Chris.
Click to expand...
 
#20
cs said:
Some time ago (1980's I think), Hitachi published an App Note for a power amp using their mosfets. It was unusual in that the VAS was configured as a diff pair, thereby improving the PSRR over the conventional arrangement.

I would like to have a go at this, but using more modern devices. Does anyone have a copy of the original App Note (or schematic) they could post please ?

TIA,
Chris.
Click to expand...
I have the appnote.
 
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