All Hitachi Lateral Fet amplifier for DIY described by Paul Kemble - Page 15 - diyAudio
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Old 21st October 2012, 02:16 AM   #141
wahab is offline wahab  Algeria
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Quote:
Originally Posted by gaborbela View Post
Hello
Thank you for all of you for the reply.
wahab I plan to use serious separate PS, I'm not after to use large 10 000uF-s on the PC board.
When that large caps start to charge up you all know what happen.
If I get the right transformer I will go with reg front end PS.
Indeed , separating the PSU is a better option as it will keep
the capacitors far from heating sources.

Quote:
Originally Posted by gaborbela View Post
Small thump not a problem while the capacitors charged but I did notice your advise and I'll take care of that, thank you for the advise!
The last update is absolutely necessary as the power on thump
will be reduced to 3V peak over 6 millisecond , otherwise , without
the mod , it will reach as much as 40V for 35 millisecond duration.

Quote:
Originally Posted by gaborbela View Post
I used BG NP caps on the boards, RPR resistors, exotic caps in the PS large Plitron toroid......... close to $$$$ parts value when I count everything including the heatsink, WBT silver solder, connectors etc I do not talk here about the work I invested.
If you go further with this amp just dont throw money in exotic parts,
use whatever you have at hand provided it is of regular industrial quality.

Only the transistors should be selected carefully but apart from
the laterals there are quite enough other popular models that would suit
the task for the rest of the circuit.



Quote:
Originally Posted by AndrewT View Post
Can LTspice look at this start up process and can it predict the voltage fluctuations on the output during the first few tens of milliseconds of start up?
Of course , you can either shape the supply voltage output function
or more simply "build" a regular power supply with two generators
and a diodes bridge + filtering caps...

For exemple , using the latter trick , the picture of this thread amp
powering on as it works with the last update discussed a few posts above.
Attached Images
File Type: gif HITACHI FFET MOD3 PWON.gif (19.6 KB, 342 views)
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Old 21st October 2012, 04:56 AM   #142
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Hello
Thank you wahab
Yes first I'll use 1% 1/2W 10Cent metal film resistors. No Dale, PRP etc for test, later I can upgrade.
Capacitors I have some good quality at home, Silmic 100uF, Cerafinen 470uF(RED) or Nichicon MUSE 220uF.
I would have a question, which "transistors" must get some heatsink > I think about the VAS and front end. Power mosfet-s of course!!!
I did check the transistors you picked, it seem some of them are special, not cheap but I'll source them.
If I work on it I want to get a better quality amp than some commercial or GrandMos etc. I know from cheap devices harder to get performance.
I hope we get a decent performance so it will have more interest from other members to!
I work on the layout but need to be total redrawn.. Those in the middle separate are saved for later use..
Thank you very much
Greetings Gabor
Attached Images
File Type: bmp All fet Hitachi amplifier.bmp (74.4 KB, 96 views)
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Old 21st October 2012, 02:54 PM   #143
wahab is offline wahab  Algeria
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Quote:
Originally Posted by gaborbela View Post
Yes first I'll use 1% 1/2W 10Cent metal film resistors. No Dale, PRP etc for test, later I can upgrade.
Hi Gabor,

The standing currents are tailored such that the hotter ones will barely dissipate 0.1W , the 0.5W/1% you re using will be more than enough from the start.

Quote:
Originally Posted by gaborbela View Post
I would have a question, which "transistors" must get some heatsink > I think about the VAS and front end.
Power mosfet-s of course!!!
I did check the transistors you picked, it seem some of them are special, not cheap but I'll source them.


As you pointed it, set apart the laterals , the VAS transistors are the ones
that need heatsinks.

In the schematic below , Q7 has to dissipate 1W while Q8 and Q10 dissipate
0.5W each.

You can mount Q7/Q8 in a common heatspreader if the design need
to be compact , just make sure the heatspreader is efficient enough.

Q11 , the input stage CCS , dissipate 0.16W and need no heatsink in principle.
The other transistors dissipation is negligible and they need no heatsinking.


For Q3/Q4/Q10/Q11 the following models will suit perfectly : 2SC2911/2SC2912/2SC3423/2SC3502/2SC3503/2SC3600/2SC3601

The complementary types are used for Q7/Q8 : 2SA1209/2SA1210/2SA1360/2SA1380/2SA1381/2SA1406/2SA1407

Just take the less expensive ones on the list....

Complementarity when chosing among those transistors is not critical , just be careful for the cascodes that must use a pair of the same device.


Quote:
Originally Posted by gaborbela View Post
If I work on it I want to get a better quality amp than some commercial or GrandMos etc.
I know from cheap devices harder to get performance.
I hope we get a decent performance so it will have more interest from other members to!
I work on the layout but need to be total redrawn.. Those in the middle separate are saved for later use..
For performances i think that it s not easy to extract much better numbers from the current design
that reach the essential of two stages amps capabilities , this without compromising stability wich is feature that is not often adressed accurately by most of the designs that hangs on audio forums...


The perfs should be quite good and can be further improved for THD by using a TMC compensation
wich i elected to not implement since it can slightly reduce stability but if you re after the lowest
possible THD i put the mod below so you can choose to implement it or not.

The mod is only around the VAS and it would be easy to go from a compensation to another using the same PCB ,
the components are tailored for minimal TMC effect , to not endanger stability , it allow THD reduction
mainly in the audio band , by 10dB at 1KHZ and about 3dB at 10Khz.

Also , there s no LR network in serial with speaker in the schematic , as such a network position
is to be implemented elsewhere than in the amp PCB.

Eventual values should be 1R in parralel with a 1uH air inductance , about 15 turns of 1mm2 copper wire
around 10mm diameter should do it perfectly.
Attached Images
File Type: gif HITACHI FFET SCH3 TMC.gif (18.7 KB, 332 views)
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Old 21st October 2012, 03:07 PM   #144
AndrewT is offline AndrewT  Scotland
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Why do you choose to apply the low frequency roll-off in the NFB (330ms) rather than at the input (4700ms) to the amplifier?

I realise that very little signal will exist at these frequencies, but could such wide-band abilities allow the NFB to interact with the PSU smoothing?

What is the purpose of the forward biased led+diode in the bias voltage string?

Roender implemented a cascode referenced to ground in the other half of the dual VAS. Thus applying ~half rail voltage to all three devices Q7, Q8 & Q10.
Do you see no advantage in such an arrangement, or worse, do you see a negative effect that should be avoided?
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Last edited by AndrewT; 21st October 2012 at 03:11 PM.
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Old 21st October 2012, 03:15 PM   #145
wahab is offline wahab  Algeria
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Yes , it increase the rejection of PSU VLF as the amp gain is reduced at those frequencies by the virtue of increased global NFB rather than with a passive attenuation at the input
that would left the amp intrinsical gain , thus PSRR , unchanged at those same frequencies.
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Old 25th October 2012, 11:20 PM   #146
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Hello
Today finally I finished the layout.
I still have to go over for double check but will look something like these.
Not the easiest layout I ever done it!
I do try to avoid to use to many jumper, keep signal away from high Voltage etc. (still I had to use 3 jumper)
There is no power source resistors.
Wahab for R17 & R18 2W resistor will be enough?
Would you please let me know.
Thank you.

Collor codes for the parts
Red transistors-fets
Green Resistors
Grey Jumpers
Blue Capacitors
Purple Diodes,LED
Yellow Trimmers


Greetings Gabor
Attached Images
File Type: bmp All fet Hitachi amplifier.bmp (81.0 KB, 82 views)

Last edited by gaborbela; 25th October 2012 at 11:25 PM.
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Old 26th October 2012, 10:41 AM   #147
wahab is offline wahab  Algeria
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Hi , Gabor

R17/18 dissipate about 0.035W each in normal conditions but at power on they may endure a relatively high voltage/current the time it takes to charge the subsequent capacitors and low TDP film resistors have trouble standing this peak power , so 2W parts are a very good thing in this respect.

As for your PCB , did you use a router ?
Because There s a peculiarity that is odd , Q8 can be simply rotated 180°
then its emitter track to Q6 collector would be shorter as well as its base
track that goes to Q7 base , the positionning of the transistors would be
exactly the same , of course , while the unexpected strap would find itself
totaly irrelevant by the same way....

I saw that you implemented a TMC compensation , should be very
helpfull as it reduce substiancialy THD as well as IMD .

The positionning of the compensation capacitors is great ,
that s optimal in respect of the VAS high frequency stability
wich is to be a concern with cascodes.
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Old 26th October 2012, 01:24 PM   #148
kees52 is offline kees52  Netherlands
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Quote:
Originally Posted by donpetru View Post
@gaborbela, and other users here, I notice that you ignored my remark in a previous post. What you want to do or has done design from Naim, I began to conceive through 2003.

To figure out what is wrong with amplifier diagram posted by you and made ​​from designer to Naim, I recommend viewing below attached project designed by me. DP400 is a project I started when I was in college and during this topic, I thought I outline a final revision. Initials project name is my name.

And please, do not ask me about PCB.
The 2n6800 and 2n6849 are very expensive 23 euro each.

just replace with irf 610 and irf9610 for 1.50 euro each.
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Old 26th October 2012, 03:33 PM   #149
wahab is offline wahab  Algeria
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Another catch about the PCB....

The current source Q10 on the right extrimity can be turned 90° to the left ,
so the collector track can go in straight line to the trimer and gate resistors
track without having to make half a turn around the emitter hole and with
a much shorter track.

The transistor Q10 would then be aligned between its reference diode and emitter resistor
both wich will stay exactly in the same holes , just the tracks are to be re drawned.

Last edited by wahab; 26th October 2012 at 03:35 PM.
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Old 26th October 2012, 04:52 PM   #150
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If we look at the latest electronic diagram previously attached, we have already left far target of this topic. They won a regular audio amplifier and what good! You should try to get the "impossible", using only MOS and J-FET transistors. And know that this was possible, just try DP400 project would be a good starting point, it could turn into something much more powerful and better. I could help you achieve this goal impossible, but seeing the direction the discussion took her away, I dropped the idea.

@kees52, I know those 2N transistor are expensive, and yes, you can try 610/9610 although it would be the version to modify a topology diagram and get much more performance.
In fact, I expect it to get to this point, with my help and others. But it was not to be! But it's not wasted time!
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