All Hitachi Lateral Fet amplifier for DIY described by Paul Kemble - Page 5 - diyAudio
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Old 7th October 2012, 04:47 PM   #41
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Quote:
Originally Posted by donpetru View Post
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.
Hello Petru
First of all thank you (multumesc) for the advise!
Of course I want performance, otherwise no reason to do anything with these circuit even if I have those devices.
To me not all the way clear what you write (I know you want to help) but we have to go step by step over the circuit.
I think I have some IRF610 at home, so I can count on it.
You can write PM to gaborzoltan2@gmail.com
Also anybody who want PM me please feel free.
Thank you

Greetings Gabor
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Old 7th October 2012, 11:38 PM   #42
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Default Several mod was done

Hello Petru

Sorry about the previous post, I really did not had time to think on your advise.
I was in hurry to the church but I wanted to write so not to appear I ignore your help!
Now I had more time and went over on the circuit. I think (if I understood well)you advised something like these.
I put several question marks because I have no idea what would be right value for those part, for those resistors, diodes and do I use Hitachi or the more avaleble IRF mosfet or somethig else.
Can you help with those please?
Also If I made a mistake how I draw the new circuit please let me know.
Now do the 470R trimmer will be OK? Or I must go back to 2.2K originaly it was.
Would you like if I ad a BJT between that trimmer and the 330R resistors like you did (MJE340)
Thanks one more time for your help!

Greetings Gabor
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File Type: jpg All fet Hitachi amplifier modified after Petru.JPG (58.3 KB, 574 views)

Last edited by gaborbela; 7th October 2012 at 11:45 PM.
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Old 8th October 2012, 12:16 AM   #43
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I have attached below the new amplifier diagram you posted above, where we numbered component values ​​(only those which are necessary in discussion).

Trimmer's value is determined taking into account two things:
- VAS circuit current value;
- The desired setting the idle current.
Current in VAS is determined by mathematical formula:
I_vas = 0.8 * Uzener_D2 / R3
or, whether, it requires a current of 5mA then we find the value of R3:
R3 = 0.8 * Uzener_D2 / I_vas
Suppose you chose a zener diode of 15V when R3 is:
R3 = 0.8 * 15 / 0.005 = 2400 Ohm or 2K4

Resistor R2 is determined by a similar way provided to choose an electric current that is supported by J-FET transistors. For example 2SK117 are three types according to the classification of IDSS:
Y: 1.2 ~ 3.0 mA, GR: 2.6 ~ 6.5 mA, BL: 6 ~ 14 mA:

Let's say you choose 2.5mA:
R3 = (0.8 * Uzener_D2 - 0.7) / I_vas
R3 = (0.8 * 15 - 0.7) / 0.0025 = 4520 Ohmi or you can choose standard value 4k7.

Diode D1 can be a common switching diode, 1N4148 or 1N4935 type.
Then capacitor C1 can be shown theoretically that can range from 10uF and 100uF.

And finally, the Rt value Trimmer. To determine this value must know opening voltage transistors T10...T13. I do not analyzed the data sheet 2SK134 / 2SK1057 but you can resume calculations applying the following formula:

Rt = Vt / I_vas

Suppose that for an idle current of 200mA opening a voltage is 8V final pair, then:

Rt = 8 / 0.005 = 1600 Ohm. You can choose in this case one trimmer about 2K.
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Last edited by donpetru; 8th October 2012 at 12:20 AM.
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Old 8th October 2012, 01:33 AM   #44
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Hello
Thank you so much!!!
I have another important question
Because now we have T8 the 33K resistor no longer good there.
The zener diode was reduced from 20V to 10 before the constant current source and the resistor value was increased from 6.8K to 30K.
I see you use 2X20K but a bit higher value zener. 1X30K no way to be good there. How much current flow true that resistor because you use 3PC? What do you think between 6.8K and 8.2 2W?
For T8 IRF610 or 2SJ77?
Some information
I have a 40-0-40VAC about 750-800VA transformer. That would give around 52-54V under these load.
For the front I will use at least 10V higher rail voltage like on the power stage.
I want to bias each channel about (total bias) 200mA. I'm not sure the transformer can take more. I use one transformer for both channel.
The 2SK170BL I plan to use. The BL grade IDSS between 6-12mA very similar than the 2SK117BL.
I think I have 2SK117 to but I'm nut sure the grade. I will stick with the 170BL. That is more popular.
I do like your amplifier a lot, If it would be lateral I would go on and build it.
Now these one became very close to yours. Thank you and thank you!!

Greetings Gabor

Last edited by gaborbela; 8th October 2012 at 01:51 AM.
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Old 8th October 2012, 02:35 AM   #45
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Hello

I upgraded the circuit once more thanks to Petru!
The red underline parts still questionable or need to be calculated.
I post the circuit if someone interested on or has more some fine idea..........
I think now these close to get tested.
Unfortunately I never run sim on amplifier circuit, usually I build it in real life to get some idea about the sound and how it will work.

Thanks one more time for the HELP!

Greetings Gabor
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Last edited by gaborbela; 8th October 2012 at 02:37 AM.
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Old 8th October 2012, 04:45 AM   #46
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any chance a GB for PCB and/or Jfet
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Old 8th October 2012, 06:03 AM   #47
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A big current IDSS means a higher probability of noise in the input stage. So BL series is not the best choice. It would be good to look series Y.
HZ10 diode voltage is too low and will work J-FET's with a voltage of less than 10V, about 9.35V (so it will saturate faster, is not good). Choose zener diode of 15V or 18V.

R1 = 2k2 has a critical value. A value too high will reduce the effectiveness of CCS (constant current source made ​​with T8), one value too low will increase noise in the input stage (including the EMI influence, "in an indirect way"). Depending on the voltage of the amplifier, saturation voltage of the transistor from CSS and electric current CSS, you need choose one resistor, initially following a theoretical calculation, then after some experimental tests. Theoretical calculation is based on the hypothesis of a voltage difference on that resistor, which is not greater than the voltage UDS J-FET transistor. I recommend it to a voltage difference of about 10V (I rate this voltage with Vcss).
If the current CSS is I_css = 0.0025A (as I said above - there I used as reference in calculating all R3 = 4520 Ohm, but is wrong... typo mistake.. is R2 = 4520 Ohm), then R1 will be:

R1 = Vcss / I_css = 10 / 0.0025 = 4K

Again, the new value R1 will be tested experimentally.
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Last edited by donpetru; 8th October 2012 at 06:13 AM.
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Old 8th October 2012, 12:34 PM   #48
wahab is offline wahab  Algeria
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Performances of this amp is globaly not better than the goldmund
iteration that was once popularized in this site wich used a bipolar
VAS and that s not by chance since it allow better perfs than
a mosfet inspired one.

Set aside this comparison , the amp has basicaly constant
distorsion in function of frequency , lower than 0.01% at mid power.




Quote:
Originally Posted by donpetru View Post

And finally, the Rt value Trimmer. To determine this value must know opening voltage transistors T10...T13. I do not analyzed the data sheet 2SK134 / 2SK1057 but you can resume calculations applying the following formula:

Rt = Vt / I_vas

Suppose that for an idle current of 200mA opening a voltage is 8V final pair, then:

Rt = 8 / 0.005 = 1600 Ohm. You can choose in this case one trimmer about 2K.
And if the threshold voltage is at most 2.2V for 100mA , what must be
the value of the trimmer resistance.?....


Quote:
Originally Posted by donpetru View Post
HZ10 diode voltage is too low and will work J-FET's with a voltage of less than 10V, about 9.35V (so it will saturate faster, is not good). Choose zener diode of 15V or 18V.
And how will it saturate ?...
As already said , excess current , wich is the parasitical
current from drain to gate , will increase exponentialy above
8 to 9V , hence linearity will much decrease.
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Old 8th October 2012, 01:31 PM   #49
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Quote:
Originally Posted by wahab View Post
Performances of this amp is globaly not better than And if the threshold voltage is at most 2.2V for 100mA , what must be
the value of the trimmer resistance.?....
You mean 2.2V between grid MOSFET's from the the positive and negative power rails? This 2.2.V seems rather small for a power MOSFET. especially if you want a current of 200mA idle! However, the formula remains the same considering the current through VAS about 0.005 A:

Rt = 2.2 / 0.005 = 440 Ohm.

Quote:
Originally Posted by wahab View Post
And how will it saturate ?...
As already said , excess current , wich is the parasitical
current from drain to gate , will increase exponentialy above
8 to 9V , hence linearity will much decrease.
I said saturate faster to the same input signal comparative with case when the voltage Uds would be more than 10V. For example, my project DP400 requires the input of a voltage 1.8Vrms to charge nominal power. If you use the J-FET with a voltage less than 10V Uds, it can not ensure a proper trip to other transistors saturation voltage, so will tend to increase the THD close to the nominal power, at a slightly higher value in the circuit input and overall the whole amplifier. These small technical quibbles are difficult to spot and deserves taken into account as long as we want them to squeezing as much performance from the amplifier.

!!! Some technical terms in Romanian with hard to find a corresponding 100% correct in English, therefore, some of the expressions used might not have exactly the right connotation.
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Old 8th October 2012, 04:02 PM   #50
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[QUOTE=wahab;3193657]Performances of this amp is globaly not better than the goldmund
iteration that was once popularized in this site wich used a bipolar
VAS and that s not by chance since it allow better perfs than
a mosfet inspired one.
QUOTE]

Hello
Thank you once more for both of you!!
wahab
Do you suggest if we change the VAS to bipolar (it will allow) we will get better performance??
We can test it, because I have those Hitachi devices or because originally was used fet for VAS not necessary to stick with that.
Performance more important.
For the front I want to stick with JFet.
I did used in my Darlington amp BC550/560, after I switch to 2SJ74BL/2SK170BL and I got a huge improvement!
Also in the SymaSym Mike replaced the MPSA18 with 2SK170BL and did improved the sound.
I did tested on my Symasym and really was better than the BJT.

donpetru
The best I can come up to get lower IDSS that would be GR grade JFet.
2SK170GR very popular among RIAA builders. Low noise devices.
Similar than the 2SK117GR.
2SK170GR still available in many stores. I have at home so I can start the test with that.
Please let me know your opinion on these!
Thank you sir!
For Rt we can go with 2K and after the first bias set up I can measure
the trimmer resistance and lower the value if it need to be (or if lower value behave better)
I will do those change you advised earlier!
HZ10 will be replaced with 15V..
I will go over on your post again and upgrade the circuit.
Thanks one more time!

-To think about GB now is way to early. Even after we get a certain performance (we satisfied with the sound) it would be useful some other guy build the amp to to get back more performance report.

Greetings Gabor
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