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Old 28th May 2009, 01:24 AM   #11
lineup is offline lineup  Sweden
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Quote:
Originally posted by Wavebourn
What if to remove that Miller cap, but to add a gate stopper?
Quote:
Originally posted by scott wurcer
lineup - Don't take such a simple component substitution so seriously. A lot of FET's would work in that position, just plug them in and see what you get no big deal.

You have yellow jackets and I had one of my father's best friends come to his wake after a whole liter of vodka so we suffer our friends because there is no other way.
You are right Wavebourn .. there is not even a need for one miller in that stage.
It was removed before I read your post.

I added a simple R C to the gate of input JFET, with a small pF to GND from gate.
This plus one gate stopper R to IRF610 follower, rolls off nicely at Overall 800 khz at gain 5.x for 2N3819 input circuit.

I doubled the output C. Paralelled two 1.000uF -> for 32 Ohm only.
For 300 Ohms HP we can use 1/10 ~ 220uF higher quality caps,
if somebody is are afraid good standard electrolyts wont do a good job.

Note:
all my testings and curver and fourier is taken after the output caps.
That is across the load.

Probably a slightly too ideal capacitance.
Real capacitors might be foumnd in Sim Library, but at least I did pick from Electrolyts = polarized caps.

PN4416A is only 15 V.
They are good FETS, but as you say Scott, there are a big number of different that will work in that position.

I prefer to look for those giving a VGS around 2 Volts at 0.5 - 2.0 mA.
Any more nice ones suggestions are most welcome.


Because 16Volt/2V gives ~ gain x5 ... set by the 2 resistors in 2nd stage.

There are not as many of those JFET (VGS 2V at 1-2 mA)
and some can be hard-to-find-for-normal-people-in southafrica and Maylasia .. not to mention Monglia Western part.

Like Nelson Pass, I try to use mainstream stuff: .. this is why IRF610 easy-to-find.
N-JFET 2N3819 is a good DiyAudio companion.
Think used in Radio-circuits.

BC560C for second stage .. wouldnt give any headache for any DiyAudio member that is used to discrete constructions.

I will keep this topic alive .. on the hitlist.
Will post my latest diagram, which made that nice and straight
AC-Analysis
- wasnt that very interesting curves to contamplate???
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Old 28th May 2009, 01:29 AM   #12
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I mean a gate stopper for a source follower. It may be needed in a physical reality.
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Old 28th May 2009, 01:34 AM   #13
lineup is offline lineup  Sweden
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Dont you read my posts. About irf610 asrrangement.
What is stopping you, Wavebourn?
Same at your forum. You didnt even read and answer a simple question.

I can see through you .. I think.
Better reading and less hurry, my dear polish freind
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Old 28th May 2009, 01:39 AM   #14
lineup is offline lineup  Sweden
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Nobody has noticed the strange diode ...
This was what would raise a lot of debate 1N4148.

You might think the designer, Lineup, made a mistake.
Because what does this diode do to the first and second stage ?????
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Old 28th May 2009, 02:57 AM   #15
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Quote:
Originally posted by lineup
Nobody has noticed the strange diode ...
This was what would raise a lot of debate 1N4148.

You might think the designer, Lineup, made a mistake.
Because what does this diode do to the first and second stage ?????

Nobody noticed something that resembles a current mirror in my headphone amp you were writing about recently?

Are you kidding Lineup?
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Old 28th May 2009, 03:12 AM   #16
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Default My MOSFET issue

Hi
Lineup here again!

I have tried all I can to optimise first and second transistor.
I got a working JFET (2N3819) and one low noise cheap BC560C.
But I reached a limit.
Where it does not matter what I do .. there are only fractional improvements to make, with the chosen devices.

So I begin to look at the remaining weak point. What has not been worked on:
- The Ouput follower = MOSFET IRF610 (This is of typr HEXFET and one TO-220 in this case)

The issue with MOSFET is that it is put outside the Feedback loop.
Below you have the before and after.
This harmonics analys speaks for itself.

This time it is one Sennheiser 300 Ohm being the load.
But there is almost no difference in quality across any load.
32 Ohm or 300 Ohm gives only minute small difference in Fourier.

This comes from 2 things:
1. The current is so high in output ~360 mA
and the load is working parallell into the 33 Ohms resistor, that loads the MOSFET.
2. No matter what we do .. the IRF610 will create the dominating distortion.
The 2 input transistors are almost uneffected by the load.

This diagram, Fourier, speaks for itself.
Some would call this MOSFET output a problem.
I would not.
Let me stay by name it 'One Issue'

IRF610 contributes not only higher 2nd + 3rd,
but also a heeellllof higher order ODD harmonics distortion.

/lineup
Attached Images
File Type: png 3t_jfet-bjt-mos_v-5a_mosfet-issue _fourier.png (6.7 KB, 487 views)
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Old 28th May 2009, 04:20 AM   #17
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What if to reduce a value of the source load resistor?
Then, what if to load it instead on a CCS capable of a full required negative current swing?
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Old 28th May 2009, 10:25 AM   #18
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Default Re: My MOSFET issue

Quote:
Originally posted by lineup
IRF610 contributes not only higher 2nd + 3rd,
but also a heeellllof higher order ODD harmonics distortion.
/lineup

Hi Lineup
good that somebody else is not afraid of N-GNFB projects,
yes, 610 in this case generates "lots" of high order harmonics, but they are bellow -100dB! They are masked by 2 and 3rdh!
I could bet that its sound is better than any high loop gnfb amp!
I could even resign in a local feedback in VAS section...
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Old 28th May 2009, 11:43 AM   #19
lineup is offline lineup  Sweden
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Music in HeadPhones Lovers!

I post the latest version 5a
This was the version used in diagram of 'Before & After' MOS testing.
You can see the circuit nodes numbered '12' and '10'.
Normally I use the amp output node '16' .. for my posted testings.

To find these 3T transistors would not be a problem.
- IRF610 is frequently used in Nelson Pass preamps and amplifiers
- BC560C is one standard Low Noise 'audio' transistor. Very much bangs for few bucks
- 2N3819 the input JFET can be found in most electronics shops


I just pulled away the diode 1N4148 from my first schematic.
Likewise now I use the full gain of BC560C (DC gain like 400-600!!)
This is utilized by removing the resistor between U1 Emitter and V+ rail.

Enjoy:
Attached Images
File Type: png 3t_jfet-bjt-mos_v-5a_n3819_bc560_irf610.png (13.6 KB, 480 views)
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Old 28th May 2009, 12:41 PM   #20
lineup is offline lineup  Sweden
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Hello musik lovers!

Some guidelines for the actual build.
---------
1. Red wires to and from potentiometer should be fair quality shielded cable.

2. Potentiometer value is not critical. Log 100k - 500kohm will work

3. Instead of pot you could use a resistor divider e.g. 100k-10k. Adjust to suit your sound source output

4. Red resistor 440 ohm sets the output to Close 12 Volt (50% of V+24V)
Temporarily you can use one 1k trimpot to find out what you need.
Start at setting the trimmer at 50% and work from there.
This is an asjustament done to suit for your 2N3819.
JFETs have a bit different parameters for each and every single Transistor we buy

5. Output cap(s) is your own choice. Depends on impedance of you phones.
For 32 Ohm you could use two 470uF - 1.000uF .. or one
For 300 Ohm impedance Sennheiser you can use two 100uF .. or one

6. R8, green resistor, is to help charge Output electrolytic caps
With two 470uF and R8=1kohm we get like 1 second to charge
if there is no headphones attached.

7. Please note! The R9 power resistor should be rated >=10Watt
You can use four 33 Ohm rated 2.5W - 5 Watt parallelled in a square.
Code:
 |  |
33 33
 |  |
33 33
 |  |

Of course, me and other DiyAudio guys will answer any questions
and guide you perfectly on your way towards a very well sounding amplifer.
No matter what headphones you use.
The sound can, will be a nice surprise to any taking my design seriously.
Ask Wavebourn!
He is using same type of circuit idea in his headphone amplifiers ...

/Lineup - your audio friend - full copyright reserved, though!!!
Attached Images
File Type: png 3t_jfet-bjt-mos_v-5a_n3819_guide.png (8.5 KB, 478 views)
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