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Old 6th June 2007, 03:11 PM   #31
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wimpy

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Old 6th June 2007, 03:18 PM   #32
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Very nice Manuel

Can anyone please explain what the pot is for and how/what to adjust?

I thought it was just the input attenuator.

Stephen
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Old 6th June 2007, 03:47 PM   #33
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Quote:
Originally posted by twitchie


I thought it was just the input attenuator.

Stephen
it is
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Old 6th June 2007, 04:58 PM   #34
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Quote:
Originally posted by stefanobilliani
Is the pot essential ?

25k pot and 1 Mohm form the input impedance.
The 1 Mohm is there for safety ... in case the glider of the pot loses contact.

If you have, like me, in your CD-Player volume control
you should be able to remove 25k pot.


But the pot has got another task. too:
If you use different sources and the amplifier gain is high (sse my prvious posts! )
Then this pot lets you adjust the level,
so that amplifier Will Not Clip
.


Rule, if you keep 25k pot.
1. Put your CD-Player output, to 80-90% of max rotation.
2. Play a record with 'normal' output level. Those your favourites!
3. While keeping the CD volume at 80-90%, adjust 25kOhm pot
for a rather high sound output.
--------------------

Wrong method to set level:
Turning up the 25k very much, and only be able to use your remote CD-Volume to maybe 15-20%
--------------------

Best is of course, to adust the gain of 2SK170 amplifier
to not amplify more than you need.
See my thinking before.

Myself, and most of us, would live happily with a Line Pre Amplifier with a gain around x4.
This value, +12dB, is some sort of 'standard for lineamps.


Regards
lineamp
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Old 6th June 2007, 05:08 PM   #35
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Quote:
Originally posted by lineup



25k pot and 1 Mohm form the input impedance.
The 1 Mohm is there for safety ... in case the glider of the pot loses contact.

If you have, like me, in your CD-Player volume control
you should be able to remove 25k pot.


But the pot has got another task. too:
If you use different sources and the amplifier gain is high (sse my prvious posts! )
Then this pot lets you adjust the level,
so that amplifier Will Not Clip
.


Rule, if you keep 25k pot.
1. Put your CD-Player output, to 80-90% of max rotation.
2. Play a record with 'normal' output level. Those your favourites!
3. While keeping the CD volume at 80-90%, adjust 25kOhm pot
for a rather high sound output.
--------------------

Wrong method to set level:
Turning up the 25k very much, and only be able to use your remote CD-Volume to maybe 15-20%
--------------------

Best is of course, to adust the gain of 2SK170 amplifier
to not amplify more than you need.
See my thinking before.

Myself, and most of us, would live happily with a Line Pre Amplifier with a gain around x4.
This value, +12dB, is some sort of 'standard for lineamps.


Regards
lineamp

Yeah , I understand .

A standard CD output will clip this Pre I believe .

The nice thing is this Pre has High gain -low noise . So it may be very good to turn up the gain of a pre stage like the Pearl .

So using the POT is essential .
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Old 6th June 2007, 05:56 PM   #36
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Quote:
Originally posted by Zen Mod
wimpy

za nas francuze ne postoji strah
he he he
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Old 6th June 2007, 06:35 PM   #37
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Since the question has come up and not answered, the
situation with the gain, bias, and resistor values is as
follows.

The device is self biased, and we want the highest value of
bias possible for lowest distortion which makes us want to
use a low value Source resistor to ground.

At the same time, it would be nice to not have too much gain
by virtue of that Source resistor value. The apparent resistance
of the JFET is about 50 ohms, so the gain into a 10 K ohm load is
about 1000 / 60 which is about 24 dB.

We can get lower gain, but the distortion will increase - it's
all a trade-off. I didn't make any effort to exactly optimize these
values - they were just thumbnail calculations.

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Old 6th June 2007, 07:06 PM   #38
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Quote:
Originally posted by Nelson Pass
......................... I didn't make any effort to exactly optimize these
values - they were just thumbnail calculations.

with all mileage Papa already have , that thumb is certainly more confident than someone's sim

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Old 6th June 2007, 07:07 PM   #39
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Could this be used as a headphone amp, and would it be possible to run it at say 18V (2 9V batteries)?

I redid the layout and etched it and it is tiny

It could dethrone CMOY in terms of sound and simplicity

Here's the (hopefully) fixed layout
Attached Files
File Type: pdf jfet_boz_all_revised.pdf (87.8 KB, 1835 views)
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Old 6th June 2007, 07:10 PM   #40
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Quote:
Originally posted by twitchie
Could this be used as a headphone amp, and would it be possible to run it at say 18V (2 9V batteries)?
...................

too wimpy
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