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Old 7th June 2007, 01:53 AM   #61
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Quote:
Originally posted by lineup


20 x log(100/6) = ??? (dB gain)
where dB is the level, the volume we actually are supposed to hear

( deci - Bell, Bell is probably the same man who invented telephone , which was the first time we could HEAR, in very long distances.
before this was 'Morse' another Man, who made some way to communicate via electrical impulses, Short and Long. = Telegrafi.
But this did not invlove actial sounds)

correct formula to get the dB, in this case:
1. Where Rs = 10 Ohm (source resistor)
2. Where Rjfet ~50 Ohm ( an imaginary resistor, representing the JFET characteristic.
3. Where Rd ~1000 Ohm (actually 991 Ohm, like )

( the paralleled value of 2k2//2k2//load, where load is selected to be 10k, which is some 'worst case' in put impedance of a 'thought up' power amplifier )

Now the combined load resistance as seen at junction of DRAIN = output
is paralleled values of: 2k2 resistor 2k2 resistor and this 10k Ohm.
Formula for getting this drain load into one value:

Rd =

1
------------------------------- ~ 991 Ohm
1 1 1
---- + ----- + ------
2200 2200 10000

If you go back to my first post, I think I mention this value. 900 Ohm something.


Now voltage gain is roughly Rd / (Rs + Rjfet)

We get 991/ ( 10 + 50 ) = 991/60 (which is almost 100/6)
Gives ~ 16.51 times higher voltage at output, compared to input
if the power amplifier side has 10 kOhm input impedance.

GainV = 16.51
now, people can not hear Voltage. Like with morse telegrafi this just electrical impulses.
They have to be translated into Air pressure Changes, for example in a Loudspeaker.
And how strong a Sound is ( SPL = sound pressure level )
is measured in deciBel ...
I am beginning to think this has nothing to do with Alexander Graham Bell. There must have been a french guy called Bel, or something whpo was heavily into the business of exploring sounds.



Now the relationship between VoltageGain magnitude and sound increase level
is this formula, as been posted by friend Zen Mod:

Gain in dB = 20 x { Log10( GainV ) }

GainV = 16.51
gives Log10 ( 16.51 ) ~ 1.217
x 20 = 24.35 dB

The amplifier will have a gain of 24 dB
.. or more correct -24.35 dB
... negative sign to tell that the signal at Drain, will be opposite Phase of input.

We call this type of amplifier Inverting Amplifier.

If we use 2 transistors in same configuration as JFET BOZ here,
and let it pass both in series, we get the signal back to normal.

The combined gain of using 2 modules after each other would:
- - (24.35+24.35) = +48.70 dB

As two - make one +

for Decibel you simply add the gain.
And expressed in VoltageGain, you multiply.




Therefor 16.51 x 16.51 = +48.70 dB
A gainV of 272.58 !

Put +0.005 Volt (5mV) at input and get +1.36 Volt at output!
This combined 2 modules amp would be suitable as a Microphone .. at least regarding GainV.




lineup do not claim this article to be fit for a Book on the subject. Far from
But you get the picture, if you can dis-regard the use of terminology, in some lines.
... it is not that easy all the time, you know,
when youre bound in writing/thinking fast .. in a FOREIGN Language:
like British english

Wow

It's time you to invent something new



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Old 7th June 2007, 04:58 AM   #62
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by Babowana



Wow

It's time you to invent something new




why I can't see his posts?

....... you really know what to quote.........
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Old 7th June 2007, 06:26 AM   #63
cviller is offline cviller  Denmark
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Quote:
Originally posted by lineup


The amplifier will have a gain of 24 dB
.. or more correct -24.35 dB
... negative sign to tell that the signal at Drain, will be opposite Phase of input.
-24dB corresponds to roughly a gain of 0.06 and not simply an inversion of the 16x gain. Normally you would characterize the system with both gain measured in dB and phase and then this phase would characterize any inversion of the signal.
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Old 7th June 2007, 08:21 AM   #64
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Quote:
Originally posted by lineup


....

But you get the picture, if you can dis-regard the use of terminology, in some lines.
... it is not that easy all the time, you know,
when youre bound in writing/thinking fast .. in a FOREIGN Language:
like British english
Yup I'm getting there, thanks alot lineup.

btw. the famous french Mr. Bel invented these, and if you think that has nothing to do with sound, show one of these to my little daughter

cheers, LC
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Old 7th June 2007, 08:39 AM   #65
Vix is offline Vix  Yugoslavia
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Quote:
Originally posted by Babowana



Mmm . . . you are going to sign the declaration of life time war . . .
When she (I believe "she") does blabla . . . just shut up your mouth and wait to the end of the blabla . . . offer her a cup of water . . . then you win . . .

Congratulations!!!
Thank you. Good advice, even though she a type that becomes silent when angry. (fortunately this happens very rarely, but is more scary than blablabla). Requires more than just a cup of water-usually a flower works(but it may not be readily available, so it takes a bit of time)...


Quote:
Originally posted by Nelson Pass
... but the best distortion numbers came from a
16V supply value.

Nelson, you confused me here. Does it mean that the circuit has lower distortion with 16V than with 35v supply

Regards,

Vix
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Old 7th June 2007, 08:45 AM   #66
cviller is offline cviller  Denmark
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Quote:
Originally posted by Vix


Nelson, you confused me here. Does it mean that the circuit has lower distortion with 16V than with 35v supply

Regards,

Vix
Puzzled me too... 16V/2.2k ~ 7mA through 2sk170! (give or take...)
If the device is BL rated, this means it runs with less distortion, when the current is not set by the jfet idss but the psu... (BL: idss 6-12mA as far as I recall)

How about a simple ccs running at ~7mA - then the poor jfet would not suffer as much. You might even be able to find two 2sk170s with different idss and use one for current limiting and the other for amplification!
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Old 7th June 2007, 09:49 AM   #67
Manu is offline Manu  Europe
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Quote:
Originally posted by cviller


Puzzled me too... 16V/2.2k ~ 7mA through 2sk170! (give or take...)
Yes and 35V supply will give ~ 15mA (so in this case BL ...)

MC
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Old 7th June 2007, 02:22 PM   #68
spencer is offline spencer  Hong Kong
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Why not parallel two K170 or use one LK389 to see what happen? Will the output impedance be lower?
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Old 7th June 2007, 04:07 PM   #69
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Quote:
Originally posted by Manu


Yes and 35V supply will give ~ 15mA (so in this case BL ...)

MC

Quote:
Originally posted by Nelson Pass


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.

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Old 7th June 2007, 05:34 PM   #70
lineup is offline lineup  Sweden
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Quote:
Originally posted by lovechild


Yup I'm getting there, thanks alot lineup.

btw. the famous french Mr. Bel invented these, and if you think that has nothing to do with sound, show one of these to my little daughter

cheers, LC
there Mr Bell - sounds

Beach Boys Barbara Ann



this one is not so bad, either
Quote:

Beach Boys lyrics » Bluebirds Over The Mountain
-------------------------------------------------------------

Bluebirds over the mountain
Seagulls over the sea-ea-ea
Bluebirds over the mountain
Bring my baby to me

A boy and a girl they once found love
To each it seemed like heaven above
He looked into her eyes and said
Ooo wee baby youre so good for my head

Bluebirds over the mountain
Seagulls over the sea-ea-ea
Bluebirds over the mountain
Bring my baby to me

Oh everyone in every land
Please give me a helping hand

... one of my Absolute BEACH BOYs song!
... what you think? isnt it a great one!


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