lineup said:
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 somethingwhpo 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
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
....... you really know what to quote.........
Babowana said:
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)...
Nelson Pass said:... 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
Vix said:
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!
lovechild said:
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
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!
inleup
Vix said:Nelson, you confused me here. Does it mean that the circuit has lower distortion with 16V than with 35v supply
Yes, it does, at least in the voltage range of interest. You will
recall from the ZV8 and 9 that the jfet responds to the Vds
forming a particular load line. By choosing the load line carefully
you can maximize the linearity by cancelling the varying gain
with current against the varying gain with voltage.
For example, as the current through the JFET increases on a
positive input, its gain also increases, causing a non-linearity.
Simultaneously, as the output voltage goes negative, the
gain of the JFET decreases slightly.
By playing these two effects off each other, you minimize the
distortion, just like the SET amplifier designers do.
cviller said:
yeah, but you got my thing, didnt you
and learn a few new things, I hope, cviller
It may come as a surprise to some of you, read this,,
that even Nelson, once a little schoolboy,
learns a few new things, every now and then.
This PROVES, that His middleaged Brain
still posseses the Ability to Learn.... as well as to teach.
There may come a day, when this ability is so low
that we can say it is no more.
A young brain is superior to very old brains, in this respect.
Old people have good compensation for this:
It is spelled: Experience
Another term for this is: Empirical Knowledge
-----------------------------------------------------------------
I told about my reservation, at the end of my paper above.
(which you did not notice/quote)
Lineup said:
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:
of Brtish English
When and if I publish my collected articles, or my memoires, as a book on Audio amplifiers
I let some korrektur-reader do the 'ground zero work'
and add all needed correct terms and facts.
... which brings us back to this question again:
Who was it?
Alexander Graham Bell or the French man Mr. Bel
that did give his name to Bel in deciBel ( dB )
deci - comes from the fact we all have 10 fingers (deci = 10)
... our foot toes are too far down,
to be comfortable, convienient to count with
compare with: deci-mal
Lineup
Nelson, thank you for kind explanation.
Surely there are ways to improve the performance of this preamp, but I find its simplicity appealing.
Still, I couldn't resist: since it works fine with 16v supply and is not (milli) amperage hungry, what about battery operation?
Uhm...that could be..2x12v (sealed lead-acid -simplest solution, even though it will give 24 v), or 14x1.2v AA Ni-Mh cells (then it becomes tricky to charge them)....
Maybe it will sound better, maybe not....there's only one way to find out....
Regards,
Vix
Surely there are ways to improve the performance of this preamp, but I find its simplicity appealing.
Still, I couldn't resist: since it works fine with 16v supply and is not (milli) amperage hungry, what about battery operation?
Uhm...that could be..2x12v (sealed lead-acid -simplest solution, even though it will give 24 v), or 14x1.2v AA Ni-Mh cells (then it becomes tricky to charge them)....
Maybe it will sound better, maybe not....there's only one way to find out....
Regards,
Vix
Hi Manuel,
I don't have 1M and 10ohm resistors
I etched it, but looking at it, I'm not that happy with it - I think the traces are too close together, although I did go as far as drilling and putting on the top layer graphics.
I started changing the layout again today.
Just wondering if anyone else has tried this one yet and if anyone has any impressions yet?
Stephen
I don't have 1M and 10ohm resistors
I etched it, but looking at it, I'm not that happy with it - I think the traces are too close together, although I did go as far as drilling and putting on the top layer graphics.
I started changing the layout again today.
Just wondering if anyone else has tried this one yet and if anyone has any impressions yet?
Stephen
okay, did some research of my own
where does Bel come from, in the unit: dB / deciBel
source number one says:
source number 2 tells this, and I think this is very close to true story:
DEFINITION
The deciBel or (dB) is a notation expressing a ratio to our way of hearing.
HISTORY
- In the early 1900's Bell Laboratories did the most comprehensive study of human hearing ever.
- They decided to come up with a standard measurement of how loud we hear things.
The initial idea was that they would increment the measurements by twice as loud as the previous.
- Each increment would be called a "Bel" out of respect for Alexander Graham Bell.
The plan was to divide the Bel into 10 equal parts (the decimal system) and call each part a "deciBel". So it was established that 1 deciBel was 1/10th of twice as loud.
A base reference was needed so that the measurement system could be used accurately.
Methodic and extensive testing yielded information leading the scientists to conclude that
black women, age 18-22, had the best hearing of all people.
Bringing in extremely sensitive barometric pressure sensors they measured the changes in the air pressure of the room the subjects were tested in.
Using a 1kHz tone they found that the quietest sound their subject could hear was at .0002 Micro-Bars pressure.
------
Boz Style JFET 2SK170 amp circuit,
raises the deciBel with something like 24dB.
In Inverted Phase, reversed Polarity.
so my bottomline is:
Sound gets louder, with use of JFET Boz
... no matter you are black or white, woman or man
/lineup