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Old 22nd July 2008, 07:45 PM   #21
lineup is offline lineup  Sweden
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Wink Lineup 1 Volt ZETEX Op-Amp

As mentioned, next step is to try a few transistor variants from ZETEX.
It is possible I will be able to squeeze down distortion a bit more.

Right now I am getting THD levels like 0.02 - 0.03 %
At some higher voltage outputs.
To me, this is not optimal.
I want the simulated circuit to show below 0.01 %
This way a real circuit will possibly perform below 0.05 % at all levels.

THD 0.05 % is one criteria Hugh 'AKSA' Dean has mentioned.
Like me, his reasoning is probably,
that such low levels of distortion, is below what human can hear.
At least, HEARING such low distortion
has NEVER in HISTORY yet
been verified in controlled BLIND Tests


-------------------------
Besides, most High-End SPEAKERS shows 0.5 - 1.0 % THD at 1 Watt RMS level.
This is the -40 dB to -50 dB level.
-------------------------

Here is simplified op-amp circuit I use.
All very standard and basic.
Of course my real circuit details & tricks are kept very secret.

So do not try this at home

Lineup
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Old 22nd July 2008, 11:24 PM   #22
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lineup,

The circuit you just posted will not work. Sorry.

Rick
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Old 24th July 2008, 02:53 PM   #23
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Why?
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Old 24th July 2008, 03:02 PM   #24
h_a is offline h_a  Europe
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Lineup, you're sure that this one will work outside the simulator?

There are 3 junctions in the LTP with current mirror and that already exceeds 1V?

Am I missing something? Have fun, Hannes
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Old 24th July 2008, 03:10 PM   #25
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Small signal transistors work quite hapily at around 0.2V Vce.
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Old 24th July 2008, 03:20 PM   #26
syn08 is offline syn08  Canada
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Quote:
Originally posted by darkfenriz
Why?

Because it needs over 3*VBEon supply to bias. Top down: VBEq1/q2+VBEq4/q5+VBEq6. At 1V supply, not a chance in h*ll, unless it's built with Ge trannies (which I would not even think building a high gain opamp with).
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Old 24th July 2008, 03:41 PM   #27
h_a is offline h_a  Europe
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Quote:
Small signal transistors work quite hapily at around 0.2V Vce.
May I ask how this should work? You get in this case a negative Collector-basis voltage...

Have fun, Hannes
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Old 24th July 2008, 04:57 PM   #28
lineup is offline lineup  Sweden
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Default Re: Lineup 1 Volt ZETEX Op-Amp

Quote:
Originally posted by sawreyrw
lineup,
The circuit you just posted will not work. Sorry.
Quote:
Originally posted by darkfenriz
Why?
Quote:
Originally posted by h_a
Lineup, you're sure that this one will work outside the simulator?
There are 3 junctions in the LTP with current mirror and that already exceeds 1V?
Am I missing something? Have fun, Hannes
Quote:
Originally posted by darkfenriz
Small signal transistors work quite hapily at around 0.2V Vce.

Quote:
Originally posted by h_a
May I ask how this should work? You get in this case a negative Collector-basis voltage...
Have fun, Hannes

Hello partners!

As I already told you:
I posted only the SIMPLIFIED circuit.
If you are of the clever sort, like darkfenriz you may figure it out:
Originally posted by darkfenriz
Small signal transistors work quite hapily at around 0.2V Vce.

Ther fact is that, like also stated well in this topic,
I use ZETEX Low VBE & Very low saturation transistors.
I have even posted links to those devices.
thanks, AndrewT, for pointing me to these nice ZETEX transistors
http://www.zetex.com/



I know ordinary small singnals works at 0.050 Volt, at very low currents.
And works quite well at 0.100 Volt,
considering those currents I have mentioned in my fists post: 200 - 700 uA


ZETEX ZTX689B & ZTX718
Now, when using these special LOW SAT transitors, with very low VBE, too,
it is no problem to get 1.0 Volt to be well enough to run a circuit
like the schematic I have posted.

Of course, not without some small additional tricks and smartness


-----------------------------------------------
Originally posted by lineup

Here is simplified op-amp circuit I use.
All very standard and basic.
Of course my real circuit details & tricks are kept very secret.

So do not try this at home

Lineup

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Old 24th July 2008, 05:36 PM   #29
lineup is offline lineup  Sweden
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I can mention a couple of figures.

first:
I do not use the freeware simulators LTspice and Eagle very much.
I use 2 different Professional Simulation softwares.
Standard Pro versions of these will cost you like 500 - 1000.
I use one called Power Pro which is a bit above standard version.

The lowest VBE I have tested in these high cost Spice programs
is 0.473 Volt for one ZETEX transistor.
( If this is not a good BJT spice sim value,
I go kill those advertising expensive but useless software )



Now, that one (vbe=0.473V) had too low gain, hFE, to be a good performer in Op-Amp.
I use only 2 stages, and need all gain I can get.
The devices I use now, have a VBE drop like 0.495- 0.505 Volt.



I would guess the final bottom limit for the topology in my posted schematic
is like at 0.75 - 0.80 Volt Supply ... ( +- 0.40 VDC )

0.500V ( top current mirror, VBE )
0.150V ( input pair, C-E )
0.150V ( constant current source, C-E )
--------------------------------------------------
0.800V


Lineup regards
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Old 24th July 2008, 05:58 PM   #30
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Quote:
Originally posted by h_a


May I ask how this should work? You get in this case a negative Collector-basis voltage...

Have fun, Hannes

Exactly
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