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Old 30th May 2003, 11:00 AM   #21
uli is offline uli  Austria
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Quote:
Originally posted by nar
Hi Uli ,

Do the 559 549 need to be matched ? Which current ?

Thanks for answer.Very nice work !!!
Hi nar,
Thanks for your kind words!

No they do not need to be matched except the 2 CCSīs
down (BC549C) connected to R9, R10. All the others are
just cascode devices and the CCSīs on top (BC559C) are
adjustable.
You can swap BC549C to BC550C and BC559C to BC560C
if you want but IMHO you wonīt hear the difference!
If you follow the circuit strictly, they run at 5mA (depends
on R9, R10)
If you do not want to match the 2SK369 (which can be a
hard timeconsuming matter) you can use one 2SK389
instead (slightly higher noise, slightly lower transconductance)
the pcb accepts both.

Uli

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Old 30th May 2003, 11:04 AM   #22
uli is offline uli  Austria
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Default Re: Acrobat

Quote:
Originally posted by uli
ok, here we go...
Here is the original Ultiboard file if anybody wants to
make his own pcbs.

Uli


Attached Files
File Type: zip ub_pre2.zip (13.5 KB, 331 views)
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Old 30th May 2003, 12:46 PM   #23
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Thanks Uli.

Do you assume if I get a 10k resistor series with R 15 / R16
and lower R17 / R 18 to 100k,I would have a gain of 10 or 20 dB?

Does it affect the X effect?

Thanks for answers ....
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Old 30th May 2003, 01:35 PM   #24
uli is offline uli  Austria
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Default gain

hi Nar,

Calculation: for 2SK389 in brackets:
the transconductance of the 2SK369 (389) is typical 40 (20) mS.
this results in an openloopgain of 72 (66) dB without load except
R21, R22 thus showing an imaginary value of R17,18 of about
400k (200k). You must parallel this value to the real value to calculate gain.
As the imaginary value is a function not only of transconductance
but also of outputload its quite difficult to calculate.
It is much easier when you use external complimentary source-
followers at the output.Then you can assume the o.l. gain to be
loadindependant.
So if you use 10k input resistance (per half!) you loose ~10% at
R19, 20 you have to put in 152k (245k!)for R17,18 to achieve 20dB gain.
The unit has a typical gain of 53 (47) dB as drawn without
external load.
As like every inverting opamp its tricky to achieve high gain AND
high input impedance!

Uli
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Old 30th May 2003, 02:19 PM   #25
nar is offline nar
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Thanks for reply.

In my case achieving a high input impedance is not a real goal.

So I guess values to be adjusted to get proper gain.

I think this design cannot accept unbalanced input to get balanced out ? In that case how to achieve it ?

Thanks for replys to the " twenty questions" !!!



PS the outputs must be a few volts above ground ...
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Old 30th May 2003, 02:34 PM   #26
uli is offline uli  Austria
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Wink input issue

Hi Nar,

Yes of course it IS possible!!!
You can feed whatever you want!
Output stays symmetric all the time.
Only thing to be careful:
inputimpedance should be the same for both.
If you have 2x 10k as R15,16, and a source impedance
lets say 1k at R15 then put 1k between R16 and ground.

Uli

PS: this 1k isnīt absolutely necessary but you might get
some DC offset at both outputs.

PPS: no the outputs should be at zero to gnd.
This is the reason for R21, 22 and R5, 6
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Old 30th May 2003, 03:06 PM   #27
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DC at the outputs ?If - input not terminated with right impedance when not used?

Damn.If you plan to use the X module as a preamp , how can you be sure that all your sources impedances has same value?

For my CD,1k perhaps but I don't know ... my DVD audio seems 200 ohms but I can't bet the farm on it ...other sources ? Honnestly I don't know....

Or to get rid of hazardous DC at the output ...why not capacitively couple the inputs ???

The question makes me extremely passionate .

If I want to drive an Aleph X with 25 k differential impedance,and have a 20 dB gain ...I am a little lost....how to calculate proper feedback resistor value ?



The thirteen devils

Best regards

Anael
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Old 30th May 2003, 03:17 PM   #28
uli is offline uli  Austria
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Default DC-issue

Hi Nar,
When you directly couple a pre you have this problem all the time.
Use either good caps (Mundorf or the like) or DC-servo.
PS: we are not talking about serious DC values. Every direct
coupled pre produces offset depending on inputimpedance.

Uli

To drive an X-Amp you better use the aforementioned source-
followers at the output to keep gain load independant!

U.
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Old 16th June 2003, 01:09 PM   #29
nar is offline nar
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Hello Uli ,

I tried to understand the PCB version may 28 2003 but I am lost with In/Out connectors.

I suppose the one on upper part is for supply rails but I can't guess where V+ and V- are !!! At least the one in the middle is Ground ....

Second problem , the 2 connectors downside of the board . There is probably a mistake

As no plot connection of the 6 plots downside is a ground

And the -in and + in are clear for me , in the middle of the board

But the outputs on the schematic are common point between R 11/13/17/21 ( or R 12/14 18/22 ) and on the bottom part of the layout , they are well alltogether but no link to output connectors and on the top plane neither

So where is the error ???

I want to try your module with output followers to have possibility to test it as a single preamp . So I propose to add Jfets output followers,conveniently self biasing ( in that case another 2sk389 per output will do the job . To add it here are the mods I propose :

R 19/20 go to 47 k instead of 100k
R 15/16 go to 10k

R 17/18 adjusted to get proper gain figure

Removal of R 21/22 or shall I let them in place ?
Output goes to the gate of 1/2 2sk389 ,its drain at V + , a small resistor (22 ohms) from its source pin to output of the final thing . Second half of 2sk 389 mounted as a current source between output and V-, gate at V- and source pin goes to V- through small resistor (22 ohms)

The DC at the outputs should be very small , i.e. 2sk389 is an already matched unit

The feedback resistor ( R 17/18 ) ..... crucial point , shall I leave it in place or shall I plug it real output from the follower and go to gates of the initial 2sk 389 ????



If it works.... this would be a total Jfet gain stage , as the cascodes are not considered to give voltage gain ...

What do you think of the ideas ? Please answer I have to build the unit !!!!

Best regards

Anael
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Old 16th June 2003, 01:45 PM   #30
uli is offline uli  Austria
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Quote:
Originally posted by nar

I suppose the one on upper part is for supply rails but I can't guess where V+ and V- are !!! At least the one in the middle is Ground ....



Second problem , the 2 connectors downside of the board . There is probably a mistake

As no plot connection of the 6 plots downside is a ground

And the -in and + in are clear for me , in the middle of the board

But the outputs on the schematic are common point between R 11/13/17/21 ( or R 12/14 18/22 ) and on the bottom part of the layout , they are well alltogether but no link to output connectors and on the top plane neither

So where is the error ???

I want to try your module with output followers to have possibility to test it as a single preamp . So I propose to add Jfets output followers,conveniently self biasing ( in that case another 2sk389 per output will do the job . To add it here are the mods I propose :

R 19/20 go to 47 k instead of 100k
R 15/16 go to 10k

R 17/18 adjusted to get proper gain figure

Removal of R 21/22 or shall I let them in place ?
Output goes to the gate of 1/2 2sk389 ,its drain at V + , a small resistor (22 ohms) from its source pin to output of the final thing . Second half of 2sk 389 mounted as a current source between output and V-, gate at V- and source pin goes to V- through small resistor (22 ohms)

The DC at the outputs should be very small , i.e. 2sk389 is an already matched unit

The feedback resistor ( R 17/18 ) ..... crucial point , shall I leave it in place or shall I plug it real output from the follower and go to gates of the initial 2sk 389 ????



If it works.... this would be a total Jfet gain stage , as the cascodes are not considered to give voltage gain ...

What do you think of the ideas ? Please answer I have to build the unit !!!!

Best regards

Anael
Dear Anael,
sorry for causing you any inconvenience!
Here we go:

CON3 pin1 = +rail, pin2 = gnd, pin3 = -rail
CON1 pin1 = +drive-, pin2 = +drive+, pin3 = -input
CON2 pin1 = +input, pin2 = -drive+, pin3 = -drive-


The drive pins are designed to be directcoupled to source-
followers gates.Therefore leave the R11, R12, R13, R14
untouched.
You are right there are no outputpins as the unit should be
coupled to sourcefollowers.
I would leave R17,18 untouched and put some FB from the
junction of the sourceresistors of the external sourcefollowers
back to the respective inputs.
I would NOT make single ended followers. Better is to use
1 2SK389 and his complementary part 2SJ109.
Lastly, do not put the fb resistor directly to the gate.
Leave the 100R (+100k) untouched and put an input-fb
network (eg 10k, 100k) outside the unit.

Uli
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