SD2000 Front end

[1843]

Hi all,

How much is the total gain of the following stage of SD2000?



Kind regards,
1843

[Max]

Hi all,

How much is the total gain of the following stage of SD2000?

[ATTACH]5610[/ATTACH]

Kind regards,
1843

Hi,
do you need it exact ???
it's high...consider that ne5534 has 6000 as typ gain at 10Khz. The supermatch pair is employed as an extern differential input stage, and will amplify too the signal... so you can expect something 6000-8000, if input signal is around 10Khz, depending on op amp selection too.

Kind regards,
Max

[1843]

Hi Max,

OK! I am building an SD2000... but with a lot difference! I want to use an AD8055 instead of the above stage...

Thanks,
1843

[gef12]

Hi
I would be keen to build one also.. what type of platform are you building on , breadboard or PCB. Also maybe a AD797 vice 5534 ??
8055 would be good too. Would be interesting project to build
cheers

[1843]

Hi gef,

I use breadboard... I don't use any 5534 because of their low slew rate, AD8055 is fast enough that Q11 and Q12 can be removed.

Regards
1843

[Qiaozhi]

The 3 Pees :
Patients, Perseverance and Persistence, will get what you desire.
73's Regards Gef

I think you mean:
The 3 Ps:
Patience, Perseverance and Persistence, will get what you desire.

Unless, of course, you're a doctor ... then you might need the patients!

[gef12]

Hmmmmm what can I say ,,
xie xie , trima kasi

[1843]

Hi gef,

I completed the my SD2000.... It works very unstable because of the breadboard and internal noises... it detects a gold ring at 12cm...
This machine must be made on pcb to get the best performance.

Regards,
1843

[Aziz]

Here is the operation of the pre-amp of SD2000 described in the following application note:

http://www.national.com/an/LB/LB-52.pdf


Aziz

[Qiaozhi]

Hmmmmm what can I say ,,
xie xie , trima kasi

mei guanxi.

[JC1]

good find

Hi Aziz,

Yet another good find Aziz,

good work, and your coil stuff

is good too.

[gef12]

Hi gef,

I completed the my SD2000.... It works very unstable because of the breadboard and internal noises... it detects a gold ring at 12cm...
This machine must be made on pcb to get the best performance.

Regards,
1843

hi
I dont suppose there is a sd2000 pcb in the making ...
Good try at the sd2000 on breadboard ..now i know I shouldnt try it as yet..
Have you try shielding the front end stage ?? or anything else ??
Anyways thanks

[Aziz]

Hi Aziz,

Yet another good find Aziz,

good work, and your coil stuff

is good too.

I have one more goody for you and others:

A Low Noise Amplifier for Phase Noise Measurements

http://www.wenzel.com/pdffiles1/pdfs/lowamp.pdf

Almost same principle. But here using two fets parallel to reduce noise. This could be even better.


Aziz

[ZED]

Caps

At a risk of saying the obvious.

Dont forget to put bypass caps on all the chips,especially the preamps.

Zed

[JC1]

yes

I have one more goody for you and others:

A Low Noise Amplifier for Phase Noise Measurements

http://www.wenzel.com/pdffiles1/pdfs/lowamp.pdf

Almost same principle. But here using two fets parallel to reduce noise. This could be even better.


Aziz

Hi Aziz,

Yes two or more of the same type in parallel will reduce noise.

Over one of the same type.

If you check the data sheets on FETs you will find that the

lower noise devices generally have higher gate capacitance Cgs.

why? because they are physically larger dies in the package,

i.e. in effect multiple FETs in parallel just made as one large one.

now the silicon can also be thicker and thinner also causing a change

in capacitance but in general you will find what I said to be the case.

The drain current required is also usually higher as well just as you would

need to double the current through a single drain resistor to use two FETs.