OP-AMP buffers, uses?

[GT Blocker]

Since I'm building Carl's HH, this question pertains to PI detectors.
As I researched Hi-Fi headphone and other amps, I noticed the use of buffer opamps within their designs. Especially when it concerns virtual ground pwr supplies (which makes sense, since they amplify current, not voltage).

My question is...are there any other points in the signal stream where a buffer amp would prove useful? For example, from the coil to the board?

http://www.national.com/pf/LM/LME49600.html is an example of these buffer amps.

Would there be any benefit to adding a buffer after the coil pre-amp, yet before the integration switching?

Or perhaps at the coil for current boosting and impedance matching?

I realize this is probably a dumb question, but oh well....I have more where this one came from, trust me.

What do those of you 'in the know' have to say?
Thanks, GTB

[Aziz]

Hi GT Blocker,

this buffer might be excellent in using for Laptop MD as a power amplifier. It delivers enough power to drive the coils. His excellent low total harmonic distortion and low noise characteristics is predetermined for such application.

It might also be very usefull for splitting single supply for typical op-amp amplifier applications. So amplifiying virtual ground or lowering the impedance of virtual ground is a usefull application.

I will try to get some samples of this chip and when I got one, I will try it in a Laptop MD.

Regards,
Aziz

[gwzd]

Or perhaps at the coil for current boosting and impedance matching?

Yes, you got it right. Mostly the first, but sometimes the second too.
Regards

[GT Blocker]

Thanks for the input

Hey Aziz, gwzd,

First to Aziz:

"It might also be very usefully for splitting single supply for typical op-amp amplifier applications. So amplifying virtual ground or lowering the impedance of virtual ground is a usefully application."

That was what led up to this post as I want to get rid of that noisy 7660 and that was my buffer of choice so far. The standard 'buffer after the TLE2426' virtual ground deal.

I had also wondered if there were other signal stream uses. I never thought of driving a laptop MD coil, though! Right on....

I already have samples of the LME49710 that the 49600 is buffering in the link. I should be firing up the HH in a day or two and intend to try the 49710 in place of the 5534, after everything checks out 'stock'.
If you get the chance, get a few 49710 samples to test (if you're so inclined), as I would love to hear how they work for you as opposed to the NE5534.
I'm gonna have a bit of a time understanding what passives might need to change to get it to work (if it will), and it seems like you might find the task 'no biggie'. A thought....

gwzd,

I'm still considering the pros/cons of moving any circuitry down near the coil.

Aziz has posted a few magnetic field maps that show a 'dead spot' at about 45 degrees off the horizontal plane of a coil, at the edge. I'm thinking of trying an SMD mini board at that angle, right at the back of the coil.

As Carl noted in response to a previous post of mine, there are pwr and sig cabling issues, signal attenuation, added noise, etc. to consider in moving circuitry down to the coil.
Since the only lines needed for the buffer are +/- (sig in/out is in the original cabling), and it allows for better impedance matching, I think it's worth playing with. The current boost might help overcome some noise. National even has a similar buffer with a 'programmable' voltage gain (-1, 1, +2).

So much to learn...so little time.


Thanks again for all the input.

Still pluggin' along (wish it would rain here),
Gregory

[gwzd]

Aziz has posted a few magnetic field maps that show a 'dead spot' at about 45 degrees off the horizontal plane of a coil, at the edge. I'm thinking of trying an SMD mini board at that angle, right at the back of the coil.

As Carl noted in response to a previous post of mine, there are pwr and sig cabling issues, signal attenuation, added noise, etc. to consider in moving circuitry down to the coil.

Take the results of simulations very careful, after all that is only a model. It is a good idea to have them as a pointer, but I would measure it first anyway.
About the Carl's remarks, yes he is probably right, but then again you are not planning to move all the circuit. Give it a try and measure the effects of placing the circuit closer to the coil.
best luck with your experiments!