Buf-03

[carlmart]

Please have a detailed look at the datasheets of LM6171 and LM6172. www.national.com
The 6172 is not the doubled 6171. For 6172 I have only shown dist. at 20kHz, as 1 kHz cannot be seen from their specs.

From your graph might be seen why the NE5532 is still being used and considered a very decent chip after almost 30 years.




Carlos

 

[PMA]

Carlos,

yes, but one might consider NE5532's quite high input bias current and current noise. This OA should be used with low source impedance and low values of resistor network.

Pavel

 

[Nicke]

do you also have the links to those first articles...?

If anyone wants them I have the articles.
Drop me a mail and I´ll send them...

Nicke

 

[tbla]

...are you in town....its saturdaynight - ......

 

[sonnya]

Hi TBLA, Where in denmark are you living?

 

[tbla]

...in kgs. lyngby - a bit north of copenhagen.....great place.

 

[carlmart]

Carlos,

yes, but one might consider NE5532's quite high input bias current and current noise. This OA should be used with low source impedance and low values of resistor network.

Please don't misunderstand me. I have tried different chips on preamps and DACs and many sounded a lot better than the 5532 they replaced, but I must admit it certainly has its merits. In fact some 5532 brands sound better than others.

On your graph the AD797 seems to be the lowest, and many don't seem to make it work. So to start with a chip has to be tamed in order to work properly, that is know how it should be handled.


Carlos

 

[PMA]

AD797 behaves a little bit strange for gains between 1 to 10. If you see the open-loop amplitude/phase diagram you will know why. But it can be compensated. For gains >10 it is a great OpAmp, again, the best with low impedance sources and inside low-impedance network (bipolar OA).

 

[PMA]

It should be said that OpAmps in general do not like HF mess and quick short spikes at the input of amp network, especially in non-inverting circuits. It is very desirable to reduce bandwidth of incoming signal to some 150 - 200 kHz (-3dB). This will eliminate rather "synthetical" sound, that some of the circuits tend to create. Also, differences between different OpAmps can be lowered be incoming signal bandwidth reduction.

 

[PGW]

Using the AD797

PMA:

Do you have any further tips - schematics, perhaps - for using the AD797?

I am thinking of using this device as the first + second stage of a MC phono preamplifier, possibly as a differential amplifier, and wonder if you have any links?

Thanks

-- John

 

[PMA]

PGW,

I have only used the AD797 in the first stage of power amplifier, this stage had non-inverting gain of +10 and needed no special compensation.
I have also tried 797 (from experimental reason) for gains from 1 to 10 and found that compensating capacitors (or serial R-C circuits) across feedback resistor must be used, the examples are shown in AD797's datasheet. Unfortunately I do not remember exact component's values.

 

[sonnya]

...in kgs. lyngby - a bit north of copenhagen.....great place.

I live in Odense, 5 min. bycycling from the city.

AD797 behaves a little bit strange for gains between 1 to 10. If you see the open-loop amplitude/phase diagram you will know why. But it can be compensated. For gains >10 it is a great OpAmp, again, the best with low impedance sources and inside low-impedance network (bipolar OA).

A guy from EW. who made an article on distortion in capacitor, sayd that the AD797 needs at least 100R from Output to the inverting input regardless of gain. It did have a huge inpact on the distortion figures.


The datasheet says it is for damping oscillation on the inputs.