[sdiy] The sound of various Op-Amps

[Scott Bernardi]

That's true, they are different.  And fast slew rate doesn't necessarily 
mean the highest GBW, either. For example, the TL* series has a 13v/usec 
slew rate and a 3MHz GBW. The NE5532  has 8v/usec slew and 10MHz GBW.  
The OP27 has a 2.7v/usec slew and an 8MHz GBW.
It has to do with the gm of the first stage.  You can get more gain out 
of a bipolar diff pair at a lower current, but that lower operating 
current means a slower slew rate (less current to charge internal 
capacitances).  The JFET diff pairs run at a higher current and so have 
more to slew the capacitances with. But, the inherent JFET gm is lower 
than bipolar so it usually has a lower GBW (and lower open loop gain).
It turns out you also get lower noise running at a higher current, so 
you get the low noise and higher slew, both good for audio. This is at 
the expense of other parameters like input bias current (for bipolar 
inputs) or offset voltage and drift (for JFET or MOS inputs).  It's all 
a bunch of trade offs.


Ingo Debus wrote:

>
> Am Sonntag, 21.09.03 um 06:09 Uhr schrieb harrybissell:
>
>> Another place that 'fast' slew rate becomes important is when really 
>> high gain
>> is expected from
>> one stage.  Because of the gain / bandwidth product of most of the 
>> plebian
>> opamps I use...
>>
> Aren't slew rate and gain-bw-product two different things? Sure, for a 
> 'fast' opamp both are high, but if you're looking for high 
> gain-bw-product, you're not looking for a fast slew rate in the first 
> place.
>
> Ingo
>
>

-- 
Scott Bernardi
sbernardi at comcast.net