I have been using OPA637s in the input buffer stage of my NHTPro A10 power amp (150W per channel, dual mono). The result is amazing as the sound has been vastly improved. However, the buffer stage is set at unity gain -- the OPA637 are not supposed to be stable at this lower gain. But I can't hear anything wrong. Everything is so smooth and clean. Is it because the 56p bypass capacitors that may have solved the problem of oscillation? Or are my OPA637s timed bombs? Thanks!
I'd not disregard manufacturers recommendations. You must have simply
gotten lucky with stability with a random sample of parts. Do you really want
to trust your power stage and speakers to this?
I really like the AD826 awhole lot... This device is unity-gain stable and is, in fact,
designed with the intentions of being a buffer. It can drive 50 ohm impedances
with tens of mA of current. Further, the op-amps output stage is Class AB, so,
for small signal excursions, the op-amp is running Class A.
People like the
AD826. It's a $5 part too.
-- Jim
gotten lucky with stability with a random sample of parts. Do you really want
to trust your power stage and speakers to this?
I really like the AD826 awhole lot... This device is unity-gain stable and is, in fact,
designed with the intentions of being a buffer. It can drive 50 ohm impedances
with tens of mA of current. Further, the op-amps output stage is Class AB, so,
for small signal excursions, the op-amp is running Class A.
People like theAD826. It's a $5 part too.
-- Jim
I like AD826 a lot too. It's different from BB chips in a very confident way. And I think it sonically it outperforms many other AD chips, such as OP270, OP275, AD823, and AD827. However, I found OPA637 to sound best in my setup. The only things that came remotely close were AD843 and LT1364.
I actually have about 4 pairs of OPA637s (mounted on Browndog adapters) and all of them SEEM (they all sound great with no distortion or over-heating deteted) to be stable. (On the other hand, my pairs of OPA627 seem to get warm easily). It's just weird.
Again, something I really need to confirm:
Is oscillation the cause of instability? If the chip sounds great and is not over-heating, does this mean that there is no oscillation (or, what are the signs of oscillation -- I don't currently have a osciloscope)?
Many thanks!
I actually have about 4 pairs of OPA637s (mounted on Browndog adapters) and all of them SEEM (they all sound great with no distortion or over-heating deteted) to be stable. (On the other hand, my pairs of OPA627 seem to get warm easily). It's just weird.
Again, something I really need to confirm:
Is oscillation the cause of instability? If the chip sounds great and is not over-heating, does this mean that there is no oscillation (or, what are the signs of oscillation -- I don't currently have a osciloscope)?
Many thanks!
Hi mudihan,
I started with a single channel basic scope for $25 back in the sixties. It was military surplus. I think it was good for about 500KHz back then. I sold it years later and even got my money back out of it.
I know the dollar figures are higher these days, but if you look around you can find a 'scope. I wonder what $25 in the late sixties is worth today?
-Chris
I started with a single channel basic scope for $25 back in the sixties. It was military surplus. I think it was good for about 500KHz back then. I sold it years later and even got my money back out of it.
I know the dollar figures are higher these days, but if you look around you can find a 'scope. I wonder what $25 in the late sixties is worth today?
-Chris
mudihan said:
Nice choice!
The rating of an Op-Amp is the rating guaranteed from the mass-production process, not the measured performance of any given device.
That said, the 56p should be fine.
For others reading this, the 637 is rated for +5
The 627 is the unity gain version.
Expensive op-amp, but very nice
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