XXHighEnd

Peter, I'm assuming you want to keep the NOS1 measurements thread (http://www.phasure.com/index.php?topic=2856.msg29934#msg29934) 'clean', as there isn't a possibility to leave a reply. In any event, I'm sure there will be people who want to ask some questions, so I thought starting a thread for this would be a good idea.

Here's one from me. In the thread, you say:


So, the NOS1 has a slew rate of 22V/µs??? Surely this is 30x too low, no?

Mani.

Well, this 90nS would imply a bandwidth of 11MHz@full scale....after 1 meter of coax...

No audio amp or ear is able to follow that.

I do not worry.

Slew rate becomes increasingly important when you need higher output voltage (like big power amps) and/or bandwidth (like with video).

regards, Coen

Coen, I'm just pointing out that Peter has stated a slew rate of 650V/µs for the NOS1 in other threads. I'm trying to understand how that equates with the measured 90ns for 2V rise time.

Mani.

Hey Mani,

I thought of announcing in some other topic that people could respond to the measurements of course, but it seemed a bit daft ...
So, very OK of course.

Now let's see about the 90ns ...

So you took 1000ns (=1us) / 90 = 11.11 and next assume that while 2V takes 90ns it takes 11.11 times that to thus go to 22V (11.11 x 2V). Well, although I didn't sort that out, I don't think it works like that; I think we must think like this :

We have a way strong elastic band and it allows some stone to go something like 650 meter high (official rating is over 650V/us) while we now need 2V only. And, somewhere halfway (!) we think "oh no, the stone is to go 2 meter (Volt) high only. Oops ... and there goes the stone to something like 325 meters (half of 650). It overshoots ...
So when the stone needs to go 2 meters high only, we need a not so strong elastic band (less current) or otherwise it will be out of our control.

Nice story eh ? I think it could be true. BUT :

While the 650V/us is the rating of the output stage, the rating of the D/A chips really are not that. I even recall that same 22V you mention as the advised opamp speed to use for the 1704 chip (as per the datasheet). I won't bet anything over it, but I'm almost sure. So, funny.

Luckily I never said anywhere that the performance of the DAC as a whole is that 650V/us but the output stage is just that. To some degree this *is* important because when anomalies would come from the D/A conversion (think very high HF stuff) then the electronics better be able to follow that or otherwise "slewing" happens, which is very similar to my outlay of the ringing running into a next sample; this then will be out of control oscillation.

Regards,
Peter

Got it. Thanks for the clarification.

Mani.

Ok, thanks, I missed that! Anyway my calculation isn't really correct, but that doesn't really matter.

Regards, Coen

The datasheet of the 1704 advises the OPA627 which is 55V/us which equates to 18MHz of bandwidth ....