sample and hold

[dan thacker]

I'm still pretty new at analogue stuff and I was wondering if temperature can effect the way this feature behaves,i.e:less tones bouncing around when it's cold , [sorry for the description,I don't know how else to describe it.]

[thealien666]

Usually no.

If you're talking about the LP/SP, I would suspect possibly the DAC circuit that could be offset by temparature, since the S&H in LP/SP is digital and has to be converted to analog control voltage by the DAC. But generally, this sort of circuit has a precise voltage reference, and is temperature compensated internally. But not having the schematics and not knowing precisely what chip Moog used as their DAC, I'm not sure of anything. All I know for certain, is that the S&H is digital in LP/SP and analog in Voyager.

What's the difference? The digital one operates in software and generates a random number in memory that is later converted into an analog control voltage by a Digital to Analog Converter (DAC). The other samples a microsecond of voltage coming out of a white noise generator, holds it in a capacitor until the next pulse from the LFO arrives. That voltage is then used as a control voltage.

[dan thacker]

Thanks Al,that is odd that the s&h in my LP sounds different than it did when I saved the preset,given that it's digital.Kind of sluggish,oh well ,sh*t happens with lots o' circuits!Oh yeah,that a/d converter,is that where the "noise" is generated also for the LP? I've also heard the LFO is digital.

[thealien666]

Thanks Al,that is odd that the s&h in my LP sounds different than it did when I saved the preset,given that it's digital.Kind of sluggish,oh well ,sh*t happens with lots o' circuits!Oh yeah,that a/d converter,is that where the "noise" is generated also for the LP? I've also heard the LFO is digital.

BTW, I'm not so sure anymore about the LFO and S&H being digital. I don't have the schematics and, if I'm relying on what I've read recently about the Phattys, according to Moog, they took some of the circuit designs from the Voyager and shrunked them using SMD components (smaller ICs). So the LFO, and S&H might be analog after all... Maybe Amos could tell us...

But I'm still intrigued by the term "sluggish" you use to describe the behavior of the random sample/hold of your LP ? Do you mean that the changes are not abrupt and seem to "glide" from one value to the next ? Or do you mean that the intensity (range) of the steps is not as high as when it's warmed-up ? Or if the speed of the changes seems slower when the unit is cold ?

[muksys]

the LFO, and S&H might be analog after all

I am almost 100% the LFO is analog. It is part of the "RAC" control, as stated in the manual. As for the S&H, that I am not too sure. It would seem to me to be digital since the only way to access it is through the menu structure.

[Portamental]

It does not matter if the S&H is analog or digital. It is stable. However, if it is used to modulate a temperature sensitive circuit like VCO's, then there will be a temperature side-effect. Vintage Moogs are well known for requiring a rather long warm-up time. Much less so with the Voyager.

At any rate, we are talking cents here. Since S&H generate random signals (unknown pitch), I would be very much surprised if you could hear the difference between a cold and a warm machine.

[dan thacker]

Sorry AL,I just read your question:When I said "sluggish",I meant that the s&h tones were slower and less animated [ I use the latter adjective with trepidation],but I didn't want to say "b*uncy" again!!

[thealien666]

Sorry AL,I just read your question:When I said "sluggish",I meant that the s&h tones were slower and less animated [ I use the latter adjective with trepidation],but I didn't want to say "b*uncy" again!!

The speed of the S&H is set by the LFO. And since the LFO is most likely analog, it is very possible that the "sluggish" speed at which steps are changing in the S&H when your LP is cold might be due to a cold LFO oscillator not warmed-up, yes.

[dan thacker]

Now that it's not -40 degrees,it is sounding great.
I know once the thing is paid off,[two more payments,] it will sound even better!