Preamplifier Specifications
alucididea
Posts: 113
in Electronics
So I’m trying to figure out why certain preamplifier specs are the way they are, particularly the output voltages. I’m looking at the NAD M12 and it lists these specs:
Output
Maximum Output Level
>8Vrms into 600 Ohms
THD (CCIF IMD, DIM 100)
>0.005% (ref. 20Hz-20kHz, 2V out)
Balanced
>2Vrms
What I don’t understand is why NAD is rating the single-ended outputs with a maximum level and the balanced with a minimum level. Does this make sense to anyone else?
Output
Maximum Output Level
>8Vrms into 600 Ohms
THD (CCIF IMD, DIM 100)
>0.005% (ref. 20Hz-20kHz, 2V out)
Balanced
>2Vrms
What I don’t understand is why NAD is rating the single-ended outputs with a maximum level and the balanced with a minimum level. Does this make sense to anyone else?
Comments
“Thank you for contacting the NAD Electronics Support Center regarding the M12 Balanced Output Level. It is rated to output at least 2V. ”
“The unbalanced outputs Maximum Output Level is greater than (>) 8Vrms into 600 Ohms.”
The unbalanced output hitting a full 8V would probably be unlikely under normal use cases. That's really high.
8v does sound halfway ludicrous, right?
Either way, I’m going to demo the M12. I’ve only got RCA cables at the moment (Kimber Hero). I wish I didn’t have to spend another $200 just to demo it with some decent XLR cables. I suppose I could always return those too.
I also had a less than pleasant experience interacting with NAD support about 6 months ago. I think they farmed out all their support overseas now.
They’ve actually given me some decent information in the very recent past. Seems like a hit or miss situation depending on who’s answering.
I've used Monoprice balanced cables for my studio monitors and observed nothing but exceptional performance. I would think that they would do just fine for your application, imo.
I'm sure that others will disagree, but I think that for balanced interconnects, the overall quality of the cable doesn't need to be as high. The inherent design benefit of the fact that they are balanced will cancel out any potential interference/noise issues. As long as the cable is not a complete piece of crap, I would wager that it would sound just fine.
*braces for impact*
Sez balanced is greater than 2 AC volts RMS, but the load's not specified.
2 V RMS ought to drive any decent power amplifier pretty well.
The classic "line level" standard was, as I recall, 1V RMS into 600 ohms, back in the day when the "line" was -- well -- a line. A telephone line, which was how remote broadcasts got back to the studio from the remote location
Output Level 2V (ref. input 0dBFS)
"0dBFS" is 0dB Full Scale which means the preamp will deliver 2Volts with the maximum digital input. There's not a separate output for single ended and another for balanced given.
The difference in the two outputs in your specifications could be related to the load impedance the measurements are taken with.
Just for reference, my amp is in the same line of products, the NAD M22. I’m not really worried about it at all. Just trying to figure out all the ins and outs.
Unbalanced MAXIMUM Output Level is >8v
But the way the support guy made it sound is the MINIMUM balanced output level is 2v.
AC volts do get a little confusing -- at least to folks like me.
2 AC volts RMS is equivalent to about a peak voltage of 2.8 volts or a peak to peak voltage of 5.6 volts.
I mention this mostly because the concept here is sort of a "maximum average value", which sort of makes one's brain hurt if one thinks too hard about it
I am guessing, then that the 8V maximum presumably means the maximum "undistorted" RMS voltage output specification, i.e., before clipping sets in.
I reckon the 2V does too - irrespective of tech support.
That being said -- I reckon that they're both probably guaranteed "minimum specifications" (i.e., any given example of the preamp in question might be capable of more output than that -- but those levels are "guaranteed").
Just musing wildly here, though
An amplifier that had no DC blocking components (e.g., a capacitor or transformer) on its input or its output, and if it had adequate bandwidth, would happily amplify 2 V DC to, say, 20 VDC and pass it along to the poor loudspeakers.
A DC voltage applied to the voicecoil of a woofer makes an electromagnet and a lot of heat. The woofer will most likely burn out quite quickly.
There will absolutely be plenty of pictures when its all set up on Thursday!
Will be the M12+M22+LSiM707s.
These are surface mount devices, which some designers find sound better than their larger counterparts.
I am clearly out of sync with this discussion so I'll drop out now.
Basically what I was expecting. You?
However, their response is interesting. It implies that these master series components get additional attention paid to them at the factory during/after production. It sounds like they do a listening test to verify functionality. I'm sure they don't do this to all of their stuff.
I would politely disagree that a listening test at the factory constitutes an acceptable/recommended break-in process though. I would wager that it's going to sound different right out of the box vs 20 hours, 50 hours, and then 100+ hours.