Amp question

[ski2xblack]

@AcuDefTechGuy, the above is an example of power cube measurements for an amp that is current limiting. I suspect that the OP's NAD exhibits this sort of behavior. Note the fairly good results into a resistve load (what S&V measure), and poor results when compounded by phase angles (which characterizes the load speakers will present to the amp).

Now, this is still all conjecture, but AVRs are notorious for current limiting, heavy handed protection circuits, and thus generally poorer performance. If the NAD were the exception I would be very surprised. Anywho, the Salks 4 ohm load already has the amp sailing pretty close to it's current delivery limits, and the 2khz dip probably enough to trigger current (thus heat) reduction safety mechanisms.

Those back of the unit impedance switches typically simply reduce supply rail voltage, thus heat, and unfortunately output power, to keep the units from cooking their other parts to death prematurely. The high impedance settings defeat some of that current limiting (the amp still has thermal protection that would kick in at some point), hence the suggestion to @tmurnin to try that. (I'm not sure if his NAD even has such a switch, but the most recent NAD I have direct experience with did.) That way, the amp may more closely reflect the sort of power that S&V measured. Your expectations are not too far off base, as the S&V measurements make the amp look pretty good, ditto the asr measurements by Amir (it was the pre section that earned the headless panther).

Hopefully some of this works, for the OP's sake. He deserves to not have to fret about amps and get back to enjoying sweet, sweet music those Salks can put out.

edit: just checked, the NAD T758 does NOT have a user selectable impedance switch. It is what it is.

 

[PENG]

the sad thing is 'back in the day' it was just the opposite, NAD was known for conservative specs whereby they offered superb headroom.

Interestingly, if you look at S&V's reviews on the older NAD AVR such as the 56 lbs $4,000 T787, their specs weren't that conservative relative to the measurements:

NAD T 787 A/V Receiver HT Labs Measures | Sound & Vision (soundandvision.com)

This graph shows that the T 787’s left channel, from A1 input to speaker output with two channels driving 8-ohm loads, reaches 0.1 percent distortion at 152.7 watts and 1 percent distortion at 184.5 watts. Into 4 ohms, the amplifier reaches 0.1 percent distortion at 180.1 watts and 1 percent distortion at 207.1 watts.

That's a lot less powerful than the 18 lb lighter Denon AVR-3808 CI, and the NAD's distortions was higher too across the board, from under 1 W to rated output.

I think their older class AB integrated amps such as the C275 are probably more truly "conservatively rated". To me, NAD, like Anthem, are good in making integrated and power amps, not as good in AVRs/AVPs, just my 2 cents.

Denon AVR-3808CI A/V Receiver HT Labs Measures | Sound & Vision (soundandvision.com)

Note that the NAD appears to have a gentle climb from clipping but that's because of the different scales.

 

[AcuDefTechGuy]

View attachment 42709
@AcuDefTechGuy, the above is an example of power cube measurements for an amp that is current limiting. I suspect that the OP's NAD exhibits this sort of behavior. Note the fairly good results into a resistve load (what S&V measure), and poor results when compounded by phase angles (which characterizes the load speakers will present to the amp).

Now, this is still all conjecture, but AVRs are notorious for current limiting, heavy handed protection circuits, and thus generally poorer performance. If the NAD were the exception I would be very surprised. Anywho, the Salks 4 ohm load already has the amp sailing pretty close to it's current delivery limits, and the 2khz dip probably enough to trigger current (thus heat) reduction safety mechanisms.

Those back of the unit impedance switches typically simply reduce supply rail voltage, thus heat, and unfortunately output power, to keep the units from cooking their other parts to death prematurely. The high impedance settings defeat some of that current limiting (the amp still has thermal protection that would kick in at some point), hence the suggestion to @tmurnin to try that. (I'm not sure if his NAD even has such a switch, but the most recent NAD I have direct experience with did.) That way, the amp may more closely reflect the sort of power that S&V measured. Your expectations are not too far off base, as the S&V measurements make the amp look pretty good, ditto the asr measurements by Amir (it was the pre section that earned the headless panther).

Hopefully some of this works, for the OP's sake. He deserves to not have to fret about amps and get back to enjoying sweet, sweet music those Salks can put out.

That’s possible. I never cared for NAD products, but I was playing devils advocate, as usual.

 

[tmurnin]

Ok, did the volume test with the SPL meter. Obv this is somewhat dependent on my mood and music choice but I think everyday listening is going to be in the 70-80db range and can’t imagine going over 95db except in rare circumstances

 

[tmurnin]

Btw, while I appreciate all the thought and effort people have dedicated to this, the engineering graphs are now well above my level of understanding.....

 

[lovinthehd]

Ok, did the volume test with the SPL meter. Obv this is somewhat dependent on my mood and music choice but I think everyday listening is going to be in the 70-80db range and can’t imagine going over 95db except in rare circumstances

That average level? What about peaks? And what weighting?

 

[PENG]

Btw, while I appreciate all the thought and effort people have dedicated to this, the engineering graphs are now well above my level of understanding.....

I assume you meant that colorful power cube ski posted. If so, the following should help, if you take the time to read the whole thing. To me, that's an overkill. For most applications, whatever those online calculator says you need, double or triple it and you are good for probably 99% of the moving coil loudspeakers.

Measuring Power Amplifiers with Reactive Loads - Audio Precision (ap.com)

PowerCube_12p_brochure_complete.pdf (audiograph.se)

Building A Reactive Load for Amplifier Testing | Page 3 | Audio Science Review (ASR) Forum

 

[ski2xblack]

One would imagine that the NAD, which can do 180w into a resistive 4 ohm load per what @PENG just posted, that it would have no problem driving 100w* into a slightly reactive load, right? (Right, NAD?!?)

I suupose it's not the first AVR to be exposed as wanting by really good, if current hungry, speakers like the OP's Salks.

*Using very conservative inputs into the myhometheater peakspl calculator (85db/w for sensitivity, 'away from walls' for placement to compensate for your sizable room), and @100w ->98.3 db at your chair, 180w -> approx 101db.

 

[tmurnin]

That average level? What about peaks? And what weighting?

Not sure what you mean by weighting. That's an average volume level. I'm sure the right music (if I'm REALLY feeling that PJ song) at peak moments goes over that, but again, probably not above 95db

 

[tmurnin]

I assume you meant that colorful power cube ski posted. If so, the following should help, if you take the time to read the whole thing. To me, that's an overkill. For most applications, whatever those online calculator says you need, double or triple it and you are good for probably 99% of the moving coil loudspeakers.

Measuring Power Amplifiers with Reactive Loads - Audio Precision (ap.com)

PowerCube_12p_brochure_complete.pdf (audiograph.se)

Building A Reactive Load for Amplifier Testing | Page 3 | Audio Science Review (ASR) Forum

But I only use moving magnet speakers?

 

[lovinthehd]

Not sure what you mean by weighting. That's an average volume level. I'm sure the right music (if I'm REALLY feeling that PJ song) at peak moments goes over that, but again, probably not above 95db

Frequency Weightings - A-Weighted, C-Weighted or Z-Weighted

A description of the frequency weightings used for sound level meters - A-Weighted, C-Weighted or Z-Weighted.

www.noisemeters.com

Does your meter not have a peak reading if these are average or is that the 95? What type of music do you tend to listen to (I have no idea what PJ refers to)?

 

[Alex2507]

if you take the time to read the whole thing

I don't like your tone.

 

[PENG]

But I only use moving magnet speakers?

Are you sure, according the their manuals, spec sheets?

 

[PENG]

One would imagine that the NAD, which can do 180w into a resistive 4 ohm load per what @PENG just posted, that it would have no problem driving 100w* into a slightly reactive load, right? (Right, NAD?!?)

I bet NAD would answer "yes".

 

[PENG]

I don't like your tone.

Let me rephrase it then, to,...Just read the whole damn thing.....!

 

[Trell]

Let me rephrase it then, to,...Just read the whole damn thing.....!

You overlooked his tl;dr that he did not write

 

[ski2xblack]

I bet NAD would answer "yes".

Oops, except that's the 787, not @tmurnin's 758, which per Amir's bench test does about 120w @ 4 ohms, and 178w @4 in dynamic power tests, which is even less for our poor OP.

Timely vid from Gene:

@tmurnin, if you've proceeded with the amp purchase, using the NAD as a pre/pro won't be as disastrous as that asr review may have you to believe. Given your listening levels, and even with the fairly low input sensitivity of the Rotel if that's the one you get, I doubt you'll be pushing it into the 2v territory very often. Below that it's not awful, probably not audibly so.

 

[tmurnin]

Ok, so after all of this, here’s what I’ve done:
- moved the speakers out from the wall another 6” or so, for a total distance of roughly 18” from the wall (maximum my wife would allow before declaring I had moved the speakers into the middle of the room)
- turned off Dirac room correction
- set crossover to 110
- added the Rotel amp (maybe the Monoboocks would have been a better choice, but the rotel was roughly $100 cheaper, I didn’t have to pay shipping, and I supported a local AV store)

These changes resulted in a noticeably better soundstage for me. I believe I can hear a more full range of music at all levels instead of what sounded before like an emphasis on the high end, and I’m hearing what I hoped for and expected out of the Salks.

Could there be some placebo effect here? Sure, I’m not discounting that at all. I bought an amp and I know I bought one hoping for sonic improvements, so it’s certainly possible that I’ve convinced myself I’m hearing a difference that may not really be there. For that reason, I’m very glad I bought a relatively cheap amp and I don’t think there would be any benefit from spending more money on a different amp. I did rerun Dirac again after everything to see if I could detect any audible difference. I would say I believe there was a small improvement with Dirac, but nothing dramatic, and could also be placebo.

Regarding some other suggestions:
- I will look at moving the subwoofer out from the back wall after the holidays (when the Christmas tree is gone). Ideally I’d add a second sub, but that probably isn’t gonna happen in this room. Given that the primary listening focus is music rather than movies, maybe this isn’t as big of a deal?
- I’d love suggestions on improving the room acoustics but they have to fit the decor. No chance I’m going to be able to do anything “ugly” in the name of sound, so all the suggestions about doing something with the ceiling are gonna be tough.
- Spending $5k to upgrade to Transparent cables and cable risers? Haven’t tried that yet but clearly something that needs to be on my list

Thanks to all for the help and commentary- I had no idea this thread would run 7 pages when I asked what I thought was a pretty easy question!

 

[AcuDefTechGuy]

Could there be some placebo effect here?

Yes, of course. Nobody is immune to bias (and the placebo effect) even if you received 2 doses of the Bias-Vaccine 21 days apart. And even then it’s only 95% effective. So you’d still be 5% bias.

 

[lovinthehd]

- Spending $5k to upgrade to Transparent cables and cable risers? Haven’t tried that yet but clearly something that needs to be on my list

LOL....at least I hope you're kidding....

Sometimes all you need to do is move stuff around to hear things differently....