[cab]

From what Bruno has said, there should be no difference in performance from 2 ohm past 8 ohm, and I would suspect much higher than that. Your experience clearly is at odds with both the published performance and Bruno's statements regarding the load independent performance. I would definitely talk with them....

[Russell Dawkins]

It must be said though that, high as the damping factor is, it will still double into double the load resistance, so quadruple from 2 to 8 ohms - and perhaps this is audible.

Another thought is that perhaps the speaker wire should be doubled up or the gauge increased as the load resistance lowers, to remove another variable. The wire almost certainly will have more resistance than the output stage as Bruno says in the white paper:
"Output impedance is lower than the resistance of three feet of 4 gauge loudspeaker cable."

[James Romeyn]

It must be said though that, high as the damping factor is, it will still double into double the load resistance, so quadruple from 2 to 8 ohms - and perhaps this is audible.

Another thought is that perhaps the speaker wire should be doubled up or the gauge increased as the load resistance lowers, to remove another variable. The wire almost certainly will have more resistance than the output stage as Bruno says in the white paper:
"Output impedance is lower than the resistance of three feet of 4 gauge loudspeaker cable."

Russell,
Huge thanks for the speaker wire gauge info above.  You may have just quadrupled my amp's power. 

My speaker wire is Stan Warren's original recipe, Quad-braid AWG12 (19-strand copper per each conductor, 2x AWG12 per polarity), about 6' total whether series or parallel.  IIRC each doubling of gauge = next thicker gauge/next lower whole gauge number: two x AWG12 = AWG11.  If correct my equivalent AWG is only 11.         

By Bruno's math, driving 2.65 Ohm load, how many times must I multiply/parallel 6' wire equivalent to two x AWG12 per polarity (4x AWG12 both polarities)?

Again, the sound quality difference was huge, swinging from unacceptable/how much can I get for these amps? to equaling or beating the best I've heard.

I certainly thought, apparently wrongly, my wire gauge was way over-spec even for parallel application.  dB loss per this wire gauge calculator http://www.bcae1.com/images/swfs/speakerwireselectorassistant.swf calls for thicker wire gauge if/when loss exceeds 1 dB, while AWG11 results in only .05 dB loss (1/20th allowable) listing 600W amp power @ 2.65 Ohms @ 6' wire.  Quite confused! 

[srb]

IIRC each doubling of gauge = next thicker gauge/next lower whole gauge number: two x AWG12 = AWG11. If correct my equivalent AWG is only 11.

Doubling conductors results in an ~ equivalent gauge 3 sizes larger.  2 X 12AWG = 9AWG.  If you are combining an odd number of conductors, or conductors of different sizes, you can use an online wire gauge calculator such as:

http://home.hiwaay.net/~rgs/awgcalculator.html
 
Steve

[Ric Schultz]

We have 3 people who have the NC1200s and have compared them to the NC400s.  They all say they are better.......but nobody is saying more than that.  In what exact ways are they better?  Can you give some details? 

I wonder how a pair of NC1200s will compare to bridged NC400s (bridged 400s are $3500 and NC1200s are $9000).....assuming both being run the same way (either balanced or unbalanced).  I am talking sound quality.....not power.  I only need 10 or so watts.

By the way, just listened to NC400s (hardwired AC, hardwired output wires, OFC unbalanced input jack, Furutech fuse and 10lbs of damped weight on top of each of them). These things are very nice......slight loss of air on top and not as directly involving in the midrange as my own amps but they are more detailed and lower distortion.  If you could marry the characteristics of the two amps I would be in total goosebump heaven.  For this reason I am interested in the bridged amps and also doing some minor mods to the module (modifying and possibly changing the output filter caps).  The Furutech fuses made the amp more palpable and rich....very nice.

[Rclark]

Well bridged NC400's are more powerful than nc1200, correct?

[James Romeyn]

...The wire almost certainly will have more resistance than the output stage as Bruno says in the white paper:
"Output impedance is lower than the resistance of three feet of 4 gauge loudspeaker cable."

Per calculator link I posted above: 3' x AWG4 = .0015 Ohms, low for any power amplifier. 

Earlier calculator specs testing the monitors in parallel:

600Wrms
6'
AWG9
2.65 Ohm load = .0095 Ohms wire resistance (6.3x the source).

I'll listen again with AWG6 x 3.5' = .0028 Ohms (still twice the source but 3.3x lower than the earlier test).

Depending on the speaker's minimum impedance and speaker cable gauge, you might consider revisiting negative Ncore conclusions.

If Hypex sells speaker cable, what is the gauge? 

[rklein]

No Guy, no need.  I was being obtuse.  My bad.  I agree that these NCore threads are getting a little snippy, and my poor excuse for an inside joke didn't help.

OMG Ted!  The last time I heard the word obtuse was in The Shawshank Redemption(one of my alltime favorites...).   

Sorry...back to the thread...

Randy

[James Romeyn]

I only need 10 or so watts.

By the way, just listened to NC400s (hardwired AC, hardwired output wires, OFC unbalanced input jack, Furutech fuse and 10lbs of damped weight on top of each of them)...

"Unbalanced input" is contrary to OFC and every assembly technique above.  Per Bruno: ideal input is balanced XLR regardless whether source is balanced or unbalanced.  Unbalanced input also negates function of Bruno's ideal unbalanced source IC, which is quasi-balanced.  A strange and cross-purpose assembly philosophy.  One should at least follow the designer's direct ideal instructions before "improving" other areas.

I bet this was the owner's logic: he has unbalanced source, some preferred unbalanced IC, some favorite OFC RCA jacks valued about $75ea, and desired not to make or purchase new quasi-balanced IC.

I don't know if it's true, but IIRC decades ago Enid Lumley wrote that when "RCA Labs" (it's almost impossible to believe that Dr. Harry F. Olson worked for RCA when he wrote "Music, Physics, and Engineering) invented the then-labeled "phono" (AKA RCA) connectors, RCA had no specific ID for the diameter of the signal tunnel, hence the wide range of tensions in the plug/jack interface.         

[Ric Schultz]

OFC means oxygen free copper.....don't know what you think it means.  Almost everyone who listened to the amps on tour unbalanced used the supplied adapters.  This simply grounds pin three to pin one......the same as using an RCA jack.....no difference whatsoever.  A great sounding rca jack will sound way way better than using an adapter.  The only possible? advantage of using an XLR would be to use a floating quasi-balanced interconnect which probably very few have done (you need to have an rca on the input side of the cable and an xlr on the output side).   Two of the three "unbalanced" inputs that Bruno shows on the NC400 data sheet use RCA jacks. 

The REAL advantage comes when you fully balance, which I will be hearing soon (fully balanced Oppo going directly into fully balanced NC400).

[jackman]

does the oppo have a digital volume control?

[James Romeyn]

OFC means oxygen free copper.....don't know what you think it means.

I know and knew what is OFC.  My point was and is that if absolute performance is the goal (tweaks, etc), XLR/quasi-balanced IC performs better than OFC RCA/unbalanced IC.  Maybe you disagree and that's fine.   

You ignore my point that Bruno's ideal for unbalanced source is XLR with quasi-balanced IC.  Your silence says much.  I don't blame you for ignoring it, because I suppose ignoring Bruno's advice in this regard is hard to defend.

Would you be so kind as to share with readers the builder's logic in choosing RCA jack/unbalanced IC rather than XLR/quasi-balanced IC.  We may all learn something from this choice.  I suspect the builder thinks he has some special RCA/unbalanced IC that negates Bruno's first choice.           

Almost everyone who listened to the amps on tour unbalanced used the supplied adapters.  This simply grounds pin three to pin one......the same as using an RCA jack.....no difference whatsoever. A great sounding rca jack will sound way way better than using an adapter.  The only possible? advantage of using an XLR would be to use a floating quasi-balanced interconnect which probably very few have done (you need to have an rca on the input side of the cable and an xlr on the output side). 

I wonder what on earth the above has to do with anything relative to my comments about the mutually exclusive assembly philosophy employed by the builder of the amp you describe: hard wired inputs/outputs, etc. while simultaneously employing inferior input jack and IC architecture.  May I ask who made these choices? 

Two of the three "unbalanced" inputs that Bruno shows on the NC400 data sheet use RCA jacks. 

What you mention above Bruno labels as only "acceptable".  About the preferred method I describe Bruno writes: ""The braided cable shield serves two duties: to connect the chassis potentials together and to shield electrostatically the signal".  I can only presume the RCA deletes these features. 
 

The REAL advantage comes when you fully balance, which I will be hearing soon (fully balanced Oppo going directly into fully balanced NC400).

About which you label (unheard I might add) "REAL advantage" Bruno says the XLR/quasi-balanced IC "benefits unbalanced setups almost equally".  I'm confused by "fully balanced NC400" because by design NC400 has fully balanced input.  Only the DIY builder, such as in the subject amp, decides to convert a fully balanced input into unbalanced with inferior RCA jack vs. XLR/quasi-balanced IC, contrary to the designer's first performance choice.  Please correct if I'm wrong.

Thanks.   

About your amp's architecture Bruno further writes:

Having made sufficiently clear that there is, in fact no reason why anyone should ever want to waste a perfectly good balanced input by putting the module in a box with RCA inputs, it is likely that some will persist.  (emphasis added)

 

 

[Ric Schultz]

The images are not the way I listened.  This is for the customer.  I ran the power wires backwords and over the front of the amp and soldered them to my powercords.  I used the speaker output wires but hardwired directly to my speaker wires.  The binding posts shown are used as clamps only.  I invented this technique and have been using it for over 10 years.  Even better sounding is to use a plastic or wooden clamping mechanism.  This is especially important at the speaker end of the wire where all the conductive mass of a connector acts as a bad "ground or hot enhancer".....more like a ground or hot ruiner.  So, at the speaker end it is seriously important to hardwire or at least have no massive metal posts.....even as clamps.  The speakers I am designing will have plastic or wooden (optional) clamping mechanisms.  The AC connector for the customer is a Furutech and you can see the blue Furutech fuse in there.  I will be modding or changing the three Wima output filter caps soon.


Jim,
Have you listened both ways?......please tell us how much better it sounds to use an xlr on the amp and reterminate your unbalanced cable with an xlr.  The only thing that makes a sonic difference/improvement is what makes a difference.....not some thought about it.

The only difference between "quasi balanced" and unbalanced is the fact the the negative input of the differential pair is grounded back at the source (one meter away) and not at the load.  How much difference sonically does this make?  Please enlighten us as to the sonic benefits.

As far as tweaks go, it does not matter which way you hook up the inputs.....you will still hear all the benefits of hardwiring, etc.  believe it or not.   The same as not using a lower distortion fuse.  Even with the stock fuse (almost everyone who has the amps still has the distorted fuse sound) you can still hear anything else you do to the amps.  You do not have to do one thing in order to hear another.  However, the more veils you remove the easier it is to hear differences and the more pronounced they are. 

It has been clearly said by several people that the best sound comes from running the amps fully balanced.  Quasi-balanced is not balanced at all.  Balanced means you have both a positive and negative going signal (relative to ground).....and fully floating differential stage.

Now we have someone raving about balanced bridged.......this is getting exciting.  If balancing gets me more (I will soon find out) and then bridging gets even more then we are all in for a big treat.   


Yes, the Oppo has a 32 bit digital volume control.....however, I bet it is not sonically as good as using a shunt attenuator directly inside the amp (what I do).  A couple of my customers say the digital volume control still messes up the sound.  I have not played with it personally.  Putting a shunt balanced attenuator in an amp would be pretty easy.  You could use a 10K resistor in series with each input and use a 24 position switch to switch resistors between the output of the 10K resistors.  Very transparent.  PRP resistors are very good for the money.  Only slighty better is nude latest Vishay.

[mikeeastman]

Ric any chance we can gets some pics of inside the amp?


  thanks, mike

[jmbulg]

The only difference between "quasi balanced" and unbalanced is the fact the the negative input of the differential pair is grounded back at the source (one meter away) and not at the load.  How much difference sonically does this make?  Please enlighten us as to the sonic benefits.

The signal itself does not need to be differential to benefit from the balanced design of the amp: any noise picked up by the balanced cable (in the quasi balanced approach the negative it is indeed grounded back at the source) between the source and the amp (noted noise hereafter) will be eliminated by the balanced design of the amp because is subtracts both signals:

cable 1: positive signal+ noise
cable 2: zero negative signal+ noise

in the amp: cable1 minus cable2 signal provides a cleaner positive signal.


In the fully balanced setup it would be

cable 1: positive signal+ noise
cable 2: negative signal+ noise

and cable1 minus cable2 would provide a signal doubled without the noise, hence evenmore improving signal/noise ratio

Hope it makes sense .

[Ric Schultz]

Someone needs to do a listening experiment to confirm if there is any benefit from "quasi balanced".   The most simple way would be to have a balanced connector on the amp and a balanced connector on the amp end of the interconnect.  One way you would ground the negative input of the differential stage directly inside the amp at the jack and the other way you would have it floating at the amp so it is only grounded at the source.  Listen for the difference and let us know.     Otherwise it is all theory. 

The only thing real is what you hear.  Your senses tell you what is real.....not a scope or measurement tool.  The NC1200 measures worse but sounds better.  Why is that?  There are many, many reasons why things sound different and most of the time we cannot measure what we hear.  A better fuse will not make the amp measure better, nor better wire, nor eliminating the jacks, nor damping nor adding an Audiomagic Pulse Gen ZX....on and on, but the ear ears the improvement.   I am totally for great engineering....and the NC400/1200 are that and more.  However, great tweaking is just as important......this has been my finding from experiments and listening tests starting in the mid 70s.

[mikeeastman]

Ric were can I get either plastic or wood speaker wire clamps.

[Ric Schultz]

US Plastics has very cheap one quarter inch x 20 nylon threaded rod, washers and wing nuts.   You can cut the threaded rod to the length you want and epoxy it into your custom speakers.  Then use a nylon nut for standoff then a nylon washer, then your speaker wire clamped to the wire coming out of your speaker then a Wing nut holding it all together.  I will have pics on my website soon.  Wooden ones you will have to have someone make you some or very carefully use metal dies and taps using hardwoods such as oak or cherry.  You can buy oak knobs that you can tap.  Use mineral oil when cutting and go slow.   

[dan92075]

"The only thing real is what you hear.  Your senses tell you what is real.....not a scope or measurement tool.  The NC1200 measures worse but sounds better"

Ric,  that does not mean that measurements cannot capture what you hear - it just means that the correct things are not getting measured. . .

I am not surprised the NC1200 sounds better than the NC400 - and I don't believe it sounds better by accident!   
Clearly the engineer designed something different in the NC1200 to optimize some kind of response - and that in turn should be measurable.
I am sure the engineer knows exactly what to measure  -  perhaps its phase response, group delay, whatever - but I am sure there is something measurable he is designing to.

So far the only measurements I have seen are distortion with static sinusoids  (THD, etc)
So not surprised from these limited tests that no measurable difference is seen between amps - both exhibit distortion from static sinusoids that is in the noise floor
I would really be interested if someone had measurements of phase response and/or group delay. . .

[Rclark]

Bruno himself said he doesn't prefer one over the other.

I think we are in a transitional phase where we can now have utterly transparent amps but people are still expecting a "sound", so someone can be there to deliver it.