[Dave H]

So on target SRB.  Dave

[Dave H]

Tom is participating in DIYaudio.com.  A lot of the guys really know their stuff over there.
Dave

[dewardh]

What the hell...so you mean I had two opposing phase in my biamp set up while auditioning recently?

It's possible . . . in fact Mr. Murphy says it's probable.  In mixed amp situations one must *always* test for proper polarity (and I've seen a "house system" that had the polarity switch set wrong on a commercial active crossover, too).  Polarity is just another of those things one must always check for when comparing amps (along with input impedance, gain, load effects etc.).  It's easy enough to see if you do a sweep or look at a noise spectrum . . .

[dewardh]

why is this information not revealed on the spec sheet on the website?

I’m not sure if it’s stated explicitly even in the IR Reference Design documentation . . . if it is I missed it.  It is shown in a block diagram (Fig 24, page 20) . . . look at the input and output “signal graphic”:

http://www.irf.com/technical-info/refdesigns/iraudamp7d.pdf

It’s one of those “too obvious to even mention” sorts of things (which are not necessarily obvious to everyone . . .).

[shadowlight]

I’m not sure if it’s stated explicitly even in the IR Reference Design documentation . . . if it is I missed it.  It is shown in a block diagram (Fig 24, page 20) . . . look at the input and output “signal graphic”:

http://www.irf.com/technical-info/refdesigns/iraudamp7d.pdf

It’s one of those “too obvious to even mention” sorts of things (which are not necessarily obvious to everyone . . .).

Ok, anyone want to dumb down the information, so I can understand what you guys are talking about.

Also, it seems that the SuperD link is onlin: http://classdaudio.com/index.php/sds-254.html?SID=3ba9c442a8c39d65ddfdb888b5f73d1b

[srb]

Also, it seems that the SuperD link is online

And amplifier model numbers for all!  Woot!
 
Steve

[dewardh]

Ok, anyone want to dumb down the information

With a non-inverting amplifier (most common) a positive-going signal at the input produces a positive-going signal at the output.  With an inverting amplifier a positive-going signal at the input produces a negative-going signal at the output.  Although people do argue about it nevertheless it is generally agreed that overall this "polarity" difference doesn't matter, since in general we cannot hear absolute polarity.

However . . . and it's a *big* "however" . . .

if polarity is switched on only one channel of a bi-amped system it typically produces a null at the crossover frequency rather than the woofer and tweeter (or woofer and sub-woofer) summing properly, and that null *will* have audible effect.  Since the classDaudio amps are inverting, and most commercial amps are non-inverting, you cannot just "swap amps" when making comparisons . . . it may be also necessary to switch the leads from the driver to maintain correct overall polarity.  If that is not done you will not be hearing (just) differences between the amplifiers, but also the difference (in frequency response) between a correctly and incorrectly wired crossover.

[dewardh]

And amplifier model numbers for all!  Woot!

Still hasn't corrected the power supply requirement for the . . . "CDA-224" . . .

[shadowlight]

@dewardh,

Thanks for the explanation.  If you are not bi-amping you do not have to worry about it correct?

[srb]

Still hasn't corrected the power supply requirement for the . . . "CDA-224" . . .

Well, the inclusion of model numbers indicate he was at least monitoring this thread, so hopefully the corrections will follow too.
 
And I still hope to see the Product Comparison matrix, so we can all quickly compare specifications and features between all of the modules at a glance.
 
Steve

[Bemopti123]

That new board design and turn around time was impressive but am I the only one getting the feeling that in terms of value, that board might be straying away from the notion of SOTA and Affordable?  Perhaps more than just terms of power, it will bring finesse and audiophile characteristics to something as under appreciated and under priced at the $175 board?

[dewardh]

If you are not bi-amping you do not have to worry about it correct?

Correct . . . though remember that if you have a subwoofer you *are* bi-amping, and switching polarity of the L&R channel amps will change subwoofer integration.  It's something to watch for when swapping amps for comparison testing.  "Convention" is to set up systems so a positive-going signal moves the mid-woofer cone forward . . . once that's done it's only an "issue" if equipment is added (or changed) that inverts polarity.

[pjchappy]

I wonder what changes were made to make the soundstage, etc. bigger? 


Paul

[dewardh]

I wonder what changes were made to make the soundstage, etc. bigger?

The changes should correct problems some people were having with impedance and gain matching to their source (which can effect overall sound).  The "sound" of the amplifier itself is not changed (so far there have been no reported changes inside the amplifier's feedback loop, or in the output filter).  It's all about the benefits, where needed, of an input buffer . . .

[steve k]

The changes should correct problems some people were having with impedance and gain matching to their source (which can effect overall sound).  The "sound" of the amplifier itself is not changed (so far there have been no reported changes inside the amplifier's feedback loop, or in the output filter).  It's all about the benefits, where needed, of an input buffer . . .

Excuse me? Have you heard it? The "sound" may not be different but the imaging sure is and much to the better.
steve

[dewardh]

Excuse me? Have you heard it? The "sound" may not be different but the imaging sure is and much to the better.

Changing amplifier input impedance (or changing polarity) may well have changed "imaging" in your system.  It's hard to tell without knowing the details of your system, the comparison, and how you switched back and forth between the amps to do it.

All that seems to have changed *in the amplifier* is the addition of an input buffer . . . different systems will have different need for and different response to that, and different people will draw different conclusions as to what that means.  My system doesn't need an additional buffer, since my crossover's output buffers can drive the "original" board just fine, and I correct for polarity at the drivers.  Adding a buffer stage would accomplish nothing for me.  I'm glad it helped with your system . . . (did you set the "new" version for normal or inverted polarity?).

[atroder]

There has been considerable discussion on the mating of the Pass B1 board to the input of the original class D amps as a (variable gain?) buffer to better impedance match input to it. Several have commented on the benefits of doing this. So given that the new amps have an input buffer built in, would it be superfluous to front end the input of the new class Ds with the Pass B1?

[toobwacky]

I just bought one of these kits (60 wpc / 8 ohms) and it's not wired up yet, but all this talk regarding an impedance mis-match is a real buzz killer.   

I'm going to be using the pre-outs of my Denon AVR and, unfortunately, Denon doesn't specify the pre-amp's output impedance.  If there is an impedance mis-match how will I know?  Will the pre distort trying to drive the low load?  Will the frequency extremes be rolled off?  Could this damage my pre?

Give me the straight dope on this.  I suppose, if I have to, I could buy the new board or a tube buffer, but I'd rather avoid spending the extra dough.

Thanks.

[Nick77]

I just bought one of these kits (60 wpc / 8 ohms) and it's not wired up yet, but all this talk regarding an impedance mis-match is a real buzz killer.   

I'm going to be using the pre-outs of my Denon AVR and, unfortunately, Denon doesn't specify the pre-amp's output impedance.  If there is an impedance mis-match how will I know?  Will the pre distort trying to drive the low load?  Will the frequency extremes be rolled off?  Could this damage my pre?

Give me the straight dope on this.  I suppose, if I have to, I could buy the new board or a tube buffer, but I'd rather avoid spending the extra dough.

Thanks.

I use my Harmon Kardon AVR with no problems. I suspect the Denon will be just fine. 

And just for the record the HK amp section wasnt even in the same leauge as the ClassD.

[toobwacky]

I use my Harmon Kardon AVR with no problems. I suspect the Denon will be just fine. 

And just for the record the HK amp section wasnt even in the same leauge as the ClassD.

Good to know.  Thanks.