Ncore Improvements

serengetiplains · « **Reply #160 on:** 11 Jul 2012, 12:00 am »

I measured one Hovland capacitor in the sheet above. It looks to have a good DA rating. Teflons are expensive, but I find their use to give good value sonically---rather more than expensive cabling. If you look at my DA test results above, you can see on line six a Customs Electronics 1uF tin/teflon cap. Its DA recovery voltage measured ave. 0.170V thereabouts, which is very low for a 1uF cap. The Solens, for their part, measure DF quite closely to the CustElec cap, suggesting a similar DA. This is, I think, due to their use of a 1000VDC dielectric. Generally speaking, for two capacitors of the same design having different DCV ratings, the higher DC-rated cap will give a lower DA figure. And the Solens being metallized, they're physically smaller than a tin foil variety. The trade-off, here, is between lower inductance and higher ESR (and whatever else differentiates tin-foil from metallized caps).

On the second page of that chart of results, take a peek at line 5, showing a 10uF 100V Mylar. Its DA recovery voltage? A whopping 31V! That's 180X that of the CustElec teflon.

I think the caps in the output filter on the Ncore are Mylar.

*Scotty* · « **Reply #161 on:** 11 Jul 2012, 01:08 am »

I have a found another take on DA. It appears that in some cases what is measured as DA may be another phenomena that is related to capacitor construction.
Here are links to the article describing the phenomena.
http://www.keith-snook.info/capacitor-soakage.html
http://www.keith-snook.info/more-capacitor-soakage.html
Scotty

serengetiplains · « **Reply #162 on:** 11 Jul 2012, 01:50 am »

Those are excellent links, Scotty. I skimmed one of them now and will read them more carefully later. It looks like the author has identified a mechanism that correlates in important ways with what is observed in capacitor recovery voltage. Notice the last document I posted in Reply 155 above. In that test, I subjected a Jensen 3.3uF PIO capacitor to successively longer charges to measure the resulting recovery voltage. The recovery voltage approximately stabilized to a peak, with subsequent +/– fluctuations, after about an hour's charge.

This increase is consistent with the author's thesis, as are phenomena of capacitors singing, of noise generated by tapping a signal-carrying capacitor with a pencil, etc.

One source of expansion/contraction is likely trapped air in the windings. An oil capacitor would have little or no such air, firming the capacitor considerably.

I suspect there's more happening than an expansion/contraction of the dielectric. Teflon is quite a soft dielectric---squishy---so it would seem most prone to dielectric compression. Yet teflons measure consistently better on recovery-voltage tests.

I also ran some tests testing the speed at which peak recovery voltage is attained in the various capacitors I tested. Here are the results:

Notice the first capacitor. That cap is a paper-in-fluorinert cap I had wound for me. True to form with other oil (wet) capacitors, recovery voltage is extremely high. But its recovery time is *fast.* Compare its results with results for other PIO caps on page 2.

Fluorinert is essentially liquid teflon. The variety I used for the PIO cap has a dielectric constant of 1.8, 10% lower than that of teflon. I suspect the liquid nature (reducing dielectric compression and possibly allowing some form of DA-voltage cancellation through physical movement of the molecules), combined with the low Dk (= low DF and low DA), allowed the fast voltage recovery. J'speculate.

Fwiw, these capacitors bettered teflons in listening tests I performed. They were really clear.

*Scotty* · « **Reply #163 on:** 11 Jul 2012, 03:32 am »

You might measure the DA of the new series of Nichicon solid polymer aluminum electrolytic capacitors.
While they have substantial leakage current which will render them unusable for some applications, they can make a pretty good coupling cap when a polarizing voltage is applied. I am using these for the output coupling cap in my preamp and the DC blocking capacitor in the feedback loop of my amp.
I think they are substantially more transparent than either the BlackGate FK series or the Non-polar NH series.
Here is a link to the part no. I used
http://www.digikey.com/product-detail/en/RR71C331MDN1/493-3718-ND/2207254
I think I noticed the presence of surface mount capacitors, if they are not already organic polymer tantalums this might be good upgrade. Organic polymer tantalums can have very low ESR as well as sounding almost as good as the solid polymer electrolytics, . They are spendy though running between $2 and $10 apiece with some over $10. Here is a link to the Mouse http://www.mouser.com/Passive-Components/Capacitors/Tantalum-Capacitors/_/N-75hqv?No=100&P=1z0ylhg
Scotty

serengetiplains · « **Reply #164 on:** 11 Jul 2012, 04:08 am »

I'll get some of those and will check them, Scotty.

serengetiplains · « **Reply #165 on:** 11 Jul 2012, 04:10 am »

Here are some pictures of the interior of an Ayre VX-R, which sells for something like $15K. I think they show what Charles Hansen thinks of bypassing electrolytics. I think the smaller yellow caps are teflons. The white may be teflons also, I can't remember.

serengetiplains · « **Reply #166 on:** 11 Jul 2012, 04:17 am »

And here is the MX-R mono version.

serengetiplains · « **Reply #167 on:** 11 Jul 2012, 04:26 am »

And here is the conrad-johnson Mini-ART and GAT interiors, respectively. I think the Mini-ART uses polypropylene and teflon caps in its power supply. The GAT uses teflon exclusively. Earlier models of the ART used styrenes, I believe. No or few electrolytics in the B+ supplies (I see one in the GAT photo).

serengetiplains · « **Reply #168 on:** 11 Jul 2012, 04:33 am »

Here's the Purity Ultra GT. Polypropylenes.

serengetiplains · « **Reply #169 on:** 11 Jul 2012, 04:35 am »

The Lyra Connoisseur. Polypropylenes, I believe. Lots of inductance on those power supply wires. Any guesses why the design as such?

serengetiplains · « **Reply #170 on:** 11 Jul 2012, 04:50 am »

Regarding electrolytics, because they're polar (not in the Mylar sense), I suspect voltage pass-through and recovery voltage effects differ depending whether the voltage is traveling from + to – or from – to + ... in some form of asymmetrical filtering. If true, it would be bad news for electrolytic-heavy differential +/– supplies as found in the Ncore. Those supplies by definition could not contain mirror or approximate mirror versions of noise on the respective + and – rails, diminishing differential noise reduction to the extent of the noise mismatch. This is one reason I think bridge mode will sound better (it does to me on tentative first listening).

*Scotty* · « **Reply #171 on:** 11 Jul 2012, 05:15 am »

The Purity Ultra GT is a tube unit with a claimed band width of 10Hz-35kHz -1dB. It doesn't appear to require a power supply that has a low dynamic impedance at RF frequencies.
The Lyra Connoisseur is a transistor based design that is out of production. I could find no information online about the circuit bandwidth. I like size of the power transformers. They must have felt that it sounded better with the polypropylene capacitor bank. I am a little more conservative in as much as my preamp and my phono preamp only have one 225 watt toroid a piece.
Thanks for being willing to satisfy my somewhat irrelevant curiosity about the DA on solid polymer electrolytics.
Scotty

serengetiplains · « **Reply #172 on:** 11 Jul 2012, 05:32 am »

You're welcome sir.

I'm fairly sure these manufacturers are targeting primarily audio frequencies by their use of psu film capacitors. Fwiw, the c-j GAT is rated to 100KHz, the Ayre models to 250KHz.

I faintly recall reading Jonathan Carr regarding his opinion on electrolytics (doesn't like them). When I was fooling with fluorinert, Carr contacted me to obtain samples of capacitors I was designing for my personal use. So did Charles Hansen. Parts quality is evidently important to them.

In the Ncore, RFs are shunted to ground on the output. Audio frequency disturbances on the power rails pass nicely through into the speakers.

*Scotty* · « **Reply #173 on:** 11 Jul 2012, 05:43 am »

As far as the Ayre VX-R and MX-R are concerned I can't figure out what all of those capacitors do in the circuit. Judging by the positive reviews however, something must have been done right.
My DM 220 amp's circuit boards don't have nearly as many caps, it's an interesting contrast in design philosophies.

My gallery has a few more shots of the amp.
Scotty

serengetiplains · « **Reply #174 on:** 11 Jul 2012, 06:05 am »

That's excellent. The fewer the capacitors the better.

I'm pretty sure (I think I recall reading) that the film caps in the Ayre supplies are largely electrolytic bypasses.

I'm not intending to suggest that using better capacitors solves the world's audio problems. I do think its an area of easy improvement. I mean, before Bateman actually measured capacitor distortion, who would have thought this about those tiny smd X7Rs:

I hope Bruno's using COGs:

They're almost as good as film/foil polypropylenes:

Which are nearly as good as polystyrenes (Bateman's measures), which are almost as good as teflons, etc.

*Scotty* · « **Reply #175 on:** 11 Jul 2012, 07:03 am »

It would have been neat if he had available to him the polymer tantalum SMDs to test.
In the photo of the amp you can see polystyrene bypass caps next to Panasonic FM caps which provide local storage for B+ and B- rails.
The bypassed BlackGate in the center of the board prevents the amp from having gain at DC and has been replaced by a Nichicon solid polymer AL electrolytic cap which does not benefit from a bypass.
Scotty

serengetiplains · « **Reply #176 on:** 12 Jul 2012, 05:47 am »

Scotty, were polymer tantalums available to Bateman when he did his tests?

*Scotty* · « **Reply #177 on:** 12 Jul 2012, 07:03 am »

Those articles were published in Wireless World in 2002. I don't really know when polymer tantalum capacitors became available. I would have thought, given the thoroughness of the the articles, that he might have tested them if they were available. However he was concerned with measuring the amount of distortion contributed by capacitors rather than conducting an overview of every type of capacitor available in the marketplace.
Both polymer tantalum caps and solid polymer electrolytic capacitors were not tested by Bateman.
In as much as these articles were written a decade ago neither type of capacitor may have been in production, but I couldn't say for sure either way.
Scotty
Here is a link to the Cyril Bateman articles in downloadable pdf form at the Pro Audio Design Forum
http://www.proaudiodesignforum.com/forum/php/viewtopic.php?f=6&t=153&start=2

serengetiplains · « **Reply #178 on:** 12 Jul 2012, 06:45 pm »

From a quick google search, the capacitors look new. Here's an article (pdf download):

http://www.google.ca/url?sa=t&rct=j&q=polymer%20tantalum&source=web&cd=9&ved=0CIABEBYwCA&url=http%3A%2F%2Fd0server1.fnal.gov%2Fusers%2Fbagby%2Fwww%2FL1_Cal%2FORC_Docs%2FFinal_Orc%2FADF_CAPS%2FKEMET_F3102PolTaPerChar.pdf&ei=Ghr_T8HaBJL9rAGE1KyMCQ&usg=AFQjCNHp1DhQolTIRURSbdLYW8w2Xgjhew&cad=rja

They look to have a very high DF ... <10% according to Mouser. That can't be right. Another data sheet puts their DF at a more reasonable 0.06 to 0.10% thereabouts.

*Scotty* · « **Reply #179 on:** 12 Jul 2012, 07:10 pm »

From the pdf doc "The inherent dielectric absorption of the solid tantalum capacitor .... typically equates to 1-2% of the voltage applied."
High but not 10%, what also has to be taken into consideration is the performance of the possible alternatives to a solid tantalum surface mount cap and how they might sound at a given position in the circuit. It makes sense to use the most appropriate part for the application in the circuit.
A ceramic might be a better choice depending on the what the cap has to do.
Scotty