McCormack DNA-750 pair is here and running

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jeffreybehr

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McCormack DNA-750 pair is here and running
« on: 28 Feb 2012, 09:52 pm »
Received them yesterday, opened them to be sure there were no loose parts, and fotografed them.  Got them running.  Their lite-gray faces match my Porsche Arctic Silver V'steen 5Bs very well, to the point that the champagne-faced Marantz MA-24 driving the CC looked quite out of place; I reinstalled the much-improved Marantz MA-500 and voila!  (But I MUST do something about those light-maple amppads!)





For those who don't know, the '750, like at least the DNA-500 and perhaps many predecessor McC amps, is fully differential/push-pull.  That means that there's a positive-polarity push-pull amp section 'pulling' and a negative-polarity push-pull amp section 'pushing'.  Note one speaker-power lead coming from one side of the board and going to one (let's call that positive) binding post (and then its twin, as the amp wears 2 pairs of posts) and also another speaker-power cable coming from the other side of the amp and to its call-it-negative bindingpost.

Altho I'm no quick-to-hear-differences GEA, the sounds are a little less harsh in the hi frequencies based on a couple discs I listened to carefully with only about 5 hours on the amps.

More later. :thumb:
« Last Edit: 3 Mar 2012, 08:14 am by jeffreybehr »

Freo-1

Re: McCormack DNA-750 pair--it's here and running
« Reply #1 on: 28 Feb 2012, 10:24 pm »
Nice score!

I was looking at those eariler.  They seem like they could easily power any speaker quite nicely.

Please let us know you impressions as they break in.

tdinut

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Re: McCormack DNA-750 pair--it's here and running
« Reply #2 on: 28 Feb 2012, 11:13 pm »
Congratulations! Let us know how the break in goes. Enjoy!

Joe

Jon L

Re: McCormack DNA-750 pair--it's here and running
« Reply #3 on: 28 Feb 2012, 11:38 pm »
Awesome!  Keep those babies powered up 24/7  :thumb:

Noseyears

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Re: McCormack DNA-750 pair--it's here and running
« Reply #4 on: 29 Feb 2012, 12:02 am »
Thats lots of power. Enjoy your setup!

timind

Re: McCormack DNA-750 pair--it's here and running
« Reply #5 on: 29 Feb 2012, 12:39 am »
So, I'm not the only one who opens new gear up for a look inside and take a few pics before hooking it up?
Beautiful amps, enjoy.

golfugh

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Re: McCormack DNA-750 pair--it's here and running
« Reply #6 on: 29 Feb 2012, 12:48 am »
Look forward to further comments!

Congrats
Mark

Big Red Machine

Re: McCormack DNA-750 pair--it's here and running
« Reply #7 on: 29 Feb 2012, 01:18 am »
Go baby!!

S Clark

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Re: McCormack DNA-750 pair--it's here and running
« Reply #8 on: 29 Feb 2012, 01:21 am »
I'm eager to hear your thoughts after a couple of weeks.  The DNA-750 was on my short list when I ran across a deal on a Moscode.  I may still end up there one day.

Scott

TONEPUB

Re: McCormack DNA-750 pair--it's here and running
« Reply #9 on: 29 Feb 2012, 01:39 am »
Those are very nice amps, you're going to love them with your Vandersteen 5's...



jeffreybehr

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Re: McCormack DNA-750 pair--it's here and running
« Reply #10 on: 29 Feb 2012, 04:34 am »
Couldn't resist.   :icon_twisted:


« Last Edit: 1 Mar 2012, 07:12 am by jeffreybehr »

jeffreybehr

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Re: McCormack DNA-750 pair--it's here and running
« Reply #11 on: 1 Mar 2012, 05:58 pm »
With about 50 hours on them Wednesday evening--they're cookin' 24 hours/day with fullband pinknoise--they continue to sound quite good.  Tonally, they're very...full-bodied, very whole sounding.  I continue to operate them and the speakers without the 1- and 1.5-Ohm resistors I had been driving the upper frequencies of the V'steens with, and the treble frequencies still sound quite there but not too much there.  Sorry for the lame descriptions. 

I'm really happy so far.  Don't know if I'll last a month without replacing the Nichicon-brand 'DNA' caps with BlackGates.    8)

The 4 smallish 'lytics close to the output transistors are, in my 2nd (?) version of the DNA-750, 470/100 Nichicons, each of which is bypassed with a 0.47uF 715-series OrangeDrop film cap.  (Rail Voltage is 61V.)  I'll be replacing them with 680/65 BlackGate-Ns, quite affordable here... http://www.partsconnexion.com/cgi-bin/sc/productsearch.cgi .  Since the bottom cover is removable, it ought to take no more than an hour to do that.   :)

TONEPUB

Re: McCormack DNA-750 pair--it's here and running
« Reply #12 on: 1 Mar 2012, 06:16 pm »
good luck ever getting those amps serviced at CJ in that case...

Personally, I'd leave well enough alone and enjoy the amps

:)

Wig

Re: McCormack DNA-750 pair--it's here and running
« Reply #13 on: 1 Mar 2012, 07:19 pm »
Looks good! Definitely replace the fuses with some Hi-Fi supremes

Wig :thumb:

jeffreybehr

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Re: McCormack DNA-750 pair--it's here and running
« Reply #14 on: 2 Mar 2012, 12:42 am »
good luck ever getting those amps serviced at CJ in that case...  Personally, I'd leave well enough alone and enjoy the amps
:)

I understand that attitude, I don't argue with anyone who chooses it, and I know that those folk enjoy their music systems as much as I do.  But that's not my attitude.  Parts costs affect the retail price of all manufactured goods, and I can afford to improve parts myself, but I couldn't afford to buy the amps if they cost maybe $3 or $4K/pr. more.  So I'll just improve some parts while NOT changing the circuitry.  Here's one little corner.

The new 'lytics--the 'DNA' caps--are Blackgate-Fs, 680uF, while the film-type bypass cap is a 1uF SoniCap Platinum (Teflon).  As improved, each 470 (times 8 per amp) will be a 680uF BlackGate, and each amp will have 4uF of Platinums instead of 3.76uF of OrangeDrops.
« Last Edit: 2 Mar 2012, 05:35 pm by jeffreybehr »

Rclark

Re: McCormack DNA-750 pair--it's here and running
« Reply #15 on: 2 Mar 2012, 01:20 am »
those look pretty cool! Why did you choose Orangedrop caps? Never heard of em.

jeffreybehr

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Re: McCormack DNA-750 pair--it's here and running
« Reply #16 on: 2 Mar 2012, 03:36 am »
those look pretty cool! Why did you choose Orangedrop caps? Never heard of em.

I didn't; c-j did.  I'm replacing many of them with SoniCap Platinums, 5-star-quality Teflon-film caps.

Orangedrops are (were?) made by Sprague for decades and are good-sounding caps, but they're sure not as good as lots of modern caps.

jeffreybehr

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Re: McCormack DNA-750 pair is here and running
« Reply #17 on: 4 Mar 2012, 07:26 pm »
Here's what a full side looks like with the BlackGate 'DNA' caps and SoniCap Platinum bypasses.

The rear and bottom panels rang a bit, and since I obsess about this stuff, I applied chunks of the thicker SoundCoat to the rear's inside and the bottom's outside.  The upper strip here is a 2nd layer.

Got almost a full sheet (which is 12"-by-13-1/2") on the bottom.


BTW, the 'smears' of white stuff on the sides of the Platinums are remnants of the double-sided plastic-foam 3M mounting tape I use on these things.  Sometimes it all comes off easily, and sometimes not.  I prefer not to scrape too much on the sides of caps, since the outer tape is quite thin.

The system sounded glorious last nite playing BIS's newish recording of Smetana's Ma Vlast (My Fatherland) performed by the Malaysian Phil. O. and Claus Peter Flor.  This is a 5-star performance and recording that sounds very natural and real on my MC system.  Here http://www.sa-cd.net/showtitle/6877 are some comments on this recording.
« Last Edit: 5 Mar 2012, 12:07 am by jeffreybehr »

jeffreybehr

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Re: McCormack DNA-750 pair is here and running
« Reply #18 on: 5 Mar 2012, 06:31 am »
My goodbuddy came over today and rebuilt the frontend powersupply.  The output caps were a pair of 470/100 Nichicons bypassed with a pair of 0.47 O'drops.  The new caps are 470/160 BlackGates, bypassed with four 0.47uF SoniCap Platinums (Teflons).  We also removed another pair of 0.47 O'drops to make room; those bypassed the feedback-loop shunt caps, huge 30uF c-j 'propylenes.  I'll replace those bypasses later.



Things are moving along.   :)

Rclark

Re: McCormack DNA-750 pair is here and running
« Reply #19 on: 5 Mar 2012, 07:01 am »
Looks like a lot of fun  :thumb: