Legato 3, Common Mode DC and You. How do you choose to deal with it? - Page 9 - diyAudio
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Old 16th September 2013, 04:29 PM   #81
goober5 is offline goober5  Canada
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I've run my Legato directly to a Aleph J. Works fine but there is a slight hum without the ground connected. The noise disappeared when I connected the ground to the amp through a cap. Sounds pretty good.
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Old 16th September 2013, 04:48 PM   #82
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Default Legato-Ncore

It turns out one of my Ncore modules had a problem. It is now back in NL getting repaired/replaced.
I suspect that when I have two properly operating modules I will be bale to run the Legato 3 without coupling caps directly into the Ncores, with no ground connection.
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Old 20th October 2013, 02:30 PM   #83
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Default Update, Legato 3-Ncore stereo amp

OK. I got a new Ncore module, and tried it. Frustrating, as I still have significant hum trying to run from the L3 direct to Ncore.
I would give up and cap couple, except that some appear to have success with this combo. So I am going to ask again for ideas. Here are my details:

Legato 3: balanced outputs only. +/- connected to pins 2 and 3 of XLR connector, G no connect.
Ncore stereo amp: +/- connected to pins 2 and 3 of XLR, pin 1 connected to chassis, G wire from Ncore modules connected to chassis.

+/- output from L3 DC offset nulled to <5 mV

Connecting G from L3 to pin 1 makes noise worse.

Another option is to transformer couple the input of the Ncore amp, taking the center tap for G to the Ncore modules and only connecting pins 2 and 3 to the input side of the transformer. I think this will work, but comes with the expense of two good coupling transformers.
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Old 23rd October 2013, 10:09 PM   #84
miero is offline miero  Czech Republic
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No hum here, but I'm using the coupling caps at the B3 caps.

I've not tried it, but what about connecting GND via cap, and keeping hot/cold conected directly?
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Old 7th January 2016, 03:54 PM   #85
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I wonder, Barrows, if you would mind giving an update on the topic of this thread, as I am now belatedly walking the same path. In my case I'm running older TPA Overture amps set up balanced with the TXD module. I'm finding that with the voltage offset the amp output is seriously diminished. Miero's suggestion above worked, BTW. ...and very preliminarily I think it might be better than caps on plus and minus. But I do buy into Russ's assertion that the best cap is no cap...
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Old 7th January 2016, 04:33 PM   #86
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Today I would amend my statement a bit. I actually have been using coupling caps with legato's balanced outputs lately because when I did some checking I got better performance out of the power amp (Sympatico) - lower THD. Probably because it was having to do less fighting against the common mode DC - more likely because I was running too close to the edges of the common mode input range. Lesson learned.

I just use the best caps I have on hand. Generally around 20uf
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Last edited by Russ White; 7th January 2016 at 04:35 PM.
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Old 8th January 2016, 12:56 AM   #87
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Thanks for the update, Russ. If amp performance is suffering, then I can live with caps. I had Auricaps on the now retired Legato 2, and the 4 of them can now cover grounds on two of three new Legato 3.1s. But the midrange is critical and I also suffer from "audiophilia nervosa". Are Clarity MRs still recommended as the most neutral of the 'likely suspect' film caps?

Many thanks in advance! Frank
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Old 8th January 2016, 04:31 PM   #88
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I decided that the only way to really know about Clarity MRs was to order a pair and test. I also will re-plumb the midrange amp with new Sympatico components. The nagging "audiophilia nervosa" symptoms are now in remission!
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Old 8th January 2016, 08:44 PM   #89
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Default yeah...

Quote:
Originally Posted by francolargo View Post
I decided that the only way to really know about Clarity MRs was to order a pair and test. I also will re-plumb the midrange amp with new Sympatico components. The nagging "audiophilia nervosa" symptoms are now in remission!
I have settled on using the caps all the time with the L-III. There are many "good" ones, but they all sound a little different, which is a bit maddening. Of course, some will opt to spend insane amounts of money on things like Duelund, I cannot afford to go that route...
I did compare (but not a straight, quick A/B) the Clarity MR to no cap at all, and found it to be hard to distinguish the difference, hence I still recommend them. If your amp has a high input impedance like 100K, then you can get away with even 1-2 uF and I noted no drop in bass impact, weight, or depth vs no cap.
MRs are not cheap, but certainly affordable vs things like Duelund or even Jupiter copper foil caps...
I have another DAC output stage coupled with 3 uF MusiCap from Alex Crispi, these are perhaps even more "neutral" than the MRs, but I might be imagining the difference. The MusiCaps are true film/foil rather than metalized.
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Old 8th January 2016, 08:47 PM   #90
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Russ, don't you mean 2.0uf?

I recently removed the couplers from the balanced outputs on my Legato 3. I lifted balanced ground instead. Pre amp is ARC Ref 3, amp is Krell KSA-250 connected via balanced. It still works but lifting ground can cause a nasty static spike when switching sources so best to mute or volume down.

V Cap has a coupling cap calculator here...

http://www.v-cap.com/coupling-capacitor-calculator.php
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Last edited by SCompRacer; 8th January 2016 at 08:49 PM.
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