Legato 3, Common Mode DC and You. How do you choose to deal with it? - Page 4 - diyAudio
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Old 27th November 2012, 03:50 AM   #31
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Oh don't worry! I don't see this as better than Legato 3 - only different.

It is not in any way ready to replace Legato 3.1 in fact there is a lot to recommend the Legato 3.1 approach - for one it is much simpler and cheaper.

I see Legato 3.1 as some of my best work. I personally have it in my current reference system. It is not going anywhere either.

In any case - counterpoint III not even close to finished yet. I just wanted to give a little window into the workshop.
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Old 27th November 2012, 12:19 PM   #32
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Another note: If/when we release the new Counterpoint, it will be a pre-built module, and not cheap (manufacturing and testing costs).
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Old 27th November 2012, 12:57 PM   #33
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Yes that's a good point Brian!

it has some rather "not-cheap" (precision voltage divider - big thin film resistors - etc) parts.

In testing I found some mild - but undesirable thermal characteristics which I will resolve with sets of dual (and maybe quad - but not likely) transistors. That will also probably add a bit to the cost.
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Old 27th November 2012, 01:07 PM   #34
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Just to be clear I have no idea if this module will even ever be a product. It's just something I am working on for myself at the moment.

So don't get your hopes up too high, and don't hold our breath.

Still if you have some feedback on the design PM me.
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Last edited by Russ White; 27th November 2012 at 01:13 PM.
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Old 27th November 2012, 01:14 PM   #35
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Hi Brian, Russ,

We really do respect what you are doing here but is this not a thread about Legato 3, DC offset discussion

I don't see any value added to discuss the dc offset on the legato3 by your comments although I may be wrong. It appears more like marketing vaporware of a product to market which never appears.

just my personal 2 cents worth.

regards.

Last edited by necplusultra; 27th November 2012 at 01:20 PM.
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Old 27th November 2012, 01:17 PM   #36
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There is no "problem" there is just a fact.

I was just answering direct questions, and discussing my own DIY pursuits along these lines. I made it clear the module may never be a product. It is a project.
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Old 27th November 2012, 01:29 PM   #37
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One of the really critical design elements of the Legato 3.1 is it's simplicity. That is one of the reasons why it is so special. It is very much like the D1 in that regard (with the same need to AC couple in some cases) except that instead of a FET it uses a hybrid CFP based approach with paralleled devices.

Legato 3.1 adds some nice touches like nulling both balanced and SE offset and BAL/SE conversion and buffering. I would say it is one of our most popular modules, and for very good reason. We leave it up to the builder to choose the coupling path best suited to their system. For some DC coupling is optimal (any truly fully differential amp), for others AC coupling is ideal - via caps or via transformer. This is an age old design choice - and many superb audio stages have employed both forms of AC coupling.

Cheers!
Russ
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Old 27th November 2012, 02:17 PM   #38
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I have no problem with some discussion of the Counterpoint III here, especially as it is a discrete output stage (OK, mostly discrete) with a solution for all DC issues. If the Counterpoint III sees the light of day it will be something to give a try and listen to. I have no problem with it being more expensive, in fact, I hope that really good resistors are chosen despite price, because many SMD resistors can sound pretty bad, and replacing them is not all that fun, and I am guessing that it wouldl be a good idea to use 0.1% tolerance parts rather than try and match them...

I do hope to hear from folks using the Legato 3 with different amps, and different solutions for how they are dealing with the DC. I would especially like to hear from some people who are not connecting the G to pin 1 at all at the output of the DAC, and how this is working for them with a given amplifier.
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Old 27th November 2012, 02:36 PM   #39
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I agree it would be good to get some feedback from other Legato users on how they use the module with their amps.

In discussing that it would be good to note the topology of the target amp.

Is it SE? Fully differential? Two bridge tied amps per channel?

Really though the discussion around how to AC couple (caps vs trafo) will come down to personal preference. It is fine to hear about that as well.
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Old 27th November 2012, 08:57 PM   #40
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If you are going to use a transformer, why use a Legato at all?
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