MiniRef Schematic and PCB layout - Page 8 - diyAudio
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Old 13th February 2013, 05:46 PM   #71
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Quote:
Originally Posted by AndrewT View Post
...
That brings in (at least for me) the question of "how did Mauro implement the local decoupling"?
He didn't do it the traditional way, i.e. rail-to-ground. Instead, he used rail-to-rail both at the opamp and the chipamp.

The key trick to eliminate HF instability is the RC network between the inputs of the chipamp - it attenuates HF without having much effect at AF.

It's one of those things that one can't cook up with just a macromodel simulation - it has little or no effect on stability in the sim. To be fair, something similar is mentioned somewhere in a NatSemi application note - IIRC, a 220 pF bypass across the inputs of the LM3886. However, I have no idea how Mauro came up with the 1nF 3k3 bypass in the MyRef, which also appears to work fine in the MiniRef.
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Old 16th July 2013, 05:16 AM   #72
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My Linuxguru, is there any new schematic which you can share?
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Old 16th July 2013, 08:37 AM   #73
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Quote:
Originally Posted by clarkynoel View Post
My Linuxguru, is there any new schematic which you can share?
I'm testing the current prototype for stability and sonics, and will give an update shortly - within a couple of weeks, hopefully. This has already taken far longer than I thought, due to digressions into discrete opamps and other stuff.
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Old 14th October 2013, 12:03 PM   #74
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Update: Presapian on this forum prototyped the MiniRef LM1875 and has succeeded in performing several important upgrades/changes/tweaks:

1) Salas shunt regulator(s) for the opamp +/- 12V rails.
2) Changes to the inner voltage-feedback loop of the Jung to allow the use of an AD797BRZ as the controlling (GNFB) opamp.

The latter is a very exciting development, since it presents the possibility of a chipamp board with audible sonics that exceed almost any discrete power amp. He's offering his bare boards here and elsewhere, so I'll leave it to him to provide further information as necessary. However, these are tantalizing extracts from personal communications from him:

"797 doesn't display any hf artifacts in your circuit (as far as i can hear) by it's bare self so i'm considering this match made in heaven..."

"all in all this must be the greatest breakthrough in chipamp development since the original myref. "

I'm awaiting some bare MiniRef 1875 boards and will try to replicate his results ASAP, but with a discrete opamp like the LF03d instead of 2x AD797B - let's see how it goes.
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Old 28th October 2013, 08:53 AM   #75
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Quote:
Originally Posted by linuxguru View Post
I'm awaiting some bare MiniRef 1875 boards and will try to replicate his results ASAP, but with a discrete opamp like the LF03d instead of 2x AD797B - let's see how it goes.
I've received some bare MiniRef boards from Eric and populated it over the weekend - the first tests with a monolithic opamp (NE5532) this morning went fine and the audible sonics are excellent, and the output DC offsets are a nominal 8.9/10 mV. I'll test it a bit further before hooking up the Salas shunt regulators and swapping out opamps for the discretes. Here's a pic of the prototype build, with moderately premium components across the board in the audio signal path, but nothing outrageously expensive.
Attached Images
File Type: jpg miniref1875_10x7.jpg (258.7 KB, 604 views)

Last edited by linuxguru; 28th October 2013 at 09:00 AM. Reason: typo
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Old 8th November 2013, 02:08 AM   #76
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Hi Mr.Siva and Mr.Eric.

I see a nice board there.
Is your schematic and pcb design open for public?
I wonder if i could join for build this one

Last edited by clarkynoel; 8th November 2013 at 02:12 AM.
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Old 8th November 2013, 06:48 AM   #77
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Quote:
Originally Posted by clarkynoel View Post
Is your schematic and pcb design open for public?
I wonder if i could join for build this one
Sure, the schematic and the layout of the LM1875-based MiniRef v1.02 have been posted earlier in this thread. Eric's board has some additional improvements, including a separate shunt regulator for the opamp - please contact him directly for his boards. My (successor) boards use LM3886 instead, and work OK but are still being refined for stability.

If you want something that works well, with moderate power (~20W) into 8 ohm loads, go with Eric's LM1875 boards and keep the rails comfortably low (say +/- 24V or lower).
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Old 8th November 2013, 08:08 PM   #78
prezden is offline prezden  Canada
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Could someone kindly post some contact info for Eric. I read through the tread but could not find anything.
I was also wondering if it was possible for someone to open a build thread to walk us not so skilled to build one. It looks like a very exciting project.
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Old 9th November 2013, 01:39 AM   #79
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Hi Prezden, I guess Mr Erick's ID is PreSapian diyAudio - View Profile: PreSapian

FS: nos copper polystyrene caps [150,220,1000pf]
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Old 12th April 2014, 09:04 AM   #80
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Update: I have tested and validated the LF06 (FET990) Class-AB and the LF05 folded-Kaneda Class-A discrete opamps as stable outer-loop opamps in the MiniRef 3886 (in almost all cases, anything that works in the MiniRef 3886 will also work in the MiniRef 1875 - though the converse isn't necessarily true).

At the moment, the best-sounding discrete that I've auditioned in the MiniRef is the FET990, while the best-sounding monolithic is hard to state with certainty - LME49720 and OPA2134 both seem to fit the bill; I'll give AD8022, LM6172 and LT1361 a try later, though they're all pretty fast and potentially unstable.
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