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Old 2nd July 2013, 10:46 AM   #21
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Quote:
Originally Posted by AndrewT View Post
...I can't recall an Email.
What is your Email name (not the full address) and rough date?
Just sent a new one titled:

Email from Jeff from diyaudio
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Old 2nd July 2013, 11:50 AM   #22
AndrewT is offline AndrewT  Scotland
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Email arrived.
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Old 17th July 2013, 09:59 PM   #23
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Hi,
Is there any progress?

I think it's important to run separate wire for signal ground & 12V ground directly to the ground star point.

Hope i am correct.

Last edited by futureboy; 17th July 2013 at 10:19 PM.
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Old 19th July 2013, 01:38 AM   #24
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Latest layout is at post #15.

What I am trying to accomplish here is to have a very tiny version of My Ref Rev C using through hole parts. Current size is only 2 x 2.65 inches!

I didn't provide onboard power supply capacitors because I am thinking of powering these mini's with an SMPS

I already etched some boards here, hopefully I can finish it this weekend.
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Old 22nd July 2013, 08:12 AM   #25
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I hate it when I started soldering and found out that I have incomplete components.
Still not yet finished

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Old 23rd July 2013, 07:15 PM   #26
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I don't understand why AndrewT suggest to change rail-rail decoupling to rail-ground decoupling?

Original design by Mauro only use rail-rail decoupling.
And if I remember correctly, some members report that rail-ground decoupling reduce this amp's performance.

Sorry for my bad English.

Last edited by futureboy; 23rd July 2013 at 07:32 PM.
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Old 23rd July 2013, 10:28 PM   #27
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Originally Posted by futureboy View Post
And if I remember correctly, some members report that rail-ground decoupling reduce this amp's performance.
This sounds a bit impossible/crazy to me.
Small caps (decoupling) are nearly the same as the bigger caps, like the 220uF one. If those doesn't reduce the power, then smaller ones wont either. Those just have a plus effect of reducing HF noises.
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Old 24th July 2013, 09:58 AM   #28
AndrewT is offline AndrewT  Scotland
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One has to look at where the current flows.
If the output current flows from the output pin to the load and from the load to the Main Audio Ground and from the Main Audio Ground to the Power Ground and finally from the Power Ground to the Power Rail, then the decoupling MUST be from Power Rail to Power Ground, by the shortest route possible AT the chip PINs.

If the amplifier were a true balanced topology where the load is between two outputs and the current flows from rail to rail then decoupling would be rail to rail.

If some builder found worse performance from Their version of rail to ground decoupling then they did it wrong !!!!
There are very many builders that get the decoupling wrong. The majority of our Members do not understand why decoupling is needed, nor how it works and thus can never locate it correctly.
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Old 24th July 2013, 10:51 AM   #29
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Quote:
Originally Posted by mrWagner View Post
This sounds a bit impossible/crazy to me.
Small caps (decoupling) are nearly the same as the bigger caps, like the 220uF one. If those doesn't reduce the power, then smaller ones wont either. Those just have a plus effect of reducing HF noises.
It has to do with the feed-forward topology and unique compensation of the MyRef. There's also HF AC bypass path through rail-to-rail bypass cap C4, through both 220uF caps in parallel, to ground, through the load, R3 and back to the LM3886 output. This only works when the ESR of C4 is much lower the the shunted ESR of C1 || C2, thus causing the sonics to be dominated by the character of the small cap C4. When there's a rail-to-ground bypass shunting the 220uF caps, the sonics will be contributed by a combination of C4 + the shunted C of both those caps. Those caps will then have to be atleast as good as C4, or audible sonics will degrade perceptibly - and you can easily verify it by adding and removing the caps bypassing the 220uF electrolytics.

*Never* attempt to bypass +Vs and -Vs of the LM3886 to the lifted small-signal ground - you'll only end up contaminating the small-signal ground with HF hash from the LM3886, which the topology has gone to great lengths to avoid.

OTOH, a larger and/or higher quality rail-to-rail cap C4 improves sonics - I've gone as high as 0.47uF metalized polypropylene, and others have used even larger ones. 0.1 or 0.22 MKP10 are good compromises between size and sonics. MKP2 or PHE426 are also fine.
It's also worth experimenting with a film/foil polyester or polycarbonate at C4 - I'm going to experiment with the Russian K73-16 at that location eventually.
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Old 24th July 2013, 11:02 AM   #30
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by linuxguru View Post
It has to do with the feed-forward topology and unique compensation of the MyRef. There's also HF AC bypass path through rail-to-rail bypass cap C4, through both 220uF caps in parallel, to ground, through the load, R3 and back to the LM3886 output. This only works when the ESR of C4 is much lower the the shunted ESR of C1 || C2, thus causing the sonics to be dominated by the character of the small cap C4. When there's a rail-to-ground bypass shunting the 220uF caps, the sonics will be contributed by a combination of C4 + the shunted C of both those caps. Those caps will then have to be atleast as good as C4, or audible sonics will degrade perceptibly - and you can easily verify it by adding and removing the caps bypassing the 220uF electrolytics.

*Never* attempt to bypass +Vs and -Vs of the LM3886 to the lifted small-signal ground - you'll only end up contaminating the small-signal ground with HF hash from the LM3886, which the topology has gone to great lengths to avoid.

OTOH, a larger and/or higher quality rail-to-rail cap C4 improves sonics - I've gone as high as 0.47uF metalized polypropylene, and others have used even larger ones. 0.1 or 0.22 MKP10 are good compromises between size and sonics. MKP2 or PHE426 are also fine.
It's also worth experimenting with a film/foil polyester or polycarbonate at C4 - I'm going to experiment with the Russian K73-16 at that location eventually.
This explanation breaks the rules of where to locate HF and MF decoupling.

Maybe the separate HF and MF decoupling of BOTH chips is being compromised by omitting at least one of the eight required rail to ground decoupling capacitors.
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