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Old 25th September 2011, 04:19 PM   #31
soongsc is offline soongsc  Taiwan
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Studied the circuit a bit, it seems C13 has to be there mainly due to the floating signal ground which might be connected to the chassis ground of other equipment. The RevC layout allowed convenient means to at a bypass cap on the trace side. I wonder whether it's worth keeping this.
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Old 25th September 2011, 04:58 PM   #32
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But the concept of the snubber itself is certainly quite widely used and studied. Some people even use it on diodes.
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I somehow recall that snubbers are more load transients dependent.
Sorry Soongsc, but I've great respect of Mauro point of view so, at least in this phase, I prefer to focus on LM318 PS and PCB verification.

BTW snubbers can be easily implemented on the prototype PCBs or in the MyRefC, you can test them and then report back to the thread.

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Studied the circuit a bit, it seems C13 has to be there mainly due to the floating signal ground which might be connected to the chassis ground of other equipment.
Wow, great!

Thanks.

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The RevC layout allowed convenient means to at a bypass cap on the trace side. I wonder whether it's worth keeping this.
Can you elaborate?

I don't get it...
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Old 25th September 2011, 05:25 PM   #33
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Dario, I am going to use a switching power supply. So anything related with snubbering is a different story. However, I will try to snubber the LM318 power.

About bypassing C13, I misread the traces on the PCB that I have. But anyway I will bypass C13 because I had very good results in speaker crossovers. The results were close to an Mcap Silver Gold.
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Old 26th September 2011, 12:08 PM   #34
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Has anyone read the application note from Calex on "Understanding Power Impedance Supply for Optimum Decoupling"?
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Old 26th September 2011, 12:23 PM   #35
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But anyway I will bypass C13 because I had very good results in speaker crossovers.
Hi Soongsc,

I've tried bypass on C13, with mixed results but one thing was clear a single better quality capacitor was everytime more coherent than inferior caps with bypass.

Probably the different lead inductance of the caps produce some phase shifts...

Though bypasses helped a lot the lesser caps.

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Has anyone read the application note from Calex on "Understanding Power Impedance Supply for Optimum Decoupling"?
Thanks, a very interesting read but two remarks:

  • the output of the My_Ref is not inductive.
  • I don't have a function generator.
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Old 26th September 2011, 04:58 PM   #36
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Sure, it's very difficult to find a right bypass for just any capacitor, and bad capacitors really cannot be improved. Some times you just have to have a little bit of luck. Even with that, it still took me a while to find a combination that matched the sound quality of an Mcap Silver Gold, I just needed something smaller, cheaper, but same sound quality.

If you are wanting to improve PS design, optimum decoupling is a must, and those are snubbers. People have tried various PS designs with mix results depending on application, which is precisely due to non-optimum match.

BTW, any circuit is inductive to some degree, it just depend whether one thinks it's of sufficient significance or not.
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Old 26th September 2011, 06:18 PM   #37
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If you are wanting to improve PS design, optimum decoupling is a must, and those are snubbers. People have tried various PS designs with mix results depending on application, which is precisely due to non-optimum match.

BTW, any circuit is inductive to some degree, it just depend whether one thinks it's of sufficient significance or not.
Hi Soongsc,

I must repeat myself...probably you're right (and more experienced) but in this phase I don't consider snubbers a priority when we're still stuck with the original LM318 PS.

When we will have a working prototype we'll be in condition to investigate such optimizations and eventually include them in the final design, IMHO.
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Old 26th September 2011, 06:22 PM   #38
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Default Eagle files

At the end of this journey I'll post the Eagle files so whoever will be able to make the PCBs.

This don't exclude a possible group buy.

In the meanwhile whoever is willing to give a more 'inside' look at them to find bugs and or optimizations can PM me, I'll send you the files.
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Old 27th September 2011, 11:08 PM   #39
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Default Small PCB update

I've rotated R3 to shorten the feedback loop on the current pump.

Other minor updates to the 0V groundplane.
Attached Images
File Type: jpg My_Ref_FE - PCB.jpg (444.1 KB, 319 views)
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Old 27th September 2011, 11:35 PM   #40
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Dario,

Here's an idea: add one more pad to the right of C13, with a trace to the input path. Label it "DC signal" so that builders can make both AC and DC connections. The label about a jumper wire (and the jumper itself) is then not needed.

When will you be ready to have a prototype made?

Peace,
Tom E
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