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Old 5th July 2012, 01:14 AM   #41
gootee is offline gootee  United States
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Quote:
Originally Posted by linuxguru View Post
Here are the exported images of the schematic and layout - hope it uploads from my GPRS phone.
It looks like the ground-planed areas got left out, on the PCB layout.
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Old 5th July 2012, 12:27 PM   #42
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Originally Posted by undefinedza View Post
Hey linuxguru, do you have a recommended BOM?
You can safely go with the same parts as the corresponding ones on the Myref Rev C monoblock BoMs. The few parts that differ are the relay, chipamp, opamp and the compensation cap (styroflex or C0G ceramic).
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Old 5th July 2012, 12:34 PM   #43
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Originally Posted by gootee View Post
It looks like the ground-planed areas got left out, on the PCB layout.
It shows only the outline of the ground plane on the exported image. However, if you run the CAM processor on the uploaded Eagle .brd file (e.g. to generate a set of Gerbers), the ground planes will be correctly rendered on the Gerbers. This can be verified using a Gerber viewer like gerbv.
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Old 31st July 2012, 10:45 PM   #44
kmibb is offline kmibb  United States
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Someone set up this group buy. I can help fund if needed.
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Old 3rd September 2012, 04:18 PM   #45
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Originally Posted by linuxguru View Post
Here are the exported images of the schematic and layout - hope it uploads from my GPRS phone.
Interconnection circuit containing transistors Q1, Q2 and Q3 with the rest of the circuit is defective, or otherwise, is not right. Something is wrong here, namely: on each LM1875 output potential is zero (in theory, neglecting offset), then you should not connect the electrical potential across the audio overlaps directly with certain points, dc voltages from the circuit with Q1 ... Q3.
That would be the biggest mistake.

And another mistake - should be tested to see if it's so - is that the output voltage alternative to LM's, its RMS value, if it exceeds a certain value could go in conduction transistors Q1 .. Q3.
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Old 3rd September 2012, 04:49 PM   #46
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Originally Posted by donpetru View Post
And another mistake - should be tested to see if it's so - is that the output voltage alternative to LM's, its RMS value, if it exceeds a certain value could go in conduction transistors Q1 .. Q3.
Q1, Q2 and Q3 are part of the speaker DC-protection circuitry only - their main function is to open the relay when the output DC offset crosses a certain threshold. It's a proven circuit, similar to that used in the MyRef Rev A-C, so it most probably will work perfectly as shown or with a few minor tweaks to the values of resistors.

To understand the amplifier topology, just ignore the protection circuitry.
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Old 3rd September 2012, 05:06 PM   #47
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I understand the circuit operation, but you do not understand me.
DC circuit protection with those transistors Q1 .. Q3 I don't think it will work properly.
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Old 3rd September 2012, 05:16 PM   #48
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Originally Posted by donpetru View Post
DC circuit protection with those transistors Q1 .. Q3 I don't think it will work properly.
It works fine in the MyRef - there isn't a single reported case of blown speakers due to a failed DC protection circuit in the MyRef.

In any event, the schematic and layout are free to modify - you're welcome to use a uPC1237 or anything else to implement a better DC protection circuit if you wish.
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Old 30th September 2012, 09:03 AM   #49
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Here's a pic of the first MiniRef 3886 prototype, almost completed. It has since been completely assembled and powered up safely today. It's stable and working as designed, thus validating the nested Jung-Howland-Penasa chipamp topology.
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Old 30th September 2012, 09:12 AM   #50
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Originally Posted by linuxguru View Post
Here's a pic of the first MiniRef 3886 prototype, almost completed. It has since been completely assembled and powered up safely today. It's stable and working as designed, thus validating the nested Jung-Howland-Penasa chipamp topology.
The image is missing! Must see...
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