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Old 22nd June 2013, 04:51 PM   #101
mcd99uk is offline mcd99uk  United Kingdom
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Quote:
Originally Posted by overall feedback View Post
I have no 1:1 filing about dimensions but looks like ground tracks can be smaller width. Two sides can be closer in that area and rectangle will be smaller.
Thank you for the feedback. What sort of track thickness would you use for signal grounds and decoupling grounds? Currently signal = 3mm and decoupling = 4mm.

I could add a scale to the drawings if that would be useful?
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Old 22nd June 2013, 07:31 PM   #102
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Quote:
Originally Posted by mcd99uk View Post
Thank you for the feedback. What sort of track thickness would you use for signal grounds and decoupling grounds? Currently signal = 3mm and decoupling = 4mm.

I could add a scale to the drawings if that would be useful?
It looks bigger on first sight .
There are small currents, and it flows separately so half width will more than suffice (2mm, 1.5mm). Spacing is not critical, there is hardly potential between those tracks. Add all widths together to get effectively ground path. Top layer tracks will be shorter.

For current source stabilizing, capacitors should be connected to base of source transistor (example u3) not to ground.

Last edited by overall feedback; 22nd June 2013 at 07:35 PM.
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Old 22nd June 2013, 07:52 PM   #103
mcd99uk is offline mcd99uk  United Kingdom
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For current source stabilizing, capacitors should be connected to base of source transistor (example u3) not to ground.
This is good news. It doesn't look to difficult to add some stabilization of this type. You mentioned using 220u // 220n for current sources. The smaller current sources run at approx 1mA and the larger 20mA. Could I get away with smaller decoupling for the 1mA sources?

I will be relaying out the PCB tomorrow eve with smaller ground tracks and additional decoupling.

Thank you

Paul
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Old 22nd June 2013, 08:39 PM   #104
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Quote:
Originally Posted by mcd99uk View Post
This is good news. It doesn't look to difficult to add some stabilization of this type. You mentioned using 220u // 220n for current sources. The smaller current sources run at approx 1mA and the larger 20mA. Could I get away with smaller decoupling for the 1mA sources?

I will be relaying out the PCB tomorrow eve with smaller ground tracks and additional decoupling.

Thank you

Paul
Let's see u3 example again. U5 is stabilizing current by keeping nearly constant voltage on emiter resistor r12 (0.6V-0.7V). Every fluctuation of supply voltage versus ground will cause current through base-emiter circuit of u5, which is amplified (hfe) through collector resistor r33. It rises voltage on r33 and voltage change on r12 stays very small. It is like that on ideal low frequency condition. As frequency rises parasitics rises, miller and phase shift spoils all work. That circuit electrically shakes on higher frequencies. We wanna keep stabile voltage on r12, and it will be as better as capacitance from emmiter u5 to collector u5 (base u3) is bigger, and as r6 is bigger of course. My experience is that overstabilization (r33 replaced with current source) makes sound improvements. Especially is evident on stage and 3d sound.
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Old 22nd June 2013, 09:33 PM   #105
mcd99uk is offline mcd99uk  United Kingdom
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Thank you for the explanation of the function of the stabilization caps. These caps can be quite low voltage and hence smaller. There should only be two diode drops across them in normal operation. The only question is, is it a good idea? If you get a transistor failure you would get 2/3 rail voltage across them.

Thinking about it I'm thinking of ditching R52 and R53. Not sure they are giving any benefit.

Last edited by mcd99uk; 22nd June 2013 at 09:42 PM.
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Old 22nd June 2013, 10:08 PM   #106
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Originally Posted by mcd99uk View Post
Thank you for the explanation of the function of the stabilization caps. These caps can be quite low voltage and hence smaller. There should only be two diode drops across them in normal operation. The only question is, is it a good idea? If you get a transistor failure you would get 2/3 rail voltage across them.

Thinking about it I'm thinking of ditching R52 and R53. Not sure they are giving any benefit.
I am not sure what "ditching" means, but those resistors have job to kill lc resonance too, I would live them there. There is good and bad things in every design, this one is unpredictable in case of transistor failure. I wouldn't say the caps only will be exposed. Voltage on input will rise and preamp or what is on input will be affected.
For that purpose smart zener protection can solve problem.
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Old 25th June 2013, 05:36 PM   #107
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What ever happened to being simpler?
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Old 25th June 2013, 05:50 PM   #108
mcd99uk is offline mcd99uk  United Kingdom
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What ever happened to being simpler?
Yes, well, errrrrrrrr......erm.... there's are no cascodes. I kept to that rule...... and I gave up with hawksford in favour of Bonsai's solution.
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Old 25th June 2013, 08:22 PM   #109
mcd99uk is offline mcd99uk  United Kingdom
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Default PCB Update and the beginnings of Parasitics

Work continues on the creation...

Attached are the latest schematics. Included the suggestions by overall feedback. Changed decoupling capacitors on output PCB to the ones suggested by transistormarkj. Added extra decoupling to the input PCB. There will no doubt be more changes to the PCBs to come.

Now it is time to start with the parasistics properly. Attached is the section of the circuit that I have started with. Does it look sane to do it this way. I think I'll start with the power rails and then the longer tracks.

The attachments are latest PCB layouts, schematic and the the section of the circuit I have started parasitics work on.
Attached Images
File Type: jpg InputPCB.jpg (482.4 KB, 83 views)
File Type: jpg OutputPCB.jpg (365.3 KB, 80 views)
File Type: jpg compdiff simple1 x out CMLC Par.jpg (403.4 KB, 77 views)
File Type: jpg compdiff simple1 x out CMLC Pa3.jpg (255.4 KB, 73 views)
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Old 25th June 2013, 08:35 PM   #110
mcd99uk is offline mcd99uk  United Kingdom
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Straight away I find ringing..... There is ringing at the point where the gate snubbers connect to the positive power rail. Sweet!
Attached Images
File Type: jpg Ringing.jpg (144.4 KB, 73 views)
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