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Old 24th September 2011, 02:13 AM   #11
soongsc is offline soongsc  Taiwan
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The current PCB seems to be a nice size. Is C13 really necessary? I have never used an input cap in 30 years. If the DC gain is low enough, then this space is really a waste. If someone needed it, it's easy to connect anywhere in the input line between connector to PCB with any type you want. There are so many caps that are too big to fit on the PCB anyway.
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Old 24th September 2011, 03:26 AM   #12
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The current PCB seems to be a nice size. Is C13 really necessary? I have never used an input cap in 30 years. If the DC gain is low enough, then this space is really a waste.
In this design the C13 input cap is tightly connected with C9, it can't be omitted without impacting on bass performance.

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There are so many caps that are too big to fit on the PCB anyway.
Quite all... in fact the cap I recommend in my BOM will fit only outboard as in the attached picture:
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Old 24th September 2011, 03:35 AM   #13
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In this design the C13 input cap is tightly connected with C9, it can't be omitted without impacting on bass performance.
...
It's my understanding that this is basically providing additional subsonic filtering (at least that is what was also previously described in the technical explanation). If it really creates a problem, then the problem would be elsewhere and system specific.
The point is, if it has to be mounted off board for best performance, why let it take up so much PCB space? All we probably need is two pads that will allow a small cap to be mounted vertically, this way we can save space for other valuable stuff.

PS. Try moving that cap in the pic around and see whether you notice a difference in sound.
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Last edited by soongsc; 24th September 2011 at 03:45 AM.
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Old 24th September 2011, 08:37 AM   #14
AndrewT is online now AndrewT  Scotland
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move C13 off board. And use it to connect the RCA/phono/input terminal to the PCB.
Then along side you can have a DC input socket as well as the AC input socket.
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Old 24th September 2011, 01:50 PM   #15
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move C13 off board. And use it to connect the RCA/phono/input terminal to the PCB.
Probably it's a good idea to do it... I'll check

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Then along side you can have a DC input socket as well as the AC input socket.
If I understand correctly you're suggesting to place two input sockets, one that goes directly to the input net (so the coupling cap can be completely off board) and another connnected to two pads that allows mounting a tiny onboard cap, right?
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Old 24th September 2011, 02:04 PM   #16
AndrewT is online now AndrewT  Scotland
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no.
Look back at Jen's Leach clone.
One of the input pins bypasses the DC blocking cap.
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Old 24th September 2011, 02:27 PM   #17
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no.
Look back at Jen's Leach clone.
One of the input pins bypasses the DC blocking cap.
So a 3 pin connector...

Not much different from what I wrote but I get it

Thanks, I'll take a look.
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Last edited by ClaveFremen; 24th September 2011 at 02:31 PM.
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Old 24th September 2011, 03:28 PM   #18
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Does C9 have a across it? Seems to me not, but I just want to make sure.
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Old 24th September 2011, 03:37 PM   #19
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If it really creates a problem, then the problem would be elsewhere and system specific.
Hi Soongsc,

it don't create any problem, simply it is part with C9 of the high-pass filter to avoid DC.

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The point is, if it has to be mounted off board for best performance, why let it take up so much PCB space? All we probably need is two pads that will allow a small cap to be mounted vertically, this way we can save space for other valuable stuff.
I'm thinking about it.

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PS. Try moving that cap in the pic around and see whether you notice a difference in sound.
I've moved the cap in the past I didn't noticed any appreciable difference.

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Does C9 have a across it? Seems to me not, but I just want to make sure.
I don't get it, can you elaborate?

Or are you refferring to the black cross?

If so it's simply an handle to move the object.
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Last edited by ClaveFremen; 24th September 2011 at 03:41 PM.
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Old 24th September 2011, 03:49 PM   #20
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C9 is an electrolytic capacitor, if there is a DC offset across this cap then it's fine. If not, then I was thinking about changing it to an bipolar type electrolytic and add a bypass cap to improve it's linearity. I probably should also try it on one of my chip amps too.
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Last edited by soongsc; 24th September 2011 at 03:56 PM.
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